Radioimmunoassay for plasma neuropeptide-Y in physiological and physiopathological states and response to sympathetic activation.

A radioimmunoassay has been developed for measuring plasma neuropeptide-Y immunoreactivity using extraction on Sep-Pak C18 cartridges. Neuropeptide-Y concentrations (mean +/- SEM) in plasma from 15 normotensive individuals were 223.6 +/- 14.7 ng/l. Plasma concentrations were raised in 10 patients with heamodialysis-dependent chronic renal failure with values of 417.6 +/- 13.6 ng/l and in 3 patients with phaeochromocytoma the concentrations were 237 ng/l, 574 ng/l and 747 ng/l. Plasma neuropeptide-Y immunoreactivity was also measured in 10 normotensive individuals in response to a, hand-in-ice, cold pressor test. Despite an immediate significant elevation in blood pressure, neuropeptide-Y immunoreactivity was not significantly raised until after the removal of the hand from the ice by which time the blood pressure had returned towards the basal levels. This dissociation in neuropeptide-Y immunoreactivity and blood pressure responses probably reflects a delay in the diffusion of synaptic neuropeptide-Y into the general circulation. This study suggests that the measurement of neuropeptide-Y immunoreactivity may be a useful index of sympathetic activation.