Activin is a hormone found in both the male and the female reproductive systems. As such, it is vital to male and female reproduction. Activin is produced within the gonads, pituitary glands, placenta, and other organs. Activin is a hormone that works by activating the follicle-stimulating hormone (FSH). Activin also plays a large part in a woman's menstrual cycle.
Women experience the growth of immature ovarian follicles in the early stages of their menstrual cycles. A similar protein called inhibin works closely with but in opposition to activin by blocking FSH secretion. When this happens, FSH levels in women will rapidly decrease causing only the most maturated follicle to ovulate.
Activin also stimulates the luteinizing hormone (LH) in the pituitary gland. The effect of activin on the LH in women is the imminent prompting of ovulation. In men, activin stimulation of the LH sky-rockets his levels of testosterone. Therefore, activin plays a large roll in augmenting the creation of sperm in men both directly and indirectly.
Understanding the significant impact that activin has on both male and female reproductive systems, it's easy to grasp why a loss of activin or any interference with activin activity can cause infertility in both sexes. Infertility in women is often due to the disruption of activin activity, thereby disrupting FSH secretion.
In the pancreas, activin works by stimulating the B cells leading to the secretion of insulin. This allows the cells to adapt to glucose increases properly. However, in the liver, muscles, and adipose tissue, activin has an adverse effect on organogenesis, which causes damaged insulin sensitivity. It is well-known that adipose inflammation goes hand-in-hand with the onset of type 2 diabetes. Activin can improve insulin resistance with its inherent anti-inflammatory property.
It's hard to discuss activin without also debating inhibin. Unfortunately, not nearly as much is known about inhibin as is known about activin. However, quantification of inhibin A is part of the prenatal screening that occurs within the 16-18 week mark of gestation. Inhibin levels can be assessed to predict if a fetus has Down syndrome. If an increased level of inhibin A is found at the time of screening (with elevated levels of other hormones and decrease in estriol), it is a reliable indicator of the presence of Down syndrome in the fetus. Of course, more definitive tests must be carried to ensure the results. Inhibin has also been used as a marker for ovarian cancer.
Indeed, activin and inhibin are very closely related protein complexes. Ironically, the two proteins have almost opposite effects. Activin increases FSH and FHS secretion, and it's an integral part of a woman's menstrual cycle. Many other functions of activin have been established, such as the ones discussed in this article. Inhibin decreases FSH and inhibits FHS secretion. Activin was first discovered in 1986, whereas inhibin was found in 1916.
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