Dissociation in the regulation of luteinizing hormone and follicle-stimulating hormone in a hyperprolactinaemic rat model: interrelationships between gonadotrophin and prolactin control.

Male and female Wistar rats were made hyperprolactinaemic by grafting two pituitary glands of litter-mate donors under the kidney capsule at 30 days of age. Other animals were sham-operated at the same age to serve as controls. Plasma levels of prolactin, LH and FSH were measured by double-antibody radioimmunoassay. Basal preoperative prolactin levels of approximately 10 ng/ml increased after the transplantation in both male and female rats, reaching values of approximately 180 ng/ml. Levels of LH were significantly reduced in these hyperprolactinaemic rats, whereas an increase in FSH values were seen. After administration of LH releasing hormone (LH-RH) a reduced LH response was seen but there was no response of FSH to LH-RH or even a decrease in FSH values. Prolactin levels were also reduced by LH-RH injection. Although an increase in prolactin levels was observed in control animals after a challenge with oestradiol benzoate, reduced increments were seen in experimental animals. The positive feedback effect of oestradiol benzoate on LH in females was reduced in pituitary-grafted rats but a potentiation of the FSH positive feedback could be clearly detected. This study suggests a dissociation of LH and FSH regulation in hyperprolactinaemia.