Introduction

The ovary secretes numerous substances including steroid hormones, prostaglandins, inhibin and activin, growth factors, proteoglycans and proteolytic enzymes. Steroid hormones appear to be among the most important and include androgens, estrogens, and progestins.

 

Androgens

Androgens are synthesised in the theca cells of the ovarian follicle and in interstitial cells surrounding the follicle. The adrenal glands are the principal source of circulating androgens in women although the ovaries and adrenals produce similar quantities of androstenedione, testosterone, most of the ovarian androgens are converted to estrogens. Plasma levels of androstenedione reflect the adrenal production of the steroid.

Nonetheless, ovarian androgens must be important since Turner's syndrome patients who do not have functional ovaries, have scant development of sexual hair. The ovaries produce slightly more testosterone than do the adrenals during both the pre-menopausal and post-menopausal periods. Most of the testosterone in the plasma of the adult female is formed by peripheral conversion of androstenedione by peripheral 17 beta hydroxy steroid dehydrogenase.

Androgens, principally androstenedione and testosterone, serve as substrates for estrogen biosynthesis within the ovary and peripheral tissues but also have their own distinct actions. Androgens are important for maturation of the hypothalamic-pituitary adrenal axis at adrenarche, the increase in adrenal androgen synthesis at puberty. They stimulate general protein anabolism throughout the body.

They stimulate the growth of pubic and axillary hair. They increase libido. At high levels, androgens suppress progesterone synthesis in granulosa cells.

 

Estrogens

Estradiol is one of the most important products of the granulosa cells of the developing follicle. Estrone has a biological potency of approximately 1/10th that of estradiol. Estradiol concentrations in plasma peak during the late follicular phase, decline after ovulation and then rise again during the luteal phase. Estrogens have numerous effects on reproductive and non-reproductive tissues in reproductive-age females.

Estradiol increases general protein anabolism though to a lesser degree than androgens. It stimulates the liver to synthesize plasma proteins including sex hormone binding globulin. Estradiol moderately increases retention of sodium chloride and water in the kidney and it maintains bone by decreasing osteoclastic activity. Estradiol has positive and negative effects on hypothalamic-pituitary function.

In the hypothalamus estradiol decreases GnRH pulse amplitude. In the pituitary, estradiol increases GnRH receptors and gonadotropes and increases the content of prolactin, FSH and LH.

Progestins

Progesterone is one of the most important products of the lutenized cells of the corpus luteum. Progesterone concentrations in plasma peak during the mid luteal phase and then decline in the latter half of the luteal phase. Progesterone has numerous effects on reproductive and non-reproductive tissues in reproductive age females. Progesterone has multiple effects on female reproductive tissues.

In the uterus, it increases secretion of a glycogen rich mucus by endometrial glands and it increases the membrane potential of myometrial smooth muscle cells to hyperpolarize them and decrease uterine contractions. In the cervix, progesterone increases the thickness of the cervical mucus. It decreases GnRH pulse frequency in the hypothalamus leading to negative modulation of gonadotropin secretion.

Progesterone also is important in terminal breast development because it increases the development of lobules and alveoli of the mammary glands.

Growth Factors

The ovary secretes numerous growth factors, insulin-like growth factor or IGF 1, which is synthesizing granulosa cells is an important intra ovarian hormone that potentiates the effect of FSH on granulosa cell function. The ovary also secrete several IGF binding proteins which combined insulin-like growth factor 1 and negatively modulator IGF 1.