A study of the response to several dipsogenic treatments in rats with mammillary polydipsia and with centrally induced diabetes insipidus.

Several brain areas have been implicated in the regulation of water intake and body fluid homeostasis. Electrolytic lesions located in the mammillary area have proved to induce a strong polydipsia. The cause of this overconsumption is not understood, although other studies have indicated a possible relationship with the mechanisms involved in sodium control. In this paper, we consider whether mammillary polydipsia is related to diabetes insipidus. In this regard, animals with mammillary lesions were submitted to several dipsogenic treatments, both osmotic and volemic. These subjects showed a differential response to hypertonic NaCl compared with controls. No effect could be seen in relation to the other treatments employed, that is, sucrose and polyethylene glycol. On the other hand, this differential response to NaCl was not observed in those animals with diabetes insipidus centrally induced by means of lesions in the median eminence. Thus, mammillary polydipsia and diabetes insipidus-related water intake seem to be different phenomena. The possible relationship between mammillary polydipsia and sodium control is discussed.