Effects of thymulin on spontaneous puberty and gonadotrophin-induced ovulation in prepubertal normal and hypothymic mice

Abstract

The effects of thymulin administration beginning on days 19 or 24 of age on spontaneous puberty and gonadotrophin-induced ovulation were analysed in female normal and hypothymic mice. In normal and hypothymic mice, the daily administration of thymulin at 24 days of age resulted in a delay in the age of vaginal opening, with an increase in serum progesterone levels. Normal mice treated with 200 ng thymulin beginning on day 19 of age and injected with pregnant mare serum gonadotrophin (PMSG) 24 h later had an increase in ovulation rate, number of ova shed and weight of the ovaries. None of the hypothymic mice treated with thymulin on day 19 and PMSG on day 20 ovulated. PMSG treatment on day 25 induced ovulation in hypothymic mice. When these animals were injected previously with 200 ng thymulin, the number of ova shed by ovulating animals was lower than in PMSG-treated animals. Administration of thymulin and sequential injection of PMSG and human chorionic gonadotrophin 54 h later resulted in an increase in ovulatory response in comparison with those receiving only PMSG. The results suggest that thymulin plays a role in the regulation of spontaneous puberty through its effects on adrenal and ovarian endocrine functions. The increase in the ovarian PMSG response-treated animals, previously given thymulin, showed that this thymic hormone participates in the regulation of gonadotrophin secretion mechanisms and seems to be dose- and age-dependent. In hypothymic mice, neuroendocrine mechanisms regulating puberty are different from those of normal mice.

Effects of Injecting Thymulin into the Anterior or Medial Hypothalamus or the Pituitary on Induced Ovulation in Prepubertal Mice

“…According to Brown et al [27] , thymulin stimulates the release of follicle-stimulating hormone (FSH) and LH on pituitary cell cultures maintained in dynamic or stationary systems, while Hinojosa et al [4] showed that injecting thymulin subcutaneously into prepubertal mice stimulates the ovulation response induced by equine chorionic gonadotrophin (eCG) treatment.…”

Effects of thymulin and GnRH on the release of gonadotropins by in vitro pituitary cells obtained from rats in each day of estrous cycle

“…Based on published results on the effects of neonatal or infantile thymectomy (Besedovsky and Sorkin, 1974;Michael et al, 1980;Kosiewicz and Michael, 1990;García et al, 2000), the congenital absence of the thymus (Rebar et al, 1981b), and the effects of thymic peptides on in vivo and in vitro models (Rebar et al, 1981a;Michael, 1983;Mendoza and Romano, 1989;Mendoza et al, 1995;Hinojosa et al, 1999), the participation of the thymus in regulating the hypothalamic-pituitary-ovary axis is widely accepted.…”

“…In both models, grafting the thymus or epithelial thymic cells results in the detection of thymulin in serum (Bach et al, 1977;Dardenne et al, 1984;Safieh et al, 1990). Injecting equine chorionic gonadotropin (eCG) to 20-day old mice does not induce ovulation; however, thymulin treatment before eCG injection results in an increase of both, ovulation rate and ovarian weight (Hinojosa et al, 1999). Infantile thymectomy in mice results in lower serum level of estrogen during the pre-pubertal phase and in a lower ovulatory response to gonadotropin stimulus; in turn, injecting thymulin immediately after surgery resulted in normal estrogen level and normal ovulation rates (García et al, 2000).…”

Effects of infantile thymectomy on ovarian functions and gonadotrophin-induced ovulation in prepubertal mice: role of thymulin

“…Thymulin is a nonapeptide that is produced exclusively by thymic epithelial cells (Dardenne et al 1974, Savino et al 1982, Safieh et al 1990, promotes activation and differentiation of T-cells (Dardenne et al 1974), and stimulates gonadotrophin-induced ovulation in prepubertal mice (Hinojosa et al 1999).…”