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- Author: J. Kucharczyk x
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ABSTRACT
Water intake elicited by microinjection of the hormone angiotensin-II into the preoptic region of cyclic female rats was significantly less on days of vaginal oestrus than at dioestrus or metoestrus, whereas the drinking of 2·7% NaCl solution, to which rats also had access, did not vary with the cycle. Administration of the same dose of angiotensin-II to the subfornical organ and the lateral cerebral ventricles induced drinking at all stages of the oestrous cycle, but the volumes of water or 2·7% NaCl ingested did not vary with the cycle. Water intake after subcutaneous injection of isoprenaline, a β-adrenergic agonist which causes increased angiotensin biosynthesis, varied cyclically with the stage of the oestrous cycle. On the other hand, water and 2·7% NaCl intakes induced by intraperitoneal injection of hypertonic NaCl (a cellular stimulus of thirst) or by 24-h water deprivation (which dehydrates both the extracellular and cellular body fluid compartments) did not differ significantly at the various stages of the oestrous cycle. The finding that fluctuations in angiotensin- and isoprenaline-induced water intake parallel the changes in spontaneous 24-h drinking suggests that the preoptic region may play an important role in the maintenance of extracellular fluid balance in synchrony with the oestrous cycle.
J. Endocr. (1984) 100, 183–188
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SUMMARY
The influence of the oestrous cycle on spontaneous and dipsogen-induced drinking was studied in female rats. Spontaneous fluid intake was lowest on the day of oestrus. Drinking induced by subcutaneous isoprenaline, and by angiotensin II (injected into the preoptic area), also showed marked cyclical variation, being lower at pro-oestrus and oestrus than at other stages of the cycle. Drinking induced by subcutaneous hypertonic NaCl or by intracranial carbachol did not vary with the oestrous cycle. Cyclicity of spontaneous and of angiotensin-induced water intake was not apparent in rats before puberty or after ovariectomy. Ovariectomy reduced drinking in response to isoprenaline. Treatment with oestradiol benzoate (20 μg) caused a reduction in spontaneous water intake, but a marked increase in the drinking response to isoprenaline. Treatment with oestradiol benzoate and progesterone (2·5 mg) caused a larger decrease in spontaneous water intake and an insignificant increase in isoprenaline-induced drinking. Water intake induced by subcutaneous hypertonic saline was unaffected by gonadal steroids. The results provide further evidence for the view that the thirst of extracellular origin, in which the renin–angiotensin system is involved, is brought about by mechanisms different from those that respond to cellular dehydration. Only drinking caused by activation of extracellular mechanisms appeared to be sensitive to the ovarian cycle and to ovarian hormones.
