LACK OF PREJUNCTIONAL AND POSTJUNCTIONAL BETA-ADRENOCEPTOR-MEDIATED EFFECTS IN THE CANINE SAPHENOUS-VEIN AT BIRTH

• Type: Article in International Scientific Journal
• Date: 1994

Authors

GUIMARAES, S (Author) Other; moura, d (Author) FMUP; PAIVA, MQ (Author) Other; Vaz Da Silva, M (Author) FMUP

Journal

Title: Journal of Pharmacology and Experimental Therapeutics

Vol. 268

Pages: 990-995

ISSN: 0022-3565

Publisher: American Society for Pharmacology and Experimental Therapeutics

Indexing

ISI Web of Knowledge - 11 Citations

Scopus - 11 Citations

Other information

Authenticus ID: P-001-KEH

Abstract (EN): The present study was undertaken to compare the relevance of alpha and beta adrenoceptor-mediated responses at pre- and postjunctional level in the canine saphenous vein of neonates and adults. To quantify prejunctional action, the effect of drugs on the neurogenic outflow of tritium from the vessel loaded previously with [H-3]norepinephrine or [H-3]epinephrine was measured. The selective alpha-2 adrenoceptor agonist UK-14,304 (5-bromo-6-(2-imidazoline-2-ylamino)-quinoxaline: 10-1000 nM reduced and the selective alpha-2 adrenoceptor antagonist yohimbine (30-300 nM) enhanced the overflow of tritium evoked by electrical stimulation (1 Hz; 2 msec; 100 V; 300 pulses) in both adult and neonate tissues. However, in strips preloaded with [H-3]norepinephrine, the beta adrenoceptor agonist isoproterenol (50 nM) increased the overflow of tritium in strips of adults but had no effect in strips of neonates; and in the strips preloaded with [H-3]epinephrine, the beta adrenoceptor antagonist propranolol (1 mu M) reduced the overflow of tritium in adults but had no effect in neonates. Postjunctionally, phenylephrine (0.1-50 mu M) caused concentration-dependent contractions of the saphenous vein rings from adults and neonates but isoproterenol, which caused concentration-dependent relaxations on rings contracted previously by phenylephrine in adults, had no effect in neonates. In contrast to isoproterenol, forskolin (0.05-5 mu M), under the same conditions, caused concentration-dependent relaxations of rings of both adults and neonates. We conclude that, at birth, there is a lack of pre- and postjunctional beta adrenoceptor-mediated responses in canine saphenous vein, whereas alpha adrenoceptor-mediated responses are fully developed; the lack of beta adrenoceptor-mediated responses is due to a failure of either the receptors or the G proteins, because the directly acting stimulant of adenylate cyclase forskolin is fully active at that age.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 6