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Gonadotropin treatment is "big-gun " therapy, and is usually reserved for patients with difficult anovulatory problems who have not responded satisfactorily to clomiphere, or for patients who need superomlation for IUI or IVF. The two gonadotropin hormones, Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) are produced in the pituitary and their secretion is controlled by a third hormone, Gonadotropin Releasing Hormone (GnRH), released by the hypothalamus. At the start of a new cycle, the hypothalamus begins to release GnRH. GnRH then acts on the pituitary gland to release FSH and LH. These two hormones stimulate the ovary, causing follicles to develop (as the name suggests, this is the primary action of the FSH - to stimulate follicular growth). When it is time for ovulation, a sudden burst of LH is released from the pituitary gland (the LH surge) which causes the egg to be released from the mature follicle in the ovary.
This system is a very finely tuned one, designed by Nature to ensure the release of a single mature egg every month. Such a process involves orchestrating a symphony of messages from the hypothalamus, the pituitary and the ovary. The messages are transmitted by hormones - which are chemical messengers in the blood stream. When the egg is ripe, the mature follicle releases an ever increasing amount of estrogen, which is produced by the granulosa cells which line the follicle. This estrogen produced by the dominant follicle progressively increases in quantity as the egg matures, until the mature follicles releases a surge of estrogen into the blood (the estrogen surge). This high level of estrogen stimulates the pituitary to release a large amount of LH hormone - the LH surge. This LH in turn acts on the mature follicle, causing it to rupture to release the mature egg. Thus it is the mature egg which signals the brain that it is ready for release, and triggers off its own ovulation!
How does Nature ensure that only one egg is released every cycle? About 30-40 follicles will start growing in response to the FSH produced by the pituitary. However, of these follicles, only one is destined to grow (become dominant) and rupture to release its mature egg. The others will die - a process called atresia. The dominant follicle releases increasing amounts of estrogen as it grows bigger. This estrogen in turn decreases the production of FSH by the pituitary (in a negative feedback control loop), so that without high levels of FSH, the smaller follicles no longer have a stimulus to grow; and they gradually die. The dominant follicle by now has become so big, that it can grow by itself, and doesn't need the additional FSH stimulation.
© Dr. Aniruddha Malpani and Dr. Anjali Malpani www.drmalpani.com
Credits: How to Have a Baby: Overcoming Infertility
