Inotropic response to endothelin-1, isoprenaline and calcium in cardiomyocytes isolated from endotoxin treated rats: effects of ethyl-isothiourea and dexamethasone.
1. The contractile effects of endothelin-1, isoprenaline and extracellular calcium were assessed on ventricular cardiomyocytes isolated from lipopolysaccharide-treated rats. The involvement of nitric oxide was investigated using dexamethasone (in vivo) and ethyl isothiourea (in vitro). 2. Male Wistar rats (n=70) were injected with either saline (1 ml kg(-1)) or lipopolysaccharide (LPS; 5 mg kg(-1)) alone, or following pre-treatment with dexamethasone (DEX+LPS; 5 mg kg(-1)). Ventricular cell shortening was recorded using a video edge detection system, and concentration-response relationships were established for endothelin-1, isoprenaline and calcium, in the absence or presence of ethyl isothiourea (ETU; 10 microM). iNOS expression was assessed using reverse transcription-polymerase chain reaction. 3. iNOS mRNA expression was greater (P<0.001) in the LPS (iNOS/GAPDH ratio: 0.90+/-0.09) treated group compared to saline (iNOS/GAPDH ratio: 0.36+/-0.02). Baseline contractile amplitude was reduced (P<0.05) in the LPS (7.3+/-0.2 microm) and DEX+LPS groups (6.7+/-0.3 microm) compared to saline (8. 0+/-0.2 microm). 4. The concentration-dependent contractile response to endothelin-1 was attenuated (P<0.05) in the LPS group compared to saline (maximum change: 0.45+/-0.2 vs 1.8+/-0.2 microm). Neither ETU nor dexamethasone improved contractile function in the LPS-treated animals. 5. The concentration-dependent increase in the contractile response to isoprenaline was attenuated in the LPS-treated group compared to saline (P<0.05; maximum change: 1.7+/-0.4 vs 3.1+/-0.4 microm). This effect was reversed by ETU (maximum change: 3.7+/-0.6 microm). Pre-treatment with dexamethasone prevented a significant fall in contraction amplitude (maximum change: 2.4+/-0.4 microm). 6. The contractile response to calcium was reduced (P<0.05) in the LPS group compared to saline (maximum change: 8.7+/-0.6 vs 10.7+/-0.8 microm). Neither ETU nor dexamethasone restored contractile function in the LPS-treated group. 7. In conclusion, a nitric oxide-mediated inhibitory pathway is not responsible for the diminished contractile response to either endothelin-1 or extracellular calcium, but contributes to the hyporesponsiveness to isoprenaline in lipopolysaccharide treated rats.
Spiers
J P
JP
Department of Physiology, School of Clinical Medicine, The Queen's University of Belfast, Medical Biology Centre, UK. spiersj@tcd.ie
Kelso
E J
EJ
Allen
J D
JD
Silke
B
B
McDermott
B J
BJ
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019332:Endothelin-1 / Q000494:pharmacology*; D004731:Endotoxins / Q000494:pharmacology*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology*; D007550:Isothiuronium / Q000031:analogs & derivatives / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D019001:Nitric Oxide Synthase / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D016276:Ventricular Function
D019332:Endothelin-1; D004731:Endotoxins; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D007550:Isothiuronium; C007687:etiron; D003907:Dexamethasone; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D007545:Isoproterenol; D002118:Calcium