Hyperprolactinaemia does not affect the development of the stimulatory mechanism of oestrogen-progesterone on LH secretion

Abstract. Previous reports indicate that prolactin induces precocious puberty in the female rat. The present investigation was designed to determine if hyperprolactinaemia affects the development of the stimulatory effect of oestrogen-progesterone on LH secretion in prepubertal rats. Hyperprolactinaemia was induced by the administration of sulpiride at the dose of 7 mg/100 g body weight/day for 6 days. The rats were sacridied 6 to 9 h after the last injection. Normal sulpiride-treated rats were injected 76 h before sacrifice with 10 μg of oestradiol benzoate and with 1 mg of progesterone on the day of sacrifice. The animals were killed at 14, 22, 24, 28 and 32 days of age. The sulpiride treatment induced a significant increase in serum prolactin levels (P < 0.01) at all ages studied. The treatment of oestrogen-progesterone induced prolactin release in controls and in the sulpiride-hyperprolactinaemic rats of 24, 28 and 32 day old but not in younger rats. The administration of oestrogen-progesterone alone in normal and in sulpiride hyperprolactinaemic rats produced a negative feed-back effect on LH secretion at 14 and 22 days of age and a significant stimulatory action at 24, 28 and 32 days. No differences were observed in the basal LH serum concentration between control and hyperprolactinaemic rats at the different ages studied. Our findings suggest that the modifications in the onset of puberty induced by hyperprolactinaemia are not connected with alterations in the maturation of the hypothalamic-pituitary mechanism involved in the positive feed-back effect of ovarian steroids on LH secretion.