The influence of ghrelin agonist ipamorelin acetate on the hypothalamic-pituitary-testicular axis in a cichlid fish, Oreochromis mossambicus.
This study investigated the effects of ipamorelin acetate (IPA), a synthetic ghrelin agonist, on the reproductive axis of male Mozambique tilapia (Oreochromis mossambicus), a cichlid fish. Fish received either 5 µg or 30 µg of IPA over 21 days and were compared to untreated controls. The study found that IPA administration produced a dose-dependent increase in food intake. Histological analysis revealed significant increases in primary spermatocytes, secondary spermatocytes, and early spermatids in both treatment groups, while the higher dose also increased late spermatids, lobule area, and lumen area. Serum concentrations of luteinizing hormone (LH) and the fish androgen 11-ketotestosterone (11-KT) were significantly elevated in both IPA groups. Androgen receptor protein expression was significantly upregulated in the high-dose group. No significant differences in hypothalamic or pituitary GnRH-immunoreactive fiber density were observed across groups. The authors conclude that ghrelin signaling may promote meiosis-I stage germ cell development through LH stimulation at the pituitary level and 11-KT and androgen receptor activity at the testicular level. Limitations include the use of a single non-mammalian species, a short treatment duration, and the absence of mechanistic pathway confirmation.
Why this grade: The study was conducted entirely in a teleost fish species (Oreochromis mossambicus), with no human subjects or clinical data, providing no direct evidence for effects in humans.
Ghrelin, a peptide found in the brain and gut, is predicted to play a significant role in the control of various physiological systems in fish. The objective of this study was to examine the impact of ipamorelin acetate (IPA), a ghrelin agonist, on the reproductive axis of the tilapia Oreochromis mossambicus. The administration of either 5 or 30 µg of IPA for 21 days led to a significant and dose-dependent rise in food intake concomitant with a significant increase in the numbers of primary spermatocytes, secondary spermatocytes, and early spermatids compared to the control group. There was a significant rise in the number of late spermatids, as well as the areas of the lobule and lumen, in fish treated with 30 µg of IPA, compared to the control group. Moreover, there was no significant difference in the percentage of gonadotropin-releasing hormone (GnRH)-immunoreactive fibres in the hypothalamus and anterior pituitary gland across different groups. However, a significant elevation in the expression of androgen receptor protein was observed in fish treated with 30 µg of IPA. Furthermore, the concentrations of luteinizing hormone (LH) and 11-ketotestosterone (11-KT) in the serum of fish treated with either 5 or 30 µg of IPA were significantly elevated in comparison to the control group. Collectively, these findings suggest that the administration of ghrelin enhances the development of germ cells during the meiosis-I phase and that this effect might be mediated via the stimulation of 11-KT and androgen receptors at the testicular level and LH at the pituitary level in the tilapia.
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