IMPROVEMENT OF ERECTILE FUNCTION IN DIABETIC RATS BY INSULIN - POSSIBLE ROLE OF THE INSULIN-LIKE-GROWTH-FACTOR SYSTEM

Erectile dysfunction is commonly experienced in men with diabetes mell itus. We report that the intracavernous pressure (ICP) rise in diabeti c rats was 55% of the control and returned to normal following insulin (I) or insulin plus free oxygen scavenger (I + S) treatment. Insulin- like growth factor (IGF) binding protein (IGFBP) -3, -4, and -5 messen ger RNA (mRNA) levels in the major pelvic ganglia (MPG) of diabetic ra ts were elevated by 2-fold, 2.6-fold, and 2.5-fold, respectively. Both I and I + S returned IGFBP-4 and 5 mRNA levels to normal, whereas IGF BP-3 gene expression was severely inhibited. IGFBP-2 gene expression w as greatly inhibited by diabetes and was unresponsive to treatment. In the penis of diabetic rats, IGFBP-2 and -4 mRNA levels were low, wher eas IGFBP-3 mRNA levels were elevated 10-fold. These effects were reve rsed by I and I + S. I and I + S also corrected the IGFBP-3 expression pattern. IGF-I gene expression in the penis and MPG was not significa ntly increased (P < 0.05) by diabetes and returned to normal levels fo llowing I or I + S treatment. Because IGFs are potent regulatory facto rs in vascular tone, this newly described activity of insulin may play an important role in the improvement of erectile function seen clinic ally and in animal models.