Cardiac morphodynamic remodelling in the growing eel (Anguilla anguilla)

The morphodynamic changes occurring during growthwere evaluated in the eel (Anguilla anguilla L.) heart.Using an in vitro working heart preparation, cardiacperformance of small (body mass 96.76±27.49·g; mean ±S.D.) and large (body mass 656±12·g; mean ± S.D.) eelswas compared under basal conditions and under loading(i.e. preload and afterload) challenges. A parallelmorphometric evaluation of the ventricle was made usinglight and transmission electron microscope images.The small eel hearts show a basal cardiac output lowerthan their large counterparts (heart rate fH, 38.93±2.82and 52.7±1.8·beats·min–1, respectively; stroke volume VS,0.27±0.017 and 0.37±0.016·ml·kg–1, respectively; means ±S.E.M.). The two groups show similar responses atincreasing preload, but differ remarkably at increasingafterload. Small eel hearts decreased VS at afterloadgreater than 3·kPa, in contrast to larger hearts, whichmaintained constant VS up to 6·kPa. These changes inmechanical performance are related to structuraldifferences.Compared with the small eels, the large eels show anincrease in the compacta thickness and in the diameter ofthe trabeculae in the spongiosa, together with reduction ofthe lacunary spaces. The increased compacta thicknessis attained by enlargements of both the muscular andvascular compartments and reduction of the interstitium;consequently, this layer appears more compacted. Bothcompacta and spongiosa show higher number of myocytestogether with reduced cross-sectional area andmyofibrillar compartment. The compacta also shows anincreased mitochondrial compartment. Our resultsdocument a cardiac morphodynamic remodelling in thegrowing eel.