EFFECTS OF ANESTRUS AND BROMOCRYPTINE TREATMENT ON THE EXPRESSION OF PROLACTIN AND LH RECEPTORS IN THE RABBIT OVARY DURING LACTATION

The aim of the present study was to correlate the number of prolactin and LH receptors in the ovary with the changes in sexual behaviour tha t occur within a few days following parturition in rabbits. Multiparou s New Zealand white rabbits at days 0, 3 and 10 of lactation were test ed for their receptivity upon presentation to a male. Rabbits were cla ssed as either receptive or nonreceptive at each stage of lactation; h alf of the animals in each class were treated with bromocryptine to ex amine the effects of prolactin deprivation. Ovarian receptors for LH a nd prolactin, as well as the concentration of their corresponding mRNA , were measured at each stage of lactation in every group. Results ind icate that receptive behaviour is correlated with significantly more f ollicles on the rabbit ovary (diameter > 1 mm; P < 0.05) and an increa se in the concentration of LH receptor mRNA (P < 0.001) and prolactin receptors (P < 0.05). In addition, on day 4 of lactation, there were s ignificantly fewer follicles in nonreceptive rabbits (P < 0.05). LH re ceptor content remained constant on days 1 and 4 of lactation but incr eased on day 11 (P < 0.05). Bromocryptine treatment had no effect on t he number of follicles or on the amount of LH receptor mRNA in does, b ut it significantly increased LH receptors (P < 0.01), and the concent ration of prolactin receptor mRNA (P < 0.001), particularly on day 11 of lactation (P < 0.05), and prolactin receptor content (P< 0.001). Re ceptive rabbit ovaries therefore display more follicles that can respo nd to an LH surge via newly transcribed LH receptors than do nonrecept ive. Bromocryptine treatment seems to relieve some repressive activity exerted by prolactin on the number of LH receptors in the rabbit ovar y.