Plasma neuropeptide Y concentration is increased after hemorrhage in conscious rats: Relative contributions of sympathetic nerves and the adrenal medulla

Most peripheral noradrenergic nerves have been shown to contain the coexisting peptide, neuropeptide Y (NPY). The aim of this study was to determine whether NPY is released together with catecholamines during activation of the sympathoadrenal system by hemorrhagic stress in conscious rats. Plasma NPY rose from a baseline value of 7.7 ± 1.2 to 14.4 ± 2.7 and 14.9 ± 2.3 ng/ml (mean ± SEM, n = 8) 10 and 30 min after hemorrhage, respectively. Plasma norepinephrine (NE) and epinephrine concentrations rose immediately after hemorrhage and at 30 min were increased twofold and ninefold, respectively. To determine the source of the increase in circulating NPY after hemorrhage, rats were subjected to adrenalectomy or to chemical sympathectomy with intravenous (i.v.) 6-hydroxydopamine (6-OHDA). 6-OHDA-treated rats had no significant increase in plasma NPY after hemorrhage, whereas adrenalectomized rats had an enhanced NPY response to hemorrhage. These results suggest that the sympathetic nerves make the major contribution to the increase in plasma NPY concentrations after activation of the sympathoadrenal system by hemorrhagic stress.