Direct effects of hypoosmolality on vascular resistance and myocardial contractile force (38587).

Hemodialysis was used to study the direct effects of acute hypoosmolality upon the resistance to blood flow through the gracilis and coronary vascular beds and upon left ventricular contractile force in the dog. When sodium chloride was removed from the blood perfusing the gracilis vascular bed, resistance increased linearly over the range 300-225 mOsm/kg. A 10% decrease in osmolality produces a 20% increase in resistance. When the removed sodium dhloride was replaced with mannitol such that plasma osmolality did not change, resistance rose slightly but failed to regularly return to the control value. Hypoosmolality also raised coronary vascular resistance and this was associated with an increase in left ventricular force. Thus direct effects of hypoosmolality on peripheral vascular beds and perhaps myocardium may participate in the compensatory mechanisms that tend to stabilize blood pressure during hypoosmotic states such as acute salt depletion.