title: Improved model for the induction of proestrus-like gonadotropin surges in long-term ovariectomized rats.
abstract: In long-term (greater than 4 wk) ovariectomized rats the positive response of the gonadotropin release apparatus to a priming dose of estradiol is moderate as compared with that of proestrous rats exposed to endogenous estradiol. In the present study, high sensitivity to estrogen was restored in long-term ovariectomized rats by pretreatment with estradiol benzoate (EB, 20 micrograms, day 0) and progesterone (P, 2.5 mg, day 3). Estradiol benzoate (20 micrograms) given on day 5 induced proestrus-like surges of LH and FSH in the afternoon on day 6. Additional administration of P (2.5 mg at noon on day 6) had a facilitatory effect. Stimulation of LH release could be evoked in rats by the described regimen 1, 6 or 50 wk after ovariectomy. The long-term ovariectomized rat injected with EB and P as described might provide a useful model for neuroendocrinological investigations on the gonadotropin surge mechanism.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D004958:Estradiol / Q000494:pharmacology*; D004971:Estrus / Q000187:drug effects*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D010052:Ovariectomy; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
chemical_list: D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone