Effects of chronic hyperprolactinaemia on experimentally induced thirsts in male rats

Chronic hyperprolactinaemia was induced in ten male Wistar rats by subcutaneous injection of tissue fragments of the MtTW 15 prolactin-secreting adenoma. Serum prolactin was elevated significantly by 3 weeks after adenoma inoculation and increased progressively thereafter. An additional ten Wister-Furth rats were inoculated with the MtTW 15 adenoma and an equal number of age-matched controls were used to evaluate the drinking response to several dipsogenic agents. The hyperprolactinaemic rats consumed twice as much water as did control rats over a 24 hr period. Administration of the beta-adrenergic agonist, isoprenaline (25 micrograms/kg, s.c.), resulted in a similar increase in water intake in both groups prior to an elevation in serum prolactin. However, as serum prolactin increased there was a corresponding significantly attenuated dipsogenic response to isoprenaline. Chronic hyperprolactinaemia did not alter the drinking response to angiotensin II (200 micrograms/kg, s.c.), to 24 hr of dehydration or to administration of hypertonic (1 M) saline. These results indicate that chronic hyperprolactinaemia selectively attenuates the dipsogenic response to beta-adrenergic stimulation and support an involvement of prolactin in modifying the responsiveness of the beta-adrenergic system.