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

Levosimendan Relaxes Pulmonary Arteries and Veins in Precision-Cut Lung Slices - The Role of KATP-Channels, cAMP and cGMP

INTRODUCTION

Levosimendan is approved for left heart failure and is also used in right heart failure to reduce right ventricular afterload. Despite the fact that pulmonary arteries (PAs) and pulmonary veins (PVs) contribute to cardiac load, their responses to levosimendan are largely unknown.

MATERIALS AND METHODS

Levosimendan-induced vasorelaxation of PAs and PVs was studied in precision-cut lung slices from guinea pigs by videomicroscopy; baseline luminal area was defined as 100%. Intracellular cAMP- and cGMP-levels were measured by ELISA and NO end products were determined by the Griess reaction.

RESULTS

Levosimendan relaxed control PVs (116%) and those pre-constricted with an endothelinA-receptor agonist (119%). PAs were only relaxed if pre-constricted (115%). Inhibition of KATP-channels (glibenclamide), adenyl cyclase (SQ 22536) and protein kinase G (KT 5823) largely attenuated the levosimendan-induced relaxation in control PVs, as well as in pre-constricted PAs and PVs. Inhibition of BKCa (2+)-channels (iberiotoxin) and Kv-channels (4-aminopyridine) only contributed to the relaxant effect of levosimendan in pre-constricted PAs. In both PAs and PVs, levosimendan increased intracellular cAMP- and cGMP-levels, whereas NO end products remained unchanged. Notably, basal NO-levels were higher in PVs. The KATP-channel activator levcromakalim relaxed PAs dependent on cAMP/PKA/PKG and increased cAMP-levels in PAs.

DISCUSSION

Levosimendan initiates complex and divergent signaling pathways in PAs and PVs. Levosimendan relaxes PAs and PVs primarily via KATP-channels and cAMP/cGMP; in PAs, BKCa (2+)- and Kv-channels are also involved. Our findings with levcromakalim do further suggest that in PAs the activation of KATP-channels leads to the production of cAMP/PKA/PKG. In conclusion, these results suggest that levosimendan might reduce right ventricular afterload by relaxation of PAs as well as pulmonary hydrostatic pressure and pulmonary edema by relaxation of PVs.

Endothelin 1 and prostacyclin attenuate increases in hydraulic permeability caused by platelet-activating factor in rats

We have previously documented that endothelin 1 (ET-1) and prostacyclin (PGI2) decrease basal state hydraulic permeability (Lp). The aim of this study was to investigate the ability of ET-1 and PGI2 to modulate transendothelial fluid flux during situations in which Lp was artificially elevated with platelet-activating factor (PAF). We hypothesized that ET-1 and PGI2 administration before PAF exposure would prevent the increase in Lp secondary to PAF. In addition, in a potentially more clinically relevant situation, we also hypothesized that ET-1 and PGI2 administration after PAF exposure would attenuate the increase in Lp secondary to PAF. Microvascular Lp was measured in rat mesenteric postcapillary venules. Exposure to 10 nM PAF increased Lp 4-fold (P < 0.001). If the administration of 80 pM ET-1 or 10 microM PGI2 was completed before PAF exposure, no PAF-associated increase in Lp was observed (P < 0.001). The administration of ET-1 or PGI2 after PAF exposure attenuated the peak increase in Lp caused by PAF alone by 55% and 57%, respectively (P < 0.001). We conclude that ET-1 and PGI2 administration before PAF exposure prevents PAF-induced elevations in Lp, and in a more clinically relevant situation, ET-1 and PGI2 administered after PAF exposure attenuate the PAF-induced increase in Lp. Endothelin 1 and PGI2 receptors may provide important therapeutic targets for decreasing the microvascular fluid leak-associated morbidity resulting from shock and sepsis.

Glucagon-like peptide-1 protects mesenteric endothelium from injury during inflammation

Glucagon-like peptide-1 (GLP-1) is a proglucagon-derived hormone with cellular protective actions. We hypothesized that GLP-1 would protect the endothelium from injury during inflammation. Our aims were to determine the: (1) effect of GLP-1 on basal microvascular permeability, (2) effect of GLP-1 on increased microvascular permeability induced by lipopolysaccaride (LPS), (3) involvement of the GLP-1 receptor in GLP-1 activity, and (4) involvement of the cAMP/PKA pathway in GLP-1 activity. Microvascular permeability (L(p)) of rat mesenteric post-capillary venules was measured in vivo. First, the effect of GLP-1 on basal L(p) was measured. Second, after systemic LPS injection, L(p) was measured after subsequent perfusion with GLP-1. Thirdly, L(p) was measured after LPS injection and perfusion with GLP-1+GLP-1 receptor antagonist. Lastly, L(p) was measured after LPS injection and perfusion with GLP-1+inhibitors of the cAMP/PKA pathway. Results are presented as mean area under the curve (AUC)+/-SEM. GLP-1 had no effect on L(p) (AUC: baseline=27+/-1.4, GLP-1=1+/-0.4, p=0.08). LPS increased L(p) two-fold (AUC: LPS=54+/-1.7, p<0.0001). GLP-1 reduced the LPS increase in L(p) by 75% (AUC: LPS+GLP-1=34+/-1.5, p<0.0001). GLP-1 antagonism reduced the effects of GLP-1 by 60% (AUC: LPS+GLP-1+antagonist=46+/-2.0, p<0.001). The cAMP synthesis inhibitor reduced the effects of GLP-1 by 60% (AUC: LPS+GLP-1+cAMP inhibitor=46+/-1.5, p<0.0001). The PKA inhibitor reduced the effects of GLP-1 by 100% (AUC: LPS+GLP-1+PKA inhibitor=56+/-1.5, p<0.0001). GLP-1 attenuates the increase in microvascular permeability induced by LPS. GLP-1 may protect the endothelium during inflammation, thus decreasing third-space fluid loss.