Morphometric studies on the lipid droplets of the interstitial cells of the renal medulla in different states of diuresis

Abstract

The volume density of lipid droplets in renal medullary interstitial cells was determined in rats in different diuretic states by electron microscope morphometry. Three different groups of animals were examined: Group I, dehydrated rats deprived of drinking water for 24 hr; group II, acutely hydrated rats treated as group I but given one dose of water 1 hr before sacrifice; group III, water-loaded animals given repeated doses of water prior to sacrifice. In the water-loaded rats which had a low urine osmolality the volume density of interstitial cell lipid droplets was 2.4 times higher than in the dehydrated ones. Correspondingly, the number of lipid droplets was higher by about 46% and the mean single lipid droplet volume was about 64% larger. The volume density of lipid droplets was not significantly different between dehydrated and acutely hydrated animals. Furthermore, there was no difference in urine osmolality between these two groups, suggesting that the acutely hydrated rats were still in a state of antidiuresis. An earlier report of an increased number of lipid droplets in the acutely hydrated rats as compared to the dehydrated ones thus could not be confirmed. It is suggested that the lipid droplets are not secreted from the interstitial cells by exocytosis but are partially or completely removed by intracellular enzymes located in the cytoplasmic ground substance or in cytomembranes.