Hyperosmolarity and Pulmonary Vascular Capacitance

Since plasma osmolarity rises during general muscle exercise and the lung is thought to have a function as a blood depot we have investigated the effect of plasma hyperosmolarity on pulmonary vascular capacitance. Hyperosmolar solutions of sodium chloride, urea and ethylene‐glycol (listed in order of potency) were infused into the pulmonary artery of an isolated rabbit lung preparation perfused with plasma at constant volume pulsatile inflow and ventilated by positive pressure. All the test‐substances caused dose‐dependent reductions in the weight of the preparations, which was followed continuously by the use of a force transducer. The effect was not related to change in bronchomotor tone or pulmonary vascular pressures. Nor could the weight reductions be explained solely as a result of loss of water from the lungs. The capacitance vessels of the lung appear to constrict when exposed to increased plasma osmolarity, a response which is in direct contrast to the effect of this stimulus on the resistance vessels of the lung. The finding strengthen the concept of the lung as a blood depot.