Inotropic response to endothelin-1, isoprenaline and calcium in cardiomyocytes isolated from endotoxin treated rats: effects of ethyl-isothiourea and dexamethasone.

J P Spiers, E J Kelso, J D Allen, B Silke, B J McDermott

Index: Br. J. Pharmacol. 130(6) , 1275-82, (2000)

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Abstract

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.