Angiotensin II induced reduction of peritubular capillary diameter in the rat kidney.

Large peritubular capillaries were infused consecutively (20 nl-min-1) in random sequence with isotonic saline and angiotensin II (20-80 ng-ml-1). The diameters of the infused capillaries were measured, without knowledge of the infusate used, from colour photographs of the infused area. Angiotensin II induced a significant (p less than 0.001) decrease in capillary diameter (delta = 1.2 +/- 0.2 (SE) micron and delta = 2.1 +/- 0.2 (SE) micron with 20 ng-ml-1 and 80 ng-ml-1 angiotensin II infusates, respectively). This decrease was shown to be independent of external tubular compression: separate experiments in which the surrounding tubules were collapsed by injection of oil blocks yielded similar results. The possibility that the observed reduction in diameter was caused by an angiotensin II induced change in capillary permeability to the staining solution was excluded, since the angiotensin II effect was unchanged when fluorescent dextran (mol. wt. 150 000) was substituted for lissamin green. These experiments indicate that peritubular capillaries contract actively when infused with angiotensin II.