Testicular Ca++ ATPase activity in mice: effects of age and gonadotropin administration

These studies describe a high affinity calcium (Ca++)-dependent ATPase in purified testicular plasma membranes, which exhibits increased activity from weaning age to adulthood. Administration of human chorionic gonadotropin (hCG; 5 IU) increased enzyme activity in 21-day old and pubertal (35 to 40-day old), but not in adult mice. In pubertal mice, these increases in testicular Ca++-ATPase activity were dose-related and evident 60 min after hCG administration. A second challenge dose of 5 IU hCG administered either 24, 48 hrs, or 5 days later, had no additional effect on Ca++ ATPase in purified testicular plasma membranes in these pubertal animals. The present findings indicate that testicular plasma membrane Ca++ATPase activity exhibits a developmental pattern concomitant with increased testicular steroidogenic activity during sexual maturation. Furthermore, enzyme activity is increased by gonadotropic stimulation and exhibits a refractoriness similar to that of androgen biosynthesis to repeated hCG stimulation.