Study of the effects of Neuropeptide Y injections on plasma concentrations of Thyroxine and triiodothyronine in goat

Introduction: Neuropeptide Y (NPY) is the most abundant peptide present in mammals' brains. The majority of NPY-producing neurons is in arcuate and paraventricular nuclei of hypothalamus which affect hypophysiotrapic factors secretion. In this study we investigated the effect of intravenous injections of various doses of NPY on thyroxine (T4) and triiodothyronine (T3) serum concentrations. Methods: Sixteen adult male sannan goats were assigned to four treatment groups. Treatments were included daily injections of 0, 10, 20 and 40 μg NPY per kg body weight named C, L, M and H, respectively. The duration of experiments was 13 consecutive days divided into three intervals pre-treatment (days 1-3), treatment (days 4-10) and posttreatment (days 11-14). Blood collections were being done throughout the experiment at 09:00 via jugular vein and injections were in treatment interval via carotid artery at 08:00. Blood samples were centrifuged and the sera were harvested and used for hormone assay via radioimmunoassay. Results: Results showed that treatment H caused 11-fold increase in T4 concentrations and 4-fold increase in T3 concentrations ones versus treatment C (P<0.001). Treatment M also increased T4 and T3 significantly (P<0.001). The effect of treatment L on T4 concentrations was significantly incremental (P<0.001) but it has no effect on T3 concentrations (P=0.877). The stimulatory effect of NPY on thyroid hormones was transient because in post-treatment interval, T4 and T3 concentrations in treatments L, M and H tended to decline but were yet significantly higher versus treatment C. Conclusion: Previous studies in rodents demonstrated inhibitory effect of NPY on thyroid hormones but in present study completely stimulatory and dose-dependent effects of NPY on these hormones secretion in goat were observed. thus, we suggest the stimulatory effect of NPY on thyrotrop axis in ruminants. This discrepancy can be due to different methodology and difference in neuroendocrine framework controlling thyrotrop axis of ruminants with rodents. Key words: Neuropeptide Y, Thyroxine, Triiodothyronine, Radioimmunoassay, Goat