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

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). 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 μM). iNOS expression was assessed using reverse transcription-polymerase chain reaction. 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 μm) and DEX+LPS groups (6.7±0.3 μm) compared to saline (8.0±0.2 μm). 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 μm). Neither ETU nor dexamethasone improved contractile function in the LPS-treated animals. 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 μm). This effect was reversed by ETU (maximum change: 3.7±0.6 μm). Pre-treatment with dexamethasone prevented a significant fall in contraction amplitude (maximum change: 2.4±0.4 μm). 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 μm). Neither ETU nor dexamethasone restored contractile function in the LPS-treated group. 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. British Journal of Pharmacology (2000) 130, 1275–1282; doi:10.1038/sj.bjp.0703435