Role of the kidney in metabolism of gonadotropins in rats.

The role of the kidney in the metabolic disposal of homologous gonadotropins [renal luteinizing hormone (rLH) and renal follicle-stimulating hormone (rFSH)] was studied in rats. In analogy with other protein hormones, renal mechanisms contributed importantly to their metabolic clearance rates (MCR), which were profoundly and comparably decreased following nephrectomy (by 94 and 78% for rLH and rFSH, respectively). Absolute MCR and renal organ clearance rates of gonadotropins were, however, markedly lower and urinary clearance rates proportionally higher than those of nonglycosylated protein hormones reported previously. Nonetheless, handling of both LH and FSH by the kidney probably involves, in addition to their excretion in the urine, also intrarenal degradation because their urinary clearance rates accounted for at most a third of their respective MCR, considerably less than the striking reduction of MCR seen after acute renal ablation. Moreover, losses of LH immunoreactivity across the renal circulation were over and above those accountable for by urinary excretion alone. Thus, handling of gonadotropins by the kidney differs from that of nonglycoprotein hormones both in magnitude and in that it involves, in addition to intrarenal degradation, also substantial urinary excretion, a pattern that appears to be representative of the way the kidney disposes of glycoprotein hormones in general.