Selective and full beta 1-adrenoceptor agonist action of a catechol derivative of denopamine (T-0509) in the guinea-pig cardiac muscle and trachea: comparison with denopamine, xamoterol and isoprenaline

Markedly reduced effects of (-)-isoprenaline but not of (-)-CGP12177 and unchanged affinity of beta-blockers at Gly389-beta1-adrenoceptors compared to Arg389-beta1-adrenoceptors

1. Substitution of arginine by glycine at position 389, a frequent beta(1)-adrenoceptor polymorphism, reduces adenylyl cyclase stimulation by (-)-isoprenaline. beta(1)-Adrenoceptors mediate the effects of catecholamines and nonconventional partial agonists ((-)-CGP12177) through different sites. We investigated the influence of the 389 polymorphism on beta blocker affinity, as well as on the responses to (-)-isoprenaline and the nonconventional partial agonist (-)-CGP12177 on cyclic AMP levels in CHO cells expressing recombinant Arg389-beta(1)-adrenoceptors (101 fmol mg(-1) protein) or Gly389-beta(1)-adrenoceptors (94 fmol mg(-1)). 2. The affinity of beta-blockers and partial agonists, estimated from competition binding with (-)-[(125)I]-cyanopindolol, was not different for Arg389-beta(1)-adrenoceptors and Gly389-beta(1)-adrenoceptors. 3. The maximum cAMP increases by (-)-isoprenaline and (-)-CGP12177 at Gly389-beta(1)-adrenoceptors were reduced by 97 and 46%, but the potencies enhanced 2 and 0.5 log units, respectively, compared to Arg389-beta(1)-adrenoceptors. The intrinsic activity of (-)-CGP12177 with respect to the (-)-isoprenaline was 0.057 at Arg389-beta(1)-adrenoceptors and 1.05 at Gly389-beta(1)-adrenoceptors. 4. We confirm in intact CHO cells that responses to (-)-isoprenaline are markedly reduced at Gly389-beta(1)-adrenoceptors compared to Arg389-beta(1)-adrenoceptors. However, the 389 polymorphism reduces considerably less the agonist responses to (-)-CGP12177, indicating that coupling to G(s) protein is different for beta(1)-adrenoceptors activated by catecholamines than for receptors activated by nonconventional partial agonists. The affinity of beta-blockers is conserved across the Arg389Gly polymorphism.

Functional beta1- and beta2-adrenoceptors in the left and right atrium of pre-hypertensive rats

There is a small increase in the functional beta2-adrenoceptor response on the spontaneously hypertensive rat (SHR) left atrium in the early stages of hypertension. In the present study, the functional beta1- and beta2-adrenoceptors of the left and right atrium in SHR pre-hypertension and age-matched (5-week-old) Wistar Kyoto (WKY) rats were characterized. Contractility methods with isoprenaline, T-0509 (a selective beta1-adrenoceptor agonist) and procaterol (a selective beta2-adrenoceptor agonist) were used. At 5 weeks, the SHRs were pre-hypertensive. Isoprenaline was more potent on the left atrium of 5-week-old SHRs than WKY rats. Bisoprolol, a selective beta1-adrenoceptor antagonist, was more potent against isoprenaline and T-0509 on the SHR than WKY rat left atrium. ICI 118,551, a selective beta(2)-adrenoceptor antagonist, was more potent against procaterol and T-0509 on the SHR than WKY rat left atrium. The results with bisoprolol and ICI 118,551 suggest that there are more functional beta(1)- and beta(2)-adrenoceptors on the left atrium of 5-week-old SHRs than WKY rats. Isoprenaline, T-0509 and procaterol were equipotent on the right atrium of 5-week-old WKY rats and SHRs. Bisoprolol was more potent against isoprenaline, T-0509 and procaterol on the SHR than WKY rat right atrium. ICI 118,551 was more potent against T-0509, but not isoprenaline and procaterol, on the SHR than WKY rat left atrium. This suggests there are more functional beta1-adrenoceptors, and probably more functional beta2-adrenoceptors, on the right atrium of 5-week-old SHRs than WKY rats. These functional differences in beta1- and beta2-adrenoceptor-mediated responses of the left and right atria of pre-hypertensive SHRs cannot be caused by hypertension, and may be associated with the onset of hypertension.

Pharmacological characterization of beta-adrenoceptors mediating relaxation of the rat urinary bladder in vitro

1. Isoproterenol relaxed KCl-precontracted rat bladder strips with a pD2 of 7.21 leaving a residual contractile response of 3.2% after 30 microM. The selective beta1-agonist, T-0509 (pD2 : 6.24, 10.1% residual contraction after 100 microM), beta2-agonist, terbutaline (pD2 : 5.43, 13.7% residual contraction after 100 microM), and beta3-agonists, BRL 37344A (pD2 : 6.60, 17.3% residual contraction after 100 microM), and SR 58611A (pD2 : 5.15, 34.0% residual contraction after 100 microM), also relaxed bladder strips. 2. The relaxant response to isoproterenol was weakly but significantly antagonized by 1 microM propranolol which produced a 3 fold shift of the concentration-response curve to the right, and significantly antagonized by the beta1-selective antagonist, metoprolol (10 microM, 3 fold shift), and the beta2-selective antagonist, butoxamine (100 microM, 6 fold shift). A combination of 10 microM metoprolol and 100 microM butoxamine caused a 15 fold shift of the concentration-response curve for isoproterenol to the right. Incubation with the beta3-antagonist, SR 59230A (1 microM), caused a 6 fold shift of the concentration response curve for isoproterenol to the right. 3. The non-conventional partial agonist, CGP 12177A, weakly relaxed KCl-precontracted bladder strips (pD2 : 3.31, 51.3% residual contraction after 300 microM); the relaxation was resistant to blockade by 1 or 10 microM propranolol. 4. In the presence of 200 microM propranolol, CGP 12177A (20 microM) or SR 59230A (10 microM) antagonized surmountably the relaxant effects of BRL 37344A. 5. The data suggest that rat urinary bladder body contains beta1, beta2, and beta3-adrenoceptors, all of which mediate relaxation.

Prolongation of the life span of cardiomyopathic hamster by the adrenergic beta 1-selective partial agonist denopamine

Influence of cardiotonic agents on the prognosis of heart failure depends on the individual therapeutic agents, and favorable and unfavorable effects of these agents have been reported in clinical trials. We studied the effect of the cardiotonic agent denopamine on the life span of cardiomyopathic hamsters (BIO 14.6 strain) in the heart failure period. Non-treated hamsters started to die at 40 weeks of age, and their survival rate decreased to 23.8% at the age of 65 weeks. Hamsters treated with denopamine (400 ppm in diet) from 36 weeks of age did not die until the age of 52 weeks, except in cases of accidental death. The survival rate of this group at 65 weeks of age was about 40%. Survival rates of these 2 groups were significantly different (P < 0.05) when animals with accidental death were excluded. To elucidate the mechanism of the effect of denopamine, we performed several experiments after dietary treatment with denopamine for 4 to 6 weeks from 37 weeks of age. Denopamine treatment lowered plasma levels of noradrenaline and dopamine (P < 0.05), but affected neither the cardiac contractility nor the beta-adrenoceptor density. In summary, denopamine significantly decreases the mortality of cardiomyopathic hamsters. Its effect to lower the plasma catecholamine levels may be responsible for the beneficial effect of denopamine.

Molecular characterization of pharmacological properties of T-0509 for beta-adrenoceptors

The pharmacological properties of T-0509, (-)-(R)-1-(3,4-dihydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)amino]ethanol, were compared with those of isoproterenol. In the radioligand binding studies of [125I]iodocyanopindolol with COS-7 cell membranes that transiently expressed beta-adrenoceptor subtypes, T-0509 exhibited 11- and 97-fold greater Ki values for beta 2- and beta 3-adrenoceptors, respectively, compared with beta 1-adrenoceptors. Affinities of beta 2- and beta 3-adrenoceptors to isoproterenol were 1.4- and 28-fold lower than that of beta 1-adrenoceptors, respectively. The maximal stimulatory effects of T-0509 on adenylyl cyclase of CHO-K1 (chinese hamster ovary K1) cell membranes expressing beta 1- or beta 2-adrenoceptors were 85% or 96% of those produced by isoproterenol, respectively. These results indicate that T-0509 is a relatively specific beta 1-adrenoceptor agonist with a high intrinsic activity as compared with isoproterenol.

Prolonging action of imidapril on the lifespan expectancy of cardiomyopathic hamsters

We studied the effect of imidapril, a novel angiotensin-converting enzyme (ACE) inhibitor, on lifespan expectancy of cardiomyopathic (CM) hamsters of BIO 14.6 strain, one of the representative models of congestive heart failure (CHF). Imidapril was consecutively administered to hamsters by mixing it in their diet at a concentration of 480 ppm (approximately 30 mg/kg/day) or 1,600 ppm (approximately 120 mg/kg/day) from age 26 weeks. Only several control hamsters died before age 54 weeks, but their survival rate decreased to 23.7% at age 73 weeks. The survival rates of 480-ppm and 1,600-ppm imidapril groups at age 73 weeks were as high as 75.7 and 68.4%, respectively (p < 0.01 vs. control hamsters). Macroscopic and microscopic pathology in imidapril-treated groups was milder than that in control animals in general, but differences were not statistically significant when animals were divided into survivors and fatalities except for the presence of mural thrombus in the heart. We further studied the effects of imidapril on blood pressure (BP), in vivo cardiac function, cardiac beta-adrenoceptor distribution, and plasma catecholamine levels after dietary treatment with 480 ppm imidapril for 8-10 weeks from age 37 weeks. Imidapril-treated animals showed improved cardiac function under urethane anesthesia. These results indicate that imidapril prolongs lifespan expectancy of CM hamsters and suggest that a hemodynamic effect of imidapril is involved in its beneficial effect.

Desensitization and selective down-regulation of rat cardiac beta 1-adrenoceptors by prolonged in vivo infusion of T-0509, a beta 1-adrenoceptor full agonist

We studied the effects of prolonged infusion of a selective beta 1-adrenoceptor (beta 1AR) full agonist, T-0509 [(-)-(R)-1-(3,4-dihydroxyphenyl)-2-[(3,4- dimethoxyphenethyl)amino]ethanol hydrochloride], with regard to its inotropic effect in vivo and cardiac beta AR density. The results were compared with those for isoproterenol. Continuous infusion of isoproterenol at doses of 2.5-40 micrograms/kg/hr, s.c. for 6 days shifted the dose-response curves of isoproterenol (i.v.) for LVdP/dtmax to the right and increased the ED50 values up to fourfold. Isoproterenol infusion at 40 micrograms/kg/hr reduced the density of both beta 1- and beta 2ARs by 36% and 43% respectively, in left ventricular membranes. Following 6-day infusion of T-0509 at doses sufficient to induce a positive inotropic effect (5-40 micrograms/kg/hr), the ED50 value of T-0509 (i.v.) for LVdP/dtmax was also increased up to fourfold. In contrast to isoproterenol, infusion of T-0509 caused selective down-regulation of beta 1ARs by 30% without changing the number of beta 2ARs. These results indicate that long-term application of a selective beta 1AR full agonist causes desensitization to its inotropy in vivo, with subtype-selective down-regulation of beta 1ARs in cardiac ventricles.

Desensitization of beta-adrenergic responses in adipocytes involves receptor subtypes and cAMP phosphodiesterase

Acute exposure of isolated adipocytes to isoproterenol induces the desensitization of lipolytic responses to norepinephrine and selective beta 1-, beta 2- and beta 3-adrenoceptor agonists, as well as the adrenocorticotropic hormone 1-24 fragment (ACTH). Forskolin and 8-bromo-cAMP responses are also desensitized. When lipolysis was measured in the presence of OPC 3911 [N-cyclohexyl-N-2-hydroxyethyl-4(6-(1,2-dihydro-2- oxoquinolyloxy))butyramide], a specific inhibitor of the cAMP phosphodiesterase of adipocytes, the desensitization of all lipolytic agents--except the beta 2-adrenoceptor agonist--was abolished. Isoproterenol induced a similar loss (35%) of both membrane beta 1- and beta 2-adrenoceptors and an uncoupling of beta 1-adrenoceptors, but did not modify the weak coupling of control beta 2-adrenoceptors. These data suggest that isoproterenol induced (i) an activation of the cAMP phosphodiesterase, which is solely responsible for the desensitization of norepinephrine response as well as beta 1- and beta 3-adrenoceptor mediated responses and (ii) an additional desensitization of the sole beta 2-adrenergic signaling system which suggests a subtype-selective pattern of regulating processes.

Functional beta-adrenoceptors in the left atrium of normotensive and hypertensive rats

1. The aim of the study was to characterize the functional beta 1-and beta 2-adrenoceptors of the rat left atrium and to investigate how these functional beta-adrenoceptor responses were altered in hypertension. The contractile responses of the left atrium from Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats to isoprenaline, T-0509 and procaterol were characterized. Subsequently, the effects of selective beta 1-(bisoprolol) and beta 2 (ICI 118,551)-adrenoceptor antagonists were investigated on these responses. 2. The maximal combined contractile responses of the rat left atrium to cardiac stimulation and CaCl2, isoprenaline, T-0509 or procaterol were not altered by hypertension. 3. The sensitivities to CaCl2 (pD2 on WKY left atrium = 2.99), isoprenaline (8.82) and T-0509 (8.84) were not altered by hypertension. There was an increase in sensitivity to procaterol from a pD2 value of 7.21 to 7.61 in the left atrium of the SH rat. 4. The basal tension induced by cardiac stimulation alone was inhibited by bisoprolol at > or = 10(-8) M and by ICI 118,551 at > or = 10(-7) M and this inhibitory effect is probably due to membrane stabilizing activity. 5. The pKB values for bisoprolol against isoprenaline, T-0509 and procaterol on the WKY were 8.43, 8.68 and 8.18, respectively, and were not different from SH rat left atrium. 6. The pKB value for ICI 118,551 against isoprenaline was increased from 7.06 on the WKY to 7.44 on the SH rat left atrium. The pKB values for ICI 118,551 against T-0509 and procaterol on the WKY were 7.18 and 8.14, respectively and were not significantly different from the SH rat left atrium values. 7. These results suggest that: (a) procaterol stimulates the beta 1-, in addition to, the beta 2-adrenoceptors of the rat left atrium; (b) functional beta 1-adrenoceptors are not altered in hypertension, and (c) there is probably an increase in the affinity of procaterol and isoprenaline for the beta 2-adrenoceptors which underlies the small increase in the functional beta 2-adrenoceptor response in hypertension.

Relaxant mechanisms of cyclic AMP-increasing agents in porcine coronary artery

We investigated the relaxant mechanisms of the cyclic AMP (cAMP)-increasing agents, isoproterenol, T-0509, forskolin and 3-isobutyl-1-methylxanthine (IBMX), on porcine coronary arteries contracted with U46619 (300 nM), a thromboxane A2 analogue, or 30 mM KCl, by measuring force simultaneously with intracellular Ca2+ concentration ([Ca2+]i) or cAMP and cyclic GMP (cGMP) levels. In U46619-contracted arteries, these agents decreased [Ca2+]i and force of contraction to almost the same extent in a concentration-dependent manner, whereas in KCl-contracted arteries these agents, except IBMX at higher concentrations, produced a relaxation with little change in [Ca2+]i. These agents all elevated tissue cAMP levels, and in addition, IBMX at higher concentrations increased cGMP levels. In Ca(2+)-free medium, these agents produced a concentration-dependent inhibition of Ca2+ release from intracellular Ca2+ stores induced by U46619 but not by 25 mM caffeine. Isoproterenol at a high concentration (3 microM) transiently decreased [Ca2+]i but steadily relaxed KCl-contracted arteries. This decrease in [Ca2+]i, but not the relaxation was inhibited by ryanodine and caffeine treatments. These results suggest that the relaxant mechanism of these agents on KCl-contracted arteries is mainly due to phosphorylation of myosin light chain kinase via cAMP-dependent protein kinase, resulting in a reduction of the Ca2+ sensitivity of contractile elements. Their relaxant mechanism in U46619-contracted arteries seems due to the inhibition of signal transduction of the agonist, resulting in a decrease in [Ca2+]i and inhibition of the Ca2+ sensitization.

Sensitive determination of (-)-isoproterenol and (-)-(R)-1-(3,4- dihydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)amino] ethanol (T-0509), a cardiotonic agent, in rat plasma utilizing a fully automated catecholamine analyser

(-)-Isoproterenol (ISO), used as bronchodilator, and (-)-(R)-1-(3,4-dihydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)amino]ethanol (T-0509), a new cardiotonic agent, were determined in rat plasma (only 25 microL) using a fully automated catecholamine (CA) analyser that includes in-line pre-extraction of CAs, coupled with an HPLC-ethylenediamine condensation reaction and a peroxyoxalate chemiluminescence detection system (HPLC-ED-PO-CL). The chromatographic conditions were: precolumn, SERUMOUT-CEX; buffer for delivering CAs in the precolumn, 10 mM potassium phosphate buffer (pH 7.5)/ethanol (92 + 8, v/v) (1 mL/min); precolumn clean-up solution, 4% phosphoric acid/acetonitrile (50 + 50, v/v) (1 mL/min); analytical column, TSKgel ODS-80Ts, 250 x 4.6 mm i.d.; eluent, 75 mM potassium acetate buffer (pH 3.2)/50 mM potassium phosphate buffer (pH 3.2)/acetonitrile (83.6 + 4.4 + 12, v/v/v for ISO and 76 + 4 + 20 v/v/v for T-0509) (1 mL/min); fluorogenic reagent solution, 105 mM ED and 175 mM imidazole in acetonitrile/ethanol (90 + 10, v/v) (0.25 mL/min); chemiluminogenic reaction solution, 0.25 mM TDPO, 150 mM hydrogen peroxide and 110 mM TFA in dioxane/ethyl acetate (50 + 50, v/v) (1.4 mL/min). Colterol, (+/-)-1-(3,4-dihydroxyphenyl)-2-[(1,1-dimethyl)ethylamino]ethanol, (+/-)-N-t-butylnorepinephrine was used as an internal standard (IS) for ISO, and (+/-)-1-(3,4-dihydroxyphenyl)-2-[(3,4,5- trimethoxyphenethyl)amino]ethanol, (+/-)-(3,4,5-trimethoxyphenethyl- aminomethyl)-3,4-dihydroxybenzylalcohol (T-1583) for T-0509. The detection limits for ISO and T-0509 were 1.3 and 0.9 fmol on injection, respectively.