Responsiveness of rat pituitary gland in vitro to pulsatile luteinising hormone-releasing hormone(LHRH) during the oestrous cycle.

Anterior pituitary gland fragments removed from female rats at various days of the oestrous cycle were perifused into small Biogel columns. After 2 hours stabilisation, the tissues were exposed at the beginning of each of five hours of perifusion to a volley of six 1-mi pulses of LHRH (10M1 8, given 4 min.apart. Pituitary glands removed during oestrus or met-oestrus showed little change in the sensitivity to pulses of LHRH, LH release being similar in response to all volleys. Pituitaries removed during di-oestrus showed a priming response to the second volley of LHRH but this was followed by desensitisation thereafter. In contrast, tissues removed at various times during pro-oestrus and exposed to LHRH pulses of different frequencies exhibited only progressive sensitisation. In conclusion, sensitivity of pituitary gland to LHRH varies throughout the oestrous cycle which plays an important role in the control of episodic secretion of LH (JPMA 38: 237, 1988).