O2 transfer from single microvessels to acinar cells in secretin-stimulated pancreas of rat

Abstract

O2 transfer from the inside to the outside of single microvessels in the resting and secretin-stimulated exocrine pancreas of rats was investigated by dual-spot microspectroscopy. Measurements of intravascular hemoglobin (Hb) concentration, O2 saturation of Hb, and velocity of flowing red blood cells were carried out in single microvessels at the edge of the exocrine pancreas of anesthetized rats. The rate of O2 release (Ro2) from a single microvessel wall was constant [approximately 2 nmol.cm-2.s-1] over a wide range of oxyhemoglobin inflow ([HbO2] inflow; 200-700 fmol/s) but decreased almost linearly with an [HbO2] inflow < 200 fmol/s, where [HbO2] inflow is defined as the product of inflowing oxyhemoglobin concentration ([HbO2]) and blood flow rate. When the exocrine pancreas was stimulated with secretin either by superfusion (> or = 0.3 nM) or by intravenous infusion (> or = 0.5 microgram.kg-1.h-1), the Ro2 as well as the pancreatic secretion increased about two times higher than the basal values. With secretin administration, it was found that 1) an inverse relationship between red blood cell velocity and intravascular Hb concentration held and thus 2) [HbO2] inflow was maintained within the basal level (i.e., 200-700 fmol/s). Furthermore, 3) the elevation of Ro2 from single microvessels was accomplished by the increased O2 extraction instead of the increased O2 supply in the microvessels.