Quantitative evaluation of pinocytosis of capillaries of the stria vascularis under normal and experimental conditions.

In order to examine evidence of high activity of pinocytosis in capillaries of the stria vascularis, quantitative morphometry of pinocytotic vesicles was carried out ultrastructurally by the horseradish peroxidase (HRP) tracer method. In guinea pigs, there was a significant difference between the stria vascularis and spiral ligament in the number of vesicles per micron 2 (p less than 0.05) and labelled vesicles per micron 2 (p less than 0.001). In normotensive control rats, the number of labelled vesicles per micron 2 in capillaries of the stria vascularis was significantly greater (p less than 0.001) than that of the spiral ligament. Results of acute hypertensive and acute hypotensive experiments both indicated that enhanced permeable capillaries of the stria vascularis showed no significant increase in the number of pinocytotic vesicles per micron 2, but that they showed a more significant increase in the number of labelled vesicles per micron 2 than non-enhanced permeable capillaries of the stria vascularis (p less than 0.01) and capillaries of the spiral ligament (p less than 0.001). These findings provide ultrastructural confirmation of our previous studies (4, 8, 9) that pinocytosis contributes to the high permeability of capillaries of the stria vascularis under normal and experimental acute hypertensive and acute hypotensive conditions.