Depression of myocardial force development after urea treatment

Left ventricle papillary muscles from Wistar male rats were studied before, during and after urea treatment. Urea was used at a concentration (17 mM) equivalent to a plasma level of 100 mg/dl. To verify whether these effects were produced by an increase in osmolarity, the study was repeated using 17 mM saccharose. The results showed that isometric force development decreased after washing out urea from the bath but inotropic responses to isoproterenol (IPA) and increased extracellular calcium attained values similar to those obtained before urea treatment. Thus, the percentual increments due to IPA and calcium were enhanced after urea treatment. The increased osmolarity due to saccharose did not produce any change in contraction or in the responses to inotropic interventions. It is suggested that urea modifies the excitation-contraction coupling mechanism in heart muscle, reducing the force developed at the steady state control level without reducing the responses to the inotropic interventions.