Influence of Adipose Tissue Blood Flow on the Lipolytic Response to Circulating Noradrenaline at Normal and Reduced pH

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Abstract
Hypercapnic acidosis (pH 7.0), a common finding in shock, inhibited the lipolytic response of canine subcutaneous adipose tissue to i.v. infused norepinephrine (NE) by 80% or more. The response to sympathetic nerve stimulation was reduced by 10-40% during acidosis. The fate of i.v. infused 3H-NA (0.35 .mu.g/kg .cntdot. min for 30 min) was not significantly altered by acidosis. The rate of disappearance of unmetabolized NE from the arterial plasma after infusion was the same at pH 7.4 and 7.0 and the calculated increase in circulating NE during infusions was 4 ng/ml at both pH. I.v. infusion of NE increases adipose tissue blood flow, an effect attenuated by acidosis. There was a significant correlation (P < 0.001) between adipose tissue blood flow and the lipolytic response at normal pH. Preventing the NE-induced increase in blood flow by constant flow perfusion reduced the lipolytic response at normal pH. The degree of inhibition by acidosis of the lipolytic response to i.v. NE was significantly reduced (from 79-56%, P < 0.05) when the adipose tissue was perfused at constant flow. Adipose tissue blood flow appears to be important in determining the lipolytic response to i.v. NE, probably by influencing the delivery of NE to the tissue. The marked inhibition by acidosis of lipolysis due to i.v. infused NE appears to be the combined effect of a direct antilipolytic effect of acidosis and a decreased delivery of NE to the adipose tissue due to the attenuated blood flow response.