EFFECTS OF A LONG-ACTING SOMATOSTATIN ANALOG ON PITUITARY, ADRENAL, AND TESTICULAR FUNCTION DURING REST AND ACUTE EXERCISE - UNEXPECTED STIMULATION OF TESTOSTERONE SECRETION

The purpose of this study was to delineate the possible endocrine effe cts of exercise-induced GH secretion. Twelve healthy adult males were studied during short (20 min) and subsequent-prolonged (2 h) physical exercise and recovery period (2 h), both after injection of a long act ing somatostatin analog [Sandostatin (ST); 0.1 or 0.05 mg, sc] and aft er a control saline injection. Additional subjects were studied during rest with similar injections of ST (0.1 mg) and saline (n = 7) or usi ng a lower ST dose (0.01 mg; n = 6). Several venous blood samples were taken during the trials and analyzed for selected hormones, monitorin g pituitary, testicular, and adrenal functions. ST injection blocked t he serum GH response to short term maximal bicycle ergometer exercise, but not to the following prolonged bicycle exercise. No relationship of the exercise-associated GH increase to the concomitant endocrine re sponses of the adrenals and testes was observed. Unexpectedly, the hig her ST doses (0.1 and 0.05 mg) increased the mean levels of serum test osterone by 18-25% in both exercise (P = 0.0017) and rest trials (P < 0.0001), respectively. ST did not affect the levels of LH, FSH, or cor tisol. ST slightly increased serum sex hormone-binding globulin (3%; P = 0.021) and albumin (4%; P = 0.017) concentrations, but not that of free testosterone. Because the testosterone response to somatostatin w as fast and without a simultaneous increase in LH, it was consistent w ith a direct testicular response. The explanation for this novel ST ef fect remains obscure, but it may be due to modulation of some paracrin e mechanisms inhibiting testicular steroidogenesis.