Effects of left atria1 pressure elevation and histamine infusion on lung lymph in awake sheep

which infused histamine increases lung fluid and solute ex-change, the effects of left atria1 pressure elevation (using a Foley catheter positioned at the mitral valve orifice) on lung lymph flow and protein content were studied in the presence and absence of histamine infusion in nine chronically instru-mented unanesthetized sheep. In six sheep, histamine infusion (l-3 pg. kg-l. min-‘) was begun 2 h before increasing left atria1 pressure by 10 and 20 cmH & for 3 h each. Control experiments were performed on the same sheep to study the effects of left atria1 pressure elevation alone and histamine infusion alone. Left atria1 pressure elevation in the presence of histamine infusion did not cause a disproportionate increase in lung lymph flow nor was the lymph-to-plasma protein concentration ratio (L/P) different from left atria1 pressure elevation alone. This argues against the presence uf increased microvascular perme