Clark R J, Rodnick K J
Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, USA.
J Exp Biol. 1998 May;201(Pt 10):1541-52. doi: 10.1242/jeb.201.10.1541.
We examined the morphometric and biochemical effects of ventricular hypertrophy in male rainbow trout (Oncorhynchus mykiss) during sexual maturation. Our investigation focused on characterizing the growth of ventricular layers, on cardiomyocyte dimensions (length, cross-sectional area and cell volume) and on the activities of enzymes involved in intermediary metabolism. Relative ventricle mass (100 x ventricle mass/body mass) increased by as much as 2.4-fold during sexual maturation [as defined by an increasing gonadosomatic index (100 x gonad mass/body mass)], and this resulted in an increased proportion of epicardium relative to endocardium. Ventricular enlargement was associated with increased length (+31 %) and transverse cross-sectional area (+83 %) of cardiomyocytes, which resulted in an expansion of up to 2.2-fold in mean myocyte volume (from 1233 to 2751 micron3). These results indicate that sexual maturation induces ventricular enlargement through myocyte hypertrophy. Cell length and cross-sectional area were similar in both myocardial layers, and myocytes were elliptical rather than circular in transverse cross section. Ventricular hypertrophy did not alter transverse cell shape, perhaps reflecting the maintenance of short diffusion distances for small molecules as cells hypertrophy. Myocyte hypertrophy could not account entirely for the sevenfold range of ventricle masses from different-sized fish, indicating that myocyte hyperplasia contributes substantially to ventricular growth as trout grow. Measurements of the maximal activities of metabolic enzymes demonstrated that ventricular hypertrophy was associated with (1) higher epicardial but not endocardial activities of citrate synthase (by 23 %) and beta-hydroxyacyl-CoA dehydrogenase (by 20 %); (2) lower activities of hexokinase (by 50 %) in both layers, and (3) no change in lactate dehydrogenase or pyruvate kinase activities, which were also similar between layers. These results suggest that the energetic needs of the hypertrophied trout ventricle may be met through increased reliance on fatty acid oxidation, particularly by the endocardium, but decreased reliance on glucose as a metabolic fuel in both layers.
我们研究了雄性虹鳟（Oncorhynchus mykiss）在性成熟过程中心室肥大的形态计量学和生化效应。我们的研究重点在于描述心室各层的生长情况、心肌细胞尺寸（长度、横截面积和细胞体积）以及参与中间代谢的酶的活性。相对心室质量（100×心室质量/体重）在性成熟期间（根据性腺体指数增加来定义，即100×性腺质量/体重）增加了高达2.4倍，这导致心外膜相对于心内膜的比例增加。心室增大与心肌细胞长度增加（+31%）和横截面积增加（+83%）相关，这导致平均心肌细胞体积扩大了2.2倍（从1233立方微米增加到2751立方微米）。这些结果表明，性成熟通过心肌细胞肥大诱导心室增大。两个心肌层的细胞长度和横截面积相似，心肌细胞在横切面上呈椭圆形而非圆形。心室肥大并未改变细胞的横向形状，这可能反映出随着细胞肥大，小分子的扩散距离保持较短。心肌细胞肥大并不能完全解释不同大小鱼类心室质量的7倍差异范围，这表明随着虹鳟生长，心肌细胞增生对心室生长有很大贡献。代谢酶最大活性的测量表明，心室肥大与以下情况相关：（1）心外膜中柠檬酸合酶（增加23%）和β-羟酰基辅酶A脱氢酶（增加20%）的活性较高，但心内膜中无此现象；（2）两层中己糖激酶的活性均较低（降低50%）；（3）乳酸脱氢酶或丙酮酸激酶的活性没有变化，且两层之间也相似。这些结果表明，肥大的虹鳟心室的能量需求可能通过增加对脂肪酸氧化的依赖来满足，特别是心内膜，但两层中对葡萄糖作为代谢燃料的依赖均降低。
