Inhibition of prostaglandin synthesis in eggshell gland mucosa as a mechanism for P,P'-DDE-induced eggshell thinning in birds—a comparison of ducks and domestic fowls

1. A recent report from the present laboratory indicated that the DDT-metabolite p,p'-DDE, which produces eggshell thinning in sensitive species of birds, inhibits prostaglandin synthesis in the eggshell gland.2. This was found to be true both after in vitro addition to a homogenate of eggshell gland mucosa from ducks, and after in vivo administration to ducks at a dose regimen that produces eggshell thinning.3. The purpose of the present study was to compare the p,p'-DDE-sensitive duck and the insensitive domestic fowl regarding the effects of p,p'-DDE administration on calcium and prostaglandin metabolism of the eggshell gland mucosa.4. Administration of p,p'-DDE caused significant eggshell thinning in ducks (−18.5%) but not in the domestic fowl.5. The shell thinning in ducks was accompanied by significant reductions in ⁴⁵Ca uptake and prostaglandin synthesis by a homogenate of the eggshell gland mucosa, as well as significant reductions of the prostaglandin E₂ content in the shell gland and the content of calcium and bicarbonate present in the shell gland lumen at the time of slaughter; the content of calcium in the eggshell gland mucosa was significantly increased.6. None of the changes was observed in the domestic fowl.7. Based on these findings, inhibition of a prostaglandin-stimulated bicarbonate transport across the eggshell gland mucosa is discussed as a possible mechanism for p,p '-DDE-induced eggshell thinning in birds.     

Progesterone stimulates prostaglandin synthesis in eggshell gland mucosa of estrogen-primed chickens.

1. Prostaglandins may be involved in calcium translocation in the avian shell gland, since indomethacin, administered at the beginning of shell formation, reduces eggshell thickness as well as 45Ca-uptake and prostaglandin synthesis by a homogenate of eggshell gland mucosa. 2. The stimulus for calcium transport in the shell gland during shell formation remains unknown. 3. The present study was undertaken to investigate the effects of progesterone on prostaglandin formation by the eggshell gland mucosa of the domestic fowl. 4. Progesterone significantly stimulated synthesis of PGF2 alpha, PGE2 and TXB2 by eggshell gland mucosa homogenate. 5. Progesterone treatment also induced the synthesis of the biotin-binding protein, avidin. 6. A microsomal fraction prepared from the eggshell gland mucosa had a high affinity for binding PGE2. 7. Progesterone treatment reduced the KD value of this binding without affecting the maximal number of binding sites. 8. Progesterone did not change the total calcium content of shell gland mucosa. 9. The role progesterone plays in prostaglandin formation and calcium transport in the eggshell gland mucosa is discussed.     

Effect of estradiol-17β on follicle-stimulating hormone secretion and egg-laying performance of Japanese quail

The aim of this study was to measure the effect of estradiol-17β (E₂) injection on follicle-stimulating hormone (FSH) secretion and egg-laying performance of Japanese quail. Female Japanese quail were housed in cages and fed ad libitum. After a 7-day adaptation period, the birds were randomly assigned to three groups, that is, one control group and two test groups. The birds were weighed, before every injection. The control group was subcutaneously injected with 0.2 ml sesame oil–ethanol mixture, whereas test groups were injected, twice in a week, with 0.2 ml sesame oil–ethanol mixture containing 0.1 or 0.2 mg E₂ along the study. One day after the first injection, egg number, egg weight, eggshell strength and food conception were daily recorded. On the last day of the experiment, the birds were injected and 3 h later seven birds from each group were randomly selected for bleeding. Blood samples (2 ml/bird) were collected from the jugular vein for the measurements of serum concentrations of E₂, FSH, calcium (Ca) and phosphorus (P). E₂ injection did not cause any significant changes in serum FSH concentrations, daily egg laid/bird, food conception/bird, serum concentrations of the Ca and the P. Egg weight was significantly increased in the 0.1 mg E₂-injected group as compared with the control and 0.2 mg E₂-injected groups. Eggshell strength in the 0.2 mg E₂-injected group was significantly high as compared with the control, whereas the difference between the 0.1 mg E₂- and 0.2 mg E₂-injected groups was not statistically important. These results show that serum FSH concentration was not increased even when slightly suppressed by subcutaneous injection of 0.1 or 0.2 mg E₂. Different doses of E₂ have different functions. The increase in BWs in the 0.1 mg E₂-injected group was a result of the dose effect, which probably increased growth hormone secretion from the pituitary or IGF-1 synthesis from the liver or both. The dose, 0.2 mg E₂, was ineffective in increasing the BW, but it significantly increased eggshell strength probably via the increase in Ca and P utilizations.     

利用转录组测序筛选鸡蛋褐壳性状相关基因

褐壳鸡蛋在许多国家深受消费者喜爱,消费者通常把蛋壳褐色深浅作为评价鸡蛋品质的重要指标。褐壳鸡蛋蛋壳颜色形成受多基因共同调控,但是具体候选基因及调控机理尚未明确。因此,本研究以纯系褐壳蛋鸡为实验材料,筛选调控褐壳鸡蛋颜色深浅的候选基因。采用转录组测序技术对产深褐壳鸡蛋和浅褐壳鸡蛋的母鸡蛋壳腺组织进行分析,结果显示,共计有8461个基因在蛋壳腺组织表达,其中34个基因在两组之间差异表达。功能分析发现,卵转铁蛋白(ovotransferrin, TF)基因、热休克蛋白70 (heat shock protein, HSP70)基因以及氧化磷酸化通路均与原卟啉Ⅸ合成通路相关,可能影响褐壳鸡蛋蛋壳色素原卟啉Ⅸ的合成和积累。     

A note on eggshell porosity,nest humidity and the effects of DDE in the grey heron (Ardea cinerea)

• 1.1. Water vapour conductance (G_H2O) was determined for 25 grey heron Ardea cinerea eggs in the laboratory, and in nests during natural incubation at two Scottish colonies.
• 2.2. The mean G_H2O of eggs measured in the nest which successfully hatched was 9.0 mgH;O/mmHg/day and the mean water vapour pressure gradient between egg and nest (ΔP_H2O), measured using “calibrated” duck eggs, averaged at 31 mmHg (4.13 kPa).
• 3.3. Based on eggshell porosity results, from the eggs which hatched, such a gradient would result in a loss of water from the eggs during incubation equivalent to 11% of their fresh weight.
• 4.4. Shell thickness, the number of pores/cm² of eggshell and DDE content were also determined for the 25 eggs measured in the laboratory.
• 5.5. Eggs containing high levels of DDE had thinner shells, more pores in the eggshell and a higher overall eggshell porosity.
• 6.6. The main problem posed by a high level of DDE would appear, however, not to be an excessive water loss from the egg during incubation, but rather eggshell thinning leading to a loss of the egg due to breakage in the nest.

     

Polymorphisms in eggshell organic matrix genes are associated with eggshell quality measurements in pedigree Rhode Island Red hens

Novel and traditional eggshell quality measurements were made from up to 2000 commercial pedigree hens for a candidate gene association analysis with organic eggshell matrix genes: ovocleidin-116 , osteopontin ( SPP1 ), ovocalyxin-32 ( RARRES1 ), ovotransferrin ( LTF ), ovalbumin and ovocalyxin-36 , as well as key genes in the maintenance and function of the shell gland [ estrogen receptor ( ESR1 ) and carbonic anhydrase II ( CAII )]. Associations were found for (i) ovalbumin with breaking strength and shell thickness; (ii) ovocleidin-116 with elastic modulus, shell thickness and egg shape; (iii) RARRES1 with mammillary layer thickness; (iv) ESR1 with dynamic stiffness; (v) SPP1 with fracture toughness and (vi) CAII with egg shape. The marker effects are as large as 17% of trait standard deviations and could be used to improve eggshell quality.     

Localization of osteopontin in oviduct tissue and eggshell during different stages of the avian egg laying cycle

The avian eggshell is an acellular bioceramic containing organic and inorganic phases that are sequentially assembled during the time the egg moves along the oviduct. As it has been demonstrated in other mineralized tissues, mineralization of the eggshell is regulated by extracellular matrix proteins especially the anionic side chains of proteoglycans. Among them, osteopontin has been found in the avian eggshell and oviduct. However, its precise localization in the eggshell or in different oviduct regions during eggshell formation, nor its function have been established. By using anti-osteopontin antibody (OPN 1), we studied its immunolocalization in the isthmus, red isthmus and shell gland of the oviduct, and in the eggshell during formation. In the eggshell, osteopontin was localized in the core of the non-mineralized shell membrane fibers, in the base of the mammillae and in the outermost part of the palisade. In the oviduct, OPN 1 was localized in the ciliated epithelial but not in the tubular gland cells of the isthmus, in the ciliated epithelial cells of the red isthmus, and in the non-ciliated epithelial cells of the shell gland. The occurrence of osteopontin in each of the oviduct regions, coincided with the concomitant presence of the egg in such region. Considering the reported inhibitory function of osteopontin in other mineralized systems, together with its main occurrence in the non-mineralized parts of the eggshell and at the outermost part of the shell, suggests that this molecule could be part of the mechanism regulating the eggshell calcification.     

Avian eggshell thickness in relation to egg morphometrics,embryonic development,and mercury contamination

Eggshell thickness is important for physiological, ecological, and ecotoxicological studies on birds; however, empirical eggshell thickness measurements for many species and regions are limited. We measured eggshell thickness at the equator and the egg poles for 12 avian species and related eggshell thickness to egg morphometrics, embryonic development, egg status, and mercury contamination. Within an egg, eggshells were approximately 5.1% thicker at the equator than the sharp pole of the egg, although this difference varied among species (0.6%–9.8%). Within Forster's tern (Sterna forsteri), where eggshell thickness was measured at 5 equally spaced positions along the longitude of the egg, eggshell thickness changed more rapidly near the sharp pole of the egg compared to near the blunt pole of the egg. Within species, eggshell thickness was related to egg width and egg volume for six of the 12 species but was not related to egg length for any species. Among species, mean eggshell thickness was strongly related to species mean egg width, egg length, egg volume, and bird body mass, although species mean body mass was the strongest predictor of species mean eggshell thickness. Using three species (American avocet [Recurvirostra americana], black‐necked stilt [Himantopus mexicanus], and Forster's tern), whose nests were carefully monitored, eggshell thickness (including the eggshell membrane) did not differ among viable, naturally abandoned, dead, or failed‐to‐hatch eggs; was not related to total mercury concentrations of the egg content; and did not decrease with embryonic age. Our study also provides a review of all existing eggshell thickness data for these 12 species.     

Schistosoma mansoni: Phenol oxidase's role in eggshell formation

Phenol oxidase may be involved in the formation of the eggshell in Schistosoma mansoni. ³H-Labeled female S. mansoni proteins were polymerized in vitro following incubation with S. mansoni phenol oxidase and excess l-tyrosine. Peroxidase inhibitors, autoxidation inhibitors, inhibitors of lipid peroxidation, and inactive analogs of phenol oxidase inhibitors did not inhibit eggshell formation. Fluorescent substances found in eggshell hydrolysates were similar to those formed from the reaction of phenol oxidase-generated quinones with protein-bound lysine. These observations support the classical concept of phenol oxidase-catalyzed protein hardening. However, fluorescent globules of egg material were still formed after the administration of 200 mg/kg of the phenol oxidase inhibitor diethyldithiocarbamate. These globules could not be destroyed by inhibitors of autoxidation and lipid peroxidation.     

Relationship between eggshell strength and keratan sulfate of eggshell membranes

Eggshell strength is an important factor in an effort to minimize eggshell breakage, which is a significant problem in the egg production industry. In the current study, we isolated and quantified the specific glycosaminoglycans (GAGs) from the calcified eggshell and shell membranes, which are related to eggshell strength. Our data suggest that GAGs exist in calcified eggshell may influence morphology of shell but do not affect on increase of shell amount while GAGs of shell membranes are maybe highly associated with shell strength with an increase of shell weight. Shell strength showed a strong correlation with the content of GAGs (r=0.942, p<0.0005) and a weak relationship with uronic acid content (r=0.564, p=0.056) in shell membranes. Monosaccharides in shell membranes were determined by Bio-LC analysis for the identification of any specific GAGs related with shell strength. It indicates that the galactose content as a component of keratan sulfate (KS) has a significant correlation with eggshell strength (r=0.985, p<0.0005). These results suggest that eggshell strength is proportional to the KS content of eggshell membranes with an increase of eggshell weight.     

Relation between Ca metabolism and ATPase activities in the subcellular fractions from duck eggshell gland mucosa after DDE administration during different stages of eggshell formation

The ATP-dependent Ca2+ uptake by and the Ca2+-Mg2+-activated ATPase activity in the subcellular fractions from the eggshell gland of two varieties of ducks, Indian Runner ducks (IRD) and the cross-breed of Swedish and Rouen ducks (SRD), showed functional changes during eggshell formation in relation to the values in the resting state. DDE inhibited the Ca2+ uptake (Ca) but increased the Ca2+-Mg2+-ATPase activity (P) of fractions from active but not of those from resting glands. DDE reduced the Ca/P ratio of several fractions from active glands. DDE inhibited the functional increase in Ca2+-Mg2+-ATPase in the IRD homogenate, however. The effect of DDE on the eggshell index of mature eggshell was greater in IRD than in SRD, the reason for this being that the effect was exerted during a shorter time period in the latter variety.     

A high-affinity calcium-stimulated ATPase activity in the hen oviduct shell gland

The hen oviduct shell gland is a highly active calcium-transporting epithelial tissue which is responsible for the mineralization of the egg shell. We have identified a calcium-stimulated ATPase present at high specific activity in membrane preparations from shell gland mucosal shavings. In the presence of optimal MgCl₂ (5 mm) and a Ca²⁺ buffer, ATP hydrolysis was stimulated by addition of low concentrations of free Ca²⁺ (K_0.5 ~0.4 μm); but not by similar concentrations of Mn²⁺, Zn²⁺, Co²⁺, or La²⁺. This stimulation was specific for ATP; there was little or no effect of Ca²⁺ on hydrolysis of ADP, AMP, GTP, ITP, or p-nitrophenyl phosphate. Calcium-stimulated ATPase activity was inhibited by chlorpromazine, trifluoperazine, and quercetin, as well as by sulfhydryl-blocking agents, but not by oligomycin or ouabain. No significant effect of calmodulin was observed. Finally, low concentrations of free Ca²⁺ (10 to 100 μm) in the presence or absence of Mg²⁺ stimulated transfer of ³²P from [γ-³²P]ATP to a 105,000 molecular weight shell gland membrane protein. This phosphoprotein was sensitive to hydrolysis by heating or by hydroxylamine treatment at acidic pH, and its formation was not inhibited by addition of K⁺. The specific activity of Ca²⁺-ATPase in total membrane preparations from laying hen shell gland ranged from 80 to 150 nmol/min/ mg protein, similar to or greater than levels found in purified plasma membrane fractions from a variety of tissues. No significant activity was found in membrane preparations from the magnum or isthmus regions of the oviduct, which are not involved in egg shell calcification. The characteristics of the Ca²⁺-ATPase, its high specific activity, and its preferential localization in the shell gland region of the oviduct suggest a role for an ATP-dependent calcium transport system in egg shell mineralization.     

Comparison of HMOX1 expression and enzyme activity in blue-shelled chickens and brown-shelled chickens

Blue egg coloring is attributed to biliverdin derived from the oxidative degradation of heme through catalysis by heme oxygenase (HO). The pigment is secreted into the eggshell by the shell gland. There is uncertainty as to whether the pigment is synthesized in the shell gland or in other tissues. To investigate the site of pigment biosynthesis, the expression of heme oxygenase (decycling) 1 (HMOX1), a gene encoding HO, and HO activity in liver and spleen were compared between blue-shelled chickens (n = 12) and brown-shelled chickens (n = 12). There were no significant differences in HMOX1 expression and HO activity in these tissues between the two groups. Since the liver and spleen, two important sites outside the shell gland where heme is degraded into biliverdin, CO and Fe²⁺, did not differ in HO expression and activity we conclude that the pigment is most likely synthesized in the shell gland.     

Effects of dietary Bacillus subtilis and inulin supplementation on performance,eggshell quality,intestinal morphology and microflora composition of laying hens in the late phase of production

Eighty Lohmann White laying hens were used to investigate the effect of dietary inclusion of Bacillus subtilis and inulin, individually or in combination, on egg production, eggshell quality, tibia traits, Ca retention, and small intestine morphology and microflora composition from 64 to 75 weeks of age. Hens were randomly distributed into 4 treatment groups, with 5 replicates per treatment and 4 hens per replicate. Treatment groups were fed basal diet (control), basal diet plus 1 g/kg B. subtilis (2.3 × 10⁸ cfu/g), basal diet plus 1 g/kg inulin, or basal diet plus a synbiotic combination of 1 g/kg B. subtilis (2.3 × 10⁸ cfu/g) and 1 g/kg inulin. Dietary supplementation of B. subtilis, inulin or synbiotic improved (P<0.05) feed conversion, egg performance, eggshell quality and calcium retention compared with the control. B. subtilis and synbiotic groups exhibited the highest (P<0.05) increase in egg production and egg weight. Inulin and synbiotic groups exhibited the highest (P<0.05) increase in eggshell thickness and eggshell calcium content, and the lowest (P<0.05) eggshell deformations. Unmarketable eggs were 8.4% (P<0.05) of the total eggs produced by the control group compared to 3.5%, 1.7%, and 1.5% for the B. subtilis, inulin and synbiotic groups, respectively. Tibia density, ash, and Ca content increased (P<0.05) by inulin and synbiotic inclusions, compared with the control. B. subtilis, inulin, and their synbiotic combination increased (P<0.05) villus height and crypt depth in all intestinal segments, compared with the control. B. subtilis and inulin modulated the ileal and caecal microflora composition by decreasing (P<0.05) numbers of Clostridium and Coliforms and increasing (P<0.05) numbers of bifidobacteria and lactobacilli, compared with the control. Colonization of the beneficial microflora along with increasing the villi–crypts absorptive area were directly associated with the improvements in performance and eggshell quality. It can be concluded that egg production and eggshell quality of laying hens can be improved (P<0.05) in the late phase of production by dietary inclusion of B. subtilis and inulin.     

Dietary supplementation with sodium bicarbonate or sodium sulfate affects eggshell quality by altering ultrastructure and components in laying hens

Dietary sodium (Na) levels were related to the content of the eggshell matrix. We therefore speculated that dietary Na supplementation as sodium bicarbonate (NaHCO₃) or sodium sulfate (Na₂SO₄) may improve eggshell quality. Additionally, dietary NaHCO₃ or Na₂SO₄ supplementation may further affect eggshell quality in different ways due to differences in anions. This study investigated and compared the effects of dietary Na supplementation in either NaHCO₃ or Na₂SO₄ form on laying performance, eggshell quality, ultrastructure and components in laying hens. A total of 576 29-week-old Hy-Line Brown laying hens were randomly allocated to 8 dietary treatments that were fed a Na-deficient basal diet (0.07% Na, 0.15% Cl) supplemented with Na₂SO₄ or NaHCO₃ at 0.08, 0.18, 0.23 or 0.33% Na for 12 weeks. No differences were observed in laying production performance with dietary Na supplementation. Dietary Na supplementation resulted in quadratic increases of eggshell breaking strength in both Na₂SO₄ and NaHCO₃ added groups (P < 0.05), and Na₂SO₄-fed groups had a quadratic increase in the eggshell ratio at week 12 (P < 0.05). Compared with supplementing 0.08% Na, dietary supplementation of 0.23% Na increased the effective thickness (P < 0.05) in both Na₂SO₄ and NaHCO₃ added groups, but decreased the thickness and knob width of the mammillary layer (P < 0.05). A linear increase on the calcium content of the shell was only observed with Na supplementation from NaHCO₃ (P < 0.05). No differences were observed in Na contents of the shell with dietary Na supplemented by both sources. Dietary Na addition had a quadratic increase on uronic acid contents of shell membrane in NaHCO₃-fed groups (P < 0.05). Moreover, the sulfated glycosaminoglycan (GAG) contents of shell membranes increased linearly with dietary Na supplementation (P < 0.05). Dietary supplementation of 0.23% Na from Na₂SO₄ increased the sulfated GAG contents of calcified eggshell (P < 0.05). Additionally, compared with NaHCO₃-fed groups, Na₂SO₄-fed groups had higher eggshell breaking strength, thickness, eggshell weight ratio, effective thickness and the sulfated GAG contents of calcified eggshell at week 12. Overall, dietary supplementation of NaHCO₃ or Na₂SO₄ could increase eggshell breaking strength, which may be related to increased sulfated GAG contents in eggshell membranes and improved ultrastructure. Higher eggshell breaking strength, thickness and eggshell ratio could be obtained when the diet was supplemented with 0.23% Na from Na₂SO₄.     

Validated quantitative trait loci for eggshell quality in experimental and commercial laying hens

Compromised eggshell quality causes considerable economic losses for the egg industry. Breeding for improved eggshell quality has been very challenging. Eggshell quality is a trait that would greatly benefit from marker‐assisted selection, which would allow the selection of sires for their direct contribution to the trait and would also allow implementation of measurements integrating a number of shell parameters that are difficult to measure. In this study, we selected the most promising autosomal quantitative trait loci (QTL) affecting eggshell quality on chromosomes 2, 3, 6 and 14 from earlier experiments and we extended the F₂ population to include 1599 F₂ females. The study was repeated on two commercial populations: Lohmann Tierzucht Rhode Island Red line (n = 692 females) and a Hy‐Line White Plymouth Rock line (n = 290 progeny tested males). We analyzed the selected autosomal QTL regions on the three populations with SNP markers at 4–13 SNPs/Mb density. QTL for eggshell quality were replicated on all studied regions in the F₂ population. New QTL were detected for eggshell color on chromosomes 3 and 6. Marker associations with eggshell quality traits were validated in the tested commercial lines on chromosomes 2, 3 and 6, thus paving the way for marker‐assisted selection for improved eggshell quality.     

Mass fragmentographic determination of prostaglandin F2α in human and rabbit urine

Analysis of prostaglandin F_2α (PGF_2α) in urine is a useful indicator of renal prostaglandin synthesis. A mass fragmentographic method for PGF_2α analysis in human urine was developed using [3,3,4,4-²H₄]PGF_2α as an internal standard and carrier. PGF_2α was extracted from urine (20 ml) with chloroform, purified by preparative thin-layer chromatography and converted to the methyl ester trimethylsilyl ether before analysis by gas chromatograph—mass spectrometry. The specificity of the urine analysis was demonstrated by retention time and the use of two pairs of fragments m/e 494/498 and 513/517 with the same results. The coefficient of variation for duplicate analysis averaged 12.6%, n = 17. Urine from recumbent women contained 4.9 ± 2.6 (S.D.) ng/ml or 4.1 ± 1.0 ng PGF_2α per mg creatinine (n = 10) with little diurnal variation. Male urine contained 5.0 ± 2.7 (S.D.) ng/ml or 3.7 ± 2.1 ng/mg creatinine (n = 10). Similar concentrations were found in boys and in girls. These observations indicate that urinary PGF_2α originates from the kidneys with little contribution from the male accessory sexual glands. This method can also be applied to analysis of PGF_2α in rabbit urine.     

Histochemical studies of Ca-ATPase, succinate and NAD+-dependent isocitrate dehydrogenases in the shell gland of laying Japanese quails: with special reference to calcium-transporting cells

Summary In order to elucidate the problem of which cells are involved in calcium transport and to estimate the role of mitochondria in calcium transport in the avian shell gland, the fine structure and the Ca-ATPase, succinate dehydrogenase (SDH) and nicotinamide adenine dinucleotide (NAD⁺)-dependent isocitrate dehydrogenase (NAD⁺-ICDH) activity of the shell gland of egg-laying Japanese quails were examined. The surface epithelial cells, consisting of ciliated cells with cilia and microvilli and non-ciliated cells with microvilli, had many large and electron-dense granules. The tubular-gland cells occupied the proprial layer and lacked secretory granules. When an egg was in the shell gland, the well-developed mitochondria of tubular-gland cells characteristically tended to accumulate in the apical cytoplasm, while they were scattered throughout the cytoplasm when an egg was not in the shell gland. Intense Ca-ATPase activity was found on the microvilli of tubular-gland cells, and moderate activity was found on the lateral-cell surface. In the surface epithelial cells, the basolateral cell surface showed moderate enzymatic activity. Both SDH and NAD⁺-ICDH activity were found in tubular-gland cells when an egg was in the shell gland. These results strongly suggest that calcium for eggshell calcification is actively transported by the tubular-gland (depending on Ca-ATPase activity) and that the mitochondria of gland cells may play an important role in this process as an energy source.     

Uterine and eggshell structure and histochemistry in a lizard with prolonged uterine egg retention (Lacertilia,Scincidae, Saiphos)

The eggshell of lizards is a complex structure composed of organic and inorganic molecules secreted by the oviduct, which protects the embryo by providing a barrier to the external environment and also allows the exchange of respiratory gases and water for life support. Calcium deposited on the surface of the eggshell provides an important nutrient source for the embryo. Variation in physical conditions encountered by eggs results in a tradeoff among these functions and influences eggshell structure. Evolution of prolonged uterine egg retention results in a significant change in the incubation environment, notably reduction in efficiency of gas exchange, and selection should favor a concomitant reduction in eggshell thickness. This model is supported by studies that demonstrate an inverse correlation between eggshell thickness and length of uterine egg retention. One mechanism leading to thinning of the eggshell is reduction in size of uterine shell glands. Saiphos equalis is an Australian scincid lizard with an unusual pattern of geographic variation in reproductive mode. All populations retain eggs in the uterus beyond the embryonic stage at oviposition typical for lizards, and some are viviparous. We compared structure and histochemistry of the uterus and eggshell of two populations of S. equalis, prolonged egg retention, and viviparous to test the hypotheses: 1) eggshell thickness is inversely correlated with length of egg retention and 2) eggshell thickness is positively correlated with size of shell glands. We found support for the first hypothesis but also found that eggshells of both populations are surprisingly thick compared with other lizards. Our histochemical data support prior conclusions that uterine shell glands are the source of protein fiber matrix of the eggshell, but we did not find a correlation between size of shell glands and eggshell thickness. Eggshell thickness is likely determined by density of uterine shell glands in this species. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

The distribution of calmodulin in the mucosa of the avian oviduct and the effect of p-p'-DDE on some of its metabolic parameters

1. Since calmodulin or some closely related peptide may activate the Ca2(+)-transporting system in the avian eggshell gland, the calmodulin content in different parts of the oviduct mucosa was determined in egg-laying birds killed at 1600 hr. 2. The highest content was noted in the shell gland mucosa both in egg-laying ducks and hens. The calmodulin content was high even in the isthmus part, where the shell formation begins. 3. Treatment of ducks (Indian runner variety) with DDE (40 ppm for 45 days) did not influence the calmodulin content of the shell gland, however. 4. The content of the protein avidin, the formation of which is stimulated by progesterone, was increased significantly in the oviduct. The carbanhydrase activity did not change significantly. 5. The dry weight of the shell gland was reduced by DDE administration in ducks but not in domestic fowls. 6. These and earlier observations indicate that DDE can act as an partial agonist which is able both to stimulate and to inhibit reactions in the shell gland and other parts of the oviduct. 7. In vivo DDE in the dose used probably acted on higher centres, influencing the activity of the shell gland and probably other parts of the oviduct. 8. A regulation centre which influences several sexual functions is the hypothalamic-hypophyseal region, but the endocrine function of the ovary has also been considered.