Ghrelin in Female and Male Reproduction

Abstract

Ghrelin and one of its functional receptors, GHS-R1a (Growth Hormone Secretagogue Receptor 1a), were firstly studied about 15 years. Ghrelin is a multifunctional peptide hormone that affects several biological functions including food intake, glucose release, cell proliferation… Ghrelin and GHS-R1a are expressed in key cells of both male and female reproductive organs in several species including fishes, birds, and mammals suggesting a well-conserved signal through the evolution and a role in the control of fertility. Ghrelin could be a component of the complex series of nutrient sensors such as adipokines, and nuclear receptors, which regulate reproduction in function of the energy stores. The objective of this paper was to report the available information about the ghrelin system and its role at the level of the hypothalamic-pituitary-gonadal axis in both sexes.

Detection of obestatin in seminal plasma and its relationship with ghrelin and semen parameters

“…Strong ghrelin immunostaining has even been detected in germ cells in adult sheep testis (8). These observations are supported by the discovery of the ghrelin receptor in rat and human Sertoli cells, Leydig cells, seminiferous tubules, and human germ cells, mainly pachytene spermatocytes (2). All this evidence suggests that ghrelin could have a pivotal impact on the regulation of spermatogenesis.…”

“…For this reason, comparisons were performed for all the considered characteristics within the following groups: [1] smokers-non smokers, [2] leukocytospermia-no leukocytospermia, [3] varicocele-no varicocele, [4] ex varicocele-no ex varicocele. The results of this investigation are reported in Table 3.…”

“…Obestatin, reputed to play a physiologic role opposite to that of ghrelin, can also be involved in improving memory, regulating sleep, secreting pancreatic juice enzymes, and cell proliferation (15). In the reproductive system, the role of ghrelin is clearly emerging (2,4,16), but the function of obestatin is still unclear. There is one other report in the literature on the presence of ghrelin in seminal plasma of men with normospermia and dyspermia (11).…”

“…Both peptides could be produced by the testes (2,4,18) and by the accessory genital gland. Alternatively, these hormones could be concentrated in semen by particular proteins, similar to the way in which the androgen-binding protein relates to testosterone, dihydrotestosterone, and 17b-estradiol.…”

“…Circulating ghrelin is mainly produced by cells, which colocalize with parietal cells in the oxyntic region of the stomach, and it strongly stimulates GH release. Ghrelin is involved in a series of biological functions, including regulation of food intake, body weight, gastrointestinal motility, sleep, cardiovascular functions, cell proliferation, and production of proinflammatory cytokines (2). Obestatin was isolated from rat stomach on the basis of a bioinformatics prediction that another peptide was encoded by the same precursor protein as ghrelin (3).…”