A blood-gas nomogram of the chick fetus: blood flow distribution between the chorioallantois and fetus

The importance of carbonic anhydrase II in red blood cells during exposure of chicken embryos to CO2

The importance of carbonic anhydrase (CA) during exposure of chicken embryos to CO(2) during the second half of incubation was investigated. The protein abundance and activity of CAII in erythrocytes was significantly higher in CO(2)-exposed embryos compared to normal conditions. Daily injections of acetazolamide (ATZ), an inhibitor of CA, increased blood P(CO2) and decreased blood pH in both control and CO(2)-incubated embryos. ATZ increased blood bicarbonate concentration in embryos exposed to normal atmosphere and in day-12 embryos exposed to high CO(2). The tendency of an increased blood potassium concentration in ATZ-injected embryos under standard atmospheric conditions might indicate that protons were exchanged with intracellular potassium. However, there was no evidence for such an exchange in CO(2)-incubated ATZ-treated embryos. This study shows for the first time that chicken embryos adapt to CO(2) during the second half of incubation by increasing CAII protein expression and function in red blood cells. This response may serve to "buffer" elevated CO(2) levels.

Development of cardiac form and function in ectothermic sauropsids

Evolutionary morphologists and physiologists have long recognized the phylogenetic significance of the ectothermic sauropsids. Sauropids have been classically considered to bridge between early tetrapods, ectotherms, and the evolution of endotherms. This transition has been associated with many modifications in cardiovascular form and function, which have changed dramatically during the course of vertebrate evolution. Most cardiovascular studies have focused upon adults, leaving the development of this critical system largely unexplored. In this essay, we attempt a synthesis of sauropsid cardiovascular development based on the limited literature and indicate fertile regions for future studies. Early morphological cardiovascular development, i.e., the basic formation of the tube heart and the major pulmonary and systemic vessels, is similar across tetrapods. Subsequent cardiac chamber development, however, varies considerably between developing chelonians, squamates, crocodilians, and birds, reflected in the diversity of adult ventricular structure across these taxa. The details of how these differences in morphology develop, including the molecular regulation of cardiac and vascular growth and differentiation, are still poorly understood. In terms of the functional maturation of the cardiovascular system, reflected in physiological mechanisms for regulating heart rate and cardiac output, recent work has illustrated that changes during ontogeny in parameters such as heart rate and arterial blood pressure are somewhat species-dependent. However, there are commonalities, such as a beta-adrenergic receptor tone on the embryonic heart appearing prior to 60% of development. Differential gross morphological responses to environmental stressors (oxygen, hydration, temperature) have been investigated interspecifically, revealing that cardiac development is relatively plastic, especially, with respect to change in heart growth. Collectively, the data assembled here reflects the current limited morphological and physiological understanding of cardiovascular development in sauropsids and identifies key areas for future studies of this diverse vertebrate lineage.

Non-invasive measurement of oxygen partial pressure, lateral diffusion and chorioallantoic blood flow under the avian eggshell

We measured P(O2) under the shell of avian eggs indirectly, by sealing 0.05 mL glass tubes to the shell, sealing them with mercury and using an oxygen microelectrode to measure the contained gas that equilibrates with the gas in the shell membranes. This technique requires a smaller area of contact with the shell and a shorter equilibration period than established techniques, and allows measurements at several locations simultaneously and over a long period of time without endangering the embryo. P(O2) under the shell of chicken eggs decreased to 14.3 kPa on the day before hatching (day 19). P(O2) was unstable during late development and differences up to 3.1 kPa occurred transiently on opposite sides of the equator. By waxing the shell around sampling tubes, we estimated Krogh's coefficient for lateral oxygen diffusion in the shell membranes at 1.1 mmol cm(-1) d(-1) kPa(-1), a value about a third of a previous estimate. Sampling of gas under sufficiently large regions of waxed shell allowed indirect measurements of chorioallantoic venous P(O2), without affecting embryonic respiration. Venous P(O2) was 3.8 kPa on day 19. Assuming 14.3 kPa represents arterialized blood leaving the chorioallantois, it became possible to calculate the effective chorioallantoic blood flow rate, which was 3.5 mL min(-1) on day 19.

The chorioallantoic artery blood flow of the chick embryo from stage 34 to 43

Chorioallantoic artery blood flow and heart rate were studied in the chick embryo from stage 34 until stage 43 (d 9-16 of 21-d incubation). Baseline blood flow profiles of the chorioallantoic artery were measured with a flow probe (Transonic) in 100 chick embryos. The eggs were opened at the air cell and placed in a small plexiglass box with a continuous gas flow of a N2/O2 mixture (5 L/min), at 38 degrees C and 60% humidity. The chorioallantoic artery was localized near the fetal abdomen and placed in the lumen of the Transonic flow probe. The heart rate was derived from the blood flow signal. The mean chorioallantoic artery blood flow rose from 0.35 +/- 0.14 mL/min (mean +/- SD) at stage 34 to 3.13 +/- 1.49 mL/min at stage 43 (R2 = 0.69, p < 0.0001), which correlated with an increase in body weight (1.51 +/- 0.18 g to 15.08 +/- 0.76 g). Heart rate increased from 195 +/- 38 beats/min at stage 34 to 289 +/- 13 beats/min at stage 43 (R2 = 0.38, p < 0.0001). The chorioallantoic artery blood flow, which in avian species correlates with umbilical blood flow in mammals, increased with incubation time as reported in the mammalian fetus. This study shows that the chick embryo could be useful as a preparation for further perinatal cardiovascular research.

Cardiogenic ballistograms of chicken eggs: comparison of measurements

In the incubated avian egg, minute movements occur that are synchronised with embryonic cardiac contractions. We previously developed two systems to noninvasively record this cardiogenic ballistic movement of the egg (referred to as the ballistocardiogram, BCG); one was based on applying an audiocartridge and the other a laser speckle phenomenon. A third system, which detects the ballistic movement as the measurement of displacement (referred to as displacement BCG), is applied in the present study, together with the previous two systems, to the ballistocardiography of the egg. The BCG is measured with three systems simultaneously for comparison. The differentiation of the displacement BCG produces a pattern identical to the BCG recorded by the cartridge method, and the integrated pattern of the latter BCG is identical to the displacement BCG. This indicates that the cartridge system detects the cardiogenic movement as the measure of velocity and it may be referred to as velocity BCG. The BCG by the laser speckle method is not related to that recorded by the other two systems, which may be referred to as movement BCG.

Oxygen uptake and chorioallantoic blood flow changes during acute hypoxia and hyperoxia in the 16 day chicken embryo

Oxygen consumption rate (MO2) of hen eggs was measured on incubation day 16 (37.8 degrees C, 55% humidity) during acute exposure (90 min) to ambient hyperoxia (FI02 = 0.42) or hypoxia (FIO2 = 0.105). During the last part of these exposures, an H2 washout method was used to estimate relative changes in chorioallantoic membrane (CAM) blood flow, taking as an index the net change in the H2 washout rate constant between any experimental condition and the circulation arrested egg. Doubling normoxic FIO2 increased MO2 to an asymptotic value which was 4% above the normal (P less than 0.05; MO2 in normoxia = 890 mumols/h) even after correcting for the normoxic increase in MO2 with time during development (delta MO2/delta t = 21.5 mumols/h2; P less than 0.001). Halving FIO2 reduced MO2 calculated in the same way to 388 mumols/h. The estimate of the CAM blood flow, relative to normoxia, was 1.12 in hyperoxia (not significant, P = 0.05) and 0.68 in hypoxia (P less than 0.001). The limited changes in CAM blood flow and MO2 during hyperoxia indicate that they are both already close to their maximal values in normoxia. During acute hypoxia the 16 day embryo behaves as an oxygen-conformer; however, the small relative decrease in MO2 per unit of the flow index observed during hyperoxia suggests that the embryo can regulate its CAM blood flow to a small extent. The survival of the embryo and its recovery from hypoxia without a detectable O2 repayment suggest small if any anaerobic regulatory pathways and indicate a true metabolic depression.