Estrogen positive feedback

Unsworth WP, Taylor J A, Robinson JE. Prenatal programming of reproductive neuroendocrine function the effect of prenatal androgens on the development of estrogen positive feedback and ovarian cycles in the ewe. BiolReprod. 2005 72 619-627. 

There are also a few examples of positive feedback mechanisms in the endocrine system.25 43 In a positive feedback loop, rising concentrations of one hormone cause an increase in other hormones, which, in turn, facilitates increased production of the first hormone. The primary example of this type of feedback occurs in the female reproductive system, where low levels of estrogen production increase the release of pituitary hormones (LH, FSH).10 43 Increased LH and FSH then facilitate further estrogen production, which further increases pituitary hormone secretion, and so on (see Chapter 30). Positive feedback mechanisms are relatively rare, however, compared with negative feedback controls in the endocrine system. 

Tanaka, Y. and K. Katayama (1982). Failure of positive feedback on the hypothalamus-pituitary-system in aged-women and its recovery in estrogen treatment. Acta Obstet. Gynecol. Jpn., 34 1907-1915. 

Fluctuation in the plasma levels of LSH have been detected during the cycle in rats just before ovulation. Plasma LSH levels in the rats increase to values almost as high as those found in ovariectomized women. At the same time, the hypophyseal LSH drops and the maturing follicle secretes estrogens and progesterone. In this situation the ovarian hormones exert a positive feedback effect on the hypophysis by stimulating LSH secretion. 

In summary, the menstrual cycle is primarily regulated by the interaction between pituitary and ovarian hormones. Also, releasing hormones from the hypothalamus plays a role in controlling female reproduction through their effects on LH and FSH release from the anterior pituitary.7 A complex series of positive and negative feedback mechanisms control the cyclic release of various female hormones.22,81,97 For instance, increased estrogen secretion in the follicular... 

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