Histamine and protein transport in canine muscle

The effect of intraarterial histamine infusion on transcapillary protein transport was determined in the constant flow pump-perfused isolated gracilis muscle of the dog. Muscle vascular resistance (MVR), the rate of net transcapillary protein transport (Js), net transcapillary fluid transport (Jv), changes in protein-free transcapillary fluid movement (delta Jo) and rubidium extraction (ERb) were calculated following four experimental manipulations. First, as a control, venous pressure was elevated by 20 mmHg; next, histamine was infused intraarterially; then venous pressure was elevated by 20 mmHg during histamine infusion; and finally, the recovery of the tissue from histamine infusion was determined. Although elevation of venous pressure produced no change in MVR, it significantly increased Js, Jv and delta Jo. Histamine infusion caused a significant decline in MVR, and increases in Js and in Jv. delta Jo did not change significantly. When venous pressure elevation was superimposed upon histamine infusion, MVR did not change; Js, Jv, and delta Jo increased but only by increments similar to venous pressure elevation alone. None of the manipulations altered Rb extraction. At the constant flow used in this study, histamine does not appear to increase either capillary hydrostatic pressure or capillary surface area, so that the small intestine in Js was probably due to a slight increase in capillary permeability.