Effects of neuropeptide Y on the renal, mesenteric and hindlimb vascular beds of the conscious rabbit

Abstract

The effects of neuropeptide Y (NPY, 10 μg/kg bolus i.v.) on renal, mesenteric and hindlimb blood flow were determined in intact conscious rabbits with chronically implanted Doppler ultrasonic flow transducers. The role of sympathetic neuro-effectors was assessed using inhibition of peripheral α-adrenoceptors with phentolamine in each group, and in the renal flow group following chemical sympathectomy with 6-hydroxydopamine. In controls, NPY caused markedly non-uniform peak responses. Renal blood flow fell from 2.16 ± 0.12 kHz to a minimum of 0.26 ± 0.07 kHz following NPY administration ( P < 0.05). Mesenteric blood flow was reduced from 2.04 ± 1.17 to 1.54 ± 0.11 kHz ( P < 0.05). Hindlimb blood flow increased transiently from 2.33 ± 0.15 to a peak of 3.33 ± 0.19 kHz ( P < 0.05). Renal vascular resistance rose by 1189 ± 309% and mesenteric resistance by 54 ± 9% ( P < 0.05), while hindlimb resistance fell by 24 ± 3% ( P < 0.05). Pretreatment with phentolamine accentuated the peak pressor response and the reduction in heart rate induced by NPY administration but had little effect on the local haemodynamic changes in each vascular bed. There was no change in the renal vascular response to NPY following sympathectomy. Indeed, the peak NPY-induced reduction in renal blood flow seen in control animals (87 ± 4%) was unaffected by either α-adrenoceptor inhibition (90 ± 5%) or by sympathectomy (86 ± 5%). In conscious rabbits with intact cardiovascular reflexes, pharmacological doses of NPY cause profound renal vasoconstriction with smaller changes in mesenteric and hindlimb flow. The effects of NPY on peripheral vascular tone are not mediated by sympathetic neuro-effectors.