Negative Inotropic Effect
of Insulin in Papillary Muscles From Control and Diabetic Rats
J. ŠVÍGLEROVÁ1, J. KUNCOVÁ1,
M. ŠTENGL1,2
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
Summary
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
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