Degranulation of renomedullary interstitial cells during reversal of hypertension.

It was demonstrated earlier that the renal venous effluent of one-kidney, one clip hypertensive rats contained a vasodepressor lipid resembling the antihypertensive neutral renomedullary lipid (ANRL), following unclipping and as the arterial pressure (MAP) was lowered. Consequently, the sham-unclipped (clip-intact) and the unclipped kidney (CK and UCK) were studied by electronmicroscopy and morphometrically (Weibel's techniques). Renomedullary interstitial cells (RIC) of the CK had abundant granules. The collecting duct (CD) had tall lining cells containing pale granules and displayed intercellular channels. Following unclipping, the RIC degranulated and the CD cells became flattened, lost their pale granules, and the intercellular channels disappeared as the MAP decreased. These changes were evident by EM appearance and volume density measurements. The renopapillary changes occurred as the kidney secreted the ANRL-like substance into the blood.