Abstract

The objective of this study was to determine whether progesterone affects: 1) basal and LHRH-induced LH release and 2) the ability of estradiol to increase basal and LHRH-induced LH release. Samples were also assayed for FSH in an effort to provide preliminary data regarding mechanisms controlling secretion of that gonadotropin in cattle. Bovine pituitary cells were grown in Dulbecco's medium and treated on day 5 of culture. Treatments were for a 4 × 3 × 2 factorial design, with concentrations of estradiol (0, 0.5, 5, and 50 ng/ml), progesterone (0, 3.1 and 31 ng/ml), and LHRH (0 and 100 ng/ml) as main effects. Cells were e×posed to these steroids throughout a 12-h incubation period on day 5, and LHRH was present during the last 6 h of this period. In the absence of progesterone, both basal and LHRH-induced LH release increased linearly (P < 0.05 and P < 0.01) with increasing concentrations of estradiol, but progesterone completely inhibited this effet of estradiol (P< 0.01). In the absence of estradiol, ...

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