ROLE OF THE KIDNEY IN THE METABOLISM OF LUTEINIZING HORMONE

Abstract

SUMMARY Autoradiographic localization of 125I-labelled luteinizing hormone (LH) in the renal proximal convoluted tubule of rats initiated a study of the role of the kidney in the metabolism of LH. Incubation of 131I-labelled LH with rat renal homogenates for 90 min failed to destroy its immunological reactivity. The plasma half-life of 131I-labelled LH injected i.v. was investigated in normal ewes and rams. Preliminary studies indicated that the use of a preparation containing a high proportion of 'damaged' iodinated hormone could erroneously prolong the plasma half-life. Before use, 131I-labelled LH was purified by gel filtration and column chromatography using DEAE-cellulose. The mean plasma half-life of 131I-labelled LH in normal ewes was 26·7 min and was not significantly altered after oophorectomy (31·1 min). After bilateral oophorectomy and nephrectomy, marked prolongation of the plasma half-life was observed (mean 70·7 min). In normal rams, mean plasma half-life of 131I-labelled LH was 32·0 min, after orchidectomy 44·0 min and after orchidectomy and nephrectomy 82·0 min. The plasma half-life of 131I-labelled LH in a nephrectomized ewe maintained on haemodialysis was also prolonged (67·5 min), the determination being performed 24 h after the last haemodialysis. Although the kidney does not degrade LH, the plasma half-life was significantly increased after nephrectomy. This suggests that the localization of 125I-labelled LH in the proximal convoluted tubule may represent a secretory mechanism allowing renal excretion of LH.