Arterial and Venous Effects of Serotonin in the Forearm of Healthy Subjects Are Not Age-Related

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Abstract
The influence of age on the regional arterial and venous effects of serotonin (5-HT) was investigated in 13 young (aged 22–31 years) and seven older (aged 50–69 years) healthy volunteers. Single-dose infusions of 5-HT (1, 10, and 80 ng/kg/min) and of the 5-HT2 receptoi antagonist ritanserin (50, 150, and 500 ng/kg/min) were administered into the brachial artery. Subsequently, the relative arterial and venous effects of the highest dose of 5-HT were investigated. Forearm blood flow (FBF) and maximum venous outflow (MVO) were measured by venous occlusion plethysmography. Heart rate (HR) and intraarterial (i.a.) blood pressure were recorded semicon tinuously. In both age groups, 5-HT induced an initia transient arterial dilation, followed by a persistent increase in FBF for the doses of 1 and 10 ng/kg/min and a relative small decrease in FBF for the highest dose. of both age groups, the highest dose of 5-HT induced a similar large reduction in MVO (p < 0.05 for both). The reduction in MVO was attenuated by ritanserin (500 ng/kg/ min, p < 0.05 for both groups). In the younger subjects, this dose of ritanserin also unmasked an arterial dilator effect of the highest dose of 5-HT (p < 0.05). The single infusions of ritanserin did not influence FBF significantly in either study group. No significant differences were observed between the age groups. These results show that in the forearm of healthy subjects arterial and venous vascular responses to 5-HT were not age-related. In the arterial vascular bed, 5-HT acted predominantly as a vasodilator; at high doses, mainly venous vasoconstriction was observed. That ritanserin did not significantly influence FBF in either age group provides evidence that 5-HT2 receptors are not involved in maintenance of basal vascular tone in the vascular bed investigated.