Kidney and bladder calculi in spontaneously hypertensive rats.

Naturally occurring kidney stones are rare in animals. The Japanese strains of spontaneously hypertensive rats (SHR) are normotensive at birth but develop high blood pressure, hyperglycaemia and hyperlipidaemia as they mature. The SHR strain is prone to develop kidney stones. A unique sub-strain of SHR has been developed in which some animals develop hypothalamic obesity concomitantly with their rising blood pressure, i.e. Obese/SHR. The Obese/SHR characteristically develop microscopic kidney stones which become detached at an early stage of formation, migrate to the bladder, and grow by concretion into huge, rounded calculi. The stone nidus starts as a subepithelial cyst-like focus containing oedema, colloidal acidic mucoprotein, and red and white blood cells suspended on a delicate network of fibrils. THe nidi grow by concretion of an admixture of calcium and acidic protein in a lamellar arrangement. The disparate morphogenesis and anatomic location of kidney stones in Obese is opposed to non-obese/SHR suggest that calculus formation may be governed by specific differences in genetic programming. The incidence of kidney stones parallels the severity and chronicity of the hypertension in SHR, non-obese and Obese/SHR, and the Cushingoid habitus in the Obese/SHR.