A cross-sectional study on 220 men, aged 41-93 yr, was conducted to determine whether age-related changes in circulating pituitary and gonadal hormone levels are related to quantitatively assessed changes in sexuality over this age span. The conclusion of most previous studies, that total and free plasma testosterone (T) levels decline with advancing age as gonadotropins increase, was corroborated. These changes were found to roughly parallel a decline in sexual function affecting the level of sexual activity, libido, and potency measures. PRL and estradiol did not change with age, and the age-related decline in free T was greater than that in total T. Decreases in free T and increases in LH manifested significant, but small, correlations with sexual hypofunction. Behavioral variables were also clearly related to LH and to the ratio of free T to LH and estradiol. The data also suggested that aging and hormonal changes were more strongly related to sexual activity and nocturnal erections that to libido (enjoyment, drive, and thoughts). Partial correlation procedures demonstrated that diseases and drugs were not responsible for the hormone-behavior relationships. Declining androgen levels, reduced sexual activity, and decreased sexual interest thus appear to be related sequelae of the aging process in men. Hormonal factors do not completely account for age-related changes in sexuality, although the full explanation of these changes must include a consideration of hormonal factors.

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ABSTRACT. Seasonal changes in body weight, plasma testosterone and ejaculatory capacity were observed in five intact and two testosterone-implanted castrated squirrel monkeys for a total of 13 months. Electroejaculation was employed for obtaining data concerning ejaculation. In the intact animals, there were significant increases in body weight, ejaculate volume and plasma testosterone during the breeding season. With the exception of one animal, there was also a decrease in ejaculation latency during the season. Seasonal differences in the sperm count and sperm motility were not observed. Testosterone-implanted castrates showed changes in both ejaculate volume and ejaculation latency similar to those seen in intact monkeys during the breeding season. The body weight and plasma testosterone of the castrates remained quite constant throughout the year.