Ultrastructural observations on the renal papilla of the rabbit

Summary

Ultrastructural studies of renal papillae of New Zealand brown rabbits under different states of water balance indicate no morphological variation between control, antidiuretic and diuretic animals; the only exception being a decrease in the amount of glycogen in the collecting duct cells in the antidiuretic state and an increase in the diuretic.

The light cells of the collecting ducts have a low electron density and show a paucity of organelles. These comprise mitochondria, Golgi apparatus, multivesicular bodies, sparse endoplasmic reticulum and free ribosomes. The centrally-placed, spherical nucleus demonstrates large numbers of nuclear pores. The lateral surfaces and bases of the cells have considerable infoldings which may have functional significance.

The attenuated endothelial cells of the vasa recta are punctuated by fenestrations which are most frequently crossed by membrane. The cells contain micropinocytotic and pinocytotic vesicles.

The loops of Henle in the papilla are lined by squamous cells which are extended longitudinally in the form of interdigitating processes. The bases of the cells of most loops are scalloped.

The interstitial cells are embedded in an amorphous matrix containing occasional collagen fibres and strands of fibrillar material. The cells are irregular in outline and have moderately developed endoplasmic reticulum and Golgi apparatuses.

Tight junctions between the cells of all collecting ducts, loops of Henle and vasa recta are a constant finding. All these tubular elements are surrounded by a prominent basement membrane; that associated with the loops of Henle tends to be multiplied, particularly at scalloped regions. The membrane associated with the vasa recta is single except at regions where it projects across the interstitium to the membranes of the collecting ducts and loops of Henle.

The functional implications of these findings are discussed.