AJP - Heart and Circulatory Physiology, Vol 246, Issue 3 453-H458, Copyright © 1984 by American Physiological Society
Effects of graded insulin therapy on cardiac function in diabetic rats
M. Rubinstein, T. F. Schaible, A. Malhotra and J. Scheuer
To determine the effects of graded insulin therapy on cardiac function and
biochemistry, rats were made diabetic by streptozotocin (50 mg/kg) and
subsequently treated with either 3 U of insulin per day (D3) or 5 U/day
(D5) and compared with untreated diabetic rats (D phi) and a nondiabetic
control group (C). Blood glucose, water consumption, and heart and body
weights in D3 and D5 showed dose-dependent responses between those of D phi
and C. Cardiac function was studied at similar heart rates and similar left
atrial and aortic pressures in an isolated working heart apparatus. Hearts
from D phi showed significant decreases in end-diastolic pressure, peak
left ventricular systolic pressure, and positive dP/dt, whereas these
values in D3 and D5 were similar to those in C. The isovolumic relaxation
period was significantly longer in the D phi group, intermediate between D
phi and C in D3, and the same in D5 and C. Ca2+-ATPase activity of myosin
and actin-activated Mg2+-ATPase activity was depressed in D phi, partially
corrected in D3, and completely corrected in D5. Myosin isoenzyme
distribution displayed a shift from the predominant V1 pattern observed in
C to a predominant V3 pattern in D phi. Treatment with 3 U of insulin per
day partially corrected the isoenzyme abnormality, and treatment with 5
U/day restored the isoenzyme distribution to normal. These results indicate
that gross cardiac contractile function can be normalized with insulin
dosages that are not sufficient to correct hyperglycemia, polydipsia, or
body and heart weight.(ABSTRACT TRUNCATED AT 250 WORDS)
