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At least 1,387 records · Page 77Linked to original sources
PubMed1983

Sgd 101/75: a sympathomimetic that can be used to identify a new subtype of alpha-adrenoceptor, the alpha 1s-adrenoceptor.

When Sgd 101/75 was compared with clonidine in a number of tests for CNS activity, Sgd 101/75 exhibited little activity in any test. Sgd 101/75 raised BP without affecting HR in several species of anaesthetised animals. The rise in BP was subject to tachyphylaxis, could be antagonised by alpha 1-adrenoceptor antagonists, and was obtainable in reserpinised animals. The vasopressor effect of NA was antagonised by Sgd 101/75. Thus Sgd 101/75 is a directly acting partial agonist for vascular alpha 1-adrenoceptors. On the coaxially stimulated guinea-pig ileum and field stimulated rat vas deferens, the twitch response to single pulse stimulation was reduced by NA or clonidine stimulating prejunctional alpha 2-adrenoceptors. Sgd 101/75 antagonised these inhibitory effects competitively (pA2 for antagonism of clonidine on the vas = 6.12). Sgd 101/75 acted as a specific partial agonist on the alpha 1-adrenoceptors of the guinea-pig taenia caecum that subserve relaxation of this tissue. Sgd 101/75 was a full agonist on the alpha 1-adrenoceptors of the rat anococcygeus in vitro. Phenoxybenzamine (300 pM for 30 min, followed by 20 washes over the next 30 min) reduced contractions of the anococcygeus to Sgd 101/75, but produced little inhibition of NA-induced contractions. In phenoxybenzamine-pretreated preparations, Sgd 101/75 (400 microM) did not antagonise NA (maximal effect and EC50 values not changed significantly), so it was concluded that Sgd 101/75 and NA interact with different alpha 1-adrenoceptor subtypes in this tissue. The subtype specifically activated by Sgd 101/75 was designated the alpha 1s-adrenoceptor. The mouse anococcygeus contained alpha 1s-adrenoceptors, whereas this receptor was absent from the rabbit anococcygeus.

Adrenergic alpha-Agonists↗
PubMed1978

Possible sites of temperature-dependent changes in sensitivity of the positive inotropic and chronotropic responses to sympathomimetic amines by comparisons of the temperature optima for a range of agonists.

The temperature optimum for the positive inotropic response of guinea-pig isolated atria to single submaximal doses of isoprenaline was 25 degrees C. This was well separated from that for rate responses (37.5 degrees C). This separation was not due to changes in catechol-0-methyl-transferase or phosphodiesterase activity since it occurred with orciprenaline alone and in the presence of theophylline. The rate optima for aminophylline, histamine, glucagon, ouabain, calcium chloride and dibutyryl cAMP were essentially the same as for isoprenaline. The temperature-dependences therefore lie at a common ultimate pathway leading to the rate response. The site of temperature-dependence of the inotropic response to isoprenaline is not at the common contractile mechanisms since its optimum differed from those of ouabain and CaCl2. Activity of cAMP and its production were also eliminated as possible sites from differing optima of aminophylline, histamine and dibutyryl cAMP. The temperature-dependence may lie at the beta-adrenoceptor itself, possibly adenyl cyclase. This may be shared by glucagon although tachyphaylaxis made its optimum difficult to determine.

Animals↗
PubMed1984

The effect of sympathomimetic agents on gastric acid secretion in rats.

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)

Animals↗
PubMed1983

[Are beta-sympathomimetic substances in resuscitation useful? Experimental studies].

Orciprenaline and epinephrine have been compared in cardiopulmonary resuscitation (CPR) in the dog. In a third group no substance was given. When orciprenaline was repeated without success, epinephrine was given. After administration of epinephrine left ventricular pressure and central aortic pressure were significantly higher. CPR was also more successful in epinephrine-treated dogs, a fact which can be attributed directly to these higher pressures. However, the attempt at resuscitation with orciprenaline, and, in the event of failure, with epinephrine, yielded significantly poorer results than treatment with epinephrine alone. Epinephrine substantially increased coronary perfusion pressure and coronary blood flow was adequate. When orciprenaline was administered, however, diastolic blood pressure decreased and no coronary blood flow could be measured. Serum CPK activity was increased. Ventricular fibrillation occurred just as often with epinephrine as with orciprenaline. In the epinephrine group defibrillation led directly to adequate circulation, whereas in the orciprenaline group subsequent electromechanical dissociation was observed. It is concluded that beta-receptor stimulators have no place in CPR. Epinephrine is the drug of choice in resuscitation after cardiac arrest.

Animals↗
PubMed1983

The role of sympathomimetic amines in the dyspnoea of thyrotoxicosis.

Nine untreated thyrotoxic patients (5 males and 4 females) aged 23 to 56 years who complained of dyspnoea on moderate exertion were studied. Measurements of forced expiratory volume (FEV1), vital capacity (VC) and total lung capacity (TLC), oxygen consumption, (VO2), carbon dioxide output (VCO2) and the minute ventilation (VE) were determined on three occasions: before treatment; after treatment with propranolol and after carbimazole. Dyspnoea disappeared in 4 patients out of 9 after treatment with propranolol, while none were dyspnoeic when they became euthyroid. There was no significant difference in FEV1, VC, TLC and FRC on the three occasions. The differences between the VO2, VCO2 and VE before treatment and these values after treatment with carbimazole were significant. We conclude that the dyspnoea of thyrotoxicosis is due to both the effect of catecholamines and the metabolic effect of thyroxine.

Adult↗
PubMed1984

Sympathomimetic activity of mazindol on rat anococcygeus muscle and vas deferens.

Mazindol contracted the isolated anococcygeus muscle of the rat. This effect was prevented by pretreatment with reserpine and antagonized by phentolamine but not by atropine, cocaine, hexamethonium, methysergide or promethazine. The drug potentiated the contractile response of the rat anococcygeus to noradrenaline and field stimulation and released tritium from the rat vas deferens and anococcygeus preloaded with [3H]-noradrenaline. The release of radioactivity was unaffected by incubation of the tissue in calcium free or high potassium (60 mM) solution.

Animals↗