DETECTION OF HORMONE-SENSITIVE LIPASE IN VARIOUS TISSUES .2. REGULATION IN THE RAT TESTIS BY HUMAN CHORIONIC-GONADOTROPIN

Hormone-sensitive lipase (HSL) is an intracellular neutral lipase foun d in a variety of tissues, primarily in adipose and steroidogenic tiss ues, that hydrolyzes triglycerides and cholesteryl esters. In the rat testis steady-state levels of HSL mRNA increase dramatically during se xual maturation. In addition, HSL-like immunoreactive proteins of 84, approximately 89, and approximately 102 kD have been observed in sexua lly immature rats with additional approximately 113 and approximately 127 kD immunoreactive proteins expressed in mature animals. In the pre sent studies the ability of human chorionic gonadotropin (hCG) to regu late the expression of HSL and HSL-like immunoreactive proteins in rat testes has been examined. Treatment of sexually immature rats with da ily injections of hCG caused a gradual increase in HSL activity that r eached an 80% rise (P < 0.01) after 5 days. This was paralleled by a 3 -fold increase (P < 0.01) in the 84 kD protein representing the active HSL enzyme. The approximately 89 kD immunoreactive protein was also i ncreased approximately 5-fold (P < 0.01) in parallel to the 84 kD prot ein and HSL activity. The approximately 102 kD immunoreactive protein was increased by hCG treatment (P < 0.01); however, its expression did not follow changes in HSL activity or in the 84 and approximately 89 kD immunoreactive proteins, peaking within 12 h and declining thereaft er. The approximately 113 and approximately 127 kD immunoreactive prot eins did not appear during the 5 days of hCG treatment. Steady-state l evels of HSL mRNA increased 60-100% (P < 0.02) in parallel to the chan ges in HSL activity and in the 84 and approximately 89 kD immunoreacti ve proteins. Thus, hCG increases the activity of HSL in the rat testis by increasing HSL mRNA levels and the amount of HSL protein. Although the approximately 102 kD HSL-like immunoreactive protein is increased by hCG treatment, it appears that it might be a functionally unique b ut immunologically related protein.