Biology of Reproduction, Vol 23, 60-63, Copyright © 1980 by Society for the Study of Reproduction

Maintenance of Receptors for Luteinizing Hormone by Ovine Placental Lactogen in Pseudopregnant Rats

¹ Montreal Clinical Research Institute, Protein and Pituitary Hormone Laboratory, 110 Pine Avenue West, Montreal, Quebec, Canada H2W 1R7.
² Agriculture Canada, Research Station, Brandon, Manitoba, Canada
³ Agriculture Canada, Animal Research Institute, Department of Reproductive Physiology, Ottawa, Ontario, Canada K1A 0C6
⁴ Department of Physiology, Medical College, University of Manitoba, Winnipeg, Manitoba, Canada R3E 0W3

In pseudopregnant rats with an intact pituitary, prostaglandin F₂ (PGF₂) and bromoergocryptine (CB-154) produced a significant decrease in the binding capacity of human chorionic gonadotropin (hCG) by ovarian homogenates in vitro (P<0.05) and in the levels of serum progesterone (P<0.001) within 20 h after administration. The effect of PGF₂ on hCG binding capacity by ovarian homogenates was prevented by pretreatment with either ovine prolactin (oPRL) or ovine placental lactogen (oPL), but the effect on serum progesterone was not inhibited by hormone pretreatment. However, both effects of CB-154 were prevented in animals pretreated with either oPRL or oPL. In oPRL- or oPL-treated animals with administration of CB-154, a significant increase of binding capacity of hCG by ovarian homogenates was observed (P<0.05). From these studies, it seems that oPL behaves like oPRL in pseudopregnant rats in the maintenance of receptors for luteinizing hormone (LH-receptor).

Note:
ACKNOWLEDGMENTS We thank Mrs. T. M. Chan for secretarial help and Mr. M, Dennis for review of the manuscript. We gratefully acknowledge Merck Institute, USA, for contribution of antiserum for assay of progesterone, and NIH for donation of human chorionic gonadotropin (CR-119). This study was supported by grant no. 18-24 from the Medical Research Council of Canada and grant no 7843 from USPHS.