Pythons are sit-and-wait predators that can eat extremely large meals under natural conditions. Digestion lasts for days and is associated with a large rise in oxygen consumption, and a rapid growth of many visceral organs (Secor and Diamond, 2005). Recently, it has been shown that the mass of the heart of Burmese pythons increases by almost 40% within 48 h after ingestion of meals amounting to 25% of the body mass of the snake (Andersen et al., 2005). This ventricular growth is associated with a large increase in mRNA for myosin heavy chain, the contractile element, and an unaltered wet to dry mass ratio (Andersen et al., 2005). In mammals, long-term changes in functional demands on the heart, for example during chronic exercise training, also increases heart size, termed physiological left ventricular hypertrophy (LVH). The training induced LVH is beneficial for cardiac function, as the increased stroke volume leads to decreased resting and submaximal heart rates, allowing for increased filling time. Cardiac growth in mammals is generally considered to be hypertrophic, whereas the heart of fish grows through both hyperplasic and hypertrophic mechanisms (Gamperl and Farrell, 2004). In the present study we examine the postprandial growth of the python heart using newly developed stereological methods (Brüel and Nyengaard, 2005). From perfusion formalin-fixed ventricles isotropic uniformly random sections were cut and embedded using isectors. The total number of myocyte nuclei per ventricle was estimated using the optical disector on thick sections. Preliminary results show that there was no change in the total number of myocytes indicating that the growth seen following feeding is hypertrophic i.e. the myocytes increase in size rather than number.
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Andersen JB, Rourke BC, Caiozzo, VJ, Bennett, AF, Hicks JW (2005). Physiology: postprandial cardiac hypertrophy in pythons.Nature 434: 37-38.
Gamperl KA, Farrell AP (2004). Cardiac plasticity in fishes: environmental influences and intraspecific differences. Journal of Experimental Biology 207: 2539-2550.
Brüel AM, Nyengaard JR (2005). Design-based stereological estimation of the total number of cardiac myocytes in histological sections. Basic Research in Cardiology 100: 1-9.