KHANDOKER, A. H.*; DIZALOWSKI, E.; BURGGREN, W. W.; TAZAWA, H.; Muroran Institute of Technology, Japan; University of North Texas, USA; University of North Texas, USA; Muroran Institute of Technology, Japan: Cardiac rhythms of late pre-pipped and pipped chick embryos in altered oxygen environments
During the final stages of embryonic development in chickens, diffusive gas exchange through the chorioallantoic membrane (CAM) is progressively replaced by pulmonary respiration that begins with internal pipping (IP) of the CAM. IP was identified by detecting the breathing (respiration) signal by a condenser microphone attached hermetically on the eggshell (i.e., acoustorespirogram) on day 19 of incubation and 19-day-old embryos were divided into two groups; i.e., embryos without IP (referred to as Pre-IP embryos and designated as pre-pipped embryos) and those with IP (IP embryos, pipped embryos). In addition, 16- and 18-day-old embryos and 20-day-old externally pipped (EP) embryos were joined to experiments as pre-pipped embryos and pipped embryos, respectively. These late chick embryos with different modes of gas exchange were exposed to hyperoxic (100% O2) and hypoxic (10% 02/N2) environments and responses of baseline heart rate (HR) and HR fluctuation patterns were investigated. In hyperoxic environment, baseline HR of pre-pipped embryos remained unchanged and that of pipped embryos was depressed. In hypoxic environment, baseline HR of 16-day-old pre-pipped embryos was depressed, that of 18-day-old and Pre-IP embryos remained unchanged and pipped (IP and EP) embryos elevated baseline HR. Different responses of baseline HR between pre-pipped and pipped embryos may be related to different modes of gas exchange. Hyperoxia tended to depress HR accelerations in EP embryos. Hypoxia markedly depressed HR accelerations of pre-pipped and pipped embryos, tended to augment HR decelerations of pre-pipped embryos and caused respiratory sinus arrhythmia in EP embryos.
