257 research outputs found
A STUDY ON THE MECHANISM OF THE NEGATIVE INOTROPIC EFFECTS INDUCED BY SOME CALCIUM ENTRY BLOCKERS IN ISOLATED GUINEA-PIG HEARTS
PROTECTIVE ACTIVITY OF CALCIUM ENTRY BLOCKERS AGAINST OUABAIN INTOXICATION IN ANESTHETIZED GUINEA-PIGS
EXTRA-SYNAPTIC LOCATION OF ALPHA-2 AND NON-INNERVATED BETA-2 ADRENOCEPTORS IN THE VASCULAR SYSTEM OF THE PITHED NORMOTENSIVE RAT
The receptors involved in the pressor and tachycardic effects of catecholamines applied systemically or released from sympathetic nerve endings were compared. Intravenously administered (-)-epinephrine activated alpha-1, alpha-2, beta-1 and beta-2 adrenoceptors as demonstrated in pithed rats, using the alpha-1 sympatholytic drug prazosin, the alpha-2 adrenoceptor blocking substance rauwolscine, the beta-1 and beta-2 sympatholytic agent(-)-propranolol, the predominantly beta-1 adrenoceptor antagonist atenolol and the selective beta-2 adrenoceptor blocking agent ICI 118,551 as tools. (-)-Norepinephrine given i.v. proved to be an alpha-1, alpha-2 and beta-1 adrenoceptor agonist. 1,1-Dimethyl-4-phenylpiperazine iodide (DMPP) releases catecholamines from noradrenergic neurons and the adrenal medulla. The i.v. injection of DMPP into pithed rats caused an increase in diastolic pressure and heart rate by this indirect effect, which has been confirmed by pretreatment with reserpine and removal of the adrenals. After bilateral adrenalectomy, there occurred a release of mainly norepinephrine, only from the neurons. Catecholamines liberated by DMPP activated alpha-1 and beta-1 receptors and, at high doses of DMPP, alpha-2 and beta-2 adrenoceptors as well. Removal of both adrenal glands abolished the alpha-2 and beta-2 adrenoceptor-mediated effects. (-)-Norepinephrine released from neurons stimulated alpha-1 and beta-1 adrenoceptors only, although after i.v. administration of this catecholamine alpha-2 adrenoceptors were also activated. There was no indication for a beta-2 adrenoceptor-mediated vasodilation by neuronally released catecholamines. A beta-2 adrenoceptor-mediated effect, however, could be demonstrated by i.v. injection of (-)-epinephrine. The results can be explained by the presence of predominantly alpha-1 and beta-1 adrenoceptors in the postganglionic sympathetic synapses and an extrasynaptic location of alpha-2 and beta-2 adrenoceptors. The extrasynaptic receptors are possibly controlled by epinephrine from the adrenals
CALCIUM ENTRY BLOCKERS UNDERESTIMATE THE CA++-INFLUX COMPONENT OF AGONIST-INDUCED CONTRACTIONS IN THE JUGULAR VEIN AND AORTA OF THE RAT
PROTECTIVE ACTIVITY OF CALCIUM ENTRY BLOCKERS AGAINST OUABAIN INTOXICATION IN ANESTHETIZED GUINEA-PIGS
A STUDY ON THE MECHANISM OF THE NEGATIVE INOTROPIC EFFECTS INDUCED BY SOME CALCIUM ENTRY BLOCKERS IN ISOLATED GUINEA-PIG HEARTS
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