Modulation by neonatal thymectomy of the reproductive axis in male and female rats during development

Effect of thymectomy on the female reproductive cycle in neonatal guinea pigs

OBJECTIVE

The appropriate function of the hypothalamic-pituitary-gonadal axis is essential for maintaining proper reproductive function. In female mammals, the hypothalamic-pituitary-gonadal axis regulates reproductive changes that take place in the estrus cycle and are necessary for successful reproduction. This study was conducted to investigate the effect of thymectomy on the estrus cycle in neonatally thymectomized guinea pigs.

METHODS

In this study, 12 female guinea pigs, six thymectomized and six sham-operated, were studied. The effects of neonatal thymectomy at 5-7 days of age on parameters of the reproductive axis were examined in female guinea pigs. Gonadotropin and 17β-estradiol levels were assessed at regular intervals (days 0, 3, 6, 9, 12, and 15) of the estrus cycle, and the time of vaginal opening in the thymectomized and shamoperated guinea pigs was determined.

RESULTS

Significant reductions in gonadotropins and 17β-estradiol levels during estrus cycle were found in neonatally thymectomized female guinea pigs compared to sham-operated guinea pigs.

CONCLUSION

The results of this study underscore the importance of the thymus in the neonatal period for normal female reproductive function.

Is immunosuppression, induced by neonatal thymectomy, compatible with poor reproductive performance in adult male rats?

With increasing knowledge that the immune system has a major impact on reproductive ‎health, the potential for cells arising in organs such as the thymus to alleviate oxidative stress ‎has been revealed. This study addresses the impact of neonatal thymectomy on male ‎reproductive function in pubertal and adult animals. Neonatal Sprague Dawley rats were allotted to four treatments consisting of fully thymectomized, partially thymectomized, intact, and sham-operated rats. Half of the rats in each treatment were sacrificed at 40 and the other half at 80 days of age. Testicular volume, ventral prostate and spleen weight, several sperm attributes (concentration, motility, livability, membrane integrity, sperm penetration into mucus, total antioxidant capacity, mitochondrial dehydrogenase activity), plasma superoxide dismutase, glutathione, and testosterone level as well as fertility decreased in thymectomized rats. Adrenal gland weight, sperm malondialdehyde level, indices of oxidative stress, sperm abnormality, testicular and sperm lipid peroxidation, protein carbonylation, and sperm reactive oxygen species generation increased in thymectomized rats. In thymectomized rats, the testes contained high levels of malondialdehyde but low levels of glutathione and ferric-reducing antioxidant power. Epididymal sperm reactive oxygen species, blood lipid peroxidation, and oxidative stress indices ‎‎in blood and spermatozoa were highest in fully thymectomized, intermediate ‎in partially thymectomized, and lowest in both pubertal and mature control rats. Blood levels of superoxide dismutase, lipid peroxidation indices, and ‎testosterone, and mitochondrial adenosine triphosphate and ‎dehydrogenase activities in epididymal spermatozoa were lowest in fully thymectomized, ‎intermediate in partially thymectomized, and highest in both pubertal and mature control rats.‎ The data indicated that increased oxidative stress and mitochondrial dysfunction might play a role in the mechanism of immunosuppression-induced testicular and sperm abnormalities.

Effects of thymectomy on reproductive function and behavior

The effects of thymectomy in perinatal Long-Evans rat pups on their reproductive function in early adulthood were examined. Thymectomized females had decreased lordotic responsivity to estrogen, while thymectomized males exhibited differences in mount latency or postejaculatory interval; these results suggest a possible influence of the thymus on the normal development of the neural substrates of sexual behavior. Gonadal histology appeared unperturbed in rats of either sex. No statistical abnormalities in luteinizing hormone or testosterone levels were seen in male animals. Likewise, no disturbances were observed in the ability of females to exhibit normal positive feedback after estrogen and progesterone administration; negative feedback after unilateral ovariectomy (as judged by ovarian compensatory hypertrophy) was also normal. The timing of puberty was not statistically delayed in females, even though slowed growth rates were observed. A heightened surgical stress response, as judged by progesterone levels in experimental females, suggests that perinatal thymectomy may possibly alter the sensitivity of adults to stress.

Effects of neonatal sexual differentiation, growth hormone and testosterone on thymic weights and thymosin-beta 4 in hypophysectomized rats

Experiments were conducted to analyze the effects of growth hormone and testosterone in conjunction with the effects of neonatal sexual differentiation (via castration of males at days 2 or 11 of age and androgenization of females at day 3 of age) on thymic weight and thymosin-beta 4 concentrations in hypophysectomized rats (day 30 of age). Ten days post-hypophysectomy, hormonal treatments were initiated on males, male castrates, females, and androgenized females. Growth hormone (25 micrograms daily), testosterone propionate (100 micrograms/day), and the combination of the two hormonal treatments were administered for seven days, then thymic weights and blood samples were collected. Administration of growth hormone to hypophysectomized rats increased thymosin-beta 4 concentration in a dose-dependent manner, but injection of testosterone had no effect on thymosin-beta 4 concentrations. Testosterone treatment decreased thymic weights whereas growth hormone increased thymic weights. Hypophysectomized males had increased thymosin-beta 4 concentrations compared with female and neonatally-androgenized female rats. However, hypophysectomy eliminated any thymic weight differences between males and females. The data support a possible endocrine role for the thymus gland and thymic peptides in that they are integrated into the control and support of other endocrine systems. Although differences in thymosin-beta 4 concentrations were noted between males and females, sexual differentiation of the immune system was unaltered by neonatal castration of males or testosterone treatment of females and may indicate sexual differences in immune function are established in utero.