MATURATION OF POSITIVE FEEDBACK ACTION OF ESTRADIOL AND ITS INHIBITION BY PROLACTIN IN FEMALE RATS
Reproduction nutrition development (Print)
In recent publications it has been shown that serum estradiol and FSH levels are very high in female rats between day 10 and 20 after birth and that at this time more or less regular « preovulatory type » LH peaks occur. These LH peaks could be prevented completely by administration of estrogen-antiserum (E-AS) suggesting a positive feedback action of estradiol on pituitary LH release. E-AS treatment on the other hand further increased serum FSH levels which indicates that physiologically
... ysiologically active estradiol levels were too low to keep the FSH levels low also, hence a « castration » type effect occurred for the FSH regulatory mechanisms. At the time when estradiol and FSH levels decrease and the LH peaks do not occur anymore serum prolactin and progesterone levels steadily increase until puberty. Evidence is given in the present contribution that hyperprolactinemia induced either by injections of prolaction or by small lesions in the median eminence or by pituitary transplants under the kidney capsule result in precocious puberty. Conversely, adrenalectomy at day 23 which results in low prolactin levels delays puberty and progesterone treatment which reportedly also reduces prolactin levels delays puberty also. Both effects potentiate in adrenalectomized and progesterone treated animals. In view of data in the literature that reduction of serum prolactin levels by the use of 2 -Brergocryptine, a dopamine receptor stimulating drug, does not delay puberty it is suggested that the timing effect of prolactin on the onset of puberty is mediated by the stimulating properties of prolactin on dopamine turnover.