Effects of polychlorinated biphenyls on thyroid hormones and liver type I monodeiodinase in the chick embryo

Polychlorinated biphenyls (PCBs) are widespread environmental contaminants which can biomagnify to higher tropic level organisms including birds. Circulating thyroid hormones (TH) and growth are decreased by PCB exposure. The first set of studies investigated the effects of PCBs on an enzyme responsible for TH homeostasis, hepatic type I monodeiodinase (MDI) in chicken embryos. Fertile chicken eggs were injected with Aroclor 1242, Aroclor 1254, 2,2',6, 6'-tetrachlorobiphenyl (TCB), 3,3',4,4'-TCB, or 3,3',5,5'-TCB on Day 0 and studies were terminated on Incubation Day 21. Hepatic MDI activity was reduced in embryos treated with the Aroclor mixtures. No effects on MDI activities were observed after PCB isomer treatment. Liver weights from embryos treated with Aroclor 1242 were decreased. In the second study, chick embryos were exposed to these same PCBs in order to evaluate their effect on circulating THs and growth. Treatment with PCBs had no effect on body weight. Femur length were decreased with Arcolor 1242 treatment. A decrease in plasma concentration of thyroxine was observed after treatment with Aroclor 1242 and Aroclor 1254. Based on these findings, it is evident that PCBs alter the thyroid axis. Bird circulating TH levels, which are generally reported, may not be a good biomarker for low-dose exposure to PCBs. However, the reduction in MDI activity was more sensitive to PCB mixture exposure and may be a useful biomarker.

Enhancement in the lysozyme activity of the hen egg white foam matrix by cross-linking in the presence of N-acetyl glucosamine

Lysozyme naturally present in raw hen egg white was immobilized by cross-linking the egg white foam with glutaraldehyde. Inclusion of N-acetyl glucosamine, a competitive inhibitor of lysozyme, was found to enhance the yield of lysozyme activity by fivefold.

Sites of aspecific ATP-phosphohydrolase activity in the branchial region of chick embryos, with particular emphasis on the myogenic cell population

The distribution pattern of unspecific ATP-phosphohydrolase (ATP-PH) activity was studied in serial sections through the branchial region of chick embryos from HH stage 14 to 27. A selective reaction was found in the prospective myogenic mesoderm of voluntary muscles of the first three branchial arches. This property initially characterized uncondensed myogenic cell populations in the mandibular and hyoid arches and appeared later on in the third arch. In each case, the positive premuscular mesoderm was closely apposed to the lateral wall of the corresponding aortic arch. Myogenic primordia retained a strong ATP-PH activity up to stage 27 when they began to segregate into smaller premuscular units. Discrete changes observed in the mandibular and hyoid blastemas suggested that non reacting cells probably of neural crest origin invade their proximal core and contribute to the subsequent pathfinding of muscular nerves. Other selective sites of ATP-PH reactivity were detected in the odd-numbered rhombomeres, rhombencephalic floorplate, notochord, arterial endothelial cells, prospective dermis and perichondrium.

Protective role of thyroxine in methylparathion intoxicated chick embryos

The efficacy of thyroxine against methylparathion poisoning in chick embryos was studied. The mortality rate and survival rate, frequency of abnormalities, growth rate and size of embryos, and also the change in cholinesterase activity were determined to evaluate the protective effect of thyroxine and atropine. It was observed that the survival rate, growth rate and size, and the cholinesterase activity significantly declined in the methylparathion treated group while the mortality rate and the frequency of abnormalities increased. When thyroxine was given, a significant reversal in these parameters was seen, indicating an effective protective action of thyroxine against methylparathion intoxication in chick embryos. The results also showed that the therapeutic treatment of the combination of thyroxine and atropine did not further improve the effects. Since in many respects, chick embryo development parallels that of mammalian embryos, a short term use of thyroxine as an effective protective agent against organophosphate methylparathion (perhaps other compounds) poisoning may have important implications.

A novel role for vitamin K1 in a tyrosine phosphorylation cascade during chick embryogenesis

The development of the embryo is dependent upon a highly coordinated repertoire of cell division, differentiation, and migration. Protein-tyrosine phosphorylation plays a pivotal role in the regulation of these processes. Vitamin K-dependent gamma-carboxylated proteins have been identified as ligands for a unique family (Tyro 3 and 7) of receptor tyrosine kinases (RTKs) with transforming ability. The involvement of vitamin K metabolism and function in two well characterized birth defects, warfarin embryopathy and vitamin K epoxide reductase deficiency, suggests that developmental signals from K-dependent pathways may be required for normal embryogenesis. Using a chick embryogenesis model, we now demonstrate the existence of a vitamin K1-dependent protein-tyrosine phosphorylation cascade involving c-Eyk, a member of the Tyro 12 family, and key intracellular proteins, including focal adhesion kinase (pp125FAK), paxillin, and pp60src. This cascade is sensitive to alteration in levels or metabolism of vitamin K1. These findings provide a major clue as to why, in the mammalian (and human) fetus, the K-dependent proteins are maintained in an undercarboxylated state, even to the point of placing the newborn at hemorrhagic risk. The precise regulation of vitamin K1-dependent regulatory pathways would appear to be critical for orderly embryogenesis.

In vivo gene transfer into the blastoderm of early developmental stage of chicken

An attempt was made to improve gene transfer into chick embryos in order to produce transgenic chickens. The beta-actin-lacZ/MiwZ, a marker gene in transfection reagent, was injected into the blastodisc of either unincubated fertilized eggs (stage X) or eggs induced from the shell gland by treating the hens intravenously with oxytocin or arginine vasotocin (stages IV-VI). All the manipulated embryos were incubated to reach stage XIV, the period at which primordial germ cells (PGCs) migrate from the germinal crescent to the gonadal anlage via the blood stream. MiwZ was detected in the embryos, extraembryonic tissues and blood by the histochemical staining method of beta-galactosidase. The MiwZ DNA was detected in 57% (127/221) of the survival embryos and in 9% (12/127) of the embryonic tissues. The expression was observed mosaically in the epidermis, heart and neural tube. The PGCs in the blood collected from the vitelline artery or dorsal aorta also showed a positive histochemical staining. However, the expression of MiwZ using the soft shelled eggs was more intense in the extraembryonic tissues, although it did not emerge in the embryos. Thus, it is possible to introduce an exogenous gene into the embryonic tissues using incubated fertilized eggs without sacrificing the hens. This technique for successive genetic operations should facilitate the production of transgenic chickens.

Involvement of transglutaminase in myofibril assembly of chick embryonic myoblasts in culture

Involvement of transglutaminase in myofibrillogenesis of chick embryonic myoblasts has been investigated in vitro. Both the activity and protein level of transglutaminase initially decreased to a minimal level at the time of burst of myoblast fusion but gradually increased thereafter. The localization of transglutaminase underwent a dramatic change from the whole cytoplasm in a diffuse pattern to the cross-striated sarcomeric A band, being strictly colocalized with the myosin thick filaments. For a brief period prior to the appearance of cross-striation, transglutaminase was localized in nonstriated filamental structures that coincided with the stress fiber-like structures. When 12-o-tetradecanoyl phorbol acetate was added to muscle cell cultures to induce the sequential disassembly of thin and thick filaments, transglutaminase was strictly colocalized with the myosin thick filaments even in the myosacs, of which most of the thin filaments were disrupted. Moreover, monodansylcadaverine, a competitive inhibitor of transglutaminase, reversibly inhibited the myofibril maturation. In addition, myosin heavy chain behaved as one of the potential intracellular substrates for transglutaminase. The cross-linked myosin complex constituted approximately 5% of the total Triton X-100-insoluble pool of myosin molecules in developing muscle cells, and its level was reduced to below 1% upon treatment with monodansylcadaverine. These results suggest that transglutaminase plays a crucial role in myofibrillogenesis of developing chick skeletal muscle.

Alteration in liver plasma membrane phospholipids and protein kinase activities during the development of chick embryo

The changes in phospholipid compositions, membrane fluidity and protein kinase A, protein kinase C, tyrosine and casein kinase activities in chick embryo liver plasma membranes during development have been investigated. The percentage participation of sphingomyelin increased while that of phosphatidylserine decreased during chick embryo development. The alterations in membrane sphingomyelin accompanied an increase of steady-state fluorescence anisotropy (rs) of membrane bilayer. Regression analysis indicated positive linear correlations between the percentage participation of sphingomyelin in total membrane phospholipids and (i) protein kinase C (r = 0.903); (ii) casein kinase (r = 0.936); (iii) protein kinase A (r = 0.850); (iv) tyrosine kinase (r = 0.960) activities. We suggest that sphingomyelin might be an specific activator for all types of protein kinase activities investigation.

A radiometric microassay for choline acetyltransferase. Some observations on the spinal cord of the chicken embryo

This paper describes cation-exchange methods for separating acetyl[3H] coenzyme A from [acetyl-3H]choline. Blanks for the routine method were approximately 0.05% of the substrate radioactivity; product recoveries were approximately 97%. The cation-exchange method was more efficient than the standard methods using either anion-exchange chromatography or periodide precipitation. The cation-exchange method was also more specific than either of the other two standard methods for estimating choline acetyltransferase (ChAT) activity. ChAT activity was detected in the chicken lumbar spinal cord on embryonic day (E) 2 1/4 with the cation-exchange method. This developmental stage is about 6 hours before the final mitosis of any neuroblast in the ventral horn. Total ChAT activity per lumbar spinal cord increased more than 10,000-fold between E 3 and E 18. Changes in ChAT activity in the lumbar spinal cord following limb-bud extirpation appeared to mirror (with a phase lag) the changes in the number of motoneurons in the lateral motor column.

Embryonic adenosine triphosphate:phosphodiesters ratios obtained with in vivo nuclear magnetic resonance spectroscopy (phosphorus-31): a new technique for selecting leaner broiler chickens

Phosphorus-containing compounds of 18-d-old embryos from two broiler chicken lines, differing in body fat content, were measured using in vivo 31P nuclear magnetic resonance (NMR) spectroscopy. Subsequently, the same birds were slaughtered at 8 wk of age and the whole body was analyzed for body fat content. The birds of the fat line had lower (P = .002) embryonic adenosine triphosphate (ATP):phosphodiester (PDE) ratios, higher (P = .002) body fat content when adjusted to common BW, and higher (P = .047) dry matter content than the lean line. No differences (P > .05) were detected for BW between the two lines. Females of the two lines had lower (P = .002) ATP:PDE ratios, lower (P = .001) BW, higher (P = .003) adjusted fat contents, and higher (P = .003) dry matter content than the males. No interaction (P > .05) between sexes and lines was detected for any variables. Regression equations indicating a linear negative relationship (Ybody fat content = 369.05 - 407.27 XATP:PDE + .1295 XBW, R2 = .62 to .78; or Ybody fat % = 30.57 - 19.4 XATP:PDE, R2 = .49 to .71) between embryonic ATP:PDE ratios and body fat content were developed.

Regulation of tyrosine aminotransferase activity by glucagon and cAMP analogues in chick embryos in ovo

Glucagon, dibutyryl cAMP (Bt2cAMP) and 8-(4-chlorophenylthio) cAMP (CptcAMP), singly or when combined, stimulated tyrosine aminotransferase (TAT) activity in 17-day-old chick embryos in ovo. Maximal induction was produced within 4 hr of injection of the inducers. The effects of glucagon and the cAMP analogues were not additive. Glucagon administration was accompanied by a rapid increase in hepatic cAMP concentration which remained elevated for at least 4 hr. The stimulated increase in TAT activity elicited by the hormone or cyclic nucleotide was prevented by injection of cycloheximide or cordycepin. These results are discussed vis-à-vis the possible regulation of TAT in ovo by physiological concentrations of glucagon and the likely role of cAMP as a second messenger in this process during chick embryogenesis.

The esterification of cholesterol in the liver of the chick embryo

The development of the chick embryo was characterised by the accumulation of large droplets of lipid in the cytoplasm of the embryonic liver, as revealed by electron microscopy. Analysis of the lipid composition of the livers indicated that this accumulation resulted from a dramatic increase in the cholesteryl ester content of the tissue during the the latter part of the embryonic period. This lipid is apparently derived from yolk cholesterol and may be taken up by the liver in the form of lipoprotein remnants. Significant levels of acyl-CoA: cholesterol acyltransferase (ACAT) activity were expressed in the liver throughout the second half of the developmental period, and this activity was maximal at the time when lipid transfer from the yolk was most intensive. The activity of microsomal cholesterol ester hydrolase (CEH) was very low throughout development, and no CEH activity was detected in the cytosolic fraction. In addition, substantial amounts of a cytosolic protein which inhibits CEH activity were present. Thus the relative activities of these enzymic systems are consistent with the net accumulation of cholesteryl ester which occurs in the liver during development.

Quantification of chicken alpha-fetoprotein: a useful tool in studies of embryo development and pathology

Chicken alpha-fetoprotein (AFP) from the plasma of 12-day-old chick embryos was purified by electroelution from SDS/PAGE gels, and used to produce polyclonal and monoclonal antibodies. Both reagents were then used to design a sandwich-type enzyme-immunoassay for the quantification of AFP in biological fluids. The assay was used to quantify AFP in the serum and amniotic fluid of chick embryos with abnormalities of the neural tube. Serum AFP was significantly greater in these embryos than in normal ones of similar age. Moreover, substantial amounts of AFP were demonstrated in the amniotic fluid, whereas this protein was undetectable in the amniotic fluid of normal embryos. This method of assay may provide a reliable tool for studies of chick embryogenesis and abnormalities of embryonal differentiation.

Cholinesterases regulate neurite growth of chick nerve cells in vitro by means of a non-enzymatic mechanism

Cholinesterases present homologies with some cell adhesion molecules; however, it is unclear whether and how they perform adhesive functions. Here, we provide the first direct evidence showing that neurite growth in vitro from various neuronal tissues of the chick embryo can be modified by some, but not all, anticholinesterase agents. By quantifying the neuritic G4 antigen in tectal cell cultures, the effect of anticholinesterases on neurite growth is directly compared with their cholinesterase inhibitory action. BW 284C51 and ethopropazine, inhibiting acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), respectively, strongly decrease neurite growth in a dose-dependent manner. However, echothiophate which inhibits both cholinesterases, does not change neuritic growth. These quantitative data are supplemented by morphological observations in retinal explant cultures grown on striped laminin carpets, viz., defasciculation of neurite bundles by BW 284C51 and Bambuterol occurs, indicating that these drugs disturb adhesive mechanisms. These data strongly suggest that a) cholinesterases can participate in regulating axonal growth, b) both AChE and BChE can perform such a nonsynaptic function, and c) this function is not the result of the enzyme activity per se, since at least one drug was found that inhibits all cholinesterase activities but not neurite growth. Thus, a secondary site on cholinesterase molecules must be responsible for adhesive functions.

Butyrylcholinesterase from intestinal epithelial cells of quail, chick and duck: a comparative study during development

1. Epithelial cells of avian intestine express non-specific cholinesterase (butyrylcholinesterase, BuChE) activity both in the embryo and adult animal. 2. Quail, duck and chick exhibit increased BuChE activity during the late embryonic period followed by decreased activity. The minimum value is reached after hatching at day 1 in quail, day 4 in chick and day 6 in duck. 3. The three species display marked sex-related differences mainly during the peri-hatching period. BuChE activity is higher in females than in males. 4. The three globular forms, G1, G2 and G4, are detected during the last days of embryonic development. After hatching, changes in the relative amounts of these forms are related to the disappearance of G2 and the gradual decrease of G4. In adult quail and duck, G4 is not detected and BuChE activity corresponds only to the G1 form. 5. The changes in BuChE activity and distribution of the molecular forms occur in a similar manner in all three species although the embryonic periods differ notably, suggesting that hormonal factors secreted during this period and involved in the preparation of hatching may regulate BuChE activity.

Erythroid carbonic anhydrases of developing chick embryos. Coordinate expression with primitive and definitive embryonic haemoglobins

Erythroid carbonic anhydrase activity of chick embryos from the 3rd day of incubation to the egg hatching has been determined. Three minor activity peaks at 3, 9 and 15 days of development and a major one at 19 days were found. The enzyme molecular forms were purified by affinity chromatography from haemolysates of embryos at several stages of development. As has been found for the adult erythrocytes, only type II isozyme was detected in the embryo red cells. Isoelectrofocusing analysis demonstrated that two different molecular forms of this isozyme are synthesized by the red cells of developing embryos. Only the early form is present up to 5 days of development; the late form, which is indistinguishable from the adult isozyme, appears in the haemolysate at 6-7 days and quickly replaces the early form. Analysis of purified primitive and definitive erythroid lines from 7-days-old embryos showed a compartmentalization of the early and late forms into the primitive and definitive erythroid cells, respectively.

Effect of magnetic fields on membrane associated enzymes in chicken embryos, permanent or transient?

Exposure to a 60Hz, 4 microT electromagnetic field resulted in a significant reduction in the activity level of 5' nucleotidase in normal live embryos. Levels of acetylcholinesterase and alkaline phosphatase were not affected. The effect of the field on 5'NT levels appears to be permanent, as incubation in a field free environment for a further 15 days did not result in enzyme levels returning to control values.

Tissue-specific changes in lipid composition and lipoprotein lipase activity during the development of the chick embryo

Lipoprotein lipase was present at a high specific activity in adipose tissue and heart of the chick embryo at the 14th day of development. The enzyme was also present in skeletal muscle but was absent from brain and liver. Major increases in the activity of lipoprotein lipase in adipose tissue and heart occurred from day 12 of development, concomitant with the beginning of the period of lipid uptake from the yolk. These results suggest that lipoprotein lipase may be involved in the utilisation of yolk-derived lipid by the tissues of the embryo. Relatively high levels of docosahexaenoic acid (22:6(n--3)) were present in the triacylglycerol isolated from plasma, adipose tissue, heart and liver. The relative proportions of this fatty acid in the triacylglycerol of the different tissues may be explicable in terms of the substrate specificity of lipoprotein lipase.

Isolation and characterization of a chicken tyrosinase cDNA

Complementary DNA clones coding for chicken tyrosinase were isolated from retinal pigmented epithelium of chicken embryo. Sequence analysis shows that one of the cDNA clones consisting of 1,997 nucleotides has an open reading frame coding for 529 amino acids. The deduced protein has nine N-glycosylation sites and a transmembrane region. A sequence comparison of the deduced chicken tyrosinase with the mouse and human homologues revealed that amino acid sequences are conserved for the entire polypeptides. Seventy-two percent and 73% of amino acids in the chicken sequence are identical to that of the mouse and human tyrosinases, respectively. Histidines neighboring the postulated copper-binding sites and the cysteines are well conserved. RNA blotting analysis showed that a major transcript of 2.5 kb is detected in retinal pigmented epithelium of a 9-day-old chicken embryo.

Ontogeny of type I and type III deiodinase activities in embryonic and posthatch chicks: Relationship with changes in plasma triiodothyronine and growth hormone levels

1. The ontogeny of type I and type III deiodinase activities was studied in embryonic and posthatch chicks. 2. Hepatic type I activity showed a 3-fold increase up to the period of pipping and hatching and decreased slowly thereafter. 3. Hepatic type III activity increased by 3-fold from E14 to E17 and decreased more than 10-fold from E17 to C0. Posthatch levels were very low. 4. Type I activity in the kidney decreased slowly after hatching while type III activity was very low over the whole period studied. 5. Developmental changes during the late embryonic period suggest a causal relationship between the increase in plasma GH and T3 levels and the decrease in hepatic type III activity.

O6-alkylguanine-DNA alkyltransferase in the chick embryo during development

In the whole embryo, O6-alkylguanine-DNA alkyltransferase (AT) activity increased until day 9 of development and declined sharply after day 13. AT activity of the liver was greatest between day 12 and day 20 and decreased fast after hatching. In the brain, AT activities reached a maximum at day 17 and 18 and declined sharply after hatching. At two developmental stages with different AT activities (day 10 and day 17) DNA alkylation in the brains was estimated 6, 12, 24 and 48 h after administration of N-methyl-N-nitrosourea in ovo by viscometric measurement of DNA fragmentation. The high AT activities of the chicken embryo brain at the 17th day of development correlated with minor DNA fragmentation following a repair period of 12-24 h. It is suggested that the high basal level of AT in the chick embryo might have a protective function against the persistence of the genotoxic lesion O6-methylguanine during development.

Comparison between avian and human prolyl 4-hydroxylases: studies on the holomeric enzymes and their constituent subunits

Prolyl 4-hydroxylase, a key enzyme in collagen biosynthesis, catalyzes the conversion of selected prolyl residues to trans-hydroxyproline in nascent or completed pro-alpha chains of procollagen. The enzyme is a tetramer composed of two nonidentical subunits, designated alpha and beta. To compare the enzyme and its subunits from different sources, the chick embryo and human placental prolyl 4-hydroxylases were purified to homogeneity and their physicochemical and immunological properties were determined. Both enzymes were glycoproteins with estimated apparent molecular weights ranging between 400 and 600 kDa. Amino acid and carbohydrate analyses showed slight differences between the two holomeric enzymes, consistent with their deduced amino acid sequences from their respective cDNAs. Human placental prolyl 4-hydroxylase contained more tightly bound iron than the chick embryo enzyme. Immunodiffusion of the human placental enzyme with antibodies raised against the purified chick embryo prolyl 4-hydroxylase demonstrated partial identity, indicating different antigenic determinants in their tertiary structures. The enzymes could be separated by high-resolution capillary electrophoresis, indicating differential charge densities for the native chick embryo and human placental proteins. Electrophoretic studies revealed that the human prolyl 4-hydroxylase is a tetrameric enzyme containing two nonidentical subunits of about 64 and 62 kDa, in a ratio of approximately 1 to 2, designated alpha and beta, respectively. In contrast, the chick embryo alpha and beta subunit ratio was 1 to 1. Notably, the human alpha subunit was partially degraded when subjected to electrophoresis under denaturing conditions. Analogously, when the chick embryo enzyme was subjected to limited proteolysis, selective degradation of the alpha subunit was observed. Finally, only the alpha subunit was bound to Concanavalin A demonstrating that the alpha subunits of prolyl 4-hydroxylase in both species were glycosylated. Using biochemical techniques, these results demonstrated that the 4-trans-hydroxy-L-proline residues in human placental collagens are synthesized by an enzyme whose primary structure and immunological properties differ from those of the previously well-characterized chick embryo enzyme, consistent with their recently deduced primary structures from cDNA sequences.

Cytochemical localization of sorbitol dehydrogenase in kidney and liver from Myiopsitta m. monachus (Boddaert, 1783), during embryonic development

A histochemical study to determine the localization of sorbitol dehydrogenase (SDH) in kidney and liver from embryionic, young and adult Myiopsitta m. monachus was performed. The enzyme activity increased with age in both organs. In the kidney, the enzyme appeared at the proximal convoluted tubules, and increased in the basal cytoplasm of the tubular cells. In the liver the localization was diffuse in the lobule but more intense in the cytoplasm of hepatocytes, especially in the perinuclear areas. These studies indicate that the cytochemical enzyme localization differs in this species, which is more evolutioned than Gallus gallus, and would be related to ontogenetic and phylogenetic differentiation.

Embryolethality and induction of 7-ethoxyresorufin O-deethylase in chick embryos by polychlorinated biphenyls and polycyclic aromatic hydrocarbons having Ah receptor affinity

The lethality and 7-ethoxyresorufin O-deethylase (EROD)-inducing potency of some individual polycyclic aromatic hydrocarbons (PAHs) and coplanar polychlorinated biphenyls (PCBs) in chick embryos were measured in order to compare the mechanisms of action of these compounds. In previous studies it was found that coplanar PCBs and certain PAHs have a high embryolethality in the chicken and that they induce embryonic EROD activity. Although the most potent PAHs were almost as embryolethal as the PCBs when injected into hens' eggs 72 h prior to measurement, they were considerably less potent EROD inducers. In the present study, three coplanar PCBs (3,3',4,4'-tetrachlorobiphenyl (TCB), 3,3',4,4',5-pentachlorobiphenyl (PeCB) and 3,3',4,4',5,5'-hexachlorobiphenyl (HCB)) and four of the most toxic PAHs (benzo[a]anthracene (BaA), benzo[k]fluoranthene (BkF), indeno[1,2,3-cd]pyrene (IP) and dibenzo[a, h]-anthracene (DBahA] were administered to chick embryos in different ways, including co-administration. Additive embryolethality was found when BkF and PeCB were co-administered as well as when BaA and DBahA were given simultaneously. The PAHs were more effective as EROD inducers when injected on day 9 (24 h prior to measurement) than when injected on day 7 (72 h prior to measurement). The opposite was found for PeCB and HCB, whereas no difference in potency was noted when comparing TCB injected 24 and 72 h before EROD determination. These substance-related differences were probably due, at least partly, to differences in biotransformation rates. EROD activities found after treatment with high doses of BkF, IP, or DBahA on day 9 were similar to those measured after treatment with PeCB in doses high enough to give maximal induction. Co-administration of high doses of BkF and PeCB did not further increase the activity, indicating that the PAHs and coplanar PCBs induce EROD to a common maximal value. To decrease the influence of metabolization of the PAHs on their EROD-inducing potency, EROD was determined early in development (day 8) and soon after treatment (24 h) in one experiment. In that experiment, the PAHs proved to be only a few times less potent EROD inducers in relation to their embryolethalities compared with the PCBs. The results of the present study, a previously observed similarity in pathology between chick embryos treated with PAHs and embryos treated with coplanar PCBs, and the fact that the most toxic PAHs also are the most avid Ah receptor binders suggest that the coplanar PCBs and the PAHs largely exert their toxicity in chick embryos via an Ah receptor-mediated mechanism. The differences between the compounds in their EROD-inducing potency/embryolethality ratios could probably be explained by their different rates of biotransformation.

Amylase activity increases in the yolk of fertilized eggs during incubation in chickens

Amylase activity was detected in the egg of chickens. In unfertilized eggs, no change of amylase activity was observed during 22 days incubation, however, in fertilized eggs, amylase activity increased markedly during embryonic development. The increase depended upon an increase of amylase in the yolk, not in the albumen. Isoamylases in the yolk were electrophoretically identical to those in the pancreas of the embryo or the hen.