Study of the role of NPY in the control of prolactin and growth hormone secretion through Y1 receptor subtype in juvenile male rhesus monkey (Macaca mulatta)

Abstract

Background Neuropeptide Y (NPY) plays an important role in controlling reproductive axis and food intake. Both prolactin (PRL) and growth hormone (GH) are important non-gonadotrophic hormones that are involved in many physiological processes. Many intrinsic and extrinsic factors are involved in modulating the secretion of PRL and GH. It is believed that NPY is also one of the factors involved in mediating the release of PRL and GH. Numerous studies in different animal models (rat, mice, sheep) have documented contradictory observations concerning NPY regulation of PRL and GH secretion via Y1 receptor subtype (NPY1R). However, the role of NPY in mediating non-gonadotropic hormones secretion by NPY1R has not been clearly defined in highly evolved non-human primates. Aims and Objectives The present study was undertaken to study the role of NPY in the control of PRL and GH secretion through Y1 receptor subtype in juvenile male rhesus monkey. For this purpose, highly specific NPY1R antagonist BIBO 3304 was used. Materials and Methods A total of four (n=4) juvenile male rhesus monkey (Macaca mulatta) were used to study the effect of NPY1R antagonist on GH and PRL secretion. These four juvenile monkeys were injected intravenously with either NPY1R antagonist 1ml of 2mg antagonist/animal or an equal amount of normal saline (1ml/animal) on two alternative days. A total of 3 boli of normal saline and antagonist in 4.8 % DMSO were injected with an interval of 60 minutes at 0, 60, and 120 min on two separate days of bleeding. On both days of bleeding, three blood samples (0.5 0.7 ml) were collected from animals at -60, -30 and 0 minutes. After taking 0-minute sample, animals were immediately injected with either vehicle or antagonist and then sequential blood samples with 30-minute interval up to 240 minutes were collected with the help of butterfly tube connected with 1cc syringe. Plasma was harvested and commercially available GH and PRL ELISA kit was used to measure GH and PRL concentration. 1 Abstract Results Plasma PRL and GH levels in juvenile male rhesus monkeys treated with antagonist showed no statistically significant difference (p>0.05) as compared to vehicle group. Thus, current findings demonstrated that NPY signaling via NPY1R may not involve in regulating PRL or GH secretion in juvenile animals. Conclusion In conclusion, our study showed that there is no effect of NPY on PRL and GH release in juvenile male rhesus monkeys. However, contemplating previous data in different animal models, amount, and route of exposure of the drug are the key concerns. Therefore, non involvement of NPY1R in mediating non-gonadotropic hormones secretion cannot be exclusively ruled out. Further investigations are required to ascertain plausible mechanisms by which NPY can regulate GH and PRL release. The study can be extended at the pituitary level to ascertain direct effect of NPY on somatotrophs and lactotrophs involved in GH and PRL release