STEREOLOGICAL STUDY OF STAGE-34 CHICKEN HEARTS WITH LOOPING DISTURBANCES AFTER RETINOIC ACID TREATMENT - DISTURBED GROWTH OF MYOCARDIUM ANDATRIOVENTRICULAR CUSHION TISSUE

Background: In a previous study retinoic acid treatment of chicken hea rts has resulted in a spectrum of looping disturbances. Because of a d ecrease in contraction force of these hearts, the myocardial volume wa s hypothesized to be altered. Because retinoic acid has been suggested to influence endocardial cushion volumes, these were estimated as wel l. Methods: The previously studied hearts were used for estimating the absolute volumes of the atrial and ventricular myocardium and of the endocardial cushions by means of Cavalieri's principle. To measure the surface density of the trabeculations according to the isector method , we used retinoic acid treated hearts, which were perfusion fixed and in which the sections were isotropic uniform random. The volumes and surface densities found in the three morphologically distinguished gro ups, i.e., intact septum, isolated ventricular septal defect and doubl e outlet right ventricle, were compared with those in shams. Results: A significant volume decrease was found in the right ventricular free wall myocardium of the double outlet right ventricle. No significant d ifferences were found in the surface densities of the trabeculae. The volume of the atrioventricular cushion tissue in the double outlet rig ht ventricle hearts was significantly increased. The morphological spe ctrum observed previously was also expressed in the right ventricular myocardial volume, which appeared to decrease from the least to the mo st malformed hearts, and in the volume of the atrioventricular cushion tissue, which appeared to increase. Conclusions: Several studies have shown pathology in myocardial and cushion tissue after retinoic acid treatment. In this study we ha ve found a decreased growth of the righ t ventricular myocardium and an increased growth of the atrioventricul ar cushion tissue. We suggest that the previously found looping distur bance causes changed hemodynamics, as reported elsewhere, and that the se result in changes in growth. We cannot exclude a direct effect of r etinoic acid on the myocardium, which has to explain the looping distu rbance. (C) 1997 Wiley-Liss, Inc.