AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 1 53-R58, Copyright © 1986 by American Physiological Society
Effect of hypophysectomy on dipsogenic stimuli: evidence for angiotensin supersensitivity
R. H. Alper, C. F. Deschepper and W. F. Ganong
The effects of long-term hypophysectomy on renin secretion and the renin
and drinking responses to isoproterenol were investigated in male rats.
Drinking responses to angiotensin II, hypertonic saline, and water
deprivation for 24 h were also measured. Plasma renin activity and plasma
angiotensin II were variably lower in rats that had been hypophysectomized
for 21 days than in intact controls. Angiotensinogen was also reduced, but
plasma renin concentration was not. Isoproterenol produced a smaller
increase in plasma renin activity in hypophysectomized rats than it did in
controls, but with the one dose of isoproterenol that was tested, the
increase in plasma renin concentration was comparable in the two groups.
However, the drinking responses to isoproterenol were greater in the
hypophysectomized rats. The drinking responses produced by infusion of
angiotensin II were also greater, but the responses to infusion of
hypertonic saline and to 24 h of water deprivation were not. The data
suggest that in rats hypophysectomized for 21 days the circumventricular
organs that mediate thirst are hyperresponsive to circulating angiotensin
II, possibly because the relatively low circulating angiotensin II levels
permit the upregulation of angiotensin II receptors in these structures.
