Sexual development of female and male rat offspring of control, pinealectomized (PIN-X) or melatonin (MEL 250 micrograms/100 g body wt)-treated mother rats during pregnancy was studied. Newborns were studied at the following phases of sexual development: neonate (5 days old), infantile (15 days old), juvenile (25 and 30 days old) and pubertal phase (55 days). In female offspring, MEL treatment during pregnancy significantly increased plasma luteinizing hormone (LH) in 15- and 25-day-old rats; however, at the end of the prepubertal period (30 days) the concentration of plasma LH decreased significantly as compared to control rats. This hormonal pattern was different from that observed in offspring of control and PIN-X rats, which had low LH levels at 25 days of age and higher LH levels at 30 days of age. Follicle-stimulating hormone (FSH) did not vary significantly among the three groups. Plasma prolactin levels were affected by PIN-X of the mother, showing significantly higher levels in the 5-day-old offspring than in the controls; plasma prolactin levels were also affected by MEL treatment of the mother, producing hyperprolactinemia in the 30-day-old female offspring. In male offspring, sexual development in control male rats progressed rapidly with significantly increased LH and FSH levels at 25 and 30 days compared to those measured during the neonatal and infantile periods.(ABSTRACT TRUNCATED AT 250 WORDS)

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The role of pinealectomy and continuous light in the regulation of sexual activity was studied in the male rat. The parameters studied in order to evaluate the sexual behavior were initial latency, ejaculatory latency, refractory period, neuromotor activity, number of ejaculations, intromissions (false, real, and total) and percentage of ejaculating male rats. Pinealectomy as well as continuous light induced a marked facilitation of the animal's sexual behavior as shown by the shorter initial latency and refractory period, as well as by the increase in the number of intromissions (real and total) showed in the tests. However, the ejaculatory latencies did not change. There was also an enhanced neuromotor activity. An increase in the number of ejaculations as well as in the percentage of ejaculating male rats was produced by continuous light. From the results it is concluded that pineal hormones play an important role in male rat sexual behavior.