Effects of chronic hyperprolactinaemia on experimentally induced thirsts in male rats.

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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.

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