Osmoregulation in uncontrolled diabetes mellitus.

Abstract

In this thesis we studied the influence of osmotic loading on vasopressin secretion and water intake in experimentally-induced diabetes mellitus, in the insulin deprived state as well as when treated with insulin, in order to investigate whether the osmotic drive for vasopressin release and thirst is altered in the diabetic state. Four dogs were used for the experiments to be reported. They were infused with hypertonic sodium sulfate to investigate the influence of osmotic loading on water intake and vasopressin secretion in the control, insulin-treated diabetic and diabetic conditions. Forty-eight hours of insulin depletion did not produce a change in the basal plasma vasopressin levels, even though there was a significant increase in plasma osmolality. In addition, forty-eight hours of insulin depletion did not alter the sensitivity of the osmoreceptors controlling vasopressin release and thirst. The effect of the diabetic condition on the osmotic threshold is subject to interpretation of the data. If glucose is considered an osmotically effective solute in the diabetic state, there is an upward resetting of the osmostat for vasopressin release and thirst, and a downward or leftward shift of the osmostat when glucose is not considered to be effective osmotically. The results of the present study provide evidence that the osmotic sensitivity of vasopressin release and thirst is not affected by the presence or absence of insulin. However, whether there is a true resetting of the osmostat for vasopressin release and thirst in the diabetic state depends on the assumption mode concerning glucose permeability.