Postnatal development of vascular beta-adrenoceptor-mediated responses and the increase in the adrenaline content of the adrenal gland have a parallel time course.
The present study was undertaken to analyse the relationship between postnatal development of vascular beta 2-adrenoceptor-mediated responses and the content of adrenaline in the adrenal gland and its concentration in plasma. Dog saphenous vein tissue from newborn, two-weeks old and adult animals were either preloaded with 3H-noradrenaline (or 3H-adrenaline) to study prejunctional beta-adrenoceptor-mediated effects or mounted in organ baths to determine isoprenaline-induced relaxation of preparations contracted by phenylephrine to about 65% of the maximum. The adrenal glands and samples of blood from the same animals were taken for estimation of adrenaline and noradrenaline. At birth, there were no beta-adrenoceptor-mediated effects pre- or postjunctionally. At two weeks, while the results at the prejunctional level were not significantly different from those obtained in newborns, at the postjunctional level there was a relaxant response to isoprenaline, which antagonised about 35% of the previous contraction to 1.75 mumol.l-1 phenylephrine. In adults, isoprenaline (50 nmol.l-1) increased by 24% tritium overflow evoked by electrical stimulation of tissues preloaded with 3H-noradrenaline but not that of tissues preloaded with 3H-adrenaline. On the other hand, propranolol (1 mumol.l-1) reduced by 21% the overflow of tritium evoked by electrical stimulation of tissues preloaded with 3H-adrenaline but not that of tissues preloaded with 3H-noradrenaline; postjunctionally, the maximal response to isoprenaline antagonised 70% of the previous contraction to 1.75 mumol.l-1 phenylephrine.(ABSTRACT TRUNCATED AT 250 WORDS)
Paiva
M Q
MQ
Institute of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal.
Moura
D
D
Vaz-da-Silva
M J
MJ
Guimarães
S
S
D000311:Adrenal Glands / Q000254:growth & development* / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D005576:Colforsin / Q000494:pharmacology; D004285:Dogs; D004837:Epinephrine / Q000097:blood / Q000378:metabolism*; D005260:Female; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D009638:Norepinephrine / Q000097:blood / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D007545:Isoproterenol; D009638:Norepinephrine; D004837:Epinephrine