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ORIGINAL ARTICLE

Systolic Elastance and Resistance in the Regulation of Cardiac Pumping Function in Early Streptozotocin-Diabetic Rats

Kuo-Chu Chang^*,1, Huey-Ming Lo and Yung-Zu Tseng^*,

^* Department of Physiology and
Department of Internal Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan; and
Department of Medicine, Provincial Tao-Yuan General Hospital, Tao-Yuan, Taiwan

We determined the roles of maximal systolic elastance (E_max) and theoretical maximum flow (_max) in the regulation of cardiac pumping function in early streptozotocin (STZ)-diabetic rats. Physically, E_max can reflect the intrinsic contractility of the myocardium as an intact heart, and _max has an inverse relation to the systolic resistance of the left ventricle. Rats given STZ 65 mg/kg i.v. (n = 17) were divided into two groups, 1 week and 4 weeks after induction of diabetes, and compared with untreated age-matched controls (n = 15). Left ventricular (LV) pressure and ascending aortic flow signals were recorded to calculate E_max and _max, using the elastance-resistance model. After 1 or 4 weeks, STZ-diabetic animals show an increase in effective LV end-diastolic volume (V_eed), no significant change in peak isovolumic pressure (P_isomax), and a decline in effective arterial volume elastance (E_a). The maximal systolic elastance E_max is reduced from 751.5 ± 23.1 mmHg/ml in controls to 514.1 ± 22.4 mmHg/ml in 1- and 538.4 ± 33.8 mmHg/ml in 4-week diabetic rats. Since E_max equals P_isomax/V_eed, an increase in V_eed with unaltered P_isomax may primarily act to diminish E_max so that the intrinsic contractility of the diabetic heart is impaired. By contrast, STZ-diabetic rats have higher theoretical maximum flow _max (40.9 ± 2.8 ml/s in 1- and 44.5 ± 3.8 ml/s in 4-week diabetic rats) than do controls (30.7 ± 1.7 ml/s). There exists an inverse relation between _max and E_a when a linear regression of _max on E_a is performed over all animals studied (r = 0.65, p < 0.01). The enhanced _max is indicative of the decline in systolic resistance of the diabetic rat heart. The opposing effects of enhanced _max and reduced E_max may negate each other, and then the cardiac pumping function of the early STZ-diabetic rat heart could be preserved before cardiac failure occurs.

Key Words: streptozotocin-diabetic rats • cardiac systolic mechanics • maximal systolic elastance • theoretical maximum flow • effective arterial volume elastance

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