The Distribution of Blood Flow Along the Small Intestine of The Dog

The presence of a blood-flow gradient along the small intestine is disputed. Geber (1), using electromagnetic flowmeters in dogs, and Steiner and Mueller (2) using the indicator fractionation technique in rats demonstrated that blood flow per unit weight was highest in the duodenum and then decreased progressively along the jejunum, ileum, and colon. On the other hand, Grim and Lindseth (3) using direct collection of venous outflow isolated loops of intestine in the dog, and Delaney and Custer (4) using the indicator fractionation technique in dogs did not observe a blood flow gradient. The negative view has also been supported by a more recent study of Goodhead (5) using the indicator fractionation technique in the dog.

This paper presents evidence that a blood flow gradient does exist in the small intestine of the dog when it is studied under basal conditions of anesthesia.

Materials and methods. Eighteen mongrel dogs weighting 15-30 kg were given water but no food for 24 hr in the preparation period. General anesthesia was then induced and maintained with intravenous pentobarbitone sodium (30 mg/kg). Blood pressure and heart rate were monitored from a femoral artery catheter and body temperature was kept at 37.5°. Care was taken to perform all blood flow measurements when these functions were stable.

Intestinal blood flow was measured by the indicator-fractionation technique with ⁴²K (15 μCi/Kg) as the indicator. The ⁴²K was injected into the inferior vena cava and tissue ⁴²K content 100 sec after the injection was used for all blood flow calculations (5-8). The cardiac output was measured by the conventional dye dilution technique (9) immediately prior to the injection of the ⁴²K. Cardiac arrest was produced by a rapid injection of saturated magnesium sulphate into the inferior vena cava and this enabled removal of 3-5 cm sleeves of intestine for ⁴²K assay from the third part of the duodenum, the jejunum (10 cm distal to the ligament of Trietz), and the distal ileum (30 cm proximal to the ileo-caecal valve).