Ultrastructural examination of pulmonary arteries and arterioles in two chicken lines following in ovo administration of angiogenic agents

Abstract

Studies were conducted to evaluate measures that may indicate an increase in the susceptibility of broiler chickens to pulmonary hypertension syndrome in comparison to the Leghorn genetic line. The purpose of this experiment was to determine the effect of in ovo administration of the angiogenic factors adenosine and basic fibroblast growth factor (bFGF) on the embryonic development and ultrastructural characteristics of pulmonary arteries and lung arterioles in broiler and Leghorn lines. Every 12 hours on days 11-14 of incubation, embryos from both broiler and Leghorn lines were injected through the eggshell via the air cell onto the chorioallantoic membrane with Ringer solution, adenosine, or bFGF. Lung and pulmonary artery samples were obtained 4 to 7 days after treatment and processed for morphometric analysis using light and electron microscopy. Thickness of the tunica media was measured and expressed as the mean relative medial thickness (MRMT). Quantitative morphometric point count analysis was used to characterize the ultrastructural differences in embryonic angiogenesis of the pulmonary arteries and lung arterioles between broiler and Leghorn chicken lines. Organelles counted included: nuclei, rough endoplasmic reticulum, pinocytotic vesicles, mitochondria, and Golgi apparatus. In the extracellular matrix, ground substance, immature and mature elastin, collagen fibers, and cell membranes were counted. The Leghorn line had a thicker MRMT than the broiler line. In addition, the Leghorns had a greater proportion of vascular smooth muscle cell nuclei and a greater collagen to elastin ratio in the medial layer of the lung arterioles than the broilers. Adenosine accelerated growth of the medial layer of the lung arterioles causing early development in both lines. Administration of bFGF also resulted in an increase in MRMT for both the broiler and Leghorn lung arterioles. According to this evidence, it appears that Leghorn pulmonary vasculature was more mature than that of broilers since they exhibited greater medial thickness and more nuclei at hatch thus indicating more cells and augmented proliferative ability. Additionally, both adenosine and bFGF stimulated an increase in the MRMT of the pulmonary arterioles, which may indicate an elevated level of proliferation. However, the mechanism by which the medial thickness increased was not identified.