Coronary blood flow in the diabetic lamb with metabolic acidosis

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Abstract
Changes in coronary blood flow (CF) evoked by insulin were studied in 18 alloxan-diabetic lambs without or with metabolic acidosis. These findings were compared with 11 nondiabetic animals with normal pH (7.38) or lactic acidemia (pH 6.96). CF was determined under constant hemodynamic conditions with simultaneous measurements of dP/dtmax [change in pressure with time] and left ventricular (LV) O2 extraction and consumption. CF rose 22 ml/min per 100 g LV in nondiabetic animals with normal pH (P < 0.01), but increased twice as much in the acidemics (P < 0.001) 30 min after insulin was given. The diabetic animals with normal pH (24 h after alloxan) showed an increase of only 8 ml/min after insulin, and this was of marginal significance. In the diabetic lambs with acidosis (pH 7.07) studied 48 h after alloxan, CF increased 40 ml/min after insulin, and the difference was highly significant (P < 0.01). A greater shift following insulin was observed in coronary pressure-flow curves from the diabetic group with acidosis than from the diabetics with normal pH. Left ventricular O2 consumption remained constant and did not differ among the groups. O2 extraction fell with increasing CF (correlati on coefficient = -0.79, P < 0.01), consistent iwth coronary dilatation. These findings were independent of changes in dP/dtmax. Insulin evidently has a direct coronary dilator action that is reduced in diabetic lambs, but enhanced by acidosis in diabetic or nondiabetic animals.

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