Gender comparison of contractile performance and beta-adrenergic response in isolated rat cardiac trabeculae

It is known that gender can affect susceptibility to development of various cardiomyopathies. However, it is unclear whether basic mechanical contractile function of the myocardium differs between genders, whether they respond differently to stressors, or both. To test for a possible gender factor, contractile parameters of healthy, isolated myocardium were investigated under near physiological conditions. Right ventricular ultra-thin trabeculae from young adult LBN-f1 rats were electrically stimulated to isometrically contract at 37°C. No differences were found in developed force or kinetic parameters. In each muscle, the force-frequency relationship was measured at 4, 6, and 8 Hz, encompassing most of the in vivo range. Again, no differences were observed in force-frequency behavior; developed force rose from 21.6 ± 4.0 at 4 Hz to 30.3 ± 5.8 mN/mm² at 8 Hz in females and from 23.4 ± 3.4 to 29.8 ± 3.4 mN/mm² in males. The response to β-adrenergic stimulation was similar; at 1 μM isoproterenol, developed force increased to 34.5 ± 6.2 mN/mm² in females and 32.3 ± 3.2 mN/mm² in males (female vs. male, not significant). We conclude that basic mechanical performance of healthy isolated myocardium under physiological conditions is not different between males and females, and a different response to stress must underlie gender-based differences in cardiac performance.