The effect of val 5 -angiotensin II amide on water drinking in sheep was studied against a background of comprehensive data on arterial blood and cerebrospinal fluid angiotensin II levels in sheep under a variety of physiological conditions. Physiological range of blood angiotensin II concentration is 1-100 ng/lOOml. Intravenous infusion of angiotensin II within the physiological range did not increase water drinking. Intracarotid infusion of angiotensin II, or injection into third ventricle or hypothalamus, consistently caused immediate drinking of large amounts of water. Dosages necessary for effect were in the supraphysiological range. Quantitative examination of data in sheep and other species suggests that a physiological role for angiotensin II in thirst is not proved.

The data emerging from the work we have been doing on the role of the brain In the regulation of Na^ bomeostasis is interesting raw material for analysis in a symposium on control systems.It is clear from many facets of contemporary physiological knowledge, including comparative studies, that the evolutionary progression of life from the oceans and estuaries and swamps to the free ranging land species has involved development of a complex organization of Biic control of salt and water.The control of sodium homeostasis involves regulation of input and output. On the intake side, the processes to be considered are:(1) The innate behavioural mechanisms of specific salt appetite drive generated by onset of body Na+ deficit. (2) The hedonistic palatal)ility determined salt ingestion-i.e., intake without any metabolic requirement occurring because the creature likes tlie taste. (3) The possibility of central nervous processes causing aversion to suit in tbe instanee of body overload-i.e.. processes over and above the recognized taste aversion normally produced by salt solutions of high concentrations. Output concerns (i) tlie regulation of aldosterone secretion (ii) the operation of mechanisms which in certain circumstances amplify the action of aldosterone on target organs such as occurs in Na deficiency, (iii) natriuretic processes, physical and possibly hormonal, which operate in the face of body surfeit.In this paper we are going to confine attention to the appetite element of intake. However, it is important to bave instanced above the several components of control. These systems luu'e emerged concurrently during phylogenesis as a result of the various environmental stresses upon Nu^ homeostasis. Whereas it is formally possible that the control mechanisms are largely independent of one

This study was undertaken to define the resting pattern of fetal pituitary-adrenocortical function. Experiments were performed at 127-145 days gestation in fetal sheep with chronic peripheral and adrenal cannulas inserted under halothane anesthesia. With the fetus in a baseline state, over 6 h, at 30-min intervals, maternal and fetal peripheral samples were collected for blood gases and cortisol (F), corticosterone (B), and adrenocorticotropic hormone (ACTH) concentrations, and three successive, 2-min adrenal samples were collected for determination of F and B secretion rates. We observed high-frequency, episodic bursts of F secretion. A lower frequency oscillation of F secretion, with a period of approximately 90 min, was defined by cosinor analysis. The mean amplitude of the oscillation increased from 45 to 507 ng/min with advancing gestation. The pattern of B secretion was similar to that for F but was quantitatively lower. An oscillatory period of approximately 90 min for plasma F was present in a majority of experiments. Pulsatile rhythms for ACTH were defined in 10 of 14 experiments, with periods ranging from 1.64 h in the least mature group to 2.37 h in the oldest fetus. Mean data revealed exponential increases in both F secretion and plasma ACTH from 129 to 145 days gestation.

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