Involvement of the human splanchnic circulation in pressor response induced by handgrip contraction

We have analysed the adjustment of blood flow and vascular conductance in the abundantly supplied splanchnic circulation to a generally released pressor reaction. Pressor responses were induced by 2-min periods of standardized, sustained handgrip in seven healthy students. The effects of handgrip tests were followed both in the fasting state and after the consumption of a substantial, mixed meal. In the first of the two sessions, changes in superior mesenteric artery blood flow were recorded and concomitant changes in local vascular conductance derived. In the other session, pressor released cardiac output changes were recorded and changes in total peripheral vascular conductance derived. Both types of flow changes were recorded using ultrasound Doppler technique. Typically, blood flow in the superior mesenteric artery increased two- to threefold after a meal. Handgrip contractions induced an initial rapid increase in heart rate, cardiac output and total peripheral conductance, followed by a gradual decline in total peripheral conductance and stroke volume and a gradual increase in heart rate and mean arterial pressure for the rest of the period. At the end of 2-min pressor periods, total peripheral conductance was only about 10% below the pre-handgrip level, whereas vascular conductance locally in the area of the superior mesenteric artery decreased by some 30%. Thus, it appears that the splanchnic vascular bed contributes markedly to the compound pressor response. Handgrips caused significantly less reduction in local vascular conductance in the post-prandial than in the pre-prandial state, indicating that blood flow to the digesting gastrointestinal tract retains a relatively high priority also in a pressor situation.