One of the major objectives of importing Chinese pig breeds into the United States and European countries was to develop an understanding of the mechanism(s) of their increased prolificacy. FSH and LH are heterodimeric glycoprotein hormones composed of a common a subunit and unique (3 subunits that confer biological specificity to each hormone. Both hormones are synthesized in the same cell type in the anterior pituitary gland. The synthesis and release of these two pituitary glycoproteins are controlled by the complex interaction of multiple factors, including hypothalamic GnRH, sex steroids, opiates, and other peptides. GnRH is transported via the hypophysial portal circulation to the pituitary gland where it binds to specific high-affinity receptors (GnRH receptor; GnRH-R) and regulates LH and FSH secretion. buy flovent inhaler
A long-standing problem in reproductive physiology concerns the differential or nonparallel secretion of FSH and LH ostensibly from a single population of cells that respond to a single hypothalamic secretagogue. After elimination of the pulsatile GnRH signal from the hypothalamus by chemical, physical, genetic, or immunological means, pituitary gonadotrophs continue to secrete substantial amounts of FSH but very little LH in vivo or in vitro.