HOME HELP CONTACT US SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Chadio, S. E. Articles by Antoni, F. A. Search for Related Content PubMed Articles by Chadio, S. E. Articles by Antoni, F. A.

Oxytocin may function as a hypothalamic releasing hormone for prolactin and ACTH secretion in the rat. In the present study we have investigated the properties of putative oxytocin receptors in the rat adenohypophysis by radioligand-binding assay.

A novel oxytocin receptor antagonist [1-(β-mercapto-β,β-cyclopentamethylene propionic acid),2-(ortho-methyl)-Tyr²-Thr⁴-Orn⁸-Tyr⁹-NH₂]-vasotocin (OTA) was radioiodinated by the iodogen method to a specific activity of 0·6 nCi/fmol. The radioiodinated derivative ¹²⁵I-labelled OTA (¹²⁵I-OTA) was reacted with membrane suspensions prepared from the uterus or adenohypophysis of female rats which were (a) ovariectomized for 7 days, (b) ovariectomized and treated with 5 µg oestradiol-17β 48 h before death or (c) implanted with a piece of silicone elastomer tubing containing 50 mg diethylstilboestrol (DES) 5 days before death. In uterine as well as the pituitary membrane suspensions, the radioligand was bound reversibly and with high affinity (dissociation constants 0·2 ± 0·1 and 0·1±0·01 nmol/l respectively; means + S.E.M., n=3) to a single class of sites with limited binding capacity, which varied with the type of pretreatment. Oestradiol-17β increased the binding capacity fivefold in the uterus in ovariectomized rats, but only very low specific radioligand binding was found in pituitary preparations from the same animals. Treatment with DES markedly increased the number of receptors in both the uterus and the adenohypophysis. Studies with several agonist and antagonist analogues revealed no difference in the ligand specificity of the uterine and adenohypophysial sites binding ¹²⁵I-OTA, indicating that they are the same species of receptor. Furthermore, ligand-binding studies, carried out with tritiated vasopressin as tracer in pituitary membrane preparations, showed that OTA is not bound by pituitary vasopressin receptors at concentrations below 1 µmol/l.

In summary, ¹²⁵I-OTA is a highly specific radioligand suitable for the analysis of pituitary oxytocin receptors. The low number of oxytocin receptors in the adenohypophysis of rats treated with oestradiol-17β suggests that the prolactin-stimulating action of oxytocin is mediated by highly efficient transmembrane signalling.

Journal of Endocrinology (1989) 122, 465–470

This article has been cited by other articles:

				D. T. McKee, M. O. Poletini, R. Bertram, and M. E. Freeman Oxytocin Action at the Lactotroph Is Required for Prolactin Surges in Cervically Stimulated Ovariectomized Rats Endocrinology, October 1, 2007; 148(10): 4649 - 4657. [Abstract] [Full Text] [PDF]

				J. J. Evans Modulation of Gonadotropin Levels by Peptides Acting at the Anterior Pituitary Gland Endocr. Rev., February 1, 1999; 20(1): 46 - 67. [Abstract] [Full Text]

				J. Gutkowska, M. Jankowski, C. Lambert, S. Mukaddam-Daher, H. H. Zingg, and S. M. McCann Oxytocin releases atrial natriuretic peptide by combining with oxytocin receptors in the heart PNAS, October 14, 1997; 94(21): 11704 - 11709. [Abstract] [Full Text] [PDF]

				J. J. Evans, W. Forrest-Owen, and C. A. McArdle Oxytocin Receptor-Mediated Activation of Phosphoinositidase C and Elevation of Cytosolic Calcium in the Gonadotrope-Derived {alpha}T3-1 Cell Line Endocrinology, May 1, 1997; 138(5): 2049 - 2055. [Abstract] [Full Text] [PDF]