Physiol. Res. 54: 661-670, 2005

Negative Inotropic Effect of Insulin in Papillary Muscles From Control and Diabetic Rats


1Department of Physiology, Faculty of Medicine, Charles University, Plzeň, Czech Republic and 2Department of Cardiology, Cardiovascular Research Institute Maastricht, Academic Hospital Maastricht, The Netherlands

Received July 1, 2004
Accepted, December 15, 2004
On-line available February 16, 2005

The inotropic effects of insulin in the rat heart are still incompletely understood. In this study, the effects of insulin on cardiac contraction were studied in right ventricular papillary muscles from both control rats and rats with chronic diabetes (lasting 16 weeks). Diabetes was induced by the application of streptozotocin (STZ) and the development of diabetes was documented by increased levels of blood glucose, by reduction in body weight and by decreased plasma concentrations of insulin. The contraction was significantly smaller in diabetic rats. Insulin (80 IU/l) reduced the contraction force in both control and diabetic groups. The post-rest potentiation of contraction was not influenced by insulin in control rats, but insulin increased it in diabetic rats. The negative inotropic effect of insulin was preserved in the presence of cyclopiazonic acid (3 μmol/l), a blocker of sarcoplasmic reticulum (SR) Ca2+ pump, in both control and diabetic groups. In contrast, the negative inotropic effect of insulin was completely prevented in the presence of nifedipine (3 μmol/l), a blocker of L-type Ca2+ current. We conclude that insulin exerts a significant negative inotropic effect in rat myocardium, both control and diabetic. This effect is probably related to processes of SR Ca2+ release triggering, whereas SR Ca2+ loading is not involved.

Key words
Insulin • Rat • Heart • Contraction • Diabetes


© 2005 by the Institute of Physiology, Czech Academy of Sciences