Post-Hypophysectomy Ovarian Senescence and Its Relation to the Spontaneous Structural Changes in the Ovary of Intact Aged Rats

Abstract

Hypophysectomy performed in 25- to 26-day-old Wistar rats leads within 1 year to the formation of ovarian testis-like tubes and epithelial cellular cords which are typical structures in the senile ovaries of normal 24-month-old rats. Testis-like tubes represent an unusual late stage of follicular degeneration; the origin of the cords is more complex; the revival of cell differentiation from stroma and/or rete ovarii in the absence of the pituitary is hypothesized. At 16 months of age, cords proliferate and are responsible for ovarian weight increase to almost twice the minimal weight seen 4 months after the operation. Variability in cord proliferation is considerable from one rat to another, but also between the two ovaries of the same animal. Thus, an intrinsic age-related ovarian factor is implicated in cord proliferation. From this study, it is inferred that during intact rat senescence, intrinsic ovarian aging is responsible for the proliferation of cords, whereas their induction depends on a hypothalamic-hypophyseal imbalance occurring at about 1 year of age.

The ovary retains male potential after the thermosensitive period for sex determination in the turtle Emys orbicularis

“…The testis-like tubes represent an unusual late stage of follicular degeneration, but the origin of the cords, stroma and/or rete ovarii, is not well established. Such epithelial structures develop also in younger hypophysectomized animals [4]. In both aged and hypophysectomized animals, the development of these structures could be due to the decrease in oestrogen levels in ovaries.…”

“…4 (series III).At stage 22 + , the beginning of treatment, the gonads of E. orbicularis embryos incubated at 30°C presented 195 Gonadal aromatase activity in turtle (Emys orbicularis) embryos and hatchlings incubated at 30°C, a temperature giving 100% females: l, controls; s, treated with Letrozole (L). The individuals were from five clutches(1)(2)(3)(4)(5). Series 0 corresponds to control individuals at the beginning of treatment.…”

Determination and Stability of Gonadal Sex

“…In fact, from a series of results that initially seemed surprising, the loss of any of a plethora of early‐ or late‐acting female genes, such as Foxl2 or the estrogen receptors, induces ovary‐to‐testis sex reversal in one or multiple somatic cell lineages at various time points after birth (eg, Crumeyrolle‐Arias and Aschheim, 1981; Taketo‐Hosotani et al, 1985; Couse et al, 1999; Guigon et al, 2005). In addition to representing a case of cell fate choice with alternative commitments, sex determination seems to assign opposed degrees of commitment to homologous cell lineages.…”