The effects of changes in osmolality and sodium concentration on angiotensin‐induced drinking and excretion in the pigeon

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Abstract
The pigeon drank copiously after a short latency in response to intracerebroventricular (i.c.v.) infusion of angiotensin II dissolved in isotonic NaCl. There were small, insignificant increases in urinary excretion so that the increased water intake caused the pigeon to go into positive fluid balance. Water was chosen in preference to 0.3 M-NaCl, which was also available to drink in these experiments. I.c.v. infusion of angiotensin dissolved in water, or in isotonic or hypertonic solutions of non-electrolytes, or in KCl or CaCl2 resulted in about half the water intake produced by angiotensin dissolved in isotonic NaCl. I.c.v. infusion of hypertonic NaCl alone caused drinking. I.c.v. infusion of angiotensin dissolved in hypertonic NaCl caused an amount of water to be drunk that was a simple addition of the amounts drunk in response to angiotensin dissolved in isotonic NaCl and to the extra amount of NaCl. Drinking in response to i.c.v. infusion of 2 other dipsogenic peptides, eledoisin and physalemin, was similarly affected by the composition of the solutions in which they were dissolved. The pigeon also drank in reponse to i.v. infusion of angiotensin II dissolved in isotonic NaCl. Urine flow and sodium excretion increased markedly so that the pigeons just maintained fluid balance. In contrast to the reduction in intake when angiotensin was infused i.c.v. dissolved in hypertonic non-electrolytes, i.v. infusions of angiotensin dissolved in hypertonic non-electrolytes caused enhanced drinking, compared with the corresponding infusions of angiotensin dissolved in isotonic NaCl. Drinking induced by i.v. infusion of angiotensin was little affected by simultaneous i.c.v. infusion of isotonic or hypertonic sucrose, or water, but it was increased by simultaneous i.c.v. infusion of hypertonic NaCl. Drinking responses were partly additive when angiotensin was given by simultaneous i.c.v. and i.v. infusion. The increased urine flow and electrolyte excretion in response to i.v. infusion of angiotensin were little affected by simultaneous i.c.v. infusion of angiotensin. In the pigeon, there may be separate sets of receptors in the cerebral ventricles for initiating drinking, 1 set responding to angiotensin, another to hypertonic NaCl. Outside the blood-brain barrier, and accessible to blood-borne substances, there may also be separate sets of receptors, 1 set responding to angiotensin, another to increases in effective osmolality of the blood.

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