CROSSLEY, Dane A; HICKS, James W; THORNBURG, Kent; University of California, Irvine; University of California, Irvine; Oregon Health Sciences University: A Comparison of Cardiovascular Regulatory Mechanisms Present during Fowl Ontogeny; White leghorn vs. Bantam chickens.

The embryonic chicken has been used to study the physiology of the developing cardiovascular system in vertebrates and general patterns of cardiovascular development have been thoroughly characterized in the avian embryo. However given the morphological, incubation length and neonatal maturity differences found between avians the specific patterns of cardiovascular development established in a chicken strain may not apply universally to avian embryos. Even two strains of chicken may differ in their cardiovascular development. Thus we hypothesized that two chicken strains, the White leghorn and the Bantam, would exhibit differing patterns of cardiovascular function and regulation during development. Following the measurement of control parameters, each strain was tested for the presence and strength of autonomic tone on the cardiovascular systems and the presence of a cardiovascular chemoreflex. Resting embryonic arterial blood pressure was similar between the two strains ranging from 1 kPa to 2.75 kPa over similar periods of development. Each strain demonstrated a depression in heart rate and arterial pressure during exposure to 10% Oxygen. However Bantam embryos maintained a resting heart rate (~275 bt/min) above that of white leghorn (~240 bt/min) during the same period of development. Further, the strains showed different levels of cholinergic tone affects on heart rate with the Bantam chicken showing obvious tone while White leghorns lacked a response during the entire period of development. Thus these data indicate that while related chicken strains share several physiologic characteristics they also exhibit distinct differences in the development of autonomic cardiovascular regulation.