The depressing (negative) effect of oestradiol benzoate on the in vitro secretion of LH and FSH by the pituitary gland of the LRH-pretreated long-term ovariectomized rat changes into the augmentative (positive) effect after discontinuation of the LRH-pretreatment.
The effect of pretreatment in vivo with oestradiol benzoate on in vitro secretion of LH and FSH was studied in long-term ovariectomized (OVX) rats both at the end of a 5-day continuous in vivo pretreatment with LRH and 4-days after cessation of such LRH pretreatment. Rats were on day 0 sc implanted with osmotic minipumps which released LRH at the rate of 250 ng/h. Control rats were implanted with a piece of silicone elastomer with the dimensions of a minipump. On days 2 and 4 the rats were injected with either 3 micrograms EB or with oil. On day 5 part of the rats were decapitated and the in vitro autonomous (i.e. non-LRH-stimulated) and 'supra-maximally' LRH-stimulated release of LH and FSH was studied using a perifusion system. From other rats the minipumps were removed on day 5 and perifusion was performed on day 9. On the 5th day of the in vivo LRH pretreatment the pituitary LH/FSH stores were partially depleted; the pituitaries of the EB-treated rats more so than those of the oil-injected rats. EB alone had no significant effect on the content of the pituitary LH- and FSH stores. On day 9, i.e. 4 days after removal of the minipumps, the pituitary LH and FSH contents had increased in both the oil- and the EB injected rats, but had not yet recovered to control values. In rats not subjected to the 5-days pretreatment with LRH EB had a positive effect on the supra-maximally LRH-stimulated secretion of LH and FSH as well as on the non-stimulated secretion of LH. EB had no effect on the non-stimulated secretion of FSH.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D004343:Drug Implants; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D010052:Ovariectomy; D010477:Perfusion; D010902:Pituitary Gland / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D004343:Drug Implants; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone