2,3,7,8-Tetrachlorodibenzo-p-dioxin alters cardiovascular and craniofacial development and function in sac fry of rainbow trout (Oncorhynchus mykiss)

Hallmark signs of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity in rainbow trout sac fry, are yolk sac edema, hemorrhage, craniofacial malformation, and growth retardation culminating in mortality. Our objective was to determine the role of cardiovascular dysfunction in the development of this toxicity. An embryotoxic TCDD dose (385 pg/g egg) caused a progressive reduction in blood how in rainbow trout sac fry manifested first and most dramatically in the 1(st) and 2(nd) branchial arches and vessels perfusing the lower jaw. Blood flow was reduced later in the infraorbital artery and occipital vein of the head as well as segmental vessels and caudal vein of the trunk. Reduced perfusion occurred last in gill branchial arteries involved with oxygen uptake and the subintestinal vein and vitelline vein involved with nutrient uptake. Although heart rate throughout sac fry development was not affected, heart size at 50 days post-fertilization (dpf) was reduced far more than body weight or length, suggesting that the progressive circulatory failure caused by TCDD is associated with reduced cardiac output. Craniofacial development was arrested near hatch, giving rise to craniofacial malformations in which the jaws and anterior nasal structures were underdeveloped. Unlike the medaka embryo, in which TCDD causes apoptosis in the medial yolk vein, endothelial cell death was not observed in rainbow trout sac fry. These findings suggest a primary role for arrested heart development and reduced perfusion of tissues with blood in the early-life stage toxicity of TCDD in trout.