Release of LH and FSH by Anterior Pituitary Cell Suspensions from Female Rats During the Estrous Cycle and from Estrogen-Treated Ovariectomized Rats1

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Abstract
Steroid-dependent changes in the responsiveness of the pituitary to LHRH [luteinizing hormone-releasing hormone] are well documented by in vivo experiments and in vitro studies using pituitary tissue incubations. An attempt was made to determine whether anterior pituitary cell suspensions derived from female rats under different reproductive conditions would maintain this characteristic hormone-dependent response to LHRH after short-term culture. Suspensions of rat anterior pituitary cells were prepared using a trypsin dissociation at 23.degree. C. This procedure produced a high yield of cells (4 .times. 106 cells/gland) with a viability of 95% or greater(dye elusion). Using cells obtained from intact female rats (mixed cycle), a significant (P < 0.01) dose-related response to LHRH was observed for both LH and FSH even when tested immediately after enzymatic dissociation; however, cells allowed to recover for an additional 6-18 h after dissociation exhibited a significantly greater response to LHRH. Following an 18 h culture period, suspensions of anterior pituitary cells derived from animals at different stages of the estrous cycle were incubated with varying concentrations of LHRH for 2 h. The LH [luteinizing hormone] responses to LHRH were significantly greater (P < 0.01) with cells taken from diestrous-II and proestrous animals compared with those from estrous or diestrous-I rats. At all stages of the estrous cycle maximal responsiveness was obtained with 10-7 M LHRH. FSH [follicle-stimulating hormone] responses to LHRH were similar to those described for LH. Cells from pituitaries of short-term (72 h) ovariectomized rats given estradiol benzoate (EB; 5 .mu.g/100 g body wt) 26-27 h prior to tissue dissociation showed a significantly (P < 0.001) greater response to LHRH (.apprx. 100%) compared with those given oil. Cell suspensions from ovariectomized animals given oil or EB failed to show this difference in hormone release when exposed to 60 mM K+ for 2 h. Gonadotrophs in short-term culture maintain their characteristic hormone-dependent responsiveness to LHRH similar to that reported in vivo; estradiol is at least partly responsible for the amount of LH and FSH available for release from these cells. The increased LH and FSH available for release after estrogen treatment appears specific for the action of LHRH.

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