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Testicular function in strains of mice selected for differences in gonadotrophin-induced ovulation
Abstract:
Mice were selected on the basis of ovulatory responses to injections of pregnant mare serum gonadotrophin (PMSG) and human chorionic gonadotrophin (hCG). Various parameters of pituitary and gonadal function as well as responsiveness to exogenous gonadotrophins were examined in males from high induced-ovulation rate (HIOV) and low induced-ovulation rate (LIOV) lines. Testicular weight, seminal vesicle weight and plasma LH levels were lower in HIOV than in LIOV males, while plasma concentrations of FSH and testosterone did not differ. Binding of FSH, but not of LH, in the testes was significantly higher in HIOV mice. Twenty-four hours after administration of hCG, plasma testosterone levels were higher and testicular LH binding sites appeared more depleted in HIOV than in LIOV males. Production of testosterone by decapsulated testes in vitro was significantly higher in HIOV than in LIOV mice under basal conditions, as well as in the presence of LH, FSH, hCG or PMSG. It was concluded that selection for differences in gonadotrophin-induced ovulation rate produced correlated differences in the steroidogenic response of the testes to gonadotrophins and that these differences may be due to divergence in the number of gonadal FSH binding sites.
Insights
Selection for high ovulation rates in mice correlated with altered testicular function. These mice showed increased testosterone production and higher follicle-stimulating hormone (FSH) binding in testes, suggesting FSH receptor differences influence reproductive traits.
Area of Science:
- Reproductive biology
- Endocrinology
- Animal genetics
Background:
- Selection experiments are crucial for understanding genetic control of complex reproductive traits.
- Gonadotropins, such as pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG), play vital roles in regulating reproductive functions.
- Investigating differences in pituitary and gonadal function can elucidate mechanisms underlying reproductive variability.
Purpose of the Study:
- To examine pituitary and gonadal function in male mice from high (HIOV) and low (LIOV) induced-ovulation rate lines.
- To assess the responsiveness of these lines to exogenous gonadotropins.
- To identify potential differences in hormone levels, receptor binding, and steroidogenic capacity.
Main Methods:
- Mice were selected based on ovulatory responses to PMSG and hCG.
- Parameters measured included testicular and seminal vesicle weights, plasma hormone levels (LH, FSH, testosterone), and testicular gonadotropin binding.
- In vitro testosterone production by decapsulated testes was assessed under basal and stimulated conditions.
Main Results:
- HIOV males exhibited lower testicular weight, seminal vesicle weight, and plasma LH levels compared to LIOV males.
- FSH binding in testes was significantly higher in HIOV mice, while LH binding did not differ.
- HIOV males showed enhanced testosterone production in vitro and higher plasma testosterone levels post-hCG administration.
Conclusions:
- Selection for gonadotropin-induced ovulation rate leads to correlated differences in testicular steroidogenic response.
- Elevated gonadal FSH binding sites may be a key factor contributing to the observed differences in reproductive traits.
- These findings highlight the complex interplay between genetic selection, gonadotropin action, and testicular function.