Evidence of Excretion of Iron Salts by Proximal Convolution of the Nephron of the Frog's Kidney

Abstract

It is becoming increasingly evident that the glomerulus and tubule constitute functionally different sites for the elimination of the various urinary constituents. Several investigators have demonstrated that the proximal convolution of the vertebrate kidney is secretory in function. The studies of Holton and Bensley 1 on the mammalian kidney when it is excreting dyes and iron salts under conditions of very low blood pressure indicate a secretory process in the elimination of these substances. Verne, 2 however, studying the aglomerular fish kidney, shows that this type of kidney does not excrete iron salts in appreciable amounts. These studies suggested that the Nussbaum experiment, with modifications, might prove valuable in determining the possible function of the proximal convolution in the excretion of iron salts.

Male frogs (Rana pipiens) were used in the experiments, the account of which follows. The animals were anesthetized by injecting from 1.0 to 1.4 cc. of a 10% solution of urethane into the submaxillary lymph sac. Operation to expose the kidney was made by using a thermocautery. Pelvic lymph hearts were removed in order to eliminate possible lymphatic circulation, the coeliacomesenteric artery ligated, and the intestine removed. The peritoneum extending from the right kidney to the right body wall was cut through and the lateral branches of the renal portal were cauterized, permitting deflection of the kidney and exposure of the dorsal aorta and the urogenital arteries. The latter were pulled out to the right with a small hook, doubly ligated, and severed, care being taken to treat in like manner all branches of the aorta between the juncture of the coeliaco-mesenteric artery and the bifurcation of the aorta to form the iliac arteries.