Tyrosine phosphorylation modulates rat vascular response to experimental endotoxemia in vivo and in vitro

Introduction

Endotoxemia is characterized by vascular hyporeactivity, hypotension and microcirculatory changes that are partially linked to the excess of nitric oxide production. The agents that can influence Ca²⁺ transport (affect Ca-ATPase) or modulate Ca²⁺ sensitivity of the smooth muscle contraction (modulate phosphorylation) may theoretically influence some of the above-mentioned effects.

Methods

We evaluated the effects of tyrosine phosphatase or kinase inhibitors, sodium orthovanadate (SOV) or genistein (GEN). The effects of these agents were examined in vitro, in a model of vascular hyporeactivity of sepsis, in rings of rat aorta (RA), with or without endothelium (± ENDO), or in human mesenteric artery (HMA). In vivo, the intestinal microcirculation (terminal ileum) of endotoxemic rats (LEW.1A) that received i.v. lipopolysaccharide (LPS), 15 mg/kg BW, was examined using intravital microscopy.

Results

In vitro

The nitric oxide production inhibitor L-NAME (5 × 10^-4) and cGMP inhibitor ODQ (5 × 10^-5) abolished LPS-induced hyporeactivity. GEN attenuated maximal tension (T_max) while SOV increased the response to PE; T_max (kg/g, dry muscle): controls vs SOV, RA (-ENDO): 0.87 ± 0.19 vs 1.42 ± 0.23 (10^-7); 1.56 ± 0.28 (10^-6) and 2.33 ± 0.69 (10^-5); RA (+ENDO): 0.88 ± 0.21 vs 1.53 ± 0.35 (10^-7); 1.35 ± 0.30 (10^-6) and 2.55 ± 0.68 (10^-5); and HMA (+ENDO): 1.12 ± 0.23 vs 0.37 ± 0.14 (10^-7); 2.06 ± 0.21 (10^-6) and 3.00 ± 0.07 (10^-5).

In vivo

In the LPS group GEN increased mucosal functional capillary density (FCD, cm/cm²; mean ± SD; LPS vs GEN, 105.5 ± 44.6 vs 174.7 ± 39.1; P = 0.018). SOV (7.5 mg/kg) increased FCD not only in mucosa (163.7 ± 40.0; P = 0.024) but also in the longitudinal muscular layer (LPS vs SOV, 111.9 ± 24.0 vs 172.2 ± 19.5; P < 0.001). Surprisingly, the SOV (15 mg/kg) alone (without LPS) increased leukocyte sticking in the venules V1 (LPS vs SOV, number of stickers/mm², 403.3 ± 113.9 vs 669.8 ± 150.8; P = 0.027).

Conclusion

The tyrosine phosphorylation pathway may play an important role in modulation of the LPS-induced vascular hyporeactivity and could enhance terminal ileum microcirculation. This might be a result of both modulation of tyrosine phosphorylation by genistein and sodium orthovanadate, and/or plasma membrane Ca-ATPase inhibition by SOV.