Comparison of VIP and beta 2-adrenoceptor-induced relaxations in the circular and longitudinal smooth muscle layers of the rat portal vein.
Acta Physiol Scand
; 130(4): 601-7, 1987 Aug.
Article
em En
| MEDLINE
| ID: mdl-3630736
ABSTRACT
The relative importance of VIP in reduction of vascular tone was studied in circular and longitudinal preparations of the VIP-innervated rat portal vein. Exogenous VIP inhibited the methoxamine-evoked contractures in the atropine-blocked preparations with a lower potency in the inner, circular (pD2 = 6.4 +/- 0.5, n = 6) than in the outer, longitudinal layer (pD2 = 7.7 +/- 0.1, n = 6). VIP was also a less efficient relaxant (intrinsic activity (alpha) = 0.60 +/- 0.16, n = 6) of the inner than of the outer layer (alpha = 1.00). The selective (salbutamol) and the non-selective (isoproterenol) beta 2-agonists completely relaxed the methoxamine contractures in both layers and the potency (isoproterenol) was higher in the inner (pD2 = 6.39 +/- 0.32, n = 6) than in the outer layer (pD2 = 5.67 +/- 0.34, n = 6). Plasma from the portal-mesenteric vein of anaesthetized, fasting rats contained 0.036 nM VIP (median, n = 17), that is, several orders of magnitude lower than the range of VIP concentrations relaxing the methoxamine contracted vein preparations via VIP receptors of the apamin-blockable category. The results support the hypothesis that alpha 1-adrenoceptor-induced contractions in the circular layer are predominately relaxed via beta 2-adrenoceptors while relaxation of the outer layer may occur via VIP receptors, probably activated by local release of the neuropeptide.
Buscar no Google
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Veia Porta
/
Peptídeo Intestinal Vasoativo
/
Albuterol
/
Isoproterenol
/
Contração Muscular
/
Relaxamento Muscular
/
Músculo Liso Vascular
Limite:
Animals
Idioma:
En
Revista:
Acta Physiol Scand
Ano de publicação:
1987
Tipo de documento:
Article