Effects of chronic estrogen treatment on water exchange in rats

Intact female rats implanted subcutaneously with Silastic tubes containing estradiol benzoate (EB) (28.7 micrograms X kg-1 X day-1) for 28 wk had a significantly greater daily intake of water, a higher water-to-food intake ratio, and a greater urine output than untreated control rats. Ovariectomized (OVX) rats also implanted for 14 wk with EB tubes (15 and 36 micrograms X kg-1 X day-1) showed identical results. Dipsogenic responses of the EB-treated rats to isoproterenol (25 micrograms/kg sc), angiotensin II (200 micrograms/kg ip), and hypertonic saline (1 M, 1% of body wt ip) were significantly attenuated. Both intact and OVX rats were subjected to a 24-h dehydration to assess renal concentrating ability. EB-treated rats lost significantly more weight and excreted significantly more urine of lower osmolality than controls. Administration of vasopressin to volume-loaded, EB-treated rats revealed no abnormalities in the ability to concentrate urine to the level of controls. Thus, in spite of a reduced responsiveness to several dipsogenic stimuli, EB-treated rats have an increased daily water turnover apparently related to an inability to concentrate their urine. This in turn may be related to abnormalities in either synthesis or release of antidiuretic hormone or both.