Luteinizing Hormone-Releasing Hormone-Induced Luteinizing Hormone Secretion in Vitro: Cyclic Changes in Responsiveness and Self-Priming*

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Abstract
Anterior pituitaries were removed from female rats at each stage of 4-day estrous cycles, quartered, placed in a chamber at time zero, and superfused at 1.0 ml/min for 360 min. At 120 and again at 240 min, a 10-min pulse of LHRH (100 ng/ml) was administered. Ten- or 2-min fractions of effluent fluid were collected for LH analysis. Both the total amount of LH secreted and the maximum LH secretory rate attained in response to pulses of LHRH were determined. The LH secretory response to the first pulse of LHRH, or pituitary responsiveness, was lowest on diestrous days 1 and 2 and maximal on proestrus, with estrus being intermediate. The LH response to LHRH was significantly greater in superfused pituitaries removed on the afternoon of proestrus before the onset of the LH surge compared to pituitaries taken on the morning of proestrus. An augmented LH secretory response to the second pulse of LHRH, the self-priming effect, was present on diestrous day 2 and proestrus only. The results demonstrate that the cyclic nature of pituitary responsiveness to LHRH and the self-priming or self-potentiating effect of LHRH on subsequent LHRH administration are retained by the anterior pituitary under these in vitro supervision conditions. The observation that the cyclic changes in anterior pituitary responsiveness to LHRH and the appearance of the LHRH self-priming effect are temporally distinct suggests that separate mechanisms are involved in their geneses. (Endocrinology106: 1430, 1980)