Human placental gonadotrophin-releasing hormone (GnRH) binding sites: III. Changes in GnRH binding levels with stage of gestation

Specific oestradiol binding to a receptor in nuclear and cytosol fractions of the rat anterior pituitary gland and pituitary responsiveness to gonadotrophin releasing hormone (GnRH) during the oestrous cycle have been studied. To accomplish this, both unoccupied and occupied oestradiol-binding sites in the cytosol and oestradiol-binding sites in the nucleus and total cell were measured during the oestrous cycle. The concentration of unoccupied and occupied sites and total oestradiol binding in the cytosol fluctuated during the cycle. At pro-oestrus, the concentration of cytosol receptor was diminished by about 40% and replenishment occurred during oestrus. On the other hand, a profound increase in concentrations of cellular and nuclear receptors occurred at pro-oestrus. Administration of GnRH significantly stimulated LH release at all stages of the cycle. The maximum stimulation of LH release by GnRH was observed at 13.00 h of pro-oestrus. From these studies, it is concluded that pituitary responsiveness to exogenous GnRH during pro-oestrus parallels the changes in the content of oestrogen receptors in the cytosol and nucleus.

Download Full-text

Specificity of gonadotrophin-releasing hormone binding sites of the human corpus luteum: comparison with receptors of rat pituitary gland

Journal of Endocrinology ◽

10.1677/joe.0.1080323 ◽

1986 ◽

Vol 108 (3) ◽

pp. 323-328 ◽

Cited By ~ 22

Author(s):

T. A. Bramley ◽

G. S. Menzies ◽

D. T. Baird

Keyword(s):

Corpus Luteum ◽

Binding Sites ◽

Specific Binding ◽

Similar Degree ◽

Releasing Hormone ◽

Pituitary Tissue ◽

Rat Pituitary ◽

Luteal Tissue ◽

Gonadotrophin Releasing Hormone ◽

Human Corpus Luteum

ABSTRACT The effects of a number of analogues of gonadotrophin-releasing hormone (GnRH) on the binding of a radiolabelled GnRH agonist (GnRH-A; d-Ser(But)6, des Gly10]GnRH-ethylamide) to homogenates of human corpus luteum (CL) and rat pituitary tissue were compared. Specific binding was inhibited by GnRH and GnRH-like peptides only. Both the C-terminal amide and N-terminal region of the GnRH molecule were required for binding in both tissues. However, amino acid substitutions at position 6 markedly enhanced, and at position 8 markedly reduced, binding potencies in rat pituitary tissue compared with human CL binding sites. These results indicate that GnRH-binding sites of rat pituitary and human luteal tissue have a similar degree of specificity for GnRH-like peptides, and a similar requirement for both N- and C-terminal regions of the peptide, but that differences in specificity related to the mid-chain region of GnRH exist between human luteal and rat pituitary binding sites. J. Endocr. (1985) 000, 000–000

Download Full-text

Human placental gonadotrophin-releasing hormone (GnRH) binding sites: II. Comparison of binding and inactivation of 125I-labelled GnRH agonist to subcellular fractions following density gradient centrifugation

Placenta ◽

10.1016/0143-4004(92)90021-k ◽

1992 ◽

Vol 13 (6) ◽

pp. 583-595 ◽

Cited By ~ 3

Author(s):

G MENZIES ◽

T BRAMLEY

Keyword(s):

Density Gradient ◽

Gnrh Agonist ◽

Binding Sites ◽

Density Gradient Centrifugation ◽

Gradient Centrifugation ◽

Subcellular Fractions ◽

Releasing Hormone ◽

Gonadotrophin Releasing Hormone

Download Full-text

Dopaminergic regulation of pituitary gonadotrophin-releasing hormone receptor activity in the goldfish (Carassius auratus)

Journal of Endocrinology ◽

10.1677/joe.0.1210239 ◽

1989 ◽

Vol 121 (2) ◽

pp. 239-247 ◽

Cited By ~ 27

Author(s):

R. De Leeuw ◽

H. R. Habibi ◽

C. S. Nahorniak ◽

R. E. Peter

Keyword(s):

Binding Affinity ◽

Binding Sites ◽

Direct Action ◽

High Capacity ◽

Dopamine Antagonist ◽

Releasing Hormone ◽

Gnrh Receptors ◽

Gonadotrophin Releasing Hormone

ABSTRACT In goldfish, dopamine acts as an endogenous inhibitor of basal and gonadotrophin-releasing hormone (GnRH)-stimulated gonadotrophin release. The purpose of the present study was to investigate the effects of dopamine on the pituitary GnRH receptors in vivo and in vitro in goldfish. The goldfish pituitary contains two classes of GnRH-binding sites, a high-affinity/low-capacity site and a low-affinity/high-capacity site. Injection of domperidone, a dopamine antagonist, resulted in a dose- and time-related increase in capacity of both the high- and low-affinity GnRH-binding sites; apomorphine, a dopamine agonist, completely reversed this effect. The effects on GnRH receptor capacity correlated very closely with changes in serum gonadotrophin concentrations. Domperidone was generally without effect on GnRH-binding affinity; however, a small but significant decrease in affinity was observed for the low- affinity binding site at 18 h after injection of the highest dose of domperidone used (40 μmol/kg body weight). Treatment with apomorphine of goldfish pituitary fragments in a perifusion system caused a decrease in the capacity of both the high- and low-affinity GnRH-binding sites without affecting binding affinity; domperidone reversed this effect. It is concluded that the dopaminergic inhibition of basal and GnRH-stimulated gonadotrophin release in goldfish might, in part, be the result of a down-regulation of the pituitary GnRH receptors; this effect of dopamine can be achieved by a direct action at the pituitary level. Journal of Endocrinology (1989) 121, 239–247

Download Full-text