Blood Hyperosmolality and Pulmonary Vascular Resistance in the Cat

Blood osmolality rises during general muscle exercise. The purpose of this work was to investigate the effect of similar slow, graded rises of blood osmolality on pulmonary vascular resistance. Hyperosmolar solutions of sodium chloride, mannitol, urea, glucose, thiourea and ethylene glycol were infused into the left lower lobe pulmonary arterial branch in the cat. Lobe blood flow, pulmonary arterial, left atrial and systemic arterial pressures were recorded. With the exception of ethylene glycol, all the test solutions caused dose-dependent, reversible reductions in lobe vascular resistance (LVR). Maximal reduction in LVR was 30% of initial value. A rise of blood osmolality of 25 milliosmols/liter, comparable with levels found during exercise, caused a 10% reduction in LVR. Hyperosmolar solutions of ethylene glycol, which has the highest rate of cell wall penetration of the test substances, caused no change in LVR. Bolus injections of 1M solutions of sodium chloride caused rapid transient rises in LVR. It appears that the resistance vessels of the lungs react to graded rises of blood osmolality in a way qualitatively similar to that seen in the resistance vessels of skeletal muscle.