Ovarian estrogen

The liver plays an important role in the endocrine system. The concentrations of hormones in plasma, and the activity of the glands which secrete them, are determined by the rate at which they are deactivated by the liver. The liver also has a major function in female reproduction since it is the target tissue of ovarian estrogen, to which it responds by producing the yolk protein vitellogenin. " Xenobiotics that affect either of these functions can therefore be considered to be potential endocrine disrupters. 

In premenopausal women the ovary is the richest source of aromatase and hence estrogen. Aromatase is confined to the granulosa cells and is produced under the influence of gonadotropins (FSH and LH). Despite being a rich source of aromatase, three separate studies have shown that aromatase inhibitors are unable to sufficiently suppress ovarian estrogen production to postmenopausal levels. One explanation for this phenomenon may be a compensatory rise in gonadotrophins which maintains adequate estrogen production, despite the presence of the inhibitor. As such aromatase inhibitors cannot be used in premenopausal breast cancer patients. After menopause, ovarian... 

Detailed studies on atrazine have shown that F-344 rats administered high doses of atrazine do not develop either an increased incidence or an early onset of mammary tumors (Wetzel et al, 1994 Thakur et al, 1998), unlike the findings noted in similarly treated female SD rats (Stevens et al, 1994 Wetzel et al, 1994 Hauswirth and Wetzel, 1998). Furthermore, when ovarian estrogen was eliminated from the female SD rats by surgical removal of the ovaries, no mammary tumors were found (Stevens et al, 1999). Likewise, atrazine is not carcinogenic in mice or male SD rats (Hauswirth and Wetzel, 1998). 

The almost exclusive focus on the role of ovarian estrogens has removed attention from the dramatic 70% fall in circulating DHEA that... 

It is well known that the pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), are indispensable for ovulation. FSH, in particular, is necessary for the stimulation of preovulatory ovarian estrogen production and the initiation of follicle maturation. This chapter will discuss the mechanisms underlying the FSH stimulation of ovarian cell differentiation and maturation. 

Mainly based on rat studies, a two-cell, two-gonadotropin hypothesis for ovarian estrogen biosynthesis has been proposed [63]. According to this model, LH stimulates the biosynthesis of androgens from cholesterol in the theca interna com-... 

Disorders of the ovary such as premature ovarian failure (POP) and loss of ovarian function can cause amenorrhea. POF has been defined as failure of ovarian estrogen production occurring in a hypergonadotropic state at any age between menarche and age If the patient is... 

Should not be used concurrently with tamoxifen not indicated for premenopausal women or women with ER-negative tumors used in postmenopausal women because peripheral conversion of adrenal androgens to estrogens is the primary source of estrogen not used in premenopausal women because it does not interfere with production of ovarian estrogens... 

The promotion of mammary development, lactation, and galactopoiesis requires growth hormone, ovarian estrogen (duct formation), ovarian progesterone (lobule-alveolar development), and adrenal corticoids, as well as prolactin and oxytocin. The secretion of prolactin is modified by snbstances that stimulate or block dopamine-receptor sites. Agents such as neuroleptics (chlorpromazine) may cause lactation in a nonpregnant woman. On the other hand,... 

The ovarian granulosa cell, in response to stimulation by follicle-stimulating hormone (FSH) from the anterior pituitary gland and through the catalytic activity of P450 aromatase, converts testosterone to estradiol, the predominant and most potent of the ovarian estrogens (see Fig. 34.23). Similarly, androstenedione is converted to estrone in the ovary, although the major site of estrone production from androstenedione occurs in extraovarian tissues, principally skeletal muscle and adipose tissue. 

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