Vascular Responses to Plasma Hypoosmolality in Man

Abstract

To study limb vascular responses to plasma hypoosmolality in man, test solutions of hypoosmolar NaCl (145 mOsm/kg) and control solutions of isosmolar NaCl (290 mOsm/kg) were infused into the brachial arteries of 14 normotensive and 13 essential hypertensive patients. Limb blood pressures were monitored, limb blood flow was measured by indicator-dilution and limb vascular resistance was calculated as mmHg/ml flow per min per 100 cm3 limb volume. The infusions did not significantly change systemic plasma osmolality, Na concentration or blood pressure. Compared to control infusions, the hypoosmolar infusions decreased limb venous plasma osmolality and serum Na concentrations by an average of 12 mOsm/kg and 7 meq/1, respectively. Compared to control infusions, limb venous serum concentrations of K, Ca, Mg or blood hematocrit were not altered by the hypoosmolar infusions. In response to the hypoosmolar infusions, limb resistance increased by 28% in normotensives and by 26% in hypertensives. The acute local vascular response to a small reduction in plasma osmolality in the limb of man is a large increase in vascular resistance. No evidence was found for abnormal responses to plasma hypoosmolality in essential hypertensives.