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Oxytocin release during suckling and parturition in rats
1504
F11 NOVEL ANTERIOR PITUITARY RECEPTOR(S) FOR NEUROHYPOPHYSIAL HORMONES. A.J.Baertschi and M.Friedli, University of Geneva, and Department of Physiology, University of Virginia, Charlottesville, VA 22908 It is generally accepted that recently isolated corticotropin releasing factors (CRF) play a dominant role in the secretion of opiomelanocortins (e.g. ACTH and 8-endorphin). Noradrenalin, vasopressin, oxytocin, Angiotensin II and vasoactive intestinal polypeptide (VIP) are less potent releasers of ACTH. Although some of these neurohormones were reported to potentiate the CRF-induced ACTH secretion, their relative contribution and specificity of actlon has not been established. We show with isolated anterior pituitary cells incubated for lh in vitro that ACTH secretion induced by 5nM CRF is doubled by O.lnM arglnine vasopressin vasotocin (AVT), 1nM oxytocin, 1OnM anglotensin (AVP), 0.2nM arginine II and 1OOnM noradrenalin; VIP has no effect. Potentiation is observed of ACTH secretion also at concentrations of 0.05 to 0.5nM. Potent$atiqn by neurohypophysial,peptides and analogs (HO(Thr Gly ]Oxytocin, dTyr[Me]VDAVP, AVT; 5nM) is related to their pressor and not to antidiuretic biological activities, nor oxytoclc but anti-pressor AVP antagonists (d[CH215Tyr[Me]AVP; dPTyr[Me]AVP; 200nM) have no effect on intrinsic or potentiating activity of AVP. These results show that vasopressin and oxytocin are dominant modulators of CRF-stimulated ACTH secretion and suggest that they act on a new type of vasopressin receptor of the anterior pituitary gland.
F12 OXYTOCIN RELEASE DURING SUCKLING AND PARTURITION IN RATS. L Higuchis, K.Honda, T.Fukuoka, H.Negoro and K.Wakabavashi"*, Department of Physiology, Fukui Medical School, Fukui 910-11, Japan and Hormone Assay Center*", Institute of Endocrinology, Gunma University, Maebashi 371, Japan. The secretory profile of oxytocin (OXT) is not yet fully documented especially in small animals like the rat. We highly sensitive and specific radioimmunoassay developed a (RIA) for OXT which could eliminate extraction process. This during suckling was applied to measure blood OXT levels RIA individual rat. In urethaneand parturition in each the suckling stimulus by 10 pups induced anesthetized rats, elevation of intramammary pressure intermittent consistently with significant (P< 0.01) elevation of serum OXT levels from 15.2 f 1.3 (mean f SEM, n=45) to 43.7 f 1.8 pg/ml (n=27) at These rises of OXT returned rapidly to the basal the peak. as expected from the short half-life (1.46 min) of OXT levels in general circulation. On day 22 or 23 of gestation, serum OXT concentrations were unchanged O-O.5 h before the first fetus was expelled. Serum OXT levels increased significantly (P< 0.01) from 27.6 f 4.6 pg/ml (n=19) in samples taken o-o.5 h before to 45.1 * 5.6 pg/ml in samples taken O-O.5 h after the expulsion of the first fetus and gradually elevated until one was expelled (64.3 * 5.3 pg/ml) and then dethe last clined. Thus our newly developed OXT RIA revealed the rise of serum OXT levels during suckling and parturition in the rat.
F11 NOVEL ANTERIOR PITUITARY RECEPTOR(S) FOR NEUROHYPOPHYSIAL HORMONES. A.J.Baertschi and M.Friedli, University of Geneva, and Department of Physiology, University of Virginia, Charlottesville, VA 22908 It is generally accepted that recently isolated corticotropin releasing factors (CRF) play a dominant role in the secretion of opiomelanocortins (e.g. ACTH and 8-endorphin). Noradrenalin, vasopressin, oxytocin, Angiotensin II and vasoactive intestinal polypeptide (VIP) are less potent releasers of ACTH. Although some of these neurohormones were reported to potentiate the CRF-induced ACTH secretion, their relative contribution and specificity of actlon has not been established. We show with isolated anterior pituitary cells incubated for lh in vitro that ACTH secretion induced by 5nM CRF is doubled by O.lnM arglnine vasopressin vasotocin (AVT), 1nM oxytocin, 1OnM anglotensin (AVP), 0.2nM arginine II and 1OOnM noradrenalin; VIP has no effect. Potentiation is observed of ACTH secretion also at concentrations of 0.05 to 0.5nM. Potent$atiqn by neurohypophysial,peptides and analogs (HO(Thr Gly ]Oxytocin, dTyr[Me]VDAVP, AVT; 5nM) is related to their pressor and not to antidiuretic biological activities, nor oxytoclc but anti-pressor AVP antagonists (d[CH215Tyr[Me]AVP; dPTyr[Me]AVP; 200nM) have no effect on intrinsic or potentiating activity of AVP. These results show that vasopressin and oxytocin are dominant modulators of CRF-stimulated ACTH secretion and suggest that they act on a new type of vasopressin receptor of the anterior pituitary gland.
F12 OXYTOCIN RELEASE DURING SUCKLING AND PARTURITION IN RATS. L Higuchis, K.Honda, T.Fukuoka, H.Negoro and K.Wakabavashi"*, Department of Physiology, Fukui Medical School, Fukui 910-11, Japan and Hormone Assay Center*", Institute of Endocrinology, Gunma University, Maebashi 371, Japan. The secretory profile of oxytocin (OXT) is not yet fully documented especially in small animals like the rat. We highly sensitive and specific radioimmunoassay developed a (RIA) for OXT which could eliminate extraction process. This during suckling was applied to measure blood OXT levels RIA individual rat. In urethaneand parturition in each the suckling stimulus by 10 pups induced anesthetized rats, elevation of intramammary pressure intermittent consistently with significant (P< 0.01) elevation of serum OXT levels from 15.2 f 1.3 (mean f SEM, n=45) to 43.7 f 1.8 pg/ml (n=27) at These rises of OXT returned rapidly to the basal the peak. as expected from the short half-life (1.46 min) of OXT levels in general circulation. On day 22 or 23 of gestation, serum OXT concentrations were unchanged O-O.5 h before the first fetus was expelled. Serum OXT levels increased significantly (P< 0.01) from 27.6 f 4.6 pg/ml (n=19) in samples taken o-o.5 h before to 45.1 * 5.6 pg/ml in samples taken O-O.5 h after the expulsion of the first fetus and gradually elevated until one was expelled (64.3 * 5.3 pg/ml) and then dethe last clined. Thus our newly developed OXT RIA revealed the rise of serum OXT levels during suckling and parturition in the rat.