Changes in GnRH pulse frequency in females is controlled by circulating levels of estrogen and progesterone.

Estrogen and progesterone are two important hormones in the female reproductive system that regulate the menstrual cycle and fertility. They are produced by the ovaries in a cyclic manner, and their levels fluctuate throughout the menstrual cycle. These hormonal changes are responsible for the various phases of the menstrual cycle, including follicular phase, ovulation, and luteal phase.

GnRH (gonadotropin-releasing hormone) is a hormone released by the hypothalamus in the brain. It plays a crucial role in the regulation of the menstrual cycle by stimulating the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary gland. FSH and LH, in turn, stimulate the growth and maturation of ovarian follicles, ovulation, and secretion of estrogen and progesterone.

The frequency of GnRH pulses is controlled by the negative feedback mechanism of estrogen and progesterone. Here's how it works:

1. Follicular Phase:
- At the beginning of the menstrual cycle, estrogen levels are low.
- Low estrogen levels stimulate the hypothalamus to release GnRH in a pulsatile manner, resulting in the secretion of FSH and LH from the pituitary gland.
- FSH stimulates the growth of ovarian follicles, which produce increasing amounts of estrogen.
- As estrogen levels rise, it exerts negative feedback on the hypothalamus and pituitary gland, reducing the frequency of GnRH pulses and the secretion of FSH and LH.

2. Ovulation:
- As the dominant follicle matures, it produces a surge of estrogen.
- The high levels of estrogen trigger a positive feedback mechanism on the hypothalamus, causing a sudden increase in GnRH pulses and a surge in LH secretion.
- The surge in LH triggers ovulation, the release of the egg from the ovary.

3. Luteal Phase:
- After ovulation, the ruptured follicle forms the corpus luteum, which produces progesterone.
- Progesterone levels increase, exerting negative feedback on the hypothalamus and pituitary gland.
- The reduced GnRH pulses result in a decrease in FSH and LH secretion, preventing the development of new follicles and ovulation.

In summary, the circulating levels of estrogen and progesterone control the frequency of GnRH pulses. Low estrogen levels stimulate GnRH release, while high levels of estrogen trigger a surge in GnRH pulses. Progesterone exerts negative feedback on GnRH secretion. These hormonal changes regulate the menstrual cycle and ensure proper follicular development, ovulation, and preparation of the uterus for potential pregnancy.

GnRH is secreted by the hypothalamus which stimulates the anterior lobe of pituitary gland to secrete luteinising hormone (LH) and FSH. FSH stimulates the growth of the ovarian follicles and stimulates the formation of estrogens. LH stimulates the corpus luteum to secrete progesterone. Rising levels of progesterone and estrogen inhibits the release of GnRH, which in turn, inhibits the production of FSH and LH.