Demonstration of action of muzolimine on the serosal side of Henle's loop cells.

Muzolimine, a new diuretic, is known to act by inhibiting Na transport along the ascending limb of Henle's loop. Because of its ineffectiveness when perfused into the lumen, and as a result of experiments on frog skin, it is believed that muzolimine acts from the serosal cell side, unlike all other diuretics. We decided to assess the site of action of muzolimine (mucosa versus serosa) by experiments on rats. The animals were anesthetized, both ureters cannulated, and a hydronephrosis established in the left kidney by applying a counterpressure to the ureter, slowly and progressively increased up to 60 cm H2O in 3 minutes and kept stable for 20 minutes. Then either muzolimine 1.2 mg, or furosemide 4 mg, was injected i.v. together with 131I-Hypaque as a glomerular marker. Three minutes later the hydronephrosis was released in the left kidney by cutting the catheter, and urine collections were started simultaneously in both kidneys into 25 microliter glass capillaries, that were filled in continuous sequence and numbered progressively. In each urine sample from each glass capillary Na and 131I-Hypaque were measured. In 5 animals receiving furosemide, UNa rose in the left post-obstructed kidney and reached a plateau level by the 3rd to 5th sample. The rise in Na concentration, indicating delivery of urine whose Na reabsorption had been inhibited along the loop of Henle paralleled that in 131I-Hypaque, indicating that the diuretic and the glomerular marker had reached Henle's loop simultaneously, following filtration after the hydronephrosis had been discontinued.(ABSTRACT TRUNCATED AT 250 WORDS)