The effect of prolactin on kidney structure of the euryhaline teleost Gasterosteus aculeatus during adaptation to fresh water.

The effect of injections of ovine prolactin on kidney structure was examined in the first 10 days following transfer of seawater sticklebacks to fresh water. In hormone injected animals as well as in controls the glomeruli increase slightly in size after transfer. The podocytes intensify the secretion of mucopolysaccharides, which is indicative of increased turnover of the components of the glomerular basal lamina. The nuclei of the podocytes become enlarged, while those of the juxtaglomerular cells decrease in size. These changes are related to the well known rise of the glomerular filtration rate following transfer to fresh water. Structural indications that prolactin is involved in the control of glomerular filtration were not found. The epithelial cells of the three nephronic segments and of the ureter become considerably better developed after transfer to fresh water. Cell height, nuclear and mitochondrial volume, and surface of the membranes of the basal labyrinth increase in all tubular epithelia, although not to the same extent. Increases are moderate in the first proximal segment, but increasingly higher for the second proximal segment, collecting duct and the ureter. Especially the growth of membrane surface of the basal labyrinth, site of ion transport mechanisms, is impressive. In controls, values characteristic for freshwater fishes are reached in 6 to 9 days for all parameters for cellular development. Prolactin injections greatly stimulate growth rates in all tubular epithelia: freshwater values are reached within 3 days. No further increase was found, however.