PRIMITIVE INTERVENTRICULAR SEPTUM, ITS PRIMORDIUM, AND ITS CONTRIBUTION IN THE DEFINITIVE INTERVENTRICULAR SEPTUM - IN-VIVO LABELING STUDY IN THE CHICK-EMBRYO HEART

Background: Because the studies on the embryological development of th e primitive interventricular septum have been done with postmortem mat erial, we do not know the site within the cardiac tube and the develop mental stage at which the primordium appears and its anatomical manife station in the mature heart, Consequently, we do not know its real con tribution to the constitution of the definitive interventricular septu m. Methods: With this purpose, we selected an adequate biological mode l, the chick embryo heart and the in vivo labelling technique, We plac ed a label of gelatin India ink in the ventral fusion line of both car diac primordia at the level of the interventricular grooves in the str aight tube heart (stage 9(+)HH), and we traced the ink up to the matur e heart (stage 36HH). We made histological sections of some hearts, of the zone where the label was found to investigate the first morpholog ical manifestation of the primitive interventricular septum, We also m ade microdissections and scanning electron microscopic studies. Result s: The label placed at stage 9(+)HH in the ventral fusion line of both cardiac primordia, at the level of the interventricular grooves, was found at stage 14HH in the greater curvature of the looped heart, oppo site the left interventricular groove, This label at stage 17HH was fo und in the apical trabecular region of the first cardiac septum (8-sha ped septum) and in the mature heart (stage 36HH) in the definitive int erventricular septum at the limit between the basal and the medial thi rd of the definitive interventricular septum. Conclusions: Firstly, th e primordium of the primitive interventricular septum appears at stage 9(+)HH, in the ventral fusion Line of both cardiac primordia at the l evel of the interventricular grooves, Secondly, its first morphologica l manifestation takes place at stage 17HH, and it forms the apical tra beculated region of the first cardiac septum (8-shaped septum), Thirdl y, the primitive interventricular septum gives origin to the middle an d apical third of the definitive interventricular septum. (C) 1997 Wil ey-Liss, Inc.