Effects of luteinizing hormone-releasing hormone on pulsatile prolactin secretion in adult hyperprolactinemic female rats.

Regulation of prolactin secretion involves complex interactions of multiple inhibitory and stimulatory factors. Among them, luteinizing hormone-releasing hormone (LHRH) has been shown, when analyzed in single samples, to exert both stimulatory and inhibitory influences on prolactin secretion. In the present study, we have further examined the effects of LHRH on prolactin secretion by studying the pulsatile pattern of the hormone after the administration of the neuropeptide. For this purpose, adult sham-operated and pituitary-grafted female rats, exhibiting diestrus smears were bled for 3 hr during the morning (1030 to 1330 hr). Two pulses of LHRH (10 ng/kg body wt) were administered 60 and 120 min after starting the bleeding period. Pituitary grafting increased the mean serum prolactin levels, absolute amplitude of the hormone peaks, and its mean half-life, compared with control animals. In sham-operated rats, LHRH administration diminished mean serum prolactin levels, the absolute pulse amplitude and frequency of prolactin peaks. In pituitary-grafted animals, LHRH administration only decreased the pulse frequency of prolactin peaks. These data suggest that LHRH significantly suppressed pulsatile prolactin secretion, and that this effect was blunted by exposure to previously elevated circulating prolactin levels.