Search

Treatment with 10 μM l-propranolol caused a rapid decrease in the high level of acetyl coenzyme A: serotonin N-acetyltransferase (EC 2.3.1.5, N-acetyltransferase) activity in pineal glands cultured in the presence of 1 μM norepinephrine. d-Propranolol was ineffective except at high concentration (1 mM). The same stereospecificity was also observed in organ culture when d- or l-propranolol was tested as a blocker of the norepinephrine-induced increase in N-acetyltransferase activity. Practolol (10–300 μM), a relatively specific β1,-blocker, also initiated a decrease and inhibited the norepinephrineinduced increase in N-acetyltransferase. Butoxamine (10–300 μM), a relatively specific β2-blocker, had no significant effect in either experimental situation. The percentage decrease in N-acetyltransferase activity after 40 min of treatment with l-propranolol was strongly dependent on temperature. At 40° C enzyme activity decreased by 92% but at 34° C enzyme activity decreased by only 50%. l-Propranolol (20 μM) did not inhibit the increase or initiate a decrease in N-acetyltransferase activity in pineal glands treated with 1 mM N6,O2 -dibutyryl adenosine cyclic 3',5'-monophosphate. The fast response observed when l-propranolol was added to the culture medium of norepinephrinetreated glands was not blocked by cycloheximide treatment. Concentrations of ouabain or K+, which are known to completely inhibit the norepinephrine-stimulated increase in N-acetyltransferase activity, caused only a small decrease in induced N-acetyltransferase activity, similar to that due to cycloheximide treatment.

Superfusion of the posterior hypothalamus of anaesthetized cats with alphaor beta-adrenoreceptor-blocking drugs increased the pressor response to electrical stimulation of the hypothalamus. The enhancing effect of noradrenaline was abolished by hypothalamic application of phenoxybenzamine. The enhancement by isoprenaline of the pressor response was slightly inhibited by butoxamine and abolished by atenolol. The spontaneous release of endogenous catecholamines from the hypothalamus into the superfusate was increased during electrical stimulation of the locus coeruleus as well as during superfusion of the hypothalamus with yohimbine. It is concluded that pre- and post-synaptic alpha-receptors as well as beta-receptors are present in the hypothalamus. The presynaptic receptors are involved in the regulation of the release of catecholamines. The postsynaptic alpha-receptors and the beta1-receptors are involved in the generation of the pressor response.

The effects of the d- and 1-isomers of epinephrine and norepinephrine have been determined on intraocular pressure (IOP) in conscious rabbits and rhesus monkeys, and on aqueous humor turnover rate (AHTR) in rabbits. Relatively specific beta-adrenergic antagonists (butoxamine and metoprolol) were used to attempt to modify the responses. The effects on IOP in both species are similar to those of racemic mixtures. The d- and 1-isomers of norepinephrine and epinephrine reduced IOP, and reduced AHTR in rabbits. The d- and 1-isomers of norepinephrine had little effect on IOP in monkeys while d- and 1-epinephrine increased IOP. Metoprolol, a beta1-antagonist was more effective than butoxamine (beta2-antagonist) at modifying the effect of the norepinephrine isomers in rabbits.

Beta-adrenoceptor agonists have been reported to inhibit gastric acid secretion in vivo but their site and mode of action is uncertain. A study of the effects of such agents on acid secretion in the rat has been made using both an in vivo preparation and an in vitro one where possible effects due to neural, hormonal or cardiovascular actions of beta-agonists are avoided. In conscious rats with Heidenhain pouches, isoprenaline (40 micrograms kg-1h-1) inhibited the response to pentagastrin (20 micrograms kg-1h-1). This inhibition was abolished by propranolol (2 mg kg-1) and butoxamine (8 mg kg-1) and partially reversed by practolol (8 mg kg-1). Propranolol alone (2 mg kg-1) significantly increased the response to pentagastrin in the pouch rats but butoxamine and practolol (both at 8 mg kg-1) and the inactive isomer (+)-propranolol were without effect on the pentagastrin response. In the rat isolated stomach preparation isoprenaline, salbutamol, salmefamol , adrenaline and nor-adrenaline all stimulated acid output over the range 2 X 10(-7) to 10(-5)M. These responses were antagonised by propranolol (2 X 10(-5)M), pindolol and timolol (10(-6)M) but only nor-adrenaline stimulated secretion was inhibited by the selective antagonists practolol, atenolol, butoxamine and ICI 118551. In vitro responses to beta-adrenoceptor agonists were not antagonised by atropine (10(-5)M), metiamide (10(-4)M) or prostaglandin E2 (10(-5)M).(ABSTRACT TRUNCATED AT 250 WORDS)

Ovalbumin-induced histamine release from passively sensitized monodispersed cells (2–4% mast cells) or purified mast cells (50–78%) from guinea-pig lung was inhibited by isoproterenol and sulfonterol and their relative potencies or maximum responses were similar in both cases. The apparent dissociation constant for butoxamine was also independent of mast cell purity. The results indicate that β-adrenoceptors mediating histamine release inhibition from lung are localized to mast cells and act independently of other cell types.

The chronotropic response of right atria isolated from 5-day-cold-exposed rats to isoproterenol and norepinephrine was studied. A large increase in the sensitivity of the pacemaker to isoproterenol and a decrease in the sensitivity to norepinephrine occurred. Determination of pA2 values of propranolol and metoprolol using isoproterenol and norepinephrine as agonists and analysis of the slopes of Schild plots suggested that in atria isolated from control rats the chronotropic effect of isoproterenol and norepinephrine resulted from the preferential interaction of the catecholamines with a homogeneous beta-1 adrenoceptor population. After cold exposure the affinity of atrial adrenoceptors for propranolol increased when the agonist was isoproterenol and decreased when norepinephrine was used. The slopes of the Schild plots of metoprolol when the agonists were isoproterenol or norepinephrine were not unitary unless the experiments were performed in the presence of butoxamine. However, butoxamine prevented the demonstration of cold-induced super-sensitivity to isoproterenol, leaving the subsensitivity to norepinephrine unaffected. It is concluded that cold-induced heterogeneity of the atrial beta adrenoceptors is responsible for the increased sensitivity to isoproterenol. Probably, subsensitivity to norepinephrine resulted from conformational alterations of the atrial beta-1 adrenoceptors.

The effect of β-adrenoceptors agonist ont the electrically induced release of 3 H-NE from the superfused rat portal vein was studied. It was observed that the β-adrenoceptor agonists isoproterenol and terbutaline produced a concentration dependent enhancement of the field-stimulation induced release of NE. In contrast to what was seen with drugs possesing β 2 -activity, the β 1 -agonist, dobutamine, was inactive. The enhancing effect of both isoproterenol and terbutaline was reduced or completely blocked by the β 1 – β 2 -antagonist, propranolol or the β 2 -antagonist butoxamine but not by the β 1 -antagonist, practolol. In the concentration used none of the three β-antagonists had any effect themselved in altering the stimulation induced release of NE. Epinephrine (EPI) at a concentration of 10 −8 M produced an enhancement of the electrically induced release of NE. The effects of EPI and terbutaline were additive with phenoxybenzamine. Higher concentrations (i.e., 10 −7 M) or norepinephrine (10 −8 or 10 −7 M) reduced the enhancement induced by the simultaneous administration of phenoxybenzamine. It is concluded that β-adrenoceptors of the β 2 type are present on adrenergic neurons innervating the rat portal vein. Activation of these receptors results in an enhancement of the electrically induced release of NE. Our data are consistent with the hypothesis of Stjarne and Brundin which suggests that the β-adrenoceptor mediated enhancement of NE release is an example of hormonal modulation of adrenergic transmission mediated by ciculating EPI of adrenal medullary origin.

Cyclic AMP phosphodiesterase has been incorporated into isolated rat submandibular acini by hypotonic swelling. This resulted in complete inhibition of the cyclic AMP rise stimulated by isoproterenol (10 μM), but had no effect on the stimulation of mucin secretion. Acini swollen in the absence of cyclic AMP phosphodiesterase showed similar cyclic AMP and mucin secretion responses to those of unswollen acini. The dissociation between cyclic AMP rise and mucin secretion was not due to stimulation of different β-receptor subtypes since both responses to isoproterenol were inhibited by the β 1 antagonist atenolol, but not by the β 2 antagonist, butoxamine. The results are the first to directly demonstrate that a maximally effective concentration of isoproterenol can increase mucin secretion in the absence of a detectable increase in cyclic AMP.

A new series of beta-adrenergic blocking amines containing an oximino-propanolic chain linked to an aromatic nucleus was synthesized. Most of the derivatives are characterized by beta2-selectivity. The structure-activity relationship are discussed. One of the compounds, selected for further studies, was more active on the trachea than on the atria of guinea pig, 155 times in vitro and 26 times in vivo. In comparison, butoxamine's beta2-selectivity is 13 in vitro and only 2 in vivo. With a series of 30 acetophenone oxime derivatives, no quantitative structure-activity relationships could be detected.

The pA 2 values for butoxamine, H35/25 and α-methylpropranolol varied with the agonist used (isoprenaline, fenoterol or noradrenaline) on guinea-pig isolated trachea but not on atria. Since the β 2 -β 1 selectivity of adrenoceptor antagonists is frequently based on the trachea-atria selectivity of the antagonist, these findings raise the question of which agonist(s) should be used for pA 2 determinations on these two tissues in selectivity studies on antagonist drugs.

The effect of albuterol, a potent beta2-adrenergic agonist, on kidney production of erythropoietin (Ep) was studied. Its effects on erythroid colony (CFU-E) formation in vitro in rabbit bone marrow cultures were also assessed. Albuterol produced a significant increase in plasma Ep levels in conscious rabbits following 7 h intravenous infusion (50 (microgram/kg)/min). This effect was blocked by pretreatment of the rabbits with butoxamine (5 mg/kg ip), a potent beta2-adrenergic blocker. Albuterol in doses of 10(-10) to 10(-8) M in combination with Ep was also found to produce a significant increase in the numbers of CFU-E in the plasma clot culture system of rabbit bone marrow. This effect was blocked completely by DL-propranolol (10(-8) M) and by butoxamine (10(-8) M). The data presented suggest that albuterol, a potent activator of beta2-adrenergic receptors, increases kidney production of Ep in vivo and also produces a direct effect in combination with Ep on the proliferation of the erythroid progenitor cell compartment.

The actions of the hexoprenaline, salbutamol and terbutaline on adrenalin-induced effects in the human artery were studied in vitro. The human uterine artery has a two-part response to adrenalin: The first, rapid (phasic component), and the second, slow and sustained (tonic component). Both beta-2 stimulators relax the tonic component and reduced the amplitude of the phasic component. The depressor effect of the responses to adrenalin is reduced in the presence of butoxamine and intensified in the presence of caffeine. These results suggest the existence on the human uterine artery of beta-2 adrenergic receptors acting as mediators of smooth muscle relaxation, and suggest also that the mechanism of this relaxation is most likely cAMP dependent.

Isolated, perfused rabbit hearts were used to identify substituted phenylethylamines selective for either chronotropic or inotropic stimulation relative to norepinephrine. Heart rate and dF/dtmax were measured; the difference in their normalized values was used as an index of selectivity. p-Octopamine (OA) showed chronotropic preference, while phenylephrine (PE) showed a significant inotropic preference. Their effects were not prevented by reserpine pretreatment, cocaine, butoxamine, or phenoxybenzamine, but were antagonized by propranolol, which suggests that OA and PE exert their selective actions directly at beta 1-receptors. These findings provide further evidence for the existence of separate chronotropic and inotropic beta-adrenergic receptors in the heart.

Publisher Summary This chapter discusses the inhibition of serotonin uptake into spleen by salbutamol (SB), a beta-adrenoceptor agonist. SB and isoprenaline (IP) are potent bronchodilators acting by beta-adrenoceptor agonism. Previous reports suggested a relationship between alpha receptor blockade and noradrenaline (NA) uptake inhibition. The chapter describes a study in which the effects of two beta adrenoceptor agonists SB and IP were determined on the in vivo uptake of 3 H-NA into mouse heart and 3 H-serotonin ( 3 H-5HT) into mouse spleen. SB produced a dose-related inhibition of the uptake of 3 H-5HT into spleen. This effect was not antagonized by beta adrenoceptor antagonists (Butoxamine, tobanum). On the other hand, SB did not act on the uptake of 3 H-NA into heart. Neither 3 H-NA nor 3 H-5HT uptake were altered by IP. These findings indicate that SB has an inhibitory property on 5HT uptake, independent of its beta adrenoceptor stimulatory effect.

A relationship between in vitro rate of oxidation by N-bromosuccinimide (NBS) and the pharmacologic activity (pA2) of different beta-adrenergic blockers for different blocking agent-tissue combinations has been studied. The rates of oxidation of the alcoholic group in the drugs by NBS, as well as their molecular conformations as represented by molecular models, were studied in order to determine requirements for selectivity and potency of action of beta-adrenergic blocking agents. Using data from all 7 drugs studied--both nonselective and selective blocking agents--no significant correlation between pA2 and -log k2 (k2 is the second order rate constant for the oxidative reaction) was found. If data from only the 4 nonselective agents were used (16 drug-tissue combinations), a correlation significant at p less than 0.01 was found. Hypotheses are presented to account for the selective action of some beta-adrenergic blocking agents.

Since beta-adrenergic blockers are effective in the therapy of hypertension by a mechanism related to the degree of activation of the renin-angiotensin system, the effect of eight beta blockers was examined on angiotensin II potentiation of nerve stimulation (NS) in isolated perfused rat mesenteric vessels. The vasoconstrictor response to periarterial NS was obtained by monitoring changes in perfusion pressure while a beta blocker or a beta blocker and angiotensin II (3 ng/ml) were added to the perfusate. Although each beta blocker tended to decrease responses to NS, in the concentrations used, only metoprolol significantly inhibited responses to NS. Angiotensin II, when infused alone, potentiated the responses to NS by 63% (p less than 0.01). These enhanced responses following angiotensin II were inhibited in a dose-related manner (10--300 ng/ml) by beta 1, beta 2, and mixed beta blockers. At the 100 ng/ml concentration, DL-propranolol, timolol, metoprolol, practolol, butoxamine, and H35/25 inhibited the angiotensin II potentiation of NS by 83%, 76%, 77%, 59%, 72%, and 41% respectively. The order of potency for this action was as follows: timolol = metoprolol = butoxamine greater than propranolol greater than practolol greater than H35/25. Administration of D- and L-propranolol also reduced the responses by 75%. The vasoconstrictor responses to injected norepinephrine (NE), in the presence and absence of angiotensin II, were not altered by DL-propranolol or timolol. In conclusion, beta-adrenergic blockers were found to interfere with the effect of angiotensin II on the sympathetic neuron, a property that could contribute to the antihypertensive action of these drugs.

Capillary fractions from rat cerebral cortex contain an adenylate cyclase system sensitive to activation by the beta adrenergic agonists in the following order of efficacy: isoproterenol, norepinephrine (NE) ⪢ metaproterenol (beta2), tazolol (beta1) > terbutaline (beta2) > dobutamine (beta1). These beta agonist-induced responses of adenylate cyclase were potently inhibited by propranolol a mixed beta antagonist. Isoproterenol- and NE-induced stimulation of the enzyme were more sensitive to inhibition by butoxamine (beta2 antagonist) than to practolol (beta)1 antagonist); however, these latter inhibitions were less than that observed with propranolol. Butoxamine produced greater antagonism than practolol of the beta2 agonist-mediated activation of adenylate cyclase, while practolol was more potent than butoxamine with regard to the stimulatory actions of dobutamine. Tazolol was a partial agonist at low concentrations. This agonist action of tazolol was reduced by propranolol > practolol > butoxamine. As a partial antagonist, tazolol at higher concentrations exerted an inhibition intermediary between propranolol and butoxamine on the enzyme activation by isoproterenol. Only one form of cyclic AMP-dependent phosphodiesterase was found to be present in the capillary preparation. The data indicate that cerebral capillaries possess a mixed population of beta adrenergic receptors mediating the stimulation of adenylate cyclase.

Adenylate cyclase in capillary fractions from rat cerebrum was activated by isoproterenol, l'norepinephrine (NE)>DA, salbutamol, terbutaline > dobutamine. These beta agonist responses were blocked by selective beta antagonists namely: propranolol (mixed beta-1 & 2)>butoxamine (beta2)>ractolol ( beta1 ). Capillary phosphodiesterase metabolized cyclic AMP over a wide concentration range. In spontaneously hypertensive rats (SHR) the capillary adenylate cyclase was less sensitive to the stimulation by beta agonists and DA than was observed in normotensive Wistar Kyoto Rats (WKY).

The participation of beta 2-adrenoceptors in the chronotropic response was evaluated in right atria isolated from rats submitted to daily footshock stress for three days. Footshock increased both the sensitivity to salbutamol and the pA2 of butoxamine. These results provide additional support for the proposal that repeated footshock stress increases the function of rat atrial postjunctional beta 2-adrenoceptors.

Cats were anaesthetized with pentobarbital sodium. A push-pull cannula was inserted into the posterior hypothalamus which was superfused through the cannula and electrically stimulated with its tip. Electrical stimulation elicited a frequency-dependent pressor response and tachycardia. Superfusion with orciprenaline, isoprenaline (beta 1- and beta 2-stimulants) or tazolol (beta 1-stimulant) led to a concentration-dependent enhancement in the pressor response. Superfusion with terbutaline caused a slight and late increase in the pressor response, while salbutamol (beta 2-stimulants) was ineffective. The tachycardia elicited by the hypothalamic stimulation was slightly increased by the hypothalamic stimulation was slightly increased by orciprenaline, tazolol and terbutaline. Superfusion with atenolol (beta 1-adrenoreceptor blocking drug) or butoxamine (beta 2-adrenoreceptor blocking drug) inhibited the pressor response and the tachycardia caused by hypothalamic stimulation. Superfusion with butoxamine prior to isoprenaline reduced the enhancing effect of isoprenaline on the pressor response, while superfusion with atenolol abolished or even reversed it. It is concluded that beta 1 and beta 2-adrenoreceptors are present in the posterior hypothalamus; apparently, beta 1- rather than beta 2-adrenoreceptors are involved in the rise of blood pressure elicited by stimulation of the hypothalamus.

The cardiovascular effects of the selective beta 2-adrenoceptor agonists salbutamol and terbutaline have been evaluated in anaesthetised, areflexic dogs. The preparation was designed to reduce the effects of changes in cardiac function mediated via reflex responses to changes in blood pressure. The effects of the selective beta 2-adrenoceptor agonists on heart rate, hindlimb blood flow, left ventricular pressure, max dP/dt and (dP/dt)/IIT (integrated isometric tension) were compared to those of isoprenaline, while blood pressure was held constant. All three drugs produced dose-dependent increases in heart rate, myocardial contractility and iliac blood flow. When equiactive inotropic doses of isoprenaline and salbutamol were compared, salbutamol produced a significantly lower chronotropic effect. A similar inotropic selectivity was found when terbutaline was compared to isoprenaline. beta 2-Adrenoceptor blockade abolished this selectivity. It is concluded that, in the absence of autonomic reflex activity, the beta 2-selective adrenoceptor agonists are relatively selective inotropic stimulants.

Responses to the beta-adrenoceptor agonists isoprenaline (Iso) (non selective), salbutamol (Sal) (beta 2-selective) and noradrenaline (NA) (beta 1-selective) were studied on incubated and superfused rat lung strip. In both conditions, Iso and Sal elicited dose-related relaxations of lung strip and these responses were unaffected by the presence of phentolamine (Phen) 10(-5) M. Contractile responses to NA were obtained when it was used alone whereas in the presence of Phen 10(-5) M, NA elicited relaxant responses. The relative potencies of Iso : Sal : NA (plus Phen) were 100 : 20 : 0.69. This demonstrates that beta 2-adrenoceptor is the predominant beta-subtype involved in responses. Propranolol (10(-4) M) completely abolished the relaxant responses to Iso. However, after the addition of Iso tissue responded normally to drugs acting by other mechanisms. Thus, relaxations were obtained with caffeine and contractions with acetylcholine (AcH) or NA. This shows that responses to Iso are mediated only by beta-adrenoceptors. Propranolol and the selective beta-blocking agents butoxamine (beta 2) and atenolol (beta 1) competitively antagonized the effects of Iso. The Schild plots obtained had slopes which did not differ significantly from -1 and mean pA2 values were: 7.82 for propranolol; 6.32 for butoxamine and 5.22 for atenolol. These experiments were carried out in the absence of catecholamine uptake inhibitors, since in a preliminary set of experiments no significant changes of lung strip responses to Iso were observed in the presence of cocaine (10(-5) M) or corticosterone (10(-5) M). In conclusion, it appears that incubated rat lung strip possesses intrinsic tone and, although it cannot be considered a representative preparation of peripheral airways, it provides a valid model for investigating the direct-effects of drugs which act at beta-adrenoceptors.

We have investigated the hormonal responsiveness of K562 cells using a serum-substituted in vitro clonogenic assay. Dexamethasone inhibited colony formation by the K562 cells, and the inhibitory effect could be reversed by progesterone (10(-6) M). Fluoxymesterone caused a prominent enhancement of K562 colony growth, whereas estriol had no effect. Stimulation by triiodothyronine was maximal at 10(-7) M, and the thyroid effect could be abrogated by the beta 2-adrenergic antagonist butoxamine in equimolar concentrations. Using standard tissue culture conditions, the beta-adrenergic agent isoproterenol, but not the alpha catecholamine phenylephrine, enhanced the proliferation of K562 cells. When K562 cells were grown under hormone-depleted conditions, they developed responsiveness to phenylephrine and were no longer stimulated by isoproterenol. DbcAMP and prostaglandins of the E series also caused K562 colony enhancement. Prostaglandin F2 alpha had no effect on cell proliferation. Insulin was an effective stimulant of colony formation of K562 cells, as were human growth hormone and ovine prolacin. Bovine growth hormone had no effect. Our results are consistent with the identificaiton of K562 as an erythroid line, and they indicate that K562 cells respond to endocrine hormones in a manner analogous to normal erythroid progenitors.

Some sympatholytic agents have been tested for the ability to counteract either the hepatotoxic or the lethal effect of A. phalloides in rats. Propranolol displayed a marked preventive action on the liver damage induced by the poison, but only a moderate influence on the lethality. Reserpine was uneffective in terms of liver derangement, but exerted some protection against the general toxic effect of A. phalloides. Other alpha- or beta-adrenolytic compounds failed to afford any significant protection with respect to both liver injury and lethality. It is suggested that propranolol might interfere with transport or binding of phallotoxins to the liver.

The cardiovascular effects of intracisternally administered butoxamine, a beta 2-adrenoceptor blocking drug, were studied in both normotensive and acute hypertensive anaesthetized dogs. Acute hypertension was elicited by sino-aortic denervation (deafferentation). Intracisternal butoxamine (25-400 microgram/kg) failed to decrease blood pressure and reduce heart rate in the two groups of animals. These results show that the decrease in blood pressure elicited by central administration of dl-propranolol is probably not related to central beta 2-adrenoceptor blockade.

The effects of class I, II, III and IV antiarrhythmic drugs (as classified by Vaughan Williams 1974), tetrodotoxin and beta 2-adrenoceptor antagonists on the extraneuronal accumulation of isoprenaline were examined in isolated rat hearts perfused with 3H-isoprenaline (1 mumol/l) and tropolone (100 mumol/l) for 30 min at a constant flow rate (6.5 ml/min) at 40 degrees C. Quinidine (class I), verapamil (IV), diltiazem (IV), dilazep (IV), nifedipine (IV), tetrodotoxin and butoxamine, at a concentration of 10 mumol/l, significantly decreased the extraneuronal accumulation of isoprenaline. The present study demonstrated that quinidine (class I) and all of the calcium channel blockers (class IV) had potent inhibitory effects on the extraneuronal accumulation of isoprenaline. The concentrations of these drugs needed for this decrease were nearly comparable to those needed to suppress isoprenaline-tropolone-induced ventricular fibrillation (Sono et al. 1985a). The antiarrhythmic effects of quinidine and calcium channel blockers in this experimental model may be partly due to a decrease in the extraneuronal accumulation of isoprenaline.

Administration of phentolamine to the rat or dog increases significantly the concentration of blood lactic acid, and reduces blood glucose. In the rat, the lacticacidemia appears due to an activation of glycogenolysis in skeletal muscle, since phentolamine administration results in an increase in phosphorylase a and a reduction of the glycogen content of this tissue. The plasma concentration of catecholamines also increases suggesting that phentolamine elicits these metabolic effects through their release. The phentolamine-induced changes in the blood lactic acid, phosphorylase a and glycogen content of skeletal muscle can be inhibited by pretreating the rat with the adrenergic blocking drugs, butoxamine or 4-(2-isopropyl-1-hydroxyethyl)methane-sulfonanilide (MJ1999). The phentolamine-induced lacticacidemia is inhibited partially if the rat is pretreated with guanethidine or reserpine; it is reduced markedly in the adrenal demedullated rat, and is eliminated if guanethidine is administered to the adrenal demedullated rat prior to phentolamine. The results suggest that phentolamine activates glycogenolysis in rat skeletal muscle, and this activation is mediated by the catecholamines.

O.D. GULATI, H.M. PARIKH and P.R. RAGHUNATH. Further studies on the α-adrenoceptor blocking action of β-adrenoceptor blocking agents, European J. Pharmacol. 22 (1973) 196–205. Isoprenaline failed to relax the isolated rat seminal vesicle contracted by potassium chloride. Dichloroisoprenaline, pronethalol, (+) and (−)-INPEA, propranolol, 1-isopropylamino-3-(4-indanoxy)-2-propanol (USVP 6524), butoxamine and bunolol blocked competitively contractile responses of the isolated rat seminal vesicle to several α-adrenoceptor stimulants. The pA2 values of propranolol with different agonists ranged between 4.94 and 5.34. The pA2 values of dichloroisoprenaline, pronethalol, (+)-INPEA, (−)-INPEA, USVP 6524, butoxamine and bunolol were 4.79, 4.73, 3.97, 3,94, 5.07, 4.44 and 4.29 respectively. Sotalol and 1-isopropylamino-3-(3-tolyloxy)-2-propanol produced non-competitive block. Noradrenaline or USVP 6524 or propranolol protected the α-adrenoceptors from blockade by phenoxybenzamine; sotalol failed to protect. Acetyleholine but not histamine, 5-hydroxytryptamine and angiotensin contracted the tissue. All the antagonists acting competitively, blocked acetylcholine-induced contractions.

CLASSIFICATION of receptor systems which are activated by sympathomimetic amines has engaged the attention of many investigators. Ahlquist1–3 has suggested the convenient designations of alpha (α) and beta (β) to distinguish major differences in the responses elicited in various organ systems. Our investigations have provided results which cannot be explained easily on the assumption that the β-type designates a single receptor population4–6. We now report additional studies which show that two distinct receptor types are at present included within this group.

1. The preparation of longitudinal smooth muscle strips from guinea-pig seminal vesicles is described. 2. Isoprenaline and salbutamol inhibited contractions produced by parasympathomimetic agents. 3. The inhibitory action of isoprenaline was blocked by low concentrations of propranolol and butoxamine. It was concluded that β2-adrenoceptors were present in the tissue. 4. The inhibitory action of isoprenaline was not apparent when adrenaline, noradrenaline, hypogastric nerve or transmural stimulation were used to contract the tissue.

Publisher Summary This chapter presents chairman's remarks on studies focusing on noradrenaline. It highlights that recent experiments in the laboratory have confirmed earlier findings that noradrenaline tends to inhibit the contractile response of the isolated guinea pig vas deferens to field stimulation in low concentrations, while higher concentrations usually enhance the effect. Tyramine and phenethylamine act similarly. However, in those cases where noradrenaline increases the response to nerve stimulation, phentolamine regularly changes the reaction in such a way that noradrenaline now produces a dose-dependent inhibition of the stimulus response. No experiment showed that the inhibitory effect of noradrenaline is prevented by phentolamine; on the contrary it is unmasked. On the other hand, propranolol given together with phentolamine, strongly diminishes the inhibition induced by noradrenaline, suggesting that the latter effect is caused by a β-agonistic action. Experiments with practolol and butoxamine indicated that the inhibitory effect of noradrenaline is of the β 2 type. The inhibitory effect of Clonidine is, however, blocked by phentolamine. Phentolamine given alone enhances the twitch response of the vas deferens to field stimulation.

α and β-adrenergic receptors in detrusor muscle and bladder base of horses were investigated by in vitro responses of smooth muscle strips to exogenous agonist and antagonist drugs. Noradrenaline, isoprenaline and salbutamol induced relaxation of detrusor muscle strips which was significantly inhibited by propranolol and butoxamine suggesting that the response is mediated by β-2 adrenergic receptors. In the urinary bladder base noradrenaline, phenylephrine and b-ht 920 induced strong contractile effects. These contractile responses were inhibited by the α antagonist phenoxybenzamine, the α-1 selective antagonist prazosin and the α-2 selective antagonist yohimbine. The inhibitory action of prazosin was more potent than that observed with yohimbine suggesting that the response in the bladder base of horses is mediated predominantly by α-1 adrenergic receptors, although α-2 receptors also participate.

The present study was undertaken in anaesthetized pigs to determine the primary reflex effects of gastric distension on the peripheral circulation. Changes in blood flow in the splenic, superior mesenteric, left renal and left external iliac arteries were assessed using electromagnetic flowmeters during distension of a balloon in the stomach, performed at constant aortic blood pressure and heart rate, with 0.6 l of Ringer solution (mean gastric transmural pressure of about 12 mmHg). In fourteen pigs, a decrease in splenic, renal and iliac flows and variable changes in mesenteric flow were obtained. A decrease in mesenteric flow and more marked decreases in the other flows occurred in response to the distension after the administration of propranolol or butoxamine. In five pigs, the vasoconstrictive responses were graded by step increments in gastric distending volume from 0.4 to 0.8 l. The above responses were abolished by the administration of phentolamine (eight pigs) and by bilateral cervical vagotomy (six pigs). The results showed that innocuous distension of the stomach in anaesthetized pigs reflexly caused vasoconstriction in the splenic, renal and iliac vascular beds; vasoconstriction also occurred in the mesenteric vascular bed but only after beta-blockade. These reflex responses were mediated by sympathetic mechanisms which involved both alpha and beta vascular adrenoceptors and their afferent limb was in the vagal nerves.

Corticotropin-releasing factor (CRF) acts within the brain to elicit changes in neuroendocrine, autonomic and behavioral activity similar to those observed after stress. A reduction of cellular immune function as measured by splenic natural killer cell activity has also been described following the central administration of CRF. In this study we evaluated the role of the sympathetic nervous system in mediating CRF-induced suppression of natural killer (NK) cytotoxicity. Synthetic rat CRF (1.0 microgram) microinjected into the lateral ventricle increased noradrenergic function and reduced NK activity in the rat spleen. Pretreatment of the animals by chemical sympathectomy (6-hydroxy-dopamine, 100 mg/kg i.p. daily over 10 days) produced a greater than 95% reduction of splenic norepinephrine concentration and abolished completely both the CRF-induced increase in plasma catecholamine levels and the reduction in splenic NK activity. In addition, beta adrenergic receptor blockade (either propranolol, 10 mg/kg i.p., or butoxamine, 25 mg/kg i.p. 30 min before i.c.v. infusion) antagonized the CRF-induced reduction in NK activity. Measurement of circulating levels of adrenocorticotrophic hormone and corticosterone demonstrated that activation of the pituitary adrenal axis by CRF was dissociated from changes in NK activity. These findings suggest that the sympathetic nervous system mediates the suppression of splenic NK cytotoxicity after i.c.v. CRF.

Erythroid burst forming units (BFU-E) were much more sensitive to the beta-2 selective adrenergic drug, salbutamol, than erythroid colony forming units (CFU-E) in an in vitro study of erythroid progenitor cells.

Isolated, perfused rabbit hearts were used to identify substituted phenylethylamines selective for either chronotropic or inotropic stimulation relative to norepinephrine. Heart rate and dF/dtmax were measured; the difference in their normalized values was used as an index of selectivity. p-Octopamine (OA) showed chronotropic preference, while phenylephrine (PE) showed a significant inotropic preference. Their effects were not prevented by reserpine pretreatment, cocaine, butoxamine, or phenoxybenzamine, but were antagonized by propranolol, which suggests that OA and PE exert their selective actions directly at beta 1-receptors. These findings provide further evidence for the existence of separate chronotropic and inotropic beta-adrenergic receptors in the heart.

The present experiments were designed to study renal effects of β-adrenoceptor agonists and antagonists with reference to β1-and β2-adrenoceptors. Wistar rats, anesthetized with urethan, were continuously hydrated with saline solution. The β-blockers used were atenolol as a selective βi-antagonist, butoxamine as a selective β2-antagonist and propranolol as a non-selective β-antagonist. The β-stimulants used were isoproterenol as a non-selective β-agonist and salbutamol as a selective β2-agonist. The different types of β-antagonists such as atenolol, butoxamine and propranolol all produced dose-related increases in urine volume and urinary sodium excretion without changing urinary potassium excretion. Isoproterenol and salbutamol decreased urine volume and urinary sodium excretion. The diuretic effects of atenolol, butoxamine and propranolol were abolished by simultaneous infusion of either isoproterenol or salbutamol without inducing any change in renal blood flow. The results obtained suggest the fact that the diuretic effects of atenolol, butoxamine and propranolol are closely related to activity of β-adrenoceptors in rat kidneys, although there is no selectivity to either β1-and β2-adrenoceptors so far as diuresis is concerned.

Effects of intrarenal boluses of epinephrine (E) (0.00625 to 0.2 ug/kg of B.W.) on renal blood flow (RBF) were studied in chronically catheterized fetal (F) lambs (125-137 days; term 145 days) and adult (A) sheep using a doppler flowmeter. Effects of E alone and during α, α1, and β2 adrenergic blockade were studied. Blood pressure was unchanged during E infusion. The E dose that reduced RBF (%ΔRBF) by 50% (ED50) was 0.0014 ug/kg/ml RBF in F and 0.0001 ug/kg/ml RBF in A; this response was blocked by the α1 antagonist prazosin. Following α blockade with phentolamine, E produced vasodilation (%Δ RBF-α) in F and A which was blocked by the β2 antagonist butoxamine. When E was given during α blockade at a dose equal to ED50 for vasoconstriction, E produced a 33% rise in RBF in F and 10% in A (p