17beta-estradiol regulation of melanin-concentrating hormone and neuropeptide-E-I contents in cynomolgus monkeys: a preliminary study.

Melanin-concentrating hormone (MCH) and neuropeptide-E-I (NEI) regulate several behaviors and neuroendocrine functions in rats. Possible influence of these peptides on sexual behavior and reproduction in mammals other than rodents prompted us to investigate: 1) The sites of synthesis of MCH and NEI in the brain of a non-human primate (M. fascicularis); 2) The effect of 17 beta-estradiol (E2) benzoate (E2B) on pro-MCH-derived peptide concentrations in the hypothalamus of the ovariectomized (OVX) cynomolgus monkeys (M. fascicularis). Expression of MCH mRNA and peptides was examined by Northern blotting, RT-PCR and RP-HPLC/RIA. Our results demonstrate that the MCH gene is predominantly expressed in hypothalamus of macaque. E2B exposure of OVX monkeys provoked parallel phasic variations in the MCH-immunoreactivity (IR) and NEI-IR. NEI-IR and to a lesser extent MCH-IR, showed a transient increase (associated with the estradiol peak) at 30 h with a final rise of both MCH-IR and NEI-IR observed at the time (72 h post E2B) of the luteinizing hormone (LH) surge. RP-HPLC analysis of peptide extracts revealed the presence, in addition to mature MCH and NEI, of different MCH-IR and NEI-IR forms in the hypothalami of control and E2B-treated monkeys. Taken together, our results indicated that hypothalamic MCH and NEI contents are regulated after E2B treatment and they suggest the possible involvement of these peptides in the regulation of the pre-ovulatory midcycle LH surge in primates.