The effects of age on human venous responsiveness to neuropeptide Y

Aims Neuropeptide Y (NPY) is a sympathetic neurotransmitter released with n oradrenaline during sympathetic stimulation. Ageing has been shown to be as sociated with a reduction in alpha(2) and beta-adrenoceptor mediated respon ses in veins, but it is not known whether NPY responsiveness is also altere d with increasing age. Methods Using a dorsal hand vein technique, we examined NPY receptor respon siveness in 24 normal, healthy subjects (20-72 years; 10 males, 14 females) . Graded infusions of NPY (25-2000 pmol min(-1)) were administered (5 min a t each dose) into a dorsal hand vein. Venous distension at 45 rnmHg was mea sured at 3-5 min of each infusion. Dose-response curves to NPY were constru cted and the peak venoconstriction was calculated. Results Dose-dependent venoconstriction was seen in all but one subject. Th e peak venoconstriction observed with NPY was significantly and negatively correlated with the age of the normal subjects (r = -0.63, P < 0.01). When subjects were ranked from youngest to oldest and divided into tertiles, (20 -40 years, n = 8; 41-55 years, it = 8; 56-72 years, n = 8), mean dose-respo nse curves were different with the oldest tertile being significantly less responsive (P < 0.05). The peak venoconstriction observed (% of control) wa s 65.1 +/- 7.0, 46.5 +/- 9.4, and 24.4 +/- 4.8%, respectively. The oldest t ertile had a significantly decreased peak venoconstriction compared with th e youngest tertile (P < 0.01). Infusion of NPY into a dorsal hand vein had no systenlic effects on heart rate or blood pressure in any oi the subjects studied. Conclusions Hand vein responsiveness to exogenously infused NPY in normal s ubjects is decreased as age increases. The reduction of NPY-receptor-mediat ed responses with age may influence sympathetic nervous system control of t he venous system with advancing age.