5-HT_1A Receptor

1. The aim of the present work was to characterize the 5-hydroxytryptamine1A (5-HT1A) antagonistic actions of (-)-pindolol and WAY 100635 (N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl) cyclohexane carboxamide). Studies were performed on 5-HT1A receptors located on 5-hydroxytryptaminergic neurones in the dorsal raphe nucleus (DRN) and on pyramidal cells in the CA1 and CA3 regions of the hippocampus in rat brain slices. 2. Intracellular electrophysiological recording of CA1 pyramidal cells and 5-hydroxytryptaminergic DRN neurones showed that the 5-HT1A receptor agonist 5-carboxamidotryptamine (5-CT) evoked in both cell types a concentration-dependent cell membrane hyperpolarization and a decrease in cell input resistance. On its own, (-)-pindolol did not modify the cell membrane potential and resistance at concentrations up to 10 microM, but it antagonized the 5-CT effects in a concentration-dependent manner. Similar antagonism of 5-CT effects was observed in the CA3 hippocampal region. (-)-Pindolol also prevented the 5-HT1A receptor-mediated hyperpolarization of CA1 pyramidal cells due to 5-HT (15 microM). In contrast, the 5-HT-induced depolarization mediated by presumed 5-HT4 receptors persisted in the presence of 3 microM (-)-pindolol [1].

The beta-blocker (-)-pindolol produces intrinsic sympathomimetic activity manifested clinically by cardiostimulation, but the beta-adrenoceptor subtype, which mediates these effects, is unknown. Recent work indicates the existence of a (-)-propranolol-resistant site of the cardiac beta(1)-adrenoceptor and we propose that it mediates the cardiostimulation evoked by (-)-pindolol. We compared the interaction of (-)-pindolol both with human atrial myocardium and with recombinant beta(1)-adrenoceptors. The effects of (-)-pindolol on paced human atrial trabeculae were studied in the presence of 3-isobutyl-1-methylxanthine (IBMX; 20 microM). (-)-Pindolol caused small negative and positive inotropic effects at nanomolar and micromolar concentrations respectively, which were unaffected by N(G)-monomethyl-L-arginine (L-NMMA, 10 microM), inconsistent with an involvement of nitric oxide. (-)-Pindolol, in the presence of (-)-propranolol, increased atrial contractile force and cAMP through recombinant beta(1)-adrenoceptors with identical potency (-logEC(50)M=6.5). The positive inotropic effects of (-)-pindolol were resistant to blockade by L-748,337 (100 nM), a beta(3)-adrenoceptor antagonist. (-)-CGP12177, known to act through the (-)-propranolol-resistant site of the beta(1)-adrenoceptor, also increased with similar potency atrial contractile force (-logEC(50)M=7.6) and cAMP at recombinant beta(1)-adrenoceptors (-logEC(50)M=7.7). (-)-Pindolol blocked the effects of (-)-CGP12177 in human atrium and recombinant beta(1)-adrenoceptors with similar equilibrium dissociation constants (pK(B)=6.5 and 6.3). Thus, stimulant potency and blocking potency of (-)-pindolol against (-)-CGP12177 agree. In contrast, (-)-pindolol was 200-400 times more effective at blocking the effects of a catecholamine than the effects of (-)-CGP12177 in both human atrium (pK(B)=9.1) and at recombinant beta(1)-adrenoceptors (pK(B)=8.6). We conclude that the cardiostimulant effects of (-)-pindolol in human atrial myocardium are mediated through a (-)-propranolol-resistant site of the beta(1)-adrenoceptor with low affinity for (-)-pindolol. In contrast, (-)-pindolol blocks the effects of catecholamines through a high-affinity site of the beta(1)-adrenoceptor. beta(3)-Adrenoceptors are not involved in the atrial effects of (-)-pindolol. [1]

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Background: It is known that S-pindolol attenuates muscle loss in animal models of cancer cachexia and sarcopenia. In cancer cachexia, it also significantly reduced mortality and improved cardiac function, which is strongly compromised in cachectic animals. Methods: Here, we tested 3 mg/kg/day of S-pindolol in two murine cancer cachexia models: pancreatic cancer cachexia (KPC) and Lewis lung carcinoma (LLC). Results: Treatment of mice with 3 mg/kg/day of S-pindolol in KPC or LLC cancer cachexia models significantly attenuated the loss of body weight, including lean mass and muscle weights, leading to improved grip strength compared with placebo-treated mice. In the KPC model, treated mice lost less than half of the total weight lost by placebo (-0.9 ± 1.0 vs. -2.2 ± 1.4 g for S-pindolol and placebo, respectively, P < 0.05) and around a third of the lean mass lost by tumour-bearing controls (-0.4 ± 1.0 vs. -1.5 ± 1.5 g for S-pindolol and placebo, respectively, P < 0.05), whereas loss of fat mass was similar. In the LLC model, the gastrocnemius weight was higher in sham (108 ± 16 mg) and S-pindolol tumour-bearing (94 ± 15 mg) mice than that in placebo (83 ± 12 mg), whereas the soleus weight was only significantly higher in the S-pindolol-treated group (7.9 ± 1.7 mg) than that in placebo (6.5 ± 0.9). Grip strength was significantly improved by S-pindolol treatment (110.8 ± 16.2 vs. 93.9 ± 17.1 g for S-pindolol and placebo, respectively). A higher grip strength was observed in all groups; whereas S-pindolol-treated mice improved by 32.7 ± 18.5 g, tumour-bearing mice only show minimal improvements (7.3 ± 19.4 g, P < 0.01). Conclusions: S-pindolol is an important candidate for clinical development in the treatment of cancer cachexia that strongly attenuates loss of body weight and lean body mass. This was also seen in the weight of individual muscles and resulted in higher grip strength[2].

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3. In the hippocampus, (-)-pindolol completely prevented the hyperpolarization of CA1 pyramidal cells by 100 nM 5-CT (IC50=92 nM; apparent KB=20.1 nM), and of CA3 neurones by 300 nM 5-CT (IC50=522 nM; apparent KB= 115.1 nM). The block by (-)-pindolol was surmounted by increasing the concentration of 5-CT, indicating a reversible and competitive antagonistic action. 4. Extracellular recording of the firing rate of 5-hydroxytryptaminergic neurones in the DRN showed that (-)-pindolol blocked, in a concentration-dependent manner, the decrease in firing elicited by 100 nM 5-CT (IC50=598 nM; apparent KB= 131.7 nM) or 100 nM ipsapirone (IC50= 132.5 nM; apparent KB= 124.9 nM). The effect of (-)-pindolol was surmountable by increasing the concentration of the agonist. Intracellular recording experiments showed that 10 microM (-)-pindolol were required to antagonize completely the hyperpolarizing effect of 100 nM 5-CT. 5. In vivo labelling of brain 5-HT1A receptors by i.v. administration of [3H]-WAY 100635 ([O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1 -piperazinyl)ethyl-N-(2-pyridyl)cyclo-hexane-carboxamide) was used to assess their occupancy following in vivo treatment with (-)-pindolol. (-)-Pindolol (15 mg kg[-1]) injected i.p. either subchronically (2 day-treatment before i.v. injection of [3H]-WAY 100635) or acutely (20 min before i.v. injection of [3H]-WAY 100635) markedly reduced [3H]-WAY 100635 accumulation in all 5-HT1A receptor-containing brain areas. In particular, no differences were observed in the capacity of (-)-pindolol to prevent [3H]-WAY 100635 accumulation in the DRN and the CAI and CA3 hippocampal areas. 6. Intracellular electrophysiological recording of 5-hydroxytryptaminergic DRN neurones showed that WAY 100635 prevented the hyperpolarizing effect of 100 nM 5-CT in a concentration-dependent manner (IC50=4.9 nM, apparent KB=0.25 nM). In CA1 pyramidal cells, hyperpolarization induced by 50 nM 5-CT was also antagonized by WAY 100635 (IC50 = 0.80 nM, apparent KB= 0.28 nM)[3].

Receptor binding assays [1]
CHO cells, stored at −80°C in 1 mM EDTA, 25 mM Tris. HCl, pH 7.4 (20°C) were thawed and pelleted for 30 min at 17,000 × g, 4°C, and then homogenized by Polytron (7 mm probe, 3×10 s, speed setting 8) in a binding buffer containing (mM): EGTA 5, EDTA 1, MgCl2 4, ascorbic acid 1, phenylmethyl-sulfonyl fluoride 0.5, Tris-HCl 50, pH 7.5 (37°C). For receptor saturation assays, homogenates were incubated for 2 h at 37°C in a final volume of 0.5 ml (10 μg protein) with 1–200 pM (-)-[125I]-cyanopindolol. Non-specific binding was defined as binding not removed with 200 μM (-)-isoprenaline. Bound radioligand was isolated by filtration through Whatman GF/B paper and radioactivity counted. To estimate the affinity of (-)-pindolol, (-)-CGP12177 and (-)-propranolol for the β1-adrenoceptor, cell membranes were labeled with ~30 pM (-)-[125I]-cyanopindolol in the absence and presence of concentrations (0.03 nM–100 μM) of competing ligand. Saturation binding assays and binding inhibition data were analyzed with non-linear regression and dissociation equilibrium constants calculated from saturation assays (KD) and binding inhibition assays (Ki).

Right atrial trabeculae were prepared and set up to contract at 1 Hz at 37°C as described (Gille et al. 1985). After a 20 min exposure to 20 μM IBMX, a single cumulative concentration-effect curve to (-)-pindolol was determined, followed by the addition of 6 μM (-)-CGP12177 and finally 600 μM (-)-isoprenaline. The effects of (-)-pindolol were further investigated in the presence of 200 nM (-)-propranolol and 20 μM IBMX in which a single cumulative concentration-effect curve to (-)-pindolol up to 6 μM was determined, followed by a curve for (-)-CGP12177 in the presence of 6 μM (-)-pindolol. For 5 of 8 patients, a curve for (-)-CGP12177 was also determined on another trabeculum from the same atrium in the presence of both (-)-propranolol and IBMX. The experiments were concluded by the administration of (-)-isoprenaline (600 μM). The −log (molar concentration) of (-)-pindolol and (-)-CGP12177 producing half-maximal increases in contractile force (−logEC50M) were determined. An estimate of the affinity of (-)-pindolol (−log dissociation equilibrium constant KB,M = pKB) for the β1-adrenoceptor site activated by (-)-CGP12177, was calculated from −logEC50 values for (-)-CGP12177 in the presence and absence of (-)-pindolol, using the law of propagation of errors (Kaumann 1990). To investigate whether β3-adrenoceptors contribute to the effects of (-)-pindolol (Gauthier et al. 1998) in human atrium two sets of experiments were carried out. Firstly, the ability of the nitric oxide-synthase inhibitor L-NMMA to abrogate possible β3-adrenenoceptor-mediated negative inotropic effects (Gauthier et al. 1998) was determined. Secondly, the cardiostimulant effects of (-)-pindolol were determined in the absence or presence of the selective human β3-adrenoceptor antagonist L-748,337 (Candelore et al. 1999) [1].

Male C57BL/6J mice were 7–12 weeks of age and 23.9 ± 0.6 g in weight for KPC and 17.5 ± 0.4 g in weight for LLC at the start of experimental procedures. Thirty‐one mice were randomized to sham (n = 8) or orthotropic tumour inoculation (n = 23) of 3 million KPC cells in a volume of 40 μL into the tail of the pancreas, as described before. 5 Tumour‐bearing mice were further randomized to treatment with placebo (n = 11) or 3 mg/kg/day of S‐pindolol (n = 12) once daily for 13 days. Body composition, that is, lean and fat mass, was assessed by nuclear magnetic resonance (NMR) spectroscopy 1 day before tumour cell inoculation and on the day of euthanasia. For the LLC model, 30 C57BL/6 mice (mean body weight of 17.5 ± 0.4 g) were randomized to treatment: no tumour injection, sham (n = 5), placebo (sterilized water, n = 15) or 3 mg/kg/day of S‐pindolol (n = 10) for 13 days. Mice received an intramuscular (hind leg) inoculum of 5 × 105 LLC cells obtained from exponential tumours, as described before. 6 , 7 Grip strength test was performed by a pull bar connected to an isometric force transducer. The animals were allowed to grasp the bar and were then pulled backwards in the horizontal plane. 8 In both models, S‐pindolol was given once daily by gavage. Results, represented as mean ± SD, were analysed using GraphPad Prism 8.0. All data were tested for normal distribution using the Kolmogorov–Smirnov test. Group comparisons were performed by one‐way analysis of variance (ANOVA) with adjustment for multiple testing of sham‐treated controls and S‐pindolol‐treated tumour‐bearing animals against tumour‐bearing vehicle controls. A P‐value of <0.05 was considered significant. [2]

Absorption, Distribution, and Excretion
Absorption
The mean oral bioavailability of indolol is 87-92%. After an oral dose of 5 mg, the peak plasma concentration (Cmax) is 33.1 ± 5.2 ng/mL, and the time to peak concentration (Tmax) is 1-2 hours.
Excretion Routes
80% of the oral dose is excreted in the urine, of which 25-40% is the unchanged drug. 6-9% of the intravenously administered dose is excreted in the feces. Overall, 60-65% of the dose is excreted as glucuronide and sulfate metabolites.
Volume of Distribution
The volume of distribution of indolol is approximately 2-3 L/kg.
Clearance
In healthy patients, the systemic clearance of indolol is 400-500 mL/min. In patients with cirrhosis, the clearance of indolol is between 50-300 mL/min. Indolol is rapidly absorbed from the gastrointestinal tract. Its bioavailability is reported to be 50-95%; however, bioavailability in uremic patients may be lower within this range. Food does not decrease bioavailability but may increase the rate of absorption in the gastrointestinal tract. First-pass metabolism of indolol in the liver is reported to be minimal;…only about 20% of the oral dose undergoes first-pass metabolism. Following a single 20 mg dose, peak plasma concentrations can reach 45-167 ng/ml within 1-2 hours. Absorption may be reduced in patients with impaired renal function. The effect of indolol on heart rate usually appears within 3 hours after administration, and acute hemodynamic effects can last up to 24 hours. Approximately 40-60% of indolol is bound to plasma proteins. In healthy adults, the apparent volume of distribution is 1.2-2 L/kg; in uremic patients, the volume of distribution may be reduced by 50%. Indolol is distributed in breast milk.
Within a dose range of 5-20 mg, the elimination of indolol appears to follow first-order kinetics. The plasma half-life of this drug in healthy adults is 3-4 hours. In patients with renal failure, the plasma half-life is prolonged to 3-11.5 hours; in elderly patients, it is prolonged to 7-15 hours; and in patients with cirrhosis, it is 2.5-30 hours. Approximately 60-65% of indolol is metabolized in the liver to hydroxylated metabolites, which are then excreted in the urine as glucuronide and ether sulfate. In healthy adults, approximately 35-50% of the drug is excreted unchanged in the urine; in patients with creatinine clearance less than 20 ml/min, the proportion excreted unchanged in the urine is less than 15%.
Indorol is rapidly and reproducibly absorbed (absorption rate >95%), reaching peak plasma concentration within 1 hour of administration… Plasma concentration is linearly related to the dose within the dosing range of 5-20 mg…Indorol binds to plasma proteins at a rate of only 40% and is uniformly distributed in plasma and erythrocytes. The volume of distribution in healthy subjects is approximately 2 L/kg.
The half-life of the polar metabolite is approximately 8 hours; therefore, multiple doses… result in a plasma accumulation of less than 50%. Approximately 6%-9% of the intravenously administered dose is excreted in feces via bile. PDR; Physician's Desk Reference Generic Drugs. 2nd ed. Montville, NJ: Medical Economics Co., p. 2488 (1996)

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Metabolites/Metabolites
30-40% of the dose of indorol is not metabolized. The remainder is hydroxylated, followed by glucuronidation or sulfate conjugation.
It has been reported that indolol undergoes minimal first-pass metabolism in the liver; only about 20% of the oral dose is metabolized in the first pass.
Approximately 60-65% of indolol is metabolized in the liver to hydroxylated metabolites, which are then excreted in the urine as glucuronide and ether sulfate.

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Biological Half-Life
The half-life of indolol is 3-4 hours, but can be as long as 30 hours in patients with cirrhosis.
The plasma half-life of this drug in healthy adults is 3-4 hours. In patients with renal failure, the plasma half-life is prolonged to 3-11.5 hours; in elderly patients, the plasma half-life is prolonged to 7-15 hours; and in patients with cirrhosis, the plasma half-life is 2.5-30 hours.

Hepatotoxicity
In patients taking indorol, the incidence of mild to moderate elevations in serum transaminase levels is less than 2%, usually transient and asymptomatic, and returns to normal with continued treatment. Despite the widespread use of indorol, there is no conclusive evidence that it is associated with clinically significant liver injury. Other beta-blockers have been thought to be associated with rare cases of clinically significant liver injury with a latency period of 4 to 24 weeks, hepatocellular elevations in serum enzymes, and mild, self-limiting course without evidence of hypersensitivity or autoimmune reactions.
Probability score: E (Unlikely a cause of clinically significant liver injury).
Effects during pregnancy and lactation
◉ Overview of medication use during lactation
Recommendations for medication use during lactation: Limited information suggests that the concentration of indorol in breast milk is low after the mother takes indorol. The drug has a short half-life and moderate renal excretion; therefore, no adverse effects are expected on breastfed infants, especially those older than 2 months.
◉ Effects on Breastfed Infants
As of the revision date, no published information was found regarding indolol. A study of mothers taking beta-blockers while breastfeeding found a numerically increased number of adverse events, but this was not statistically significant. Although the infants were age-matched to the control group, the age of the affected infants was not specified. None of the mothers were taking indolol.
◉ Effects on Lactation and Breast Milk
As of the revision date, no published information was found regarding the effects of beta-blockers or indolol during normal breastfeeding. A study of six patients with hyperprolactinemia and galactorrhea found no change in serum prolactin levels after beta-adrenergic blockade with propranolol.

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Protein Binding
Indolol binds to plasma proteins at a rate of 40%. Indolol primarily binds to α1-acid glycoproteins, with a stronger binding affinity than to serum albumin.

[1]. Discovery of Novel 1-Cyclopentenyl-3-phenylureas as Selective, Brain Penetrant, and Orally Bioavailable CXCR2 Antagonists. J Med Chem. 2018;61(6):2518-2532.

[2]. Effects of S-pindolol in mouse pancreatic and lung cancer cachexia models. J Cachexia Sarcopenia Muscle. 2023 Jun;14(3):1244-1248.

[3]. Antagonist properties of (-)-pindolol and WAY 100635 at somatodendritic and postsynaptic 5-HT1A receptors in the rat brain. Br J Pharmacol. 1998 Feb;123(3):449-62.

Previous studies (Kaumann 1989) have shown that (-)-indolol-induced tachycardia observed in humans (Man In't Veld and Schalekamp 1981; Man In't Veld et al. 1982; Iskos et al. 1998; Benditt et al. 1999) is mediated by atypical β-adrenergic receptors. Our results support the hypothesis that (-)-indolol exerts its cardiac excitatory effect through the (-)-propranolol tolerance site on β1-adrenergic receptors for the following reasons: 1. In the presence of (-)-propranolol and IBMX, (-)-indolol increases atrial contractility and cAMP levels with the same potency by remodeling β1-adrenergic receptors. 2. In CHO cells expressing recombinant β1-adrenergic receptors, (-)-indolol antagonizes the excitatory effects of (-)-CGP12177 on atrial contractility and cAMP levels in a similar manner. In both systems, the blocking potency of (-)-indolol against (-)-CGP12177 matches its excitatory potency (pKB≈-logEC50, Table 1). This quantitative consistency supports the hypothesis that (-)-indolol not only acts through a site on the β1-adrenergic receptor insensitive to (-)-propranolol (Konkar et al., 2000; Kaumann, 2000; Granneman, 2001), as (-)-CGP12177 acts through this site (Konkar et al., 2000; Kaumann, 2000; Granneman, 2001). Contrary to our evidence, Baker et al. (2003) recently reported that indolol exerts its agonistic effect through two sites on the β1-adrenergic receptor, one with high affinity and the other with low affinity. Our evidence is consistent with the hypothesis that (-)-indolol exerts its agonistic effect solely by activating the recombinant β1-adrenergic receptor and the low-affinity site in the atrium. The reason for the discrepancy in results is unclear. Unfortunately, it is currently unclear whether Baker et al.'s findings are related to this. (2003) used racemic indolol or the (-)-indolol isomer. Furthermore, the polymorphic variant used in Baker et al.'s (2003) study is also unclear. We also confirmed that both (-)-indolol and (-)-propranolol bind with high affinity to and block the recombinant β1-adrenergic receptor. These nanomolar affinity estimates are consistent with previous affinity estimates for (-)-indolol (Kaumann and Lobnig 1986) and (-)-propranolol (Gille et al. 1985) obtained from the human atrium. Our estimated sub-nanomolar affinity of the recombinant β1-adrenergic receptor for (-)-CGP12177 is consistent with similar high affinity estimates (KB = 0.2 nM) obtained by blocking the positive inotropic effect of (-)-norepinephrine in the human right atrium. In summary, this evidence, both in the atrium and in CHO cells, is consistent with the mechanism by which (-)-indolol, (-)-propranolol, and (-)-CGP12177 block catecholamine action through high-affinity β1-adrenergic receptor sites. The second site of the β1-adrenergic receptor, with an affinity for the three β-receptor blockers approximately 200-400 times lower than that for the high-affinity site, is activated only by (-)-indolol and (-)-CGP12177 to mediate cardiac stimulation, while (-)-propranolol has no such effect. (-)-Indolol not only enhances atrial contractility but also accelerates diastole, consistent with cAMP-dependent phosphorylation of phosphoproteins and troponin I observed in the human atrium induced by β-adrenergic receptor stimulation (Kaumann et al., 1996; Sarsero et al., 2003). The increase in cAMP induced by (-)-indolol and (-)-CGP12177 in CHO cells via β1-adrenergic receptors is consistent with activation of the cAMP pathway. However, compared to the effects of (-)-isoproterenol, the intrinsic activity of these two drugs in CHO cells was lower than their corresponding intrinsic activity against atrial contractility (Table 1). This difference may be related to the fact that the (-)-propranolol tolerance receptor site in the native atrial cellular environment is closer to the physiological state of the cAMP pathway, whereas this coupling is not present in CHO cells containing β1-adrenergic receptors. (-)-Indrolol can induce tachycardia that is unresponsive to propranolol blockade, as observed in anesthetized dogs and a patient with autonomic dysfunction and undetectable plasma norepinephrine levels (Clark et al., 1982). The degree of tachycardia may depend on pathology; for example, low (-)-norepinephrine levels and the resulting “hypersensitivity” favor the observation of tachycardia (Man In't Veld and Schelekamp 1981; Man In't et al. 1982). Our in vitro human right atrial model relied on the use of phosphodiesterase inhibitors to reveal the positive inotropic effect of (-)-indolol, which showed to be less potent than (-)-CGP12177 (this study; Kaumann 1996; Sarsero et al. 2003) or (-)-norepinephrine (this study; Molenaar et al. 2002). However, it must be considered that clinically used indolol is a racemic mixture containing equal proportions of (-)-indolol and (+)-indolol (Kaumann 1989). Studies have found that (+)-indolol selectively binds to cardiac β2-adrenergic receptors on the ventricular membrane of cats (Morris and Kaumann, 1984) and can induce sinoatrial node tachycardia in guinea pigs via β2-adrenergic receptor mediation (Walter et al., 1984). Racemic indolol is unlikely to induce tachycardia via the interaction of its (+)-enantiomer with the human sinoatrial node β2-adrenergic receptor, as propranolol cannot block the tachycardia induced by racemic indolol in dogs (Clark et al., 1982). Although studies have shown that indolol induces a slight increase in cAMP levels via the β2-adrenergic receptor in S49 cells pretreated with foscrichine (Jasper et al., 1990), propranolol antagonizes this effect, and there is little dissociation between the excitatory potency and affinity of the two (whether estimated by binding or antagonism) (Jasper et al., 1990). It has also been reported that indolol has a binding affinity to the recombinant β2-adrenergic receptor that is 40-fold higher than our estimated affinity for the recombinant β1-adrenergic receptor (Ballesteros et al., 2001), suggesting that (-)-indolol interacts differently with these two receptor subtypes. Considering the above, β2-adrenergic receptors are unlikely to be involved in the cardiac excitatory effects induced by indolarist in humans. For various reasons, β3-adrenergic receptors are also unlikely to be involved in the cardiac excitatory effects of (-)-indolarist. β3-adrenergic receptors have been reported to mediate cardiac inhibition in ventricular specimens via a nitric oxide (NO)-dependent pathway (Gauthier et al., 1998). Our experimental results using L-NMMA are inconsistent with the involvement of NO and β3-adrenergic receptors in the effects of (-)-indolarist and (-)-CGP12177. Studies have found that β3-adrenergic receptors only enhance myocardial contractility when overexpressed in the hearts of transgenic mice (Kohout et al., 2001). We found that the selective β3-adrenergic receptor blocker L-748,337 (Candelore et al., 1999) had no effect on the positive inotropic effects of (-)-indolarist. Indolol is also a partial agonist, with intrinsically lower activity than the typical β3-selective agonist BRL37344, which acts on recombinant β3-adrenergic receptors expressed at high density in CHO cells (Emorine et al., 1989). Unlike the affinity estimates for low-affinity sites of β1-adrenergic receptors (KB = 300–500 nM in this study), (-)-indolol has a much higher affinity for recombinant β3-adrenergic receptors (Ki = 11 nM) (Emorine et al., 1989). Contrary to our findings on β1-adrenergic receptors, low micromolar and nanomolar concentrations of (-)-indolol antagonize the effects of (-)-CGP12177 and (-)-isoproterenol, respectively, at β1-adrenergic receptors, while 100 μM indolol does not block the effect of isoproterenol on recombinant β3-adrenergic receptors (Emorine et al., 1989). The free plasma (-)-indolol concentrations obtained after therapeutic administration of racemic (±)-indolol are expected to partially occupy low-affinity sites on β1-adrenergic receptors. We calculated that oral administration of one 15 mg tablet (Gross et al., 2001) or two 10 mg indolol tablets (Hsyu and Giacomini, 1985) can result in plasma (-)-indolol concentrations of 60–120 nM, sufficient to induce direct cardiac excitation. More significant effects may be observed with higher doses (45 mg/day). We hypothesize that plasma concentrations of (-)-indolol at 60–120 nM, particularly when parasympathetic activity is high and sympathetic activity is low, significantly increase nocturnal sinoatrial node heart rate (Van de Borne et al., 1994; Vanolie et al., 1995). The bradycardic effect of (-)-indolol is diminished at night due to negligible interaction with endogenous catecholamines. Consistent with this view, the increase in heart rate induced by indolol is more pronounced at night (Fitscha et al., 1982; Kantelip et al., 1984; Channer et al., 1994). We conclude that the dissociation between the blocking and stimulating effects of (-)-indolol, previously observed in isolated myocardium in various animals, has been confirmed in the human atrium and recombinant β1-adrenergic receptors. (-)-Indolol exerts its intrinsic sympathomimetic activity through low-affinity receptor sites insensitive to (-)-propranolol, and blocks the effects of catecholamines through high-affinity β1-adrenergic receptor sites. We hypothesize that low-affinity β1-adrenergic receptor sites mediate racemic indolol-induced tachycardia. [1]

248.15

C, 67.71; H, 8.12; N, 11.28; O, 12.89

13523-86-9

Pindolol-d7; 1185031-19-9

4828

White to off-white solid powder

1.2±0.1 g/cm3

457.1±35.0 °C at 760 mmHg

167-171 °C(lit.)

230.3±25.9 °C

0.0±1.2 mmHg at 25°C

1.597

1.97

3

3

6

18

248

0

JZQKKSLKJUAGIC-UHFFFAOYSA-N

InChI=1S/C14H20N2O2/c1-10(2)16-8-11(17)9-18-14-5-3-4-13-12(14)6-7-15-13/h3-7,10-11,15-17H,8-9H2,1-2H3

1-(1H-indol-4-yloxy)-3-(propan-2-ylamino)propan-2-ol

Prinodolol; Betapindol; Pindolol; Visken; Calvisken; LB-46; LB46; Pindolol; Prindolol; Carvisken; LB 46; Visken; urapindol; Pinbetol;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: ~50 mg/mL (~201.4 mM)

Solubility in Formulation 1: ≥ 2.08 mg/mL (8.38 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (8.38 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.08 mg/mL (8.38 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)