The Physiologic Effect of Vasodilators On the Omentum of the Dog in Low Flow States

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Abstract
The purpose of this study was to observe the microcircuiation of the dog omentum in low flow states while the vasodilator pentaerythritol tetranitrate (PETN) was injected intravenously to determine if this drug increased peripheral perfusion. Thirtyfive mongrel dogs, standardized as to sex and weight, were anesthetized with sodium pentobarbital, 15 mg/kg. Two No. 14 polyethylene catheters were placed in the right femoral artery and vein; the artery for bleeding and the vein for injection. A No. 14 catheter was placed in the left femoral artery and vein and connected to a Beckman physiologic measuring monitor in order to record blood pressure. A small, lateral flank incision was performed from which the omentum was mobilized on the stage of a microscope. The microcircuiation was visualized at a magnification of 100 to 360 x. The dog was bled qt 10% volume increments, 30minutes intervals until the volume to be studied was withdrawn. Control blood volumes were measured with the radioactive iodinated albumin technique. Previous investigations have revealed the lethal bleeding dose was approximately 55% of volume, +4.6%; however, PETNtreated dogs were bled passed the lethal dose to 65% without returning volume. PETN, 2 mg/kg, was injected at 40% and 60% of bleeding. The effect of this vasodilator was: PETN increases peripheral tissue perfusion. Survival rates with the use of PETN at 45% and 65% of volume bled increase significantly. (The mortality was 5 out of 35 animals after infusion of PETN at 65% of voume bled; while 9 out of 10 control animals died.) PETN does not significantly decrease blood pressure. There is no definite correlation between blood pressure and microcirculatory changes. A series of microphotographs illustrate the sequence of microcirculatory changes during the studies of the control and PETNtreated animals.