Effects of histamine and increased venous pressure on transmicrovascular protein transport

Abstract

Histamine administered locally into canine forelimbs increases lymph flow, lymph protein concentration, and lymph protein transport. In this study we examined the time course of these changes and compared them to the changes produced by mechanically increasing venous pressure alone and during the infusion of histamine or acetylcholine. Intrabrachial infusion of histamine at 4 μg base/min produced 25- and 45-fold increases in lymph flow and protein transport, respectively, and a 50% increase in lymph protein concentration. These effects, however, waned with time. Qualitatively similar changes were seen with histamine infused at 16 and 64 μg base/min. Increased venous pressure alone produced 8- and 5-fold increases in lymph flow and protein transport, respectively, and decreased total protein concentration. Increasing venous pressure during histamine infusion further increased lymph flow and protein transport, which then waned with time. However, protein transport during histamine plus increased venous pressure was always greater than with the infusion of histamine alone. Increasing venous pressure during acetylcholine infusion increased lymph flow but decreased lymph protein concentration, resulting in only a small increase in total protein transport. These data indicate that the effects of histamine on protein transport are much greater than during increased venous pressure alone but that they wane with time. Increasing venous pressure during histamine infusion further increases protein transport relative to histamine alone. Histamine appears to increase microvascular efflux of protein, at least in part, through a mechanism which is sensitive to changes in microvascular pressure.