Expression of ghrelin in the porcine hypothalamo-pituitary-ovary axis during the estrous cycle

Ghrelin, a 28-amino acid acylated peptide produced mainly by the stomach, has various functions. Recent studies focus on its endocrine and/or paracrine effects in the regulation of the hypothalamo-pituitary-gonadal axis, that is, the role in reproduction. Previous data have shown that variation of ghrelin depended on the phases of estrous cycle in adult rat ovary. This study was to investigate the expression of ghrelin in the cyclic porcine hypothalamo-pituitary-ovary axis and stomach by semiquantitative RT-PCR and immunohistochemical method. Twenty virginal gilts were classified into four groups as the proestrus, estrus, diestrus1 and diestrus2. Results showed that expression of ghrelin mRNA in the hypothalamus changed with the estrous cycle, i.e., with the highest level in the proestrus and the lowest in the estrus. In the pituitary, the pattern of ghrelin mRNA expression during estrous cycle markedly decreased in the estrus and diestrus1. In the ovary, ghrelin mRNA exhibited with the highest level in the diestrus2 and the lowest in the proestrus, which was different from those in the hypothalamus and pituitary. In the stomach, the expression of ghrelin mRNA had the same tendency as that of the porcine ovary. In immunohistochemical experiment, ghrelin immunoreactive cells were predominantly located in the luteal compartment and growing follicles in the luteal phase of ovary. However, only few ghrelin immunoreactive cells were found in the proestrus ovary. In gastric mucosa, ghrelin immunoreactive cells were detected in the estrus, diestrus1 and diestrus2, but few ghrelin positive cells were seen in the proestrus. Results suggest that ghrelin may play a major role in the endocrine network that integrates energy balance and reproduction.