No abstract

The effect of water deprivation for 1 day on Na balance was measured in rats, rabbits, and sheep. In all three species, dehydration induced a considerable increase in the daily output of Na in urine. This resulted in the water-deprived animals becoming Na depleted as well as water deficient. Experiments were also designed to control for the reduced food intake that results from water deprivation in rats and rabbits. The results showed that decreased food intake was not the cause of the natriuresis and subsequent Na depletion that occurred during dehydration. When water was again made available to the dehydrated animals, a period of urinary Na retention ensued. This Na retention usually continued until the Na deficit that had accrued during the period of dehydration had been ameliorated. It seems likely that natriuresis in response to dehydration is common in mammals. We postulate that such a natriuretic response may serve a homeostatic function in buffering increases in plasma [Na] and osmolality that result from dehydration.

1. The subfornical organ, median preoptic nucleus and the organum vasculosum of the lamina terminalis (OVLT) are a series of structures situated in the anterior wall of the third ventricle and form the lamina terminalis. The OVLT and ventral part of the median preoptic nucleus are part of a region known as the anteroventral third ventricle region. 2. Data from many laboratories, using techniques ranging from lesions, electrophysiology, neuropharmacology, Fos expression, immunohistochemistry and receptor localization, indicate that the tissue in the lamina terminalis plays a major role in many aspects of body fluid and electrolyte balance. 3. The subfornical organ and OVLT lack the blood-brain barrier and detect alterations in plasma tonicity and the concentrations of circulating hormones such as angiotensin II and possibly atrial natriuretic peptide and relaxin. 4. This information is then integrated within the lamina terminalis (probably in the median preoptic nucleus) with neural signals from other brain regions. The neural output from the lamina terminalis is distributed to a number of effector sites including the paraventricular (both parvo- and magno-cellular parts) and supraoptic nuclei and influences vasopressin secretion, water drinking, salt intake, renin secretion, renal sodium excretion and cardiovascular regulation.