Some properties of a preparation of rat colon perfused in vitro through the vascular bed.

1. A technique is described for the perfusion of the isolated colon of the rat, involving the infusion of an appropriate fluid through both the inferior and the superior mesenteric arteries. During neither the preparation nor the subsequent perfusion is the colon without an adequate supply of oxygen. The preparation remains histologically intact and metabolically viable and is capable of actively transporting ions for up to 5 hr.2. The addition of at least 3 g albumin/100 ml. perfusate is necessary to prevent the formation of large quantities of serosal exudate. With erythrocytes added to the vascular perfusate the preparation appears to be adequately oxygenated as judged by measurements of the rate of glycolysis. The mean rate of oxygen utilization over 4 hr is 9.2 +/- 0.3 (4) mumole. hr(-1).g(-1) fat free dry weight.3. Ion transport rates approaching those found in vivo are found only after the administration of an antihistamine substance to the colon donor rat before operation. In the absence of an antihistamine substance there appears to be an ultrafiltration of the plasma fluid into the lumen.4. Vasodilatory substances accumulate in the recycled perfusate. In a ;single pass' perfusion, the transport capacity of the preparation decreases at high perfusion pressures. It is suggested that this is due to some form of autoregulation whereby perfusate is shunted away from the epithelium into deeper layers as the pressure is increased.5. With CO(2) absent from the vascular infusate there is an increase in the net lumen to blood flux of total CO(2). This increased flux is accompanied by an equivalent amount of cation, comprising Na(+) and K(+) in the ratio of 12:1.6. The presence of ammonium in the lumen, a physiological constituent of the contents of rat distal colon in vivo, has a marked inhibitory effect upon the secretion of CO(2) into the contents of the lumen of the colon.