Long term effect of hypophysectomy and prolactin treatment on kidney structure in the eel in fresh water.

Long term effects of hypophysectomy and ovine prolactin treatment on the histological picture of the kidney were investigated in European eels. The epithelial cell height is very slowly affected after hypophysectomy, the decrease being highly significant after 50 days only in the distal and the initial collecting tubules. Nuclear surfaces were more rapidly reduced, the regressive changes being first detected in the initial collecting tubule (5 days), then in the distal portion and the two proximal segments. No degenerative changes were observed. These structural responses may be correlated with the slow reduction of the urine flow and of the plasma electrolytes in the same species. Ovine prolactin treatment (10mug/g/day) overcompensates the effects of hypophysectomy on the epithelial cell height and the nuclear area, and even after 50 days still induces the proliferation of new tubules although its action remains less intense than in intact eels. Other histological criteria (brush border thickness, mitotic activity, basal structure of proximal 2 cells) and sodium retention do suggest that these structural modifications reflect an increased functional activity of the kidney in addition to the effect of prolactin on sodium fluxes in the gills.