The beta-adrenoceptor of pig coronary arteries: determination of beta 1 and beta 2 subtypes by radioligand binding

beta-Adrenoceptors of pig coronary arteries were investigated by the use of a new ligand, 125iodocyanopindolol (ICYP) in binding studies. Inhibition of ICYP binding by betaxolol (a selective beta 1-antagonist), zinterol (a selective beta 2-agonist) and ICI 118551 (a selective beta 2-blocking drug) resulted in non-linear Scatchard plots, suggesting that both beta-adrenoceptor subtypes are present in pig coronary arteries. Computer analysis of the data gave a beta 1:beta 2-adrenoceptor ratio of approximately 65:35.

[Pharmacokinetics of S 3341. Analysis by inhibition of the specific binding of 3H-clonidine]

1. The radioreceptor assay for S 3341, an alpha 2-adrenergic agonist, is based on the ability of the S 3341 to compete with the specific binding of [3H] clonidine to alpha-receptors of rat cerebral cortex membranes. The technique described was used for S 3341 plasma determination. 2. S 3341 levels in plasma and blood pressure were measured in hypertensive subjects 1, 3, 5, 8, 12, 24 and 48 hours after ingestion of the drug. 3. The s 3341 plasma level rose to a maximum between the first and the third hours after ingestion and then declined, with a mean half-life of 14 hours. There were substantial inter-individual variations, ranging from 3 to 24 hours. 4. The fall in blood pressure mirrored the increase in the s 3341 plasma level during the three hours following the ingestion of the drug.

Effects of N-aralkyl substitution of beta-agonists on alpha- and beta-adrenoceptor subtypes: pharmacological studies and binding assays

The pharmacological and binding properties of four beta-adrenomimetic drugs with N-alkyl substitutions (isoprenaline, terbutaline, salbutamol and soterenol) were compared with those of four corresponding drugs with N-aralkyl substitutions (protokylol, ME 506, salmefamol and zinterol). BD-40 A, a very powerful beta 2-agonist with a related chemical structure, was also included in this study. The beta 1- and beta 2-activities of these drugs were determined on guinea-pig atria and trachea, their alpha-adrenolytic activity was measured on rat aorta and their affinities (Ki) for alpha 1- and alpha 2-adrenoceptors on rat cortical membranes were assessed using [3H]prazosin and [3H]yohimbine. In this group of beta-agonists, substitution of the N-alkyl by an N-aralkyl group had a variable effect on the beta 2-selectivity whereas alpha-adrenolytic properties were always enhanced. An increase of the affinities (Ki) for both alpha 1- and alpha 2-adrenoceptors was found but the effect was much more pronounced for alpha 1-adrenoceptors. These results indicated that the alpha-adrenolytic activity observed with the N-aralkyl beta-agonists was selective for alpha 1-adrenoceptors.

Comparison of pharmacological and binding assays for ten beta-adrenoceptor blocking agents and two beta-adrenoceptor agonists

1 The inhibition constants evaluated by binding assays for ten beta-adrenoceptor blocking agents and two beta-adrenoceptor agonists, were compared with the pA2 and pD2 values determined in vitro and in vivo. 2 There was only a limited correlation between beta 1 or beta 2 selectivities observed with the different methods. 3 Selectivity is generally less pronounced in binding assays than for in vivo and in vitro experiments.

Studies on some para-substituted clonidine derivatives that exhibit an alpha-adrenoceptor stimulant activity

1 alpha-Adrenoceptor stimulant activity was determined for noradrenaline (NA), clonidine and a series of para-substituted derivatives of clonidine on rat aortic strips, a rat brain synaptosome preparation, and anaesthetized pithed rats. The effects on the blood pressure of intraventricular (i.c.v.) injections of para-aminoclonidine were also determined in anaesthetized rats. 2 Para-substituted derivatives of clonidine (amino-, diethylamino-, ethylamino-, acetamido-, bromoacetamido-, N-chloroethyl-N-methyl-amino and N-beta-chloroethyl-N-methylaminomethyl-) retain alpha-adrenoceptor stimulant activity. 3 pD2 values determined on rat aortic strips were 11.2, 7.67 and 9.05 respectively for para-aminoclonidine, clonidine and noradrenaline. The Ki values of these agents, determined on a rat brain synaptosomal preparation with a radioreceptor assay using [3H]-clonidine as ligand, were 1.3, 8.0 and 23 nM respectively for para-aminoclonidine, clonidine and NA. When given by i.c.v. injection in rats, para-aminoclonidine lowered the blood pressure. 4 N-beta-chloroethyl-N-methylaminomethylclonidine is an alkylating agent with an unusual agonist activity. It elicits contractions of the rat aorta that persist despite repeated washing. 5 alpha-Adrenoceptor affinities are discussed in relation to their structural features.

A potent new beta2-adrenoceptor blocking agent

1 (t-Butyl-amino-3-ol-2-propyl) oximino-9 fluorene is a new beta2-adrenoceptor blocking agent with a pA2 of 9.23+/-0.25 on isolated trachea. 2 It provokes hypertension in normotensive rats and does not prevent arterial hypertension in SHR rats, although it does prevent the renin secretion normally induced by isoprenaline infusion.

Comparison of the effect of two groups of diuretics on renin secretion in the anaesthetized dog

1. The effects of two groups of diuretics on renin secretion have been compared in dogs anaesthetized with pentobarbital. 2. Frusemide, ethacrynic acid and bumetanide cause an immediate rise in renin secretion which is not inhibited either by DL-propranolol or by a bilateral ureterovenous anastomosis which prevents salt and water loss. 3. Clopamide, metolazone and indapamide do not cause an immediate rise in renin secretion. Renin hypersecretion is induced only 1 h after intravenous injection of these diuretics. 4. Renin secretion was studied for 6 h after frusemide injection: the immediate rise was followed by a later increase in renin secretion. This later rise was inhibited by propranolol and by ureterovenous anastomosis. 5. These results allow us to distinguish between a direct renal mechanism responsible for early renin hypersecretion, which appears to be connected with the action of the diuretic on the ascending limb of Henle's loop, and an indirect mechanism responsible for late renin hypersecretion, which appears to be connected with salt and water loss.

Effects of apomorphine and of pimozide on renin secretion in the anaesthetized dog

This paper presents the results of a study of the receptors involved in renin hypersecretion induced by dopamine. Apomorphine induces renin hypersecretion without significantly modifying the renal blood flow. This renin hypersecretion is inhibited by haloperidol. However, pimozide, a selective dopaminolytic agent, is incapable of inhibiting the renin hypersecretion induced by dopamine. These results provide supplementary evidence for the existence of renal dopaminergic receptors which would appear to differ from the central dopaminergic receptors.

Role of the ventral surface of the brain stem in the hypotensive action of clonidine

The areas S of the ventral surface of the brain stem and the immediately surrounding zone were superficially destroyed by the means of electro-coagulation, in 14 cats. This destruction produced a drop in blood pressure, which was transient in 9 and definitive in 4 animals; in one cat only the arterial pressure did not change after the destruction. In 6 animals which have been sham-operated, clonidine (15 mug/kg, i.v.) always induced a marked fall in blood pressure whereas in 10 animals which had maintained or recovered a normal blood pressure after the destruction of the area S, clonidine (15 mug/kg) injected intravenously no longer produced any decrease of the arterial pressure. These results suggest that the integrity of the areas S is necessary for the development of the hypotensive action of clonidine. This hypotensive drug may act, at least at the level of the ventral surface of the brain stem, through inhibition of a vasopressive structure.

Effect of catecholamines on renin release in vitro

Beta receptor activation by isoproterenol stimulates renin release by kidney slices "in vitro". This effect is dose-dependent and blocked by propranolol. High norepinephrine concentration has an inhibitory effect on renin secretion which is reversed by phentolamine: activation of alpha receptors probably decreases renin release.