Effect of long term administration of ovine prolactin on hypothalamic-pituitary testicular axis in rat

The effect of hyperprolactinaemia on testicular morphology and on hypothalamic-pituitary-testicular axis was studied in adult male Wistar rats. Animals received ovine prolactin (oPRL) 200 micrograms twice daily s.c.) for 24 and 36 days and were killed by exanguination. Blood was collected for hormonal determinations and sex accessory glands were removed for histological studies. Circulating testosterone (T) and luteinizing hormone (LH) levels showed a significant reduction after 36 days of treatment whereas plasma follicle-stimulating hormone (FSH) levels were unchanged in all animals. No macroscopic or light microscopic histological modifications were observed in the testes. The present results, while excluding a direct effect of hyperprolactinaemia on seminiferous tubules, suggest that LH suppression is the consequence of a central effect of the ovine PRL long-term administration. The increased DA turnover in the hypothalamus suggested as inhibitory on GnRH neurons could account for this effect. The reduction of T levels seems to be mediated by the LH suppression, even though a direct effect of oPRL on Leydig cell receptors could be hypothesized.