Ontogeny of endocrine control of osmoregulation in chick embryo. II. Actions of prolactin, arginine vasopressin, and aldosterone

Evidence for the Existence of Two Prolactin Isoforms in the Developing Pituitary Gland of the Goose (Anser cygnoides)

Compared to Galliformes such as chicken and turkey, very little is known about the existence and expression of isoforms of prolactin (PRL) in the pituitary glands of Anseriformes. In this study, by generating a rabbit-anti-goose (Anser cygnoides) PRL polyclonal antibody, we analysed the expression patterns of goose PRL isoforms in the embryonic and post-hatch development of the pituitary gland. Our results showed that two immunoreactive bands with molecular weights of about 23 and 26 kDa were detected using the Western blot technique, corresponding to the non-glycosylated (NG-) and the glycosylated (G-) isoform of PRL, respectively. The protein levels of the total PRL in a goose increased gradually from the embryonic day (ED) 22 to the post-hatch day (PD) 28, with a non-significant decrease on PD6. Furthermore, the percentage of G-PRL in the pituitary gland of the goose fluctuated from about 30.3% to 54.7% throughout the embryonic and post-hatch development. At the mRNA level, the expression of PRL increased steadily during the development and reached the highest levels on PD12, but later showed a non-significant decrease on PD28. The inconsistent expression patterns between the PRL mRNA and protein during the stages from PD6 to PD28 indicated that the PRL gene expression involves both transcriptional and post-translational regulation. Taken together, our data unequivocally demonstrated the existence of NG- and G-PRL in the pituitary gland of a goose and that the expression of the total PRL as well as the percentage of G-PRL significantly changed during embryonic and post-hatch development, indicating that the versatile biological functions of PRL during the ontogenesis of a goose could be closely related to changes in both its total expression and the degree of glycosylation in the pituitary gland.

Mycotoxin ochratoxin A disrupts renal development via a miR-731/prolactin receptor axis in zebrafish

Mycotoxin ochratoxin A (OTA) frequently contaminates various food and feed products, including cereals, coffee and wine. While the nephrotoxicity and teratogenicity of OTA have been extensively documented, the molecular mechanisms associated with OTA toxicity remained poorly understood in a developing organism. We showed that zebrafish embryos exposed to OTA demonstrated incorrect heart looping and small heart chambers. OTA also impaired the renal morphology and reduced the glomerular filtration rate of the embryonic zebrafish. The treatment of embryos with OTA attenuated the expression of the prolactin receptor, a gene (PRLRa) that has a key role in organogenesis and osmoregulation in vertebrates. OTA not only inhibited the phosphorylation of STAT5 and AKT, but also down-regulated the level of serpina1 mRNA in a dose-dependent manner. On the other hand, the microRNA profiling based on RNA sequencing revealed the up-regulation of microRNA-731 (miR-731) in the OTA-treated embryos. Further in silico analysis predicted that PRLRa was a target gene of miR-731. AntagomiR-731 restored PRLRa levels that had been reduced by OTA and also recovered the pronephros morphology that was damaged by OTA. These observations suggest that the exposure to OTA adversely affected the organogenesis of zebrafish, and the modulation of miR-731 and the PRLR signaling cascade contributed to the abnormal renal development mediated by OTA.

Extra-pituitary prolactin (PRL) and prolactin-like protein (PRL-L) in chickens and zebrafish

It is generally believed that in vertebrates, prolactin (PRL) is predominantly synthesized and released by pituitary lactotrophs and plays important roles in many physiological processes via activation of PRL receptor (PRLR), including water and electrolyte balance, reproduction, growth and development, metabolism, immuno-modulation, and behavior. However, there is increasing evidence showing that PRL and the newly identified 'prolactin-like protein (PRL-L)', a novel ligand of PRL receptor, are also expressed in a variety of extra-pituitary tissues, such as the brain, skin, ovary, and testes in non-mammalian vertebrates. In this brief review, we summarize the recent research progress on the structure, biological activities, and extra-pituitary expression of PRL and PRL-L in chickens (Gallus gallus) and zebrafish (Danio rerio) from our and other laboratories and briefly discuss their potential paracrine/autocrine roles in non-mammalian vertebrates, which may promote us to rethink the broad spectrum of PRL actions previously attributed to pituitary PRL only.

Characterization of the novel duplicated PRLR gene at the late-feathering K locus in Lohmann chickens

A partial duplication of the prolactin (PRL) receptor gene (designated as dPRLR) has been identified at the late-feathering (LF) K locus on chromosome Z of some chicken strains recently, implying that dPRLR is probably a candidate gene associated with LF development in chickens. However, little is known about the structure, functionality, and spatiotemporal expression of the dPRLR gene in chickens. In this study, using 3'-RACE and RT-PCR, the full-length cDNA of the dPRLR obtained from the kidneys of male Lohmann layer chickens carrying a K allele was cloned. The cloned dPRLR is predicted to encode a membrane-spanning receptor of 683 amino acids, which is nearly identical to the original PRLR, except for its lack of a 149-amino acid C-terminal tail. Using a 5× STAT5-Luciferase reporter system and western blot analysis, we demonstrated that dPRLR expressed in HepG2 cells could be potently activated by chicken PRL and functionally coupled to the intracellular STAT5 signaling pathway, suggesting that dPRLR may function as a novel receptor for PRL. RT-PCR assays revealed that similar to the original PRLR gene, dPRLR mRNA is widely expressed in all embryonic and adult tissues examined including the skin of male Lohmann chickens with a K allele. These findings, together with the expression of PRL mRNA detected in the skin of embryos at embryonic day 20 and 1-week-old chicks, suggest that skin-expressed dPRLR and PRLR, together with plasma and skin-derived PRL, may be involved in the control of the LF development of chicks at hatching. Moreover, the wide tissue expression of dPRLR implies that dPRLR may regulate other physiological processes of chickens carrying the K allele.

Metanephric kidney development in the chicken embryo: Glomerular numbers, characteristics and perfusion

The developing metanephric kidneys and chorioallantoic membrane (CAM) work in unison to ensure ion and water homeostasis in the avian embryo within its egg. This study focused on how avian renal structure and glomerular perfusion change in concert during development, as well as on changes in body fluid compartment osmolalities. White leghorn chicken eggs were incubated at 37.5°C and 55-60% relative humidity and were examined during days (D) 10-18 of development. Alcian blue, a stain that forms solid aggregations in actively perfused glomeruli of the metanephric kidney, was used to identify the proportion of glomeruli actually perfused. Total nephron number increased from 4705±1599 nephrons/kidney on day 12 to 39,825±3051 nephrons/kidney on day 18. Actively perfused nephrons increased ~23-fold from 761±481 nephrons/kidney on day 12 (~16% of total nephrons) to 17,313±2750 nephrons/kidney on 18 (~43% of total nephrons). Glomerular volume increased from days 12 to 14, remaining constant thereafter. Blood and cloacal fluid osmolality ranged from 270 to 280 mOsm/L. Amniotic fluid osmolality changed in a complex fashion during development but was comparable to blood on days 10 and 18. Allantoic fluid had the lowest osmolalities (175-215 mOsm/L) across development. Uric acid increased steadily within the allantoic fluid compartment, from 36±1mmol/L to 63±4mmol/L. The avian metanephric kidney thus shows a dramatic increase in both recruitment of nephrons and potential filtering capacity during the last half of incubation, in preparation for the degeneration of the allantoic membranes prior to internal piping and subsequent hatching.

Molecular characterization of prolactin receptor (cPRLR) gene in chickens: gene structure, tissue expression, promoter analysis, and its interaction with chicken prolactin (cPRL) and prolactin-like protein (cPRL-L)

In this study, gene structure, tissue expression, and promoter usage of prolactin receptor (PRLR) and its interaction with prolactin (PRL) and the newly identified prolactin-like protein (PRL-L) were investigated in chickens. The results showed that (1) PRLR gene was found to consist of at least 25 exons by 5'-RACE and RT-PCR assays; (2) multiple PRLR 5'-UTR sequences different in exon composition were isolated from chicken liver or intestine by 5'-RACE and could be subdivided into type I and type II transcripts according to the first exon used (exon 1G or exon 1A); (3) PRLR Type I transcripts with exon 1G were detected to be predominantly expressed in adult kidney and small intestine by RT-PCR, implying their expression is likely controlled by a tissue-specific promoter (P1). By contrast, PRLR type II transcripts containing exon 1A are widely expressed in adult and embryonic tissues examined and their expression is controlled by a generic promoter (P2) near exon 1A, which was demonstrated to display promoter activities in cultured DF-1, HEK293 and LoVo cells by the dual-luciferase reporter assay; (4) Using a 5×STAT5-luciferase reporter system, cPRLR expressed in HepG2 cells was shown to be activated by recombinant cPRL and cPRL-L via interaction with PRLR membrane-proximal ligand-binding domain, suggesting that like cPRL, cPRL-L is also a functional ligand of cPRLR. Collectively, characterization of cPRLR gene helps to elucidate the roles of PRLR and its ligands in birds and provides insights into the regulatory mechanisms of PRLR expression conserved in birds and mammals.

A novel prolactin-like protein (PRL-L) gene in chickens and zebrafish: cloning and characterization of its tissue expression

In this study, a full-length cDNA encoding a prolactin-like protein (PRL-L) was cloned from chicken brain tissues using RT-PCR. This putative PRL-L precursor has 225 amino acids in length and shares 30-35% amino acid sequence identity with prolactin (PRL) of chicken, zebrafish, Xenopus, rat and human. Using RT-PCR, the mRNA expression of PRL-L in chicken tissues was further examined. Unlike the predominant expression of PRL in pituitary, PRL-L was found to be widely expressed in adult chicken extra-pituitary tissues with only minimal expression detected in pituitary. In day-7 chicken embryos, the expression of PRL-L, but not PRL, was also detected in all extra-pituitary tissues examined. In line with this finding, the 5'-flanking region of chicken PRL-L (cPRL-L) gene, but not PRL gene, displayed a strong promoter activity in cultured DF-1 cell (a chicken embryo fibroblast cell line), suggesting that the basal expression of PRL-L gene is controlled by a transcriptional regulatory mechanism different from that of PRL gene. As the same findings in chickens, PRL-like protein(s), which share high amino acid sequence (42-86%) identity with chicken PRL-L, was identified in several non-mammalian vertebrate species including zebra finch, tiger puffer, green puffer and zebrafish. RT-PCR assay demonstrated that zebrafish PRL-L, similar to chicken PRL-L, is expressed in extra-pituitary tissues including brain, gill, muscle, ovary and testis. Taken together, these findings strongly suggest that a novel PRL-like protein exists in some non-mammalian vertebrates and may play an important role in target tissues, such as extra-pituitary tissues of chickens and zebrafish.

Expression patterns of the prolactin receptor gene in chicken lymphoid tissues during embryogenesis and posthatch period

Prolactin (PRL) is a pituitary hormone with multiple homeostatic roles among vertebrates. Although it has mainly been studied in relation to its role during the initiation and maintenance of incubation behavior in avian species, it has also been shown to act on the immune system. In this study, levels of PRL receptor (PRLR) mRNA were quantified by real-time PCR, and tissue expression was localized by in situ hybridization in primary and secondary lymphoid organs. Prolactin receptor was shown to be expressed in the bursa follicles, thymus lobules, and splenic pulp at all stages of development examined. Levels of PRLR expression were consistently higher in the bursa of Fabricius when compared with other lymphoid organs, suggesting that PRL acts primarily on bursal development. Furthermore, levels of PRLR mRNA appeared to fluctuate during embryogenesis, with a significant increase observed at embryonic day 19 in the bursa, at 7 d of age in the thymus, and on hatching day in the spleen. Thus, PRL might play an important role during the development of the immune system in chickens.

Ontogenesis of the Expression of Prolactin Receptor Messenger Ribonucleic Acid During Late Embryogenesis in Turkeys and Chickens

Changes in circulating levels of prolactin (PRL) and tissue content of PRL receptor (PRLR) messenger RNA (mRNA) in the liver, pancreas, kidney, and gonads (testis/ovary) were measured in turkey and chicken embryos from embryonic day (ED) 21 or ED15, respectively, to 1 d after hatch by real-time PCR. There were no differences between the sexes in chickens or turkeys. Both species had very similar patterns of PRL release and expression of PRLR mRNA, and no major differences were observed between turkey or chicken embryos. Plasma levels of PRL increased from low levels during the last week of embryonic development and were at significantly higher levels (about 4-fold) by 1 d after hatch. Similarly, in all tissues the content of PRLR mRNA was minimal at the outset and increased to reach maxima about the time of hatch. In both species, the highest levels of transcript were observed in the kidney followed by the gonad, liver, and pancreas. The tissue content of PRLR was correlated (0.6 to 0.8 dependent on the tissue) to circulating levels of PRL, which suggested that PRL may be associated with an increase in its receptor number around the time of hatch. Because levels of PRL and tissue content of PRLR mRNA increased around the time of hatch, this suggests that these tissues may be targets for PRL and may be involved in the physiologic changes occurring in embryos around the time of hatching.

Insulin-like growth factor-I affects amino compounds in the fluids of the chicken embryo

The concentration differences of more than 40 amino acids and related compounds in the amniotic fluid, allantoic fluid, and plasma of the chicken embryo are maintained by specific barriers. Since the amniotic and allantoic membranes are not innervated, we proposed that these barriers are controlled by hormones. Specific effects of insulin and prolactin on the amino compounds in the three fluids confirmed this hypothesis and raised the question of the possible role of growth factors. Application of insulin-like growth factor-I (IGF-I) to the chorioallantoic membrane of day 13 chicken embryos caused the following concentration changes in 41 amino compounds measured 1 and 2 h later: (1) in the amniotic fluid, an increase of 40 compounds, regardless of the presence or absence of a concomitant stress effect on these compounds; only NH3 was not affected; (2) in the allantoic fluid, a decrease of reduced glutathione (GSH) and anserine, and an increase of NH3; (3) in the plasma, a decrease of 24 compounds. Within the same time frame, stress caused in the amniotic fluid a drop of the concentration of 29, and an increase of 5, amino compounds; IGF-I reversed the stress effect on all 29 compounds the concentrations of which had dropped and enhanced the stress-induced increase of the other 5 compounds. In the allantoic fluid, stress induced an increase of GSH; IGF-I reversed this effect. In the plasma, stress caused an increase of 9 compounds; IGF-I counteracted the increase in 7 cases. These findings indicate new and unexpected roles of IGF-I in the prenatal regulation of amino compounds.

Molecular cloning of chicken vasoactive intestinal polypeptide receptor complementary DNA, tissue distribution and chromosomal localization

Chicken vasoactive intestinal polypeptide receptor (VIPR) cDNA was cloned by the reverse transcription-polymerase chain reaction method using primers designed on the basis of other species of VIPR cDNA. The cDNA obtained was sequenced by the dideoxy-mediated chain-termination method. Of the 2227 nucleotides that were sequenced, 84, 855, and 1338 bases represent the 5'-untranslated region (UTR), the 3'-UTR, and the open reading frame that predicts a peptide of 446 amino acids. The cDNA of the chicken VIPR shows 65% and 60% homologies to human cDNA of VIP1 and VIP2 receptors, respectively. The clone had the expected similarity to highly conserved features of the other G protein-coupled receptors (GPCRs) such as six cysteine residues that are functionally important in the VIPR subfamily. In addition, the seven potential membrane-spanning domains characteristic of the family B group III GPCR superfamily and highly conserved motif within the third cellular loop between transmembrane regions 5 and 6. Northern blot hybridization analysis in this study indicated mRNA expression of VIPRs in the various tissues of the chicken. Strong signal was detected in the brain and anterior pituitary gland. High levels of VIPR mRNA in the brain was consistent with VIP-binding experiments and with the function of VIP in the brain as a neuroendocrine factor or neurotransmitter. Expression of VIPR was detected in the anterior pituitary gland of chick embryos. The expression of VIPR mRNA in the chick anterior pituitary gland may indicate a regulatory function of VIP on prolactin (PRL) production or PRL cell proliferation during embryogenesis. Chicken VIPR shows high homology with mammalian type I VIPR but, in some part, possesses similarity of amino acid sequence. Expression of VIPR in various tissues supports diverse functions for VIP in the chicken.

Quantification of prolactin messenger ribonucleic acid, pituitary content and plasma levels of prolactin, and detection of immunoreactive isoforms of prolactin in pituitaries from turkey embryos during ontogeny

The content of prolactin mRNA as well as total prolactin content and type of isoforms of prolactin were measured in single pituitary glands from turkey embryos and poults. Levels of mRNA and pituitary content of prolactin remained low until 5 days before hatching, while plasma concentrations remained low until 2 days before hatching. Levels of prolactin mRNA then increased until the day of hatch, stayed stable during the 3 first days of age, and significantly increased until 2 wk of age. Similar changes were observed in pituitary content and plasma levels of prolactin. Two immunoreactive bands of apparent molecular masses of 24 and 27 kDa, corresponding to the nonglycosylated and glycosylated form of prolactin, respectively, were visualized on Western blots. In pituitary glands from embryos at 22 days of incubation, 31.5% of the protein was glycosylated, whereas in embryos at 27 days of incubation and poults at 1 and 7 days of age, 48.6%, 48.0%, and 56. 0% of prolactin was glycosylated, respectively. The results indicate that the increases in the synthesis and the release of prolactin occur mainly around and after the time of hatching in the turkey embryo. Higher percentages of glycosylated isoforms were associated with increasing levels of total prolactin in the pituitary gland. Thus, the synthesis of prolactin and its post-translational modifications may be important factors involved in the physiologic changes occurring around the time of hatching.

Hormonal effects on amino acids and related compounds in plasma, amniotic fluid, and allantoic fluid of the chicken embryo

So far, more than 40 free amino acids and related compounds have been identified in plasma, amniotic fluid, and/or allantoic fluid of the 13-day chicken embryo. Concentration differences, and greatly varying behavior of these compounds under experimental conditions, revealed the presence of specific barriers among the three fluids. We tested the hypotheses that (1) the absence of an innervation of amnion and allantois indicates a hormonal control of their barriers, and (2) changes in the concentrations of certain amino compounds in the three fluids indicate anabolic or catabolic actions of hormones. Insulin, prolactin, and stress caused complex changes of the concentrations of amino compounds in all three fluids within 30 min. Some of these changes indicated breakdown of embryonic tissues, while others must have been due to transfer of amino compounds among the three fluid compartments. However, there was no significant effect on the glucose concentration in any of the three compartments under any of the experimental conditions. This is the first demonstration of hormonal effects on the amino compounds in the extraembryonic fluids of nonmammalian amniotes.

Developmental expression of the prolactin gene in the chicken

Steady-state levels of prolactin (PRL) mRNA in the pituitary gland during embryonic development were determined by dot blot analyses to relate the changes with those of pituitary and plasma levels of PRL. Steady-state levels of the 1.38-kb mRNA encoding the PRL prohormone remained low until Day 18 of incubation, increased on Day 19 of incubation, and reached maximum levels on the day of hatch but decreased 1 day after hatch. Changes in both pituitary and plasma concentrations of PRL closely mimicked those changes in PRL mRNA levels. Subsequently, both the levels of the pituitary PRL mRNA and PRL remained unchanged whereas those of plasma PRL increased 7 days after hatch. The results indicate that a progressive expression of PRL gene in the pituitary gland occurs 1-2 days before the hatch and concomitant increases in plasma concentrations of prolactin may be associated with physiologic changes in pulmonary respiration and hatching.

Embryonic osmoregulation: consequences of high and low water loss during incubation of the chicken egg

The rates of water loss of domestic chicken eggs were varied during incubation to measure the osmoregulatory ability of the avian embryo. Egg water loss was increased by drilling holes in the eggshell over the airspace on day 13 (I = 21 days) and then placing these eggs in a low relative humidity (r.h.: 0-10%) incubator until hatch. Egg water loss was decreased by placing other eggs in a high-r.h. (85-90%) incubator on day 0. Eggs with low water loss (approximately 6% of initial fresh mass [IFM]) produced embryos and yolks that were not different in wet or dry mass when compared to control eggs that lost approximately 12% of IFM. However, 1-4 gm of excess albumen were left in low-water-loss eggs on day 21. Hatching success was 71% and 89% for low and control eggs, respectively. Low egg water loss did not appear to disturb embryonic growth. The allantoic fluid volume and millimolar allantoic Na+ and Cl- ions declined faster with high and slower with low rates of water loss. Thus, excess water was lost as a result of increased movement of water out of allantoic fluid, which was due to increased active transport of Na+ ions by the chorioallantoic membrane (CAM). Eggs with high water loss had elevated Cl- levels after day 17 in plasma and amniotic fluid, which indicated a period of osmotic stress after depletion of allantoic fluid between day 18 and hatch. The decrease in wet embryo mass measured in embryos from high-water-loss eggs was due principally to dehydration of skin. Embryonic skin may serve as an emergency water reservoir during osmotic stress. Dehydrated chicks produced from high-water-loss eggs were 6 gm less in wet mass at hatch compared to controls. However, these chicks regained the water deficit 7 days after hatch and grew at a rate not different from control chicks through 6 weeks of age. Total egg water loss of 12% of IFM results in highest hatching success. However, water losses between 6% and 20% of IFM do not appear to affect adversely the growth or water content of the chick. Water losses above 20% of IFM cause early depletion of allantoic fluid, prolong the period of osmotic stress, and result in subsequent dehydration of blood, amniotic fluid, and embryonic skin.(ABSTRACT TRUNCATED AT 400 WORDS)

Prolactin binding sites in Xenopus laevis tissues: comparison between normal and dehydrated animals

The binding of 125I-labeled ovine prolactin (125I-oPRL) to membranes from the kidney, epidermis, liver, and testis of Xenopus laevis adult specimens either kept in an aquatic environment or exposed for 2 weeks to dehydrating conditions was studied. Prolactin binding specificity was assayed through competition with several unlabeled hormones (oPRL, hGH, rGH, rLH, and porcine insulin). In the animal exposed to dehydrating conditions a statistically highly significant reduction in prolactin binding to the membranes from the kidney and epidermis was recorded. No significant variations were revealed by the membranes from the liver and testis. The reduction detected in the binding of 125I-oPRL is not related to the dissociation constant, but to the number of PRL binding sites. Since PRL ranks among the few peptide hormones whose rise in the bloodstream promotes an increase in the number of their own receptors, the reduction of its binding sites in Xenopus specimens exposed to dehydration might lend some support to our earlier hypothesis that transfer to a dehydrating environment may bring about, in this totally aquatic species, some decrease in the blood PRL levels.

Embryonic chick allantois: functional isolation and development of sodium transport

By removing the shell membranes from the chorioallantoic membrane, the chorion is damaged, as visualized by electron microscopy, and rendered permeable, as evidenced by penetration of horseradish peroxidase and increased inhibition of the allantoic Na+-K+ pump by ouabain applied on the chorionic side. The short-circuit current (SCC) of this functionally isolated allantoic epithelium is augmented by nystatin, a channel-forming ionophore, when applied to the mucosal surface. Electrical parameters were determined for three age groups between 12 and 19 days of incubation. The SCC approximately doubled from the youngest (12-13 days) to the oldest (18-19 days) groups, whereas the transepithelial resistance (Re) of 700-900 omega X cm2 remained the same. Amiloride, an inhibitor of apical Na+ uptake, inhibited 98-100% of the SCC at 10(-4) M in both 15-16 and 18-19 day epithelia. In the 12- to 13-day preparation 20-25% of the SCC was insensitive to 10(-3) M amiloride. The Ki's for amiloride were similar in all preparations, at about 5 X 10(-7) M. Determination of the Hill coefficients for inhibition revealed a lower value (0.75 +/- 0.03) for the 12-13 day preparation compared with the two older preparations with coefficients not significantly different from unity. Replacing Na+ in the bathing solutions abolished the SCC of 18-19 day epithelia, whereas about 15% of the SCC remained at 12-13 days. Thus, during development, the SCC of the allantoic epithelium increases in magnitude and becomes increasingly (to 100%) amiloride-sensitive and Na+-dependent.

Urates and allantoic regulation in embryonic Japanese quail, Coturnix coturnix japonica

During embryonic development, allantoic fluid represents the shifting balance between renal excretion and reabsorption by chorioallantoic membranes. Allantoic contents of Na+, K+, Cl-, urate, pH, and water were followed over days 10-15 of the 16 day incubation. Water volume remained near 0.9 ml until day 13, then declined very rapidly. The pH declined more steadily, from 8 to 5.5. Contents of Na+ and Cl- fell regularly to final values 80-88% below day 10. The K+ content changed differently and nearly doubled by day 13 but returned to day 10 values at the end. Urate content rose until day 13, then fell suddenly to low levels. This was due to the abrupt precipitation of most urate into masses not sampled by our method, so that after day 13, urate was underestimated (probably by 90-96%). Ion binding by urates was low (about 3% of Na+ and Cl-, 10% of K+) and appeared to be nonspecific. The underestimate of urate contents means, however, that in late incubation about one third of allantoic Na+ and 65-70% of K+ and Cl- are bound to precipitated urate and do not appear in balance sheets of allantoic ions. These precipitated ions account for the significant amounts of Na+ and K+ that remain in the allantoic remnant, left in the eggshell after hatching, but whose presence is not predicted by analysis of allantoic fluid.

Osmoregulatory effects of prolactin and growth hormone in embryonic chicks

Intact White Leghorn chick embryos were treated daily (on Days 6-13) with bovine prolactin (PRL) or ovine growth hormone (GH) at doses of 4-10 micrograms/g embryo wet wt. A control group received an equal volume of avian saline. [Na+] and [Cl-] were determined in allantoic fluid samples taken on Days 10, 12, and 14, and in amniotic fluid and blood plasma on Day 14. Allantoic fluid, amniotic fluid, and plasma osmolarities, embryo wet weight, hematocrit, and allantoic fluid volume were also determined on Day 14. PRL-treated embryos showed significantly lower allantoic [Na+] and [Cl-] compared to controls at Days 10, 12, and 14. Allantoic fluid osmolarity was reduced, and plasma osmolarity increased, at Day 14 in PRL-treated embryos. By contrast, PRL had no effect on allantoic volume, amniotic fluid [Na+], [Cl-], or osmolarity, plasma [Na+] or [Cl-], hematocrit, or embryo wet weight. GH-treated embryos showed significantly reduced allantoic [Na+] at both Days 10 and 14, but no other treatment effect. Calculations show that the decrease in total allantoic Na+ seen in PRL-treated embryos is equivalent in magnitude to 10% of the total egg Na+. Results from studies on embryonic amphibians and mammals suggest that this sodium is likely to be sequestered in an expanded extracellular volume.

Ontogeny of embryonic chicken lung: effects of pituitary gland, corticosterone, and other hormones upon pulmonary growth and synthesis of surfactant phospholipids

The actions of hormones on growth, cellular proliferation, and on synthetic rates of the major surfactant phospholipids, phosphatidylcholine (PC) and disaturated PC (DSPC), were studied in the lung of the chick embryo. Particular emphasis was placed on the effects of hypophysectomy, pituitary transplantation, and treatment with corticosterone (CORT). One study was concerned with hydrocortisone (HYCORT), estrogen (E2), thyroxine (T4), ovine prolactin (oPRL), and insulin. Hypophysectomy interfered with the normal gain in protein, the progressive dehydration of the embryonic lung, and also caused a reduction in the number of pulmonary cells on Days 16 and 18 of incubation. Absence of the pituitary gland diminished pulmonary PC by Day 16. Transplantation of one pituitary gland or exogenous CORT partially restored pulmonary phospholipid and PC (normalized per wet weight) in hypophysectomized (hypox) embryos. Transplantation also restored relative protein content in lungs of hypox individuals. Beyond this, transplantation was generally ineffective in reversing deficits of hypox individuals. All concentrations of CORT administered (30-100-300 micrograms) reduced the rate of pulmonary cell division. The highest dose was toxic as judged by its capacity to cause cellular death. Treatment of intact chicken embryos with CORT or E2 for two days stimulated incorporation of [14C]choline into PC and DSPC (the most surface-active component of PC) in the lungs of Day 17 embryos. CORT, but not E2, stimulated DSPC synthesis when treatment was increased to 3 days. Other hormones tested (T4, oPRL, insulin, and HYCORT) had no effect upon the rate of incorporation of [14C]choline into PC or DSPC. These results indicate that during ontogeny the avian lung becomes sensitive to CORT, and possibly E2, prior to 16 days of incubation. CORT, in particular, acts both to trigger the prehatching stimulation of surfactant phospholipid synthesis, especially the vital DSPC fraction, and to slow the rate of pulmonary cellular division coincident with biochemical differentiation of the surfactant system.