Androgenic Activity in 15-Day-Old Male Rats: Role of the Maternal Pineal Gland

Female Sprague-Dawley rats, exposed to a long (18L:6D) or a short (6L: 18D) photoperiod from 21 days of age, were mated when they reached 55 days of age. On Day 2 of gestation, dams were pinealectomized or sham-operated. Pre- and postnatal photoperiods were identical, and oftpring were killed at 15 days of age. Maternal pinealectomy had no effect when rats were kept on 1 8L: 6D. Rats born to sham-operated mothers and kept on 6L: 1 8D had higher testicular testosterone and androstenedione content than offspring raised on the long photoperiod. This stimulatory effect of the short photoperiod was blocked by maternal pinealectomy and was not dependent on the offpring’s own pineal since it was observed in both sham-operated and neonatally (on Day 5 after birth) pinealectomized rats. When sham-operated mothers housed on 18L: 6D were treated daily during pregnancy and lactation by s.c. melatonin injection, there was an increase in the testicular testosterone content of offspring. It was concluded that when rats are maintained on a 6L: 18D cycle the maternal pineal gland enhances the testicular testosterone and androstene-dione content in 15-day-old offspring. This effect is probably mediated by maternally derived melatonin, At 15 days of age, the pineal of the offspring had no influence on testicular function