Effects of short-term injection of gonadotrophins on ovarian follicle development in hypogonadal (hpg) mice

Abstract

Summary. Twice

Follicle-stimulating hormone increases primordial follicle reserve in mature female hypogonadal mice

“…Alternatively, the rate at which primordial follicles enter the growth phase may be reduced in tg hpg mice by the presence of more secondary/antral follicles (Faddy et al 1987). However, we did not observe decreased numbers of downstream primary follicles in tg hpg ovaries compared with controls, consistent with studies in hpg females treated with exogenous FSH for 4-20 days (Halpin & Charlton 1988, Wang et al 2005. Instead, primary follicle numbers were equivalent to controls, suggesting that reduced primordial recruitment may not explain our results.…”

“…Therefore, increased numbers of primordial follicles in tg-FSH hpg females may also reflect the absence of an opposing LH effect on the resting primordial follicle pool. Despite the lack of LH activity in hpg ovaries, the expression of tg-FSH increased secondary and stimulated antral follicle development, confirming previous in vivo studies demonstrating that antral follicle development is highly regulated by FSH (Halpin & Charlton 1988, Wang & Greenwald 1993, Kumar et al 1997, McGee et al 1997, Dierich et al 1998, Oktay et al 1998, Abel et al 2000.…”

“…In the present study, tg-FSH expression is driven by the rat insulin II gene promoter that confers postnatal expression of heterologous transgenes (Epstein et al 1992, Takamura et al 1998, as confirmed by equivalent serum tg-FSH levels in 10-dayold mice (data not shown). Therefore, the tg-hpg model will provide FSH expression during the important postnatal period of follicular development, unlike previous studies of short-term exogenous FSH actions in hpg females only after complete postnatal gonadotrophin deficiency (Halpin & Charlton 1988, Wang et al 2005.…”

“…While small preantral follicular development may occur independently of FSH, the total number of early growing follicles is increased by FSH action (Halpin & Charlton 1988, McGee et al 1997, Oktay et al 1998. Furthermore, FSH-mediated follicle growth may also indirectly accelerate the age-dependent depletion of the finite primordial pool initially established after birth.…”

Vascular endothelial growth factor receptor 2–mediated angiogenesis is essential for gonadotropin-dependent follicle development

“…Follicle development in such animals arrests at the advanced preantral or early antral stage due to the absence of gonadotropins (9), and mature, preovulatory follicles are generally absent. Advanced preantral follicles are highly responsive to gonadotropins, and the development of mature, antral follicles can be induced by exogenously administered gonadotropins over a 3-to 4-day period (gonadotropindependent growth) (9)(10)(11). Absence of pituitary glands in such a model can be verified indirectly by demonstrating (a) insignificant weight gain (< 1.5 g) over a 1-week period after arrival in the laboratory (12) and (b) vaginal smears typical for a low-estrogenic state.…”