Gender and post-ischemic recovery of hypertrophied rat hearts

Abstract

Background: Gender influences the cardiac response to prolonged increases in workload, with differences at structural, functional, and molecular levels. However, it is unknown if post-ischemic function or metabolism of female hypertrophied hearts differ from male hypertrophied hearts. Thus, we tested the hypothesis that gender influences post-ischemic function of pressure-overload hypertrophied hearts and determined if the effect of gender on post-ischemic outcome could be explained by differences in metabolism, especially the catabolic fate of glucose.

Methods: Function and metabolism of isolated working hearts from sham-operated and aortic-constricted male and female Sprague-Dawley rats before and after 20 min of no-flow ischemia (N = 17 to 27 per group) were compared. Parallel series of hearts were perfused with Krebs-Henseleit solution containing 5.5 mM [5-3H/U-14C]-glucose, 1.2 mM [1-14C]-palmitate, 0.5 mM [U-14C]-lactate, and 100 mU/L insulin to measure glycolysis and glucose oxidation in one series and oxidation of palmitate and lactate in the second. Statistical analysis was performed using two-way analysis of variance. The sequential rejective Bonferroni procedure was used to correct for multiple comparisons and tests.

Results: Female gender negatively influenced post-ischemic function of non-hypertrophied hearts, but did not significantly influence function of hypertrophied hearts after ischemia such that mass-corrected hypertrophied heart function did not differ between genders. Before ischemia, glycolysis was accelerated in hypertrophied hearts, but to a greater extent in males, and did not differ between male and female non-hypertrophied hearts. Glycolysis fell in all groups after ischemia, except in non-hypertrophied female hearts, with the reduction in glycolysis after ischemia being greatest in males. Post-ischemic glycolytic rates were, therefore, similarly accelerated in hypertrophied male and female hearts and higher in female than male non-hypertrophied hearts. Glucose oxidation was lower in female than male hearts and was unaffected by hypertrophy or ischemia. Consequently, non-oxidative catabolism of glucose after ischemia was lowest in male non-hypertrophied hearts and comparably elevated in hypertrophied hearts of both sexes. These differences in non-oxidative glucose catabolism were inversely related to post-ischemic functional recovery.

Conclusion: Gender does not significantly influence post-ischemic function of hypertrophied hearts, even though female sex is detrimental to post-ischemic function in non-hypertrophied hearts. Differences in glucose catabolism may contribute to hypertrophy-induced and gender-related differences in post-ischemic function.

Figure 1

Post-ischemic mass-corrected function of hypertrophied and non-hypertrophied hearts from male and female rats. Open circle, male non-hypertrophied hearts; open square, male hypertrophied hearts; filled circle, female non-hypertrophied hearts; filled square, female hypertrophied hearts. *, vs. sex-matched non-hypertrophied hearts (p < 0.05). #, vs. corresponding male hearts (p < 0.05). Numbers per group: 27 male non-hypertrophied hearts, 21 male hypertrophied hearts, 17 female non-hypertrophied hearts, and 18 female hypertrophied hearts. Values are mean ± SEM.

Figure 2

Glycolysis (A), glucose oxidation (B), palmitate oxidation (C), and lactate oxidation (D) in hypertrophied and non-hypertrophied hearts from male and female rats. White bar, male non-hypertrophied hearts; black bar, male hypertrophied hearts; light grey bar, female non-hypertrophied hearts; dark grey bar, female hypertrophied hearts. *, vs. sex-matched non-hypertrophied hearts at same time period (p < 0.05). #, vs. pre-ischemic value (p < 0.05). $, vs. corresponding male hearts at same time period (p < 0.05). Numbers per group: 12 to 16 male non-hypertrophied hearts, 8 to 14 male hypertrophied hearts, and 6 to 8 female non-hypertrophied hearts, 6 to 8 female hypertrophied hearts. Values are mean ± SEM.

Figure 3

Relationship of post-ischemic contractile function to rates of non-oxidative glycolysis in hypertrophied and non-hypertrophied hearts from male and female rats. Percent (%) Recovery of left ventricular external work was calculated as the quotient of post-ischemic and pre-ischemic hydraulic power multiplied by 100. Non-oxidative glycolysis was calculated as the difference between rates of glycolysis and glucose oxidation. Regression analysis was performed using data from individual hearts (N = 33 hearts; R = -0.49, p < 0.05) and is expressed as mean data per group (N = 5 to 12 per group). Values are mean ± SEM. Open circle, Male Control. Closed circle, Male hypertrophy. Open square, Female Control. Closed square, Female Hypertrophy.

Figure 4

Representative immunoblots of key myocardial enzymes and proteins involved in glucose metabolism in non-hypertrophied (Control) and hypertrophied (Hypertrophy) hearts from male (Male Pathologic Hypertrophy) and female (Female Pathologic Hypertrophy) hearts. Each lane represents a single heart. GLUT-4, glucose transport protein-4; HKII, hexokinase-II; PFK-1, phosphofructokinase-1; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; PDC E1α, pyruvate dehydrogeanse complex E1α subunit.

Figure 5

Representative immunoblots of myocardial enzymes and proteins involved in fatty acid oxidation in non-hypertrophied (Control) and hypertrophied (Hypertrophy) hearts from male (Male Pathologic Hypertrophy) and female (Female Pathologic Hypertrophy) hearts. Each lane represents a different heart. MCAD, medium chain acyl-CoA dehydrogenase; LCAD, long-chain acyl-CoA dehydrogenase.

Figure 6

Densitometric analysis of selected myocardial enzymes and proteins involved in myocardial glucose metabolism in non-hypertrophied and hypertrophied hearts from male and female rats. (A) Enolase-α, (B) Enolase-β, (C) phosphofructokinase-1, and (D) pyruvate dehydrogeanse complex E1α subunit. White bar, male non-hypertrophied hearts; black bar, male hypertrophied hearts; light grey bar, female non-hypertrophied hearts; dark grey bar, female hypertrophied hearts. *, vs. sex-matched non-hypertrophied hearts (p < 0.05). $, vs. corresponding male hearts (p < 0.05). Values are expressed in arbitrary densitometry units, normalized to corresponding GAPDH densitometry units obtained from the same immunoblot. Numbers per group: 12 to 16 male non-hypertrophied hearts, 8 to 14 male hypertrophied hearts, and 6 to 8 female non-hypertrophied hearts, 6 to 8 female hypertrophied hearts. Values are mean ± SEM.