Vital microscopy of islet blood flow: catecholamine effects in normal and ob/ob mice.

The pancreatic microcirculation in noninbred ob/ob mice and normal controls was visualized in a fluorescence microscope and examined for responses to intravenous infusions of epinephrine or norepinephrine. Evaluations of coded video recordings revealed a smooth dose-response relationship and validated a semiquantitative method of analysis. In ob/ob mice the islet microcirculation was markedly and reversibly inhibited by 0.14-4 micrograms of epinephrine X min-1 X kg body wt-1; the flow was almost totally stopped at the highest infusion rates. Capillary flow in the exocrine pancreas appeared unaffected, except for some inhibition at 4.0 micrograms X min-1 X kg-1. Norepinephrine was less potent an inhibitor of islet blood flow. Normal lean mice exhibited minor responses to 1-11.3 micrograms of epinephrine X min-1 X kg-1; in most cases there was no visible effect. It is concluded that there is a selective regulation of blood flow through the endocrine portion of the pancreas and that the islet microcirculation is hypersensitive to catecholamines in noninbred ob/ob mice. A defective inhibitory influence from the brain may play a role in the development of excessive hyperinsulinemia in ob/ob mice.