Reproductive Regulation of PrRPs in Teleost: The Link Between Feeding and Reproduction.

Prolactin-releasing peptide (PrRP), a sort of vital hypothalamic neuropeptide, has been found to exert an enormous function on the food intake of mammals. However, little is known about the functional role of PrRP in teleost. In the present study, two PrRP isoforms and four PrRP receptors were isolated from grass carp. Ligand-receptor selectivity displayed that PrRP1 preferentially binds with PrRP-R1a and PrRP-R1b, while PrRP-R2a and PrRP-R2b were special receptors for PrRP2. Tissue distribution indicated that both PrRPs and PrRP-Rs were highly expressed in the hypothalamus-pituitary-gonad axis and intestine, suggesting a latent function on food intake and reproduction. Using grass carp as a model, we found that food intake could significantly induce hypothalamus PrRP mRNA expression, which suggested that PrRP should be also an anorexigenic peptide in teleost. Interestingly, intraperitoneal (IP) injection of PrRPs could significantly induce serum luteinizing hormone (LH) secretion and pituitary LHß and GtHα mRNA expression in grass carp. Moreover, using primary culture grass carp pituitary cells as a model, we further found that PrRPs could directly induce pituitary LH secretion and synthesis mediated by AC/PKA, PLC/IP3/PKC, and Ca2+/CaM/CaMK-II pathways. Finally, estrogen treatment of prepubertal fish elicited increases in PrRPs and PrPR receptors expression in primary cultured grass carp hypothalamus cells, which further confirmed that the PrRP/PrRPR system may participate in the neuroendocrine control of fish reproduction. These results, taken together, suggest that PrRPs might act as a coupling factor in feeding metabolism and reproductive activities in teleost.

Prolactin-releasing peptide mRNA expression in mouse medulla remains relatively stable during pregnancy and lactation.

We compared levels of prolactin-releasing peptide (PrRP) mRNA expression in mouse medulla at different stages of pregnancy and lactation. Mouse medulla samples were collected on days 6, 12 and 18 of pregnancy and lactation, respectively (six per group), for mRNA. Expression levels of PrRP mRNA in the medulla were measured by semi-quantitative RT-PCR, with glyceraldehyde 3-phosphate dehydrogenase as a control. PrRP mRNA was highly expressed in mouse medulla oblongata on day 6 of pregnancy (0.53), followed by 0.43 at lactation day 6, and 0.42 at lactation day 12. The expression level of PrRP mRNA on days 12 and 18 of pregnancy and day 18 of lactation shared the same value of 0.36. PrRP mRNA levels during lactation decreased slightly compared with that during pregnancy, but the differences between them were not significant. In summary, PrRP mRNA levels in the medulla oblongata remain relatively stable during pregnancy and lactation. This is evidence that medulla PrRP is not involved in the regulation of prolactin secretion.