Temporal aspects of oestrogen stimulated increases in plasma and pituitary follicle stimulating hormone.

Abstract

Plasma and pituitary follicle stimulating hormone (FSH) were studied in immature female rats treated with oestradiol benzoate (OB), testosterone propionate (TP) or a combination. Plasma FSH changes were evaluated by use of an endogenous augmented ovarian weight assay. A single dose of 1 μg OB caused an increase in plasma and pituitary FSH within 24 h. Glandular level then fell, as plasma level rose to a peak at 60 h. After 60 h the amount in plasma decreased to a low point at 84 hours and remained unchanged until 156 h. A second dose of OB at 60 h produced an increase in pituitary content, without lowering the plasma level, within 12 h. After this rise, pituitary content decreased rapidly to a low level, but plasma FSH continued to rise to another peak within 48 h. After this peak, plasma content fell to that of controls while pituitary content remained very low. TP (100 μg) in a single dose did not cause any profound changes in pituitary content. When given with 1 μg OB the glandular content remained at control level for 96 h, while plasma content rose a moderate amount. The amount stored decreased at 120 h in animals receiving the double treatment. TP stimulated FSH synthesis in OB treated animals even when given 60 h later, but it had no effect upon plasma FSH in these animals. The results demonstrate that oestrogen has a distinct positive feedback effect upon pituitary FSH and stimulates both synthesis and release of this hormone.