Effect of Environmental Hypothermia on Vitelline Artery Blood Pressure and Vascular Resistance in the Stage 18, 21, and 24 Chick Embryo

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Abstract
We studied the effect of environmental hypothermia on arterial blood pressure, dorsal aortic blood flow, and vascular resistance in stage 18, 21, and 24 chick embryos. The arterial pressure was measured with a servo-null micropressure system. Mean dorsal aortic blood flow was calculated from pulsed-Doppler measurement of mean dorsal aortic blood velocity and dorsal aortic diameter. Vascular resistance was calculated by dividing mean vitelline arterial blood pressure by dorsal aortic blood flow. Sequential data were obtained at temperatures of 34.7, 31.1, and 34.1° C. At stage 21, the vitelline arterial blood pressure decreased from 0.82 ± 0.03 (x̄ ± SEM) to 0.72 ± 0.03 mm Hg on cooling and increased from 0.66 ± 0.05 to 0.87 ± 0.06 mm Hg on rewarming (p < 0.05). At stage 21, mean dorsal aortic blood flow decreased from 0.49 ± 0.02 to 0.33 ± 0.02 mm3/s with cooling and increased from 0.34 ± 0.02 to 0.47 ± 0.02 mm3/s with rewarming. The vascular resistance in stage 21 embryos increased after cooling from 1.68 ± 0.19 to 2.23 ± 0.39 mm Hg/mm3/s (x̄ ± 95% confidence interval). The changes were similar in stage 18 and 24 embryos. We conclude that the reduction of vitelline artery blood pressure resulted from a decrease in cardiac output. In addition, we noted that the vitelline arterial vascular bed can constrict in response to hypothermia prior to autonomic innervation. These changes in hemodynamics may be a teratogenic mechanism for hypothermia-induced cardiac defects in the chick embryo.