Extract

Since GnRH was first isolated from the pig brain more than three decades ago, an additional 16 novel GnRH structural variants, all of which are composed of 10 amino acids, have been identified in the animal kingdom (1–6). Among them, chicken GnRH II (pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly·NH2), the second form isolated from the chicken brain, is the evolutionarily conserved form, as it was found in the brains of jawed fish to humans (1). After the isolation of this form from the human brain recently (7), it has been renamed GnRH II, and pGlu-His-Trp-Ser-Try-Gly-Leu-Arg-Pro-Gly·NH2 has been renamed GnRH I (7). Whereas perikarya of GnRH I are distributed widely in the preoptic area and hypothalamus with their fibers converging in the median eminence and pituitary stalk, perikarya of GnRH II are primarily present in the midbrain and extrahypothalamic regions (8, 9). Hypophysiotropic GnRH in all mammals, except for in guinea pigs, is GnRH I, whereas the molecular structure of hypophysiotropic GnRH among nonmammalian species is quite diverse (1).

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