The beta 1- and beta 2-adrenoceptor stimulatory effects of alprenolol, oxprenolol and pindolol: a study in the isolated right atrium and uterus of the rat

The small molecule ACM-001 improves cardiac function in a rat model of severe cancer cachexia

AIMS

Cachexia, a common manifestation of malignant cancer, is not only associated with weight loss, but also with severe cardiac atrophy and impaired cardiac function. Here, we investigated the effects of ACM-001 (0.3 or 3 mg/kg/day) in comparison to carvedilol (3 or 30 mg/kg/day), metropolol (50 or 100 mg/kg/day), nebivolol (1 or 10 mg/kg/day) and tertatolol (0.5 or 5 mg/kg/day) on cardiac mass and function in a rat cancer cachexia model.

METHODS AND RESULTS

Young male Wistar Han rats were inoculated i.p. with 108 Yoshida hepatoma AH-130 cells and treated once daily with verum or placebo by gavage. Cardiac function (echocardiography), body weight and body composition (nuclear magnetic resonance scans) were assessed. The hearts of animals were euthanized on day 11 (placebo and 3 mg/kg/day ACM-001) were used for signalling studies. Beta-blockers had no effect on tumour burden. ACM-001 reduced body weight loss (placebo: -34 ± 2.4 g vs. 3 mg/kg/day ACM-001: -14.8 ± 8.4 g, p = 0.033). Lean mass wasting was attenuated (placebo: -16.5 ± 2.34 g vs. 3 mg/kg/day ACM-001: -2.4 ± 6.7 g, p = 0.037), while fat loss was similar (p = 0.4) on day 11. Placebo animals lost left ventricular mass (-101 ± 14 mg), which was prevented only by 3 mg/kg/day ACM-001 (7 ± 25 mg, p < 0.01 vs. placebo). ACM-001 improved the ejection fraction (EF) (ΔEF: placebo: -24.3 ± 2.6 vs. 3 mg/kg/day ACM-001: 0.1 ± 2.9, p < 0.001). Cardiac output was 50% lower in the placebo group (-41 ± 4 ml/min) compared to baseline, while 3 mg/kg/day ACM-001 preserved cardiac output (-5 ± 8 ml/min, p < 0.01). The molecular mechanisms involved inhibition of protein degradation and activation of protein synthesis pathways.

CONCLUSION

This study shows that 3 mg/kg/day ACM-001 restores the anabolic/catabolic balance in cardiac muscle leading to improved function. Moreover, not all beta-blockers have similar effects.

The Association Between β-Blocker Use and Cardiorespiratory Fitness: The Maastricht Study

Purpose:

β-Blockers (BBs) have been associated with a reduced cardiorespiratory fitness (CRF). This is possibly caused by inhibition of β2-receptors in the airways. However, there are limited data available on β-receptor selectivity and CRF. We therefore aimed to assess the association between BB use and CRF and to assess the association between β-receptor selectivity and CRF.

Methods:

Participants in the Maastricht Study were aged between 40 and 75 years. Exposure to BB use was determined by use of pharmacy records. General linear models were used to obtain adjusted means of 2 proxies for CRF: covered distance during the 6-minute walk test (6MWT) and estimated maximum power output adjusted for body mass (W_max kg⁻¹) during the submaximal cycle ergometer test. Adjusted means were compared between current, past, and never BB users. Current users were subsequently stratified by β-receptor selectivity and dose.

Results:

Compared to never use, current use was associated with a lower CRF, based on the 6MWT (current use: 569.7 m; never use: 580.4 m [P = .010]), but not based on the cycling test (current use: 2.14 W kg⁻¹; never use: 2.13 W kg⁻¹ [P = .690]). There was no difference between current selective and current nonselective BB use.

Conclusion:

β-Blockers use was associated with CRF based on the 6MWT but not the cycling test. There was no difference between current selective and nonselective BB users, possibly due to the small number of nonselective BB users, differential underlying diseases, other pharmacological properties, and limitations related to the proxies of the outcome.

Pharmacological effects of an aldehyde type alpha/beta-adrenoceptor blocking agent with vasodilating properties

KMUP 880723 (0.5, 1.0, and 3.0 mg/kg, iv) produced dose-dependent hypotensive and bradycardia responses in pentobarbital-anesthetized Wistar rats. KMUP 880723 (1.0 mg/kg, iv) also markedly inhibited both the tachycardia effects induced by (-)isoproterenol and arterial pressor responses induced by phenylephrine. In the isolated Wistar rat right atria, left atria, and guinea pig tracheal strips, KMUP 880723 competitively antagonized the (-)isoproterenol-induced positive chronotropic effects, inotropic effects, and tracheal relaxation effects in a concentration-dependent manner. The parallel shift to the right of the concentration-response curve of (-)isoproterenol suggested that KMUP 880723 was a beta(1)/beta(2)-adrenoceptor competitive antagonist. The apparent pA(2) values were 6.89+/-0.10 in the right atria, 7.02+/-0.09 in the left atria, and 6.59+/-0.11 in the trachea, indicating that KMUP 880723 was a nonselective beta-adrenoceptor blocker. In thoracic aorta experiments, KMUP 880723 also produced a competitive antagonism of norepinephrine-induced contraction with a pA(2) value of 7.14+/-0.06. In isolated rat thoracic aorta, KMUP 880723 more potently relaxed the contractions induced by norepinephrine (3 x 10(-6) M) than those by high K(+) (75 mM). In the radioligand-binding assay, the pK(i) values of [3H]CGP-12177 binding to rat ventricle and lung membranes were 6.56 and 6.40, respectively, and the value of [3H]prazosin binding to rat brain membranes was 6.66. These results further confirmed the alpha/beta-adrenoceptor blocking activities of KMUP 880723 reported in the functional studies. We conclude that KMUP 880723 is a nonselective beta-adrenoceptor antagonist with alpha-adrenoceptor blocking-associated vasorelaxant activity.

Eugenodilol: a third-generation beta-adrenoceptor blocker, derived from eugenol, with alpha-adrenoceptor blocking and beta2-adrenoceptor agonist-associated vasorelaxant activities

Eugenodilol, derived from natural eugenol, was first investigated with in vivo and in vitro models. In our in vivo study, eugenodilol (0.5, 1.0, and 1.5 mg/kg, i.v.) produced dose-dependent hypotensive and bradycardic responses in pentobarbital-anesthetized Wistar rats. Eugenodilol also inhibited the tachycardia and arterial pressor effects induced by (-)isoproterenol and phenylephrine, respectively. In our in vitro study, eugenodilol competitively antagonized (-)isoproterenol-induced positive inotropic and chronotropic effects and tracheal-relaxation responses on isolated guinea pig tissues in a concentration-dependent manner. The apparent pA2 values were 7.88+/-0.12 for right atria, 7.52+/-0.05 for left atria, and 7.33+/-0.15 for trachea, indicating that eugenodilol was a nonselective beta-adrenoceptor blocker. In thoracic aorta experiments, the apparent pA2 values of alpha-adrenoceptor blockade were 7.05+/-0.25 and 6.87+/-0.08 for eugenodilol and labetalol, respectively. In addition, eugenodilol produced cumulative relaxation responses on isolated guinea pig tracheal strips. The effects were competitively antagonized by ICI 118,551 (10(-8)-10(-6) M), a relatively selective beta2-adrenoceptor antagonist. In the radioligand-binding assay, the Ki values of [3H]CGP-12177 binding to rat ventricle and lung membranes were 9.72 and 48.29 nM, respectively, and the value of [3H]prazosin binding to rat brain membrane was 38.72 nM. These results further confirmed the alpha/beta-adrenoceptors-blocking activities of eugenodilol reported in the functional studies. We conclude that eugenodilol is a novel third-generation beta-adrenoceptor blocker with ancillary blocking activity at alpha-adrenoceptors and weak sympathomimetic activity at beta2-adrenoceptors.

Potent inhibition of spontaneous rhythmic contraction by a novel beta 2-adrenoceptor agonist, HSR-81, in pregnant rat uterus

We examined the effect of HSR-81 ((-)-(R)-alpha-[(tert-butylamino)methyl]-2-chloro-4-hydroxybenzyl alcohol L-tartrate), a newly developed, potent and selective beta 2-adrenoceptor agonist, as well as ritodrine and isoproterenol, on the spontaneous rhythmic contraction in uteri isolated from late pregnant, middle pregnant and non-pregnant (dioestrous and oestrous) rats. The three agonists inhibited the spontaneous rhythmic contraction at all the stages in a concentration-dependent manner. The pD2 value for HSR-81 was greater in late pregnancy than in dioestrus and oestrus. In the uterine preparations of late pregnancy and dioestrus, ICI-118,551 (1-(7-methylindan-4-yloxy)-3-isopropyl-aminobutan-2-ol , a selective beta 2-adrenoceptor antagonist) and atenolol (a selective beta 1-adrenoceptor antagonist) produced a parallel rightward shift of the concentration-response curves for HSR-81. The pKB values for ICI-118,551 and atenolol suggest that the inhibitory effect of HSR-81 was mediated through beta 2-adrenoceptors in the two stages. In the membranes prepared from rat uteri in late pregnancy and dioestrus, the equilibrium dissociation constant for [125I]iodocyanopindolol binding was not significantly different between the two stages. The three beta-adrenoceptor agonists and the two antagonists competed for the specific [125I]iodocyanopindolol binding and the pKi values were not significantly different between the two stages. However, the maximum number of binding sites was significantly greater in late pregnancy than in dioestrus. The configuration of the competition curves and the pKi values for the two antagonists confirmed the fact that these membranes contain predominantly beta 2-adrenoceptor subtype. These results indicate that the potent inhibition of the spontaneous rhythmic contraction by HSR-81 in the pregnant uterus may be due to the increased number of beta 2-adrenoceptors.

Cardioprotective effect of pindolol in ischemic-reperfused isolated rat hearts

The effects of pindolol and timolol on ischemia reperfusion damage were studied in isolated working rat hearts. Ischemia (15 min) decreased the mechanical function and the energy state, and increased the tissue levels of free fatty acids (FFA). During reperfusion (20 min), the mechanical function did not recover, but the energy state recovered incompletely, whereas FFA increased further. Pindolol (50 microM) accelerated recovery of the mechanical function and the energy state that had been decreased by ischemia during reperfusion, and inhibited the accumulation of FFA during ischemia and reperfusion, especially when it was applied during the whole period of reperfusion. Timolol (50 microM), however, did not accelerate recovery of the mechanical function and the energy state during reperfusion, although it attenuated FFA accumulation during reperfusion. The pindolol-induced recovery of the mechanical function during reperfusion was reduced by timolol. The results suggest that the intrinsic sympathomimetic activity of pindolol may play an important role, at least in part, in producing the cardioprotective effect, especially during reperfusion.

Effects of chronic pindolol treatment on human myocardial beta 1- and beta 2-adrenoceptor function

To evaluate the effects of chronic pindolol treatment on human myocardial beta-adrenoceptor, membrane preparations from right atrial auricles from patients on chronic pindolol treatment and from patients not treated with beta-blocker were compared with respect to specific binding of [125I]-iodocyanopindolol [( 125I]-ICYP) and adenylate cyclase (AC) activity. Pindolol treatment was associated with a 25% increase in total beta-adrenoceptor density (72.3 vs. 58.3 fmol/mg protein). This increase was due a 40% increase of the beta 1-adrenoceptor subtype (62.2 vs. 44.3 fmol/mg protein), while beta 2-adrenoceptor density was decreased by about 25% (10.0 vs. 14.0 fmol/mg). Isoprenaline 5 mumol/l (9.7 vs. 14.2 pmol/min/mg) and terbutaline 50 mumol/l (4.9 vs. 8.3 pmol/min/mg protein) stimulated adenylate cyclase activity was reduced, whereas fluoride (10 mmol/l) stimulated cAMP production to the same extent in both groups (9.4 vs 9.4 pmol/min/mg protein). Thus, chronic treatment with pindolol was associated with upregulation of the beta 1-adrenoceptors and a down-regulation of the beta 2-adrenoceptors. The total level of beta-adrenoceptors was slightly increased. In spite of this, adenylate cyclase activity and response was reduced.

Desensitization pattern of cardiac beta-adrenoceptor subtypes by prolonged in vivo infusion of pindolol and celiprolol in rats

The regulatory effects of pindolol and celiprolol on cardiac beta-adrenoceptor density were studied in vivo in order to assess the subtype selectivity of their partial agonistic activity (PAA). The substances were continuously administered to rats for 1 week by means of implanted osmotic minipumps. The density of beta-adrenoceptor subtypes were estimated from ICYP saturation binding experiments performed on cardiac ventricular plasma membranes in the presence of a highly selective antagonist (CGP 20172 A or ICI 118,551). Both antagonists were employed at concentrations as high as to block one subtype only without affecting the complementary subtype. For control purposes, rats were also treated with isoprenaline (0.4 mg/kg/h) and propranolol (0.15 mg/kg/h), or vehicle. Pindolol (0.036 mg/kg/h) and celiprolol (0.36 mg/kg/h) reduced the density of ventricular beta 2-adrenoceptors by 46% and 23%, respectively, which--in the case of pindolol--was significant when compared to the non-treated controls. Both compounds, however, produced a small, but distinct increase in the number of beta 1-adrenoceptors by approximately 26%. This finding is in contrast to the propranolol--induced up-regulation of both beta 1- and beta 2-adrenoceptors by approximately 80%. Since supramaximal doses of each drug were administered, a significant smaller increase of beta 1-adrenoceptors by pindolol and celiprolol--as compared to the increase produced by propranolol--can be interpreted as evidence for a PAA of pindolol and celiprolol on beta 1-adrenoceptors as well. Isoprenaline as a full agonist caused a marked loss of of both beta-adrenoceptor subtypes.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrinsic sympathomimetic activity of beta-adrenoceptor antagonists: down-regulation of cardiac beta 1- and beta 2-adrenoceptors

Prolonged treatment of cultured rat heart muscle cells containing beta 1- and non-muscle cells containing beta 2-adrenoceptors with beta-adrenoceptor antagonists devoid of intrinsic sympathomimetic activity had no effect on beta-adrenoceptor density. In contrast, antagonists with intrinsic sympathomimetic activity decreased beta-adrenoceptor density and response (adenylate cyclase stimulation) in both heart muscle (beta 1) and non-muscle cells (beta 2) by a maximum of about 50%. An even larger down-regulation of beta-adrenoceptors and loss of receptor-stimulated adenylate cyclase activity was induced by the full endogenous agonist, noradrenaline, with the beta-adrenoceptors of heart muscle cells (beta 1) being much more sensitive to the beta 1-selective noradrenaline than the heart non-muscle cell beta 2-adrenoceptors. When combined with noradrenaline, the antagonists with intrinsic sympathomimetic activity prevented the action of noradrenaline at both beta 1- and beta 2-adrenoceptors, thereby leading to an apparent up-regulation of receptor density and response. This apparent reversal from an agonist to an antagonist action was observed at much lower concentrations of noradrenaline at beta 1- than at beta 2-adrenoceptors. The data presented indicate that the beta-adrenoceptor antagonists with intrinsic sympathomimetic activity, but not those without, upon prolonged treatment decrease the density and responsiveness of both beta 1- and beta 2-adrenoceptors in cultured rat heart cells. This suggests that the intrinsic sympathomimetic activity of these agents is not a subtype-selective component. Furthermore, the agonist and antagonist activity of these agents apparently depends on the concomitant presence of an endogenous full agonist and an its own affinity and that of the partial agonist for the beta-adrenoceptor subtype.

Characterization of the beta 1-adrenoceptor stimulatory effects of the partial beta 1-agonists acebutolol, xamoterol, H142/08 and H201/70

The beta 1-adrenoceptor stimulatory effects of the partial beta 1-agonists acebutolol, xamoterol, H142/08 and H201/70 were investigated in the isolated right atrium (frequency response) of the rat. All the partial agonists studied induced a concentration-dependent increase in atrial rate. This effect was antagonized by the beta 1-selective blocker pafenolol. The concentrations of H142/08 and H201/70 needed to produce a half maximal response (-log EC50: pD2) were significantly greater than those required to occupy half the receptor population (-log equilibrium dissociation constant: pKB). These compounds required a fractional receptor occupancy of 80-90% to produce half the maximal stimulatory effect while the corresponding receptor occupancy for the other partial agonists studied was about 20%. The maximal stimulatory effect (intrinsic activity) generated by the compounds in the right atrium was (mean +/- S.D.): xamoterol 60 +/- 11%, H142/08 30 +/- 9%, H201/70 18 +/- 3% and acebutolol 17 +/- 8%. In addition, the stimulatory potency of the partial agonists was calculated as the efficacy (e) of the compounds relative to that of isoprenaline. The relative efficacy, expressed as -log[e(partial agonist/e(isoprenaline)] was: xamoterol 2.2 +/- 0.4, acebutolol 3.0 +/- 0.2, H142/08 3.4 +/- 0.2 and H201/70 3.6 +/- 0.2. It is concluded that partial beta 1-agonists have different relationships between their stimulatory effect and fractional receptor occupancy. There was a poor correlation between the intrinsic activity and relative efficacy of partial beta 1-agonists in the right atrium.

Uterotropic 6-methoxybenzoxazolinone is an adrenergic agonist and a melatonin analog

6-Methoxybenzoxazolinone (MBOA) is a compound isolated from grasses which has gonadotropic effects in a variety of animals. The weak beta-adrenergic agonist character of MBOA is shown by its in vitro stimulation of adenylate cyclase from several tissues. Tritiated MBOA bound specifically to particulate fractions from uterus is also displaced by alpha- and beta-adrenergic compounds. The adrenergic properties of MBOA suggest it may exert diverse effects including direct actions on gonadotropin synthesis and release. The mixed adrenergic agonist ephedrine and the antidepressant imipramine were also found to be uterotropic in the vole Microtus montanus following injection protocols used with MBOA. MBOA is structurally similar to melatonin (5-methoxy-N-acetyltryptamine); [3H]melatonin which binds to uterine and pineal membranes is displaced by MBOA and by other adrenergic agents. The fact that MBOA is a beta-adrenergic agonist and a melatonin analog can account for stimulatory and inhibitory effects of this compound on sexual development.

The role of endogenous noradrenaline in the beta-blocker withdrawal phenomenon--studies with cultured heart cells

An in vitro model to evaluate the role of endogenous noradrenaline in the beta-blocker withdrawal phenomenon is described: Beating chicken heart muscle cells (5000 beta 1-adrenoceptors/cell) and heart nonmuscle cells (3000 beta 2-adrenoceptors/cell) were cultured in serum-free, hormone-supplemented medium. Basal state, subtype selective down-regulation of beta-adrenoceptors by endogenous noradrenaline (decrease in receptor number, beta 1 more than beta 2) was simulated by addition of noradrenaline to the culture medium; chronic beta-blockade was simulated by exposure of the cells for 3 days to various beta-blockers (propranolol, no ISA; timolol, slight ISA; pindolol, strong ISA). Beta-blocker withdrawal phenomenon--increased response in isoproterenol-induced cAMP production and positive inotropy--is correlated with the increase in the number of beta-adrenoceptors after withdrawal of the drugs. Propranolol induces a withdrawal phenomenon at every degree of noradrenaline-induced basal state down-regulation of beta-adrenoceptors; in contrast, a withdrawal phenomenon by pindolol is only seen at a higher degree of beta-adrenoceptor down-regulation. In the presence of physiological noradrenaline concentrations pindolol affects beta-adrenoceptor subtypes in a qualitatively different manner: the number of beta 1-adrenoceptors is increased, the number of beta 2-adrenoceptors is decreased. This finding demonstrates that the intrinsic sympathomimetic activity of nonselective beta-blockers can manifest itself only if the receptors are not strongly down-regulated. As beta 2-adrenoceptors are present in a much less down-regulated state than beta 1, ISA mainly acts on beta 2-adrenoceptor subtype, thus, presenting a beta 2-"pseudo-selectivity" of ISA.

Beta 1- and beta 2-adrenoceptor affinity and stimulatory effects of (S)-pindolol and iodinated (S)-pindolol

The beta 1- and beta 2-adrenoceptor affinity and stimulatory effects of iodinated (S)-pindolol (IPIN) and (S)-pindolol were investigated in vitro using beta-adrenoceptor binding technique and isolated right atrium (rate increase, beta 1) and uterus (relaxation, beta 2) of the rat. IPIN had a higher affinity towards beta-adrenoceptors compared to (S)-pindolol, with some beta 2-adrenoceptor selectivity. In the rat uterus, IPIN produced only marginal stimulatory effects, while (S)-pindolol caused a concentration-dependent relaxation with a maximal effect that was 55% of that generated by isoprenaline. In the right atrium IPIN caused an increase in the atrial rate similar to that caused by (S)-pindolol. The concentration of IPIN required in the right atrium for a half-maximal response (pD2 = 7.81) was markedly greater than that required for occupation of half the beta-adrenoceptor population (pKB = 9.81). The beta 1-selective blocker metoprolol antagonized the effect of (S)-pindolol and IPIN on the atrial rate but a greater concentration of metoprolol (5 X 10(-6) M compared with 5 X 10(-7) M) was required to antagonize the effect of IPIN significantly. It is concluded that iodination of (S)-pindolol increased its affinity and decreased its efficacy towards beta-adrenoceptors.