Stress responses in avian embryos

American Zoologist, Dec 1997 by Epple, August, Gower, Barbara, Busch, Marc Ten, Gill, Tejendra, Et al

Messenger Substances in the allantoic fluid

As shown in Table 1, a number of messenger substances has so far been identified in the allantoic fluid; however, there is also a conspicuous absence of substances that occur at this stage in the plasma, amniotic fluid, tissues and/or yolk: free steroids; free thyroid hormones; insulin (Gill et al., 1983; Table 1 of this study). The absence of free testosterone is surprising since we detected it in the amniotic fluid. The presence of conjugated catecholamines and steroids in the allantoic fluid is also noteworthy. Clearly, these preliminary data need to be extended to understand the spectrum of messengers in the allantoic fluid. In particular, the presence of peptide hormones needs to be addressed since the amniotic fluid contains the glycoprotein inhibin (Rombauts et al., 1992). Furthermore, the time pattern of the appearance of hormones in the allantoic fluid must be considered. Woods et al. ( 1971 ) detected unidentified corticoids whose concentration strongly increased after day 14.

Catecholamines in allantoic and amniotic fluid, and in plasma

Figure 1 shows the distribution and total amounts of the free catecholamines in the three fluids. While the concentrations of dopamine (DA), norepinephrine (NE) and (E) epinephrine are identical in both plasma and allantoic fluid of the unstressed chicken embryo, the situation in the amniotic fluid differs. Here, the DA concentration is virtually identical with that of the other two fluids, but NE and E concentrations are essentially lower. The total estimated amounts of DA, NE and E in the allantoic fluid are 4 times higher than in plasma, while the total amount of DA in the amniotic fluid is twice that in the plasma. On the other hand, total NE and E in the amniotic fluid are much lower than in plasma. These findings (1) show that the NE and E concentrations in the amniotic fluid are hyporegulated vs. plasma and allantoic fluid, and (2) they suggest that there is an equilibrium of DA between all three fluids under non-stress conditions. On the other hand, the large total amounts of CAs in the allantoic fluid indicate a potential depot function. Excitatory amino acids in allantoic and amniotic fluid, and in plasma

Figure 2 shows the concentrations of six amino acids with potential messenger functions ("excitatory amino acids": Bloom, 1996). Once more, the amniotic fluid turns out to be a hyporegulated environment when compared with the other two fluids. Only ASP has approximately equal concentrations in all three fluids, and the GLU concentrations are about the same in amniotic and allantoic fluid. GABA and ASP concentrations are about the same in plasma and allantoic fluid, suggesting a possible equilibrium. On the other hand, the plasma concentrations of GLY and GLU are higher than in the allantoic fluid, whereas the opposite holds true for BALA and TAU. Thus, there are complex barriers between the three fluid compartments that affect five out of six potential messenger substances, ASP being an exception. Furthermore, the estimated total amounts of BALA and TAU in the allantoic fluid are 6 times and 2.8 times, respectively, higher than in plasma, indicating a storage function of the allantoic fluid.