Seasonal variations of capillary hydraulic conductivity and volume status

The purpose of this study was to determine whether circulating plasma protein concentration, capillary hydraulic conductivity (Lp), and overall volume status in frogs were correlated and whether these correlations varied with season. Individual vessel Lp was thus examined on a monthly basis and correlated with changes in protein content in three body compartments (blood, lymph, and body cavity) over a 10-yr period. The frogs were anesthetized, blood and fluid samples collected, Lp assessed, and samples assayed for overall protein content. Volume status indicators varied cyclically over the course of 1 yr. Protein levels reached their peak in winter and were lowest in summer for all compartments. Lp for venular and arteriolar capillaries reached maximal levels in summer and fell steadily throughout the remainder of the year. Basal true capillary Lp was stable over the course of the year. Lp and total protein concentration were inversely proportional to each other on a seasonal basis but did not correlate on a monthly basis. Therefore, we conclude that the lack of a simple relationship between Lp and volume status suggests an independent driver such as a hormonal signal for the hydraulic conductivity.