Neuropeptide y potentiates norepinephrine-stimulated inositol phosphate production in the rat tail artery

Abstract

We have recently demonstrated the ability of neuropeptide Y to augment norepinephrine-sti,ulated contractions of rat tail artery. In [ 3H]myo- inositol labeled segments of rat tail artery, addition of a concentration of neuropeptide Y (10 −8 M) known to potentiate contractile responses produced no effect on the basal accumulation of [ 3H]inositol phosphates. Addition of norepinephrine (10 −7 M), however, resulted in the rapid accumulation of [ 3H]inositol 1,4,5-trisphosphate to 325 ± 29 % of basal levels within 5 min. This effect of norepinephrine on [ 3H]inositol 1,4,5-trisphosphate accumulation was mirrored by significant increases (274 ± 25 % of control) in total [ 3H]inositol phosphates. When neuropeptide Y and norepinephrine were added together, the norepinephrine-stimulated increase in [ 3H]inositol 1,4,5-trisphosphate was significantly augmented (467 ± 35 % of control) as was the increase measured in total [ 3H]inositol phosphates (366 ± 21 % of control). We suggest that the ability of neuropeptide Y to augment norepinephrine-induced contraction of the rat tail artery is due, at least in part, to the ability of neuropeptide Y to increase norepinephrine-stimulated phospholipase C activity in vascular smooth muscle and may represent the mechanism of action of this co-neurotransmitter in vivo.