Secretion of luteinizing hormone caused by continuous infusions of luteinizing hormone releasing hormone in the long-term ovariectomized rat: effect of oestrogen pretreatment.
Continuous infusions of luteinizing hormone releasing hormone (LH-RH) into phenobarbitone-treated long-term ovariectomized rats, resulted in patterns of LH secretion which were determined by the blood LH-RH concentration. Infusions of 52 ng LH-RH/h caused steadily increasing ple maintained for the rest of the experiment (9h). A similar course of plasma LH concentration was observed as a result of infusions of 104 ng LH-RH/h, though in this case LH concentrations reached higher levels than those induced by infusion of 52 ng LH-RH/h. Higher rates of LH-RH infusion (208 and 416 ng/h), however, induced clear-cut LH peaks, which reached their maximal plasma values after 2-3 h of infusion and then declined again until, at the end of the experiment, they were only slightly higher than the LH levels induced by infusions of 52 ng LH-RH/h. A similar series of LH-RH infusions given to ovariectomized rats pretreated with oestradiol benzoate during 3 days (the rats were injected daily with 7 mug steroid), produced a highly augmented response of the pituitary gland, but all LH-RH concentrations infused induced rather sharp LH peaks, reaching their maximum after 2-3 h of infusion. After 5 h of infusion the descending parts of all these peaks appeared to converge. In both control and oestradiol benzoate-pretreated rats there appeared to be a linear relationship between the logarithm of the blood LH-RH concentration and the maximal plasma LH values on one hand, and the amount of LH secreted during the first 5 h of infusion on the other. Furthermore, it appeared that the longer the period of oestrogen action, the more the response of the pituitary gland to a certain dose of LH-RH was enhanced.
D000818:Animals; D002369:Castration; D003864:Depression, Chemical; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects*; D051381:Rats
D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007986:Luteinizing Hormone; D010634:Phenobarbital