Quantitative Structural Analysis of Athletic Hearts of Racing Pigeons

Abstract

Morphometric measurements of the hearts in 48 racing pigeons (RP), a breed selected for long-distance flying, aged from 3 months to 10 years were compared with data from 65 feral pigeons (FP), the same breed as RP (Columva livia domestica), in order to clarify the quantitative morphologic features of athletic hearts of RP. Heart weight to body weight ratios were 15.3-16.8% higher in RP than in FP at a given age (P<0.01). Although there was no difference between RP and FP in cross-sectional area of the septal and left ventricular wall in a given transverse plane, myocyte cross-sectional area, and the capillary density calculated as number of capillaries per unit area of the myocardium, the dimensions of the left ventricular cavity and myocyte length were both significantly greater in RP (29.7% and 16.2-20.1%, respectively; P<0.001). From these findings, the greater myocyte length contributed to the higher heart weight to body weight ratio of RP and to the enlargement of the dimensions of the left ventricular cavity without a proportionate increase in the septal and left ventricular free wall area. In conclusion, the results of the present study suggest that athletic hearts observed in RP can be viewed as a form of the eccentric hypertrophy typical of volume-overloaded hearts that occurs with dynamic exercise training in long-distance runners, and that large hearts in RP has a genetic basis.