Effect of the endothelin receptor antagonist CPU0213, and its modulation by rifampin, on cardiac and vascular tissue following chronic isoproterenol treatment

1. The aim of the present study was to investigate the effects of the endothelin (ET) receptor antagonist CPU0213 on cardiac and vascular tissues after impairment by chronic isoproterenol treatment. Because rifampin reduces plasma concentrations of CPU0213, the modulation of the effects of CPU0213 by rifampin was also investigated. 2. Thirty rats were randomly divided into five groups as follows: (i) control; (ii) isoproterenol treated (1 mg/kg, s.c., for 10 days); (iii) isoproterenol treated with a single injection of CPU0213 (30 mg/kg, s.c., on Day 11); (iv) isoproterenol treated with a single injection of rifampin (50 mg/kg, p.o., on Day 11); and (v) isoproterenol treated with rifampin gvien 3 h before CPU0213 on Day 11. Serum concentrations of CPU0213, haemodynamic and biochemical parameters, mRNA and protein expression levels of the ET(A) receptor (ET(A)R), calstabin 2 (FKBP12.6) and sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA2a), and vasoactivity of the thoracic aorta were determined. 3. Haemodynamic parameters, serum creatine phosphokinase, lactate dehydrogenase and malondialdehyde levels, mRNA and protein expression of FKBP12.6, SERCA2a and vascular responses were altered following isoproterenol treatment for 10 days. These effects were significantly reversed by CPU0213. Rifampin caused a reduction in serum concentrations of CPU0213 to 36% of control values. However, this reduction in the serum concentrations of CPU0213 did not affect its effects on the heart, but did eliminate its beneficial action on vascular responses. Rifampin alone had no effect these paramters. 4. The data suggest that isoproterenol acts on the myocardium to cause cardiac insufficiency by upregulating ET(A)R and downregulating FKBP12.6 and SERCA2a. These effects were ameliorated by CPU0213, but were resistant to rifampin-induced decreases in plasma CPU0213 concentrations. In vascular tissue, the pathological effects of isoproterenol were ameliorated by CPU0213; however, lowering plasma CPU0213 concentrations with rifampin did partly eliminate the amelioration in vascular activity in respones to CPU0213.