VIP inhibition of vascular smooth muscle: complementary to beta 2-adrenoceptor mediated relaxation in the isolated rat portal vein.
Exogenous VIP caused a concentration dependent inhibition of the spontaneous mechanical activity in the isolated rat mesenteric-portal vein preparation via a mechanism which was completely independent of the propranolol-blocked beta-adrenoceptor, of high K+ in the medium and of exogenous bovine pancreatic polypeptide, neurotensin and opioids. The potency of VIP (pD2 = 7.52 +/- 0.18, n = 6) was about 30 times higher than that of isoprenaline in the atropine and phentolamine-blocked preparation. The isoprenaline inhibition was mediated via a beta 2-type of adrenoceptor with low apparent affinity for noradrenaline (intrinsic activity (alpha) = 0.27 +/- 0.01, n = 8). Opposite effects of exogenous VIP and noradrenaline were on the other hand observed in the atropinized and beta-blocked preparation. These results suggest that in the rat portal vein neuronal VIP and circulating adrenaline may be complementary in their antagonism of the alpha-adrenoceptor mediated increase in contractility.
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D003042:Cocaine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009496:Neurotensin / Q000494:pharmacology; D010191:Pancreatic Polypeptide / Q000494:pharmacology; D011169:Portal Vein / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology*
D000318:Adrenergic beta-Agonists; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D014660:Vasoactive Intestinal Peptide; D009496:Neurotensin; D010191:Pancreatic Polypeptide; D003042:Cocaine; D011188:Potassium