Tissue oxygen partial pressure in organs of chickens in the second half of embryogenesis and first days after hatching

The aim of this study is to measure the oxygen partial pressure (pO₂) in developing chicken tissues, namely, in the cerebral hemispheres, liver, m. pectoralis, and m. gastrocnemius, and to estimate the correlation of pO₂ with the earlier measured values (laser Doppler flowmetry) of volume blood flow (BF) in these organs. We have studied 10-, 15-, and 19-day-old embryos and 4-day-old chickens anesthetized with urethane. The pO₂ has been measured in the surface layers of organs with a membrane amperometric Clark-type O₂ electrode (cathode diameter of approximately 50 μm) placed in the center of the sensor unit (outer diameter of 3.4 mm). Noticeable distinctions between both the tissue pO₂ values in different organs and the dynamics of their changes during the observation time have been recorded. The following differences are the most important: (1) the lowest pO₂} {cm(and BF) is observed in the brain and, especially, in the liver of 10-day-old embryos; (2) in the subsequent period of embryogenesis, the pO₂ in the brain increases 1.9-fold (BF also increases), falls 1.7-fold in m. pectoralis, and displays minor changes in the liver and m. gastrocnemius on the background of constant BF value in the liver and both muscles; and (3) after hatching, pO₂ in the liver and m. pectoralis increases severalfold (BF increases too) but does not change in a statistically significant manner in the brain and m. gastrocnemius despite an increase in BF (more pronouncedly in the muscle). Two possible mechanisms underlying the changes in the tissue pO₂ in developing chicken organs have been proposed: one is determined by the specific features of intracardiac blood flows and the other is associated with the oxyhemoglobin dissociation pattern in the blood capillary circulation in the organs, determined by the specific features in its oxidative metabolism.