Recent findings that LH stimulates renal growth have prompted us to examine whether LH exercises renotropic effects on the growing kidney following uninephrectomy. Intact (not castrated) male rats were used for sham uninephrectomy to induce surgical stress suppressing plasma LH and testosterone levels. Compared to sham surgery, uninephrectomy caused a transient 240% increase in plasma LH with a transient increase in plasma testosterone (80%) and in prostate weight on day 2. Although pituitary LH content did not change, chromatofocusing of pituitary extract revealed changed distribution patterns among seven LH isoforms, suggesting selective synthesis or secretion of LH isoforms. Castrated rats were then used so that surgical stress did not affect LH. Uninephrectomy caused sustained increases in plasma LH levels (60-110% increase) for up to six days. Three days after uninephrectomy, pituitary LH content increased significantly (30% increase) with a change in chromatofocusing profiles of LH isoforms. Plasma and pituitary FSH levels did not change. In summary, uninephrectomy changed LH isoforms quantitatively and qualitatively. These changes imply a change in gonadotropic and renotropic activities of LH after uninephrectomy.