ABSTRACT
All reproductive events are regulated by hormones. A classical definition for a hormone is that it is a substance produced in one tissue that is transported to another tissue to exert a specific effect. Gonadotropin-releasing hormone (GnRH) is composed of amino acids and is thus a polypeptide in nature. The follicle-stimulating hormone and luteinizing hormone are glycoproteins. The diversity of the composition of hormones leads to the variation in their biological functions. Most hormone concentrations are in billionths or trillionths of a gram per milliliter of blood. The ability of one tissue to respond to a particular hormone rests in whether that tissue possesses a receptor to the particular hormone. The major reproductive hormone of the hypothalamus is GnRH that is sometimes called luteinizing-hormone-releasing hormone. Administration of a hormone to mimic the effect of that hormone in the animal can be used to regulate the cycle. Estrogen is the hormone produced by follicles as they develop on the ovary.
