The two important regions of the brain that release these hormones are the hypothalamus and the pituitary. The hypothalamic hormones usually stimulate the release of the pituitary hormones.
Gonadotropin releasing hormone (GnRH):
- Often called the “conductor” of the reproductive hormones, GnRH is released in very precise fashion by the hypothalamus and sent to the pituitary, where it stimulates the release of the gonadotropins, FSH and LH. GnRH is rarely used to bring about ovulation (it must be administered over many days by an indwelling IV pump). Imprecise release of GnRH can bring the entire reproductive hormone system to a halt, a process that is the basis of GnRH agonists such as Lupron.
- Follicle stimulating hormone (FSH)
- GnRH tells the pituitary to release the gonadotropins LH and FSH. FSH stimulates the ovaries to release hormones (principally estrogen) and to mature eggs in preparation for ovulation. Natural cycles usually result in the release of a single egg. Over-riding the body’s normal levels of FSH stimulation results in the release of extra eggs and higher hormone levels, a process that is the basis for the HMG medications Pergonal, Metrodin, Fertinex and Humagon. A rise in FSH levels early in the menstrual cycle can indicate a problem with egg quality, making FSH testing an important diagnostic procedure.
- Luteinizing hormone (LH):
- LH is the other gonadotropin released by the pituitary after stimulation by GnRH. While FSH stimulates the eggs and the production of estrogen, LH stimulates the release of androgens (hormones like testosterone). Ovulation is usually preceded by a sudden rush of LH (the “LH surge”) and detection of this surge is the basis for home ovulation kits. High LH levels are also common in polycystic ovary syndrome.
- Prolactin (PRL):
- Prolactin is also released by the pituitary and is included here because high prolactin levels seem to interfere with ovulation, either preventing it completely or interfering with the efficiency by which the eggs are matured. High prolactin levels are easy to detect by blood tests and respond rapidly to treatment with a medication called bromocriptine. A prolactin level is a common early test in an infertility workup.
- Thyroid Stimulating Hormone (TSH):
- The thyroid is a very important hormone releasing organ that is located on the front of the neck. Under- or over-release of thyroid hormone (also called thyroxine) can interfere with the menstrual cycle and contribute to infertility. The most accurate measurement of thyroid activity is checking TSH, a hormone from the pituitary that controls the activity of the thyroid.
- Ovarian hormones:
The ovaries produce many hormones, most of which affect reproduction in one way or the other. The hormones listed below are those most commonly tested and referred to during fertility treatment.
- The most important estrogen in reproductive-aged women, estradiol is released by the ovary in increasing amounts as the egg or eggs are matured. The higher estradiol levels thicken the uterine lining, make the cervical mucous clear and penetrable by sperm, and tell the brain to modify the release of GnRH,LH and FSH. Monitoring of estradiol levels is an important aspect of cycle monitoring when using certain fertility drugs (paticularly the injectable gonadotropins). Failure of estradiol levles to rise appropriately in response to stimulation is another sign of possible egg problems.
- Progesterone (P4):
- After ovulation, the cells that surrounded the just-released egg switch much of their hormone production from estradiol to progesterone. Progesterone levels rise markedly in the second half of the cycle and probably contribute greatly to nurturing the very early pregnancy. Continued release of preogesterone requires the presence of pregnancy hormone (HCG). In the absence of HCG, progesterone levels fall and the period comes. With HCG present, further release of progesterone by the ovaries continues to support the lining. Progesterone supplementation is a common and logical treatment, although its benefits are uncertain, both in the treatment of causes of infertility and protection against miscarriage.
All women produce androgens, and androgens are an important part of the reproductive process. Elevations in androgens can interfere with normal egg development and release and in severe cases can cause unwanted facial or body hair. Androgens principally come from two sources: the ovary or the adrenal gland, a hormone producing organ next to the kidney.
- Testosterone is usually released into the bloodstream by the ovaries in relatively small quantities, then quickly bound to a protein so that it remains inactive. High levels of testosterone are common with polycystic ovary syndrome (PCO), and are rarely encountered with certain tumors.
- The combination of an irregular menstrual pattern and excessive facial or body hair growth can indicate a disorder of adrenal androgen release. One such disorder is called “congenital adrenal hyperplasia” or CAH. This rare disorder is screened by testing for the hormone 17-hydroxy-progesterone.
- DHEAS is the only androgen released exclusively by the adrenal gland. In cases of androgen excess, usually presenting as irregular menstrual function plus excess facial or body hair, a DHEAS level is usually drawn to determine if the extra hormone is coming only from the adrenal.