Influence of steroid hormone treatments or pregnancy on [3H]prazosin and [3H]rauwolscine binding to myometrial α-adrenoceptors in the ewe

• Published in: Journal of endocrinology Vol. 127; no. 3; pp. 471 - 479
• Main Authors: VASS-LOPEZ, A, GARCIA-VILLAR, R, LAFONTAN, M, TOUTAIN, P. L
• Format: Journal Article
• Language: English
• Published: Colchester BioScientifica 01.12.1990; Portland Press
• Subjects: Adrenergic alpha-Antagonists - metabolism; Animals; Biological and medical sciences; Estradiol - pharmacology; Female; Flurogestone Acetate - pharmacology; Fundamental and applied biological sciences. Psychology; Gonadal Steroid Hormones - pharmacology; Kinetics; Mammalian female genital system; Morphology. Physiology; Myometrium - metabolism; Ovariectomy; Phentolamine - pharmacology; Prazosin - metabolism; Pregnancy; Pregnancy, Animal - metabolism; Protein Binding - drug effects; Receptors, Adrenergic, alpha - metabolism; Sheep - metabolism; Vertebrates: reproduction; Yohimbine - metabolism; Myometrium; Catecholamine; Progestagen; Pregnancy; Vertebrata; Mammalia; Uterus; α-Adrenergic receptor; Female genital system; Sheep; 17β»-Estradiol; Artiodactyla; Antagonist; Sex steroid hormone; Ungulata
• ISSN: 0022-0795; 1479-6805
• DOI: 10.1677/joe.0.1270471

ABSTRACT The adrenergic antagonists [3H]prazosin and [3H] rauwolscine were used to identify α1- and α2-adrenoceptors respectively in the ovine myometrium. Ewes were allocated to four groups according to steroid hormone treatments or physiological status, namely ovariectomized ewes either as untreated controls, treated with oestradiol-17β or progestagen plus oestradiol-17β, and pregnant ewes at mid-gestation. Binding of both [3H]prazosin and [3H]rauwolscine to membrane preparations from the ovine myometrium was saturable, of high affinity and rapidly reversed by phentolamine (10 μmol/l). Based on the relative order of potency of selected adrenergic agonists and antagonists, the myometrial binding sites labelled by [3H]prazosin and [3H]rauwolscine were characterized as α1- and α2adrenoceptors respectively. Saturation binding studies with [3H]prazosin showed that the number of α1adrenoceptors was low (maximal binding capacity, Bmax, between 19 and 24 fmol/mg protein) and there were no noticeable differences between the animal groups. Moreover, the equilibrium dissociation constant (Kd) did not vary significantly between groups (Kd between 0·10 and 0·17 nmol/l). In contrast, saturation binding studies with [3H]rauwolscine revealed the presence of a high number of α2-adrenoceptors. Values of Bmax were far higher in the pregnant ewes (1096±241 fmol/mg protein; means ± s.d.) than in any of the non-pregnant ovariectomized ewes. For these latter groups, the highest Bmax values were found in the group treated with both progestagen and oestrogen (382±77 fmol/mg protein) compared with treatment with oestrogen alone (101±8 fmol/mg protein) or with controls (82±12 fmol/mg protein). The results of the present study, especially those obtained under a high-progesterone environment (e.g. pregnancy), strongly suggest a role of steroid hormones in the control of the number of α2-adrenoceptors in the ovine myometrium. In contrast, they did not yield any supporting data for a similar role on myometrial α1-adrenoceptors in the ewe. Journal of Endocrinology (1990) 127, 471–479