Positive Feed-Back Effect of Progesterone on the Release of FSH and the Influence of Sex in Rats

Abstract

Plasma fsh activity (as measured by the ovarian augmentation test in mice) was increased in gonadectomized male and female rats. A single injection of 20 \g=m\g oestradiol benzoate (OB) or one or two doses of 2\m=.\5 mg testosterone propionate (TP) 3 days later reduced the raised values significantly. Progesterone injected into spayed rats, primed 3 days before with OB or TP, induced, a few hours later, a significant increase in plasma fsh. By contrast, in male rats progesterone failed to exert a positive feed-back effect on the release of fsh. This sex difference was suppressed by the injection of testosterone into female rats on the 4th day of life. In male rats castrated soon after birth, progesterone showed a tendency to increase the activity of fsh in plasma in animals primed either with OB or TP, but the difference of the values as compared to the controls did not reach the level of significance. It is concluded that the sex difference of the positive feed-back effect of progesterone on the release of fsh could be due to a post-natal differentiation of a neural mechanism.

Adrenal Involvement in Determining the Time of Onset of Puberty in the Rat1

“…Following estrogen treatment if a second steroid is given GTH levels are raised. Progesterone is capable of raising FSH or LH, and estrogen of raising LH (29,199). This substantiated the theory that estrogen, in conjunction with some signal as to the time of day, stimulates the precisely timed (2-4pm) LH release (59) for ovulation in tbe rat (177).…”

Differentiation of Steroid Metabolism in the Rat and Mechanisms of Neonatal Androgen Action

“…All these hormones also have sex-specific effects on LH, FSH, and prolactin secretion (13,26,54,(79)(80)(81). Their regulatory role is reversible since sexual behavior diminishes and pituitary activity changes after gonadectomy (13,26).…”

“…The sex differences, however, do not always disappear completely after gonadectomy and, when testosterone is given to the female and estradiol to the male, behavioral and neuroendocrine functions typical of the opposite sex can not be fully induced (54,(79)(80)(81). Apparently the brain responds in a highly sex-specific way to sex hormones, and differences between males and females can persist even in the absence of sex hormones.…”