Control of O2 supply to the pancreas during a vasopressin-induced vasoconstriction

In the anesthetized dog, the metabolic level of the pancreas was elevated by a secretin infusion (1.2 U/kg/hr iv), displaying a metabolic control of tissue oxygenation and blood flow. Question was raised how this system would response to a decrease in O2 supply, as induced by increasing doses of vasopressin (2-131 mU/kg, iv). These vasopressin administrations progressively diminished blood flow (down to 20%), as well as secretory rate (down to 7%) and O2 consumption (down to 33%). The O2 extraction was increased up to 227%. Capillary density, mitochondrial O2 consumption, capillary PO2 and cellular PO2 were calculated by simulating these data with the model of the metabolic control of tissue oxygenation. The changes mentioned above could be simulated adequately. These simulations revealed that a. in the pancreas vasopressin primarily increases arteriolar resistance; the inhibition of metabolism is secondary to the vasopressin-induced vasoconstriction. b. The pancreas responds with a small compensatory capillary recruitment (up to 29%), which in itself would increase tissue oxygenation. c. The main consequence of the lowering of blood flow is a dramatic decrease of mean capillary PO2 (down to 38%), as well as a lowering in mean cellular PO2 (down to 41%). This lowering of O2 supply to the tissue will slow down the metabolic rate, as evidenced by the decrease of the volume of the excretion.