Regional blood flow changes underlying the hypotensive action of 5‐HT:Studies using Doppler and Microsphere technologies

Abstract

Serotonin (5‐hydroxytryptamine, 5‐HT) causes a sustained decrease in mean arterial pressure (MAP) and elicits a fall in total peripheral resistance (TPR) in normal conscious rats. We hypothesized that the decrease in TPR induced by 5‐HT is caused by relaxation (direct or indirect) of arteries serving one or more major regional vascular beds. Alzet pumps containing vehicle or 5‐HT (25 ug/kg/min) were implanted in male Sprague‐Dawley rats and 24 hours later the rats were anesthetized and underwent: 1) ear and tail blood flow measurements using Doppler to determine cutaneous vascular contribution; or 2) left ventricular injection of fluorescent microspheres (300,000 yellow green microspheres) to determine global organ blood flow. Infusion of 5‐HT increased ear (69.1±20.5% time‐controlled vehicle) and tail (23.5±2.5%) blood flow (Doppler) while elevating small intestinal (50% increase) flow (microsphere) over vehicle‐infused rats. In the microsphere experiments there was no alteration in blood flow by 5‐HT infusion (vs vehicle) in spleen, liver, lung, right or left kidney, leg muscle, abdominal skin, visceral fat or brain, and right and left kidney flows were statistically similar (R; 3.78±0.69 vs L: 4.00±0.74 ml/min/g tissue, p> 0.05). These findings define the cutaneous and splanchnic vasculature as regions of interest to study the mechanism of 5‐HT ability to lower MAP and TPR. NIH HL081115.