The metabolism of luteinizing hormone. Plasma clearance, urinary excretion, and tissue uptake

The kinetics of plasma clearance, tissue uptake, and urinary excretion of tritiated ovine pituitary luteinizing hormone in adult male rats are reported. Most of the intravenously injected tritiated gonadotropin is cleared from circulation with a half-life of five minutes, and this is independent of the injected amount of hormone over a wide dose range. It was found that the hormone is rapidly removed from circulation by the kidneys, probably by glomerular filtration, and excreted in the urine. The radioactivity present in the urine is associated with material of the same molecular size as the native hormone and, moreover, the urinary hormone retains a significant amount of biological activity. A small amount of the hormone is catabolized by the kidney and liver, and our data suggest that this occurs in the cortex and hepatocytes, respectively.