Endothelin-1 reduces mesenteric microvascular hydraulic permeability via cyclic AMP and protein kinase A signal transduction

We have previously shown that endothelin-1 (ET-1) decreases microvascular hydraulic permeability. In this study, we tested the hypothesis that ET-1 exerts its permeability-decreasing effect through cAMP, cGMP, and protein kinase A (PKA) by determining the effect of ET-1 on venular fluid leak during inhibition of cAMP synthesis, inhibition of cGMP degredation, and inhibition of PKA. Rat mesenteric venules were cannulated to measure hydraulic permeability, Lp (units × 10−7 cm/(s cmH2O)). Lp was measured during continuous perfusion of 80 pM ET-1 and either (1) an inhibitor of cAMP synthesis (10 μM 2′,5′ddA), (2) an inhibitor of cGMP degradation (100 μM Zaprinast), or (3) an inhibitor of PKA (10 μM H-89). Inhibition of cAMP synthesis blocked the permeability decreasing effects of ET-1. The peak Lp of the cAMP inhibitor alone and with ET-1 was 4.11 ± 0.53 and 3.86 ± 0.19, respectively (p = 0.36, n = 6). Inhibition of cGMP degradation did not block the permeability decreasing effects of ET-1. The peak Lp during inhibition of cGMP degradation alone and with ET-1 was 2.26 ± 0.15 and 1.44 ± 0.09, respectively (p < 0.001, n = 6). Inhibition of PKA activation blocked the permeability decreasing effects of ET-1. The peak Lp of the PKA inhibitor alone and with ET-1 was 2.70 ± 0.15 and 2.59 ± 0.15, respectively (p = 0.38, n = 6). The data support the notion that the signal transduction mechanism of ET-1 with regard to decreasing microvascular fluid leak involves cAMP production and PKA activation, but not cGMP degradation. Further understanding of intracellular mechanisms that control microvascular fluid leak could lead to the development of a pharmacologic therapy to control third space fluid loss in severely injured or septic patients.