AJP - Endocrinology and Metabolism, Vol 245, Issue 6 568-E574, Copyright © 1983 by American Physiological Society
Hyperosmolarity and cardiac function in chronic diabetic rat heart
D. R. Bielefeld, C. S. Pace and B. R. Boshell
Serum hyperosmolarity is commonly associated with the poorly controlled
diabetic state. The current investigation revealed that increased perfusate
osmolarity using either glucose or mannitol caused a gradual decline in the
aortic output of hearts from both normal and diabetic rats. However, aortic
output decreased less rapidly in hearts from diabetic rats. Decreasing the
extracellular calcium concentration to a level resulting in one-third of
the maximal aortic output elicited a greater and more prolonged increase in
aortic output from the diabetic compared with the normal heart when
perfusate osmolarity was progressively increased. The coronary conductance
of diabetic rat hearts improved when hyperosmolar solutions of either
mannitol or glucose were utilized, irrespective of the external calcium ion
concentration. In normal hearts, the coronary conductance tended to decline
at higher perfusate osmolarities. The increased coronary conductance may
play a role in the enhanced performance of diabetic hearts at higher levels
of osmolarity. Hyperosmolar solutions influence the performance of hearts
from chronic diabetic rats in a positive inotropic manner at low
extracellular calcium concentrations (1 mM). These lower calcium levels are
close to the normal physiological range of the freely ionized serum
calcium. This effect is greater in hearts from diabetic animals than from
normal animals and is similar to that obtained when perfusate calcium is
increased. The results suggest that hyperosmolar solutions enhance calcium
availability in the hearts of diabetic animals.
