Abstract
Effects of daily injections of melatonin on male rat reproductive and accessory reproductive organs were studied. The weight of the prostate was decreased by treatment with a high dose of melatonin (8.0 mg/kg, s.c., injection time; 17 : 00) once daily for 30 d. The weights of the other accessory reproductive organs and testes were not influenced by melatonin. Lower doses (0.8, 2.4, 4.8 mg/kg), had no effect. After the successive treatment with melatonin (8.0 mg/kg), the testosterone levels in testes and in serum and the conversion rate of [3H]testosterone to [3H]dihydrotestosterone in the prostate were not influenced. They activity of acid phosphatase and the uptake of [3H]testosterone by the prostate, in contrast, were significantly decreased after the succesive treatment with melatonin. These data suggest that melatonin may have a direct inhibitory action on male rat prostate, though only at a high dose.
