Action of estriol on the uropygial gland activity in pigeon

Administration of estriol (Sigma Chemical Co., U.S.A.) in the female young-adult pigeons at a dose of 50 micrograms/bird/day for 7 consecutive days caused atrophy of the uropygial gland, associated with increased cytopycnosis and drastic cell loss within the holocrine alveoli and reduction in the content of the glandular lipids. Probable mode of action of this steroid upon the uropygial gland has been suggested in the light of the recent data on its anti-estradiol property manifested in rat uterus.     

Alteration in the histochemical profile of steroid dehydrogenases in the uropygial gland of male domestic pigeons following androgen deprivation and testosterone supplement

Activities of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-HSDH) and 17 beta-hydroxysteroid dehydrogenase (17 beta-HSDH)) were histochemically demonstrated in the alveoli of the uropygial glands of male domestic pigeons (Columba livia Gmelin). The level of 3 beta-HSDH (Substrates: pregnenolone and dehydroepiandrosterone) was very low. On the other hand, an intense activity of 17 beta-HSDH was observed in the glandular alveoli of both sexually immature and adult pigeons when testosterone was used as the substrate. In the adult specimens, bilateral castration resulted in a moderate increase of the level of 17 beta-HSDH indicating a faster rate of conversion of testosterone into the weaker androgen, namely, delta 4-androstene-3,17-dione. On the other hand, administration of testosterone propionate (TP), 500 micrograms/bird/day for 15 days in the intact prepubertal and castrated adult pigeons caused a perceptible depletion of 17 beta-HSDH, which may be correlated with the increase in the local concentration of testosterone. Low dose of TP (100 micrograms/day) had no effect. When estradiol-17 beta was used as the substrate for 17 beta-HSDH, there was only a feeble response within the alveoli.     

Effect of combined treatment with imipramine and metyrapone on the immobility time, the activity of hypothalamo-pituitary-adrenocortical axis and immunological parameters in the forced swimming test in the rat.

Major depression is frequently associated with the hyperactivity of the hypothalamic-pituitary-adrenocortical axis, and glucocorticoid synthesis inhibitors have been shown to exert antidepressant action. The aim of the present study was to examine the effect of joint administration of metyrapone (50 mg/kg) and imipramine (5 and/or 10 mg/kg) on immobility time, plasma corticosterone concentration, the weight of spleens and thymuses and the proliferative activity of splenocytes in rats subjected to the forced swimming test--an animal model of depression. Metyrapone alone (50 mg/kg) reduced the immobility time of rats in the forced swimming test and decreased plasma corticosterone level, but did not change immunological parameters. Joint administration of metyrapone and imipramine (5 and 10 mg/kg) produced a more pronounced antidepressant-like effect than either of the drugs given alone. The forced swimming procedure significantly increased the proliferative activity of splenocytes, that parameter being reduced only by co-administration of metyrapone and imipramine. Joint administration of metyrapone and imipramine inhibited to a similar extend the corticosterone level as did treatment with metyrapone alone (about twofold); however, the plasma corticosterone level in animals treated with metyrapone and the higher dose of imipramine did not differ from the concentration of this steroid in control, not-stressed rats. The obtained results indicate that metyrapone potentiates the antidepressant-like activity of imipramine and exerts a beneficial effect on the stress-induced increase in plasma corticosterone concentration and the proliferative activity of splenocytes. These finding suggest that a combination of metyrapone and an antidepressant drug may be useful for the treatment drug-resistant depression and/or depression associated with a high cortisol level.     

Hypophyseal corticosteroids stimulate somatotrope differentiation in the embryonic chicken pituitary gland

Although it is known that glucocorticoids induce differentiation of growth hormone (GH)-producing cells in rodents and birds, the effect of mineralocorticoids on GH mRNA expression and the origin of corticosteroids affecting somatotrope differentiation have not been elucidated. In this study, we therefore carried out experiments to determine the effect of mineralocorticoids on GH mRNA expression in the chicken anterior pituitary gland in vitro and to determine whether corticosteroids are synthesized in the chicken embryonic pituitary gland. In a pituitary culture experiment with E11 embryos, both corticosterone and aldosterone stimulated GH mRNA expression and increased the number of GH cells in both lobes of the pituitary gland in a dose-dependent manner. These effects of the corticosteroids were significantly reversed by pretreatment with mifepristone, a glucocorticoid receptor (GR) antagonist, or spironolactone, a mineralocorticoid receptor (MR) antagonist. Interestingly, an in vitro serum-free culture experiment with an E11 pituitary gland showed that the GH mRNA level spontaneously increased during cultivation for 2 days without any extra stimulation, and this increase in GH mRNA level was completely suppressed by metyrapone, a corticosterone-producing enzyme P450C11 inhibitor. Moreover, progesterone, the corticosterone precursor, also stimulated GH mRNA expression in the cultured chicken pituitary gland, and this effect was blocked by pretreatment with metyrapone. We also detected mRNA expression of enzymes of cytochrome P450 cholesterol side chain cleavage (P450scc) and 3β-hydroxysteroid dehydrogenase1 (3β-HSD1) in the developmental chicken pituitary gland from E14 and E18, respectively. These results suggest that mineralocorticoids as well as glucocorticoids can stimulate GH mRNA expression and that corticosteroids generated in the embryonic pituitary gland by intrinsic steroidogenic enzymes stimulate somatotrope differentiation.     

Histological and histochemical study of the uropygial gland of chimango caracara (Milvago chimango vieillot, 1816)

The uropygial glands of birds are sebaceous organs that contribute to the water-repellent properties of the feather coat. We studied the histological and histochemical characteristics of the uropygial gland of chimango caracara using hematoxylin and eosin (H & E), Gomori´s trichrome, orcein, Gomori´s reticulin, periodic acid-Schiff (PAS), Alcian blue (AB) and a variety of lectins. The gland is composed of two lobes and a papilla with 20 downy feathers. It is surrounded by a capsule of dense connective tissue that contains elastic, reticular and smooth muscle fibers. The papilla is delicate and has two excretory ducts. The gland mass relative to body mass was 0.143%. Both adenomer cells and their secretions were stained with Sudan IV, PAS and AB, and were positive for numerous lectins that indicated the presence of lipids and carbohydrates. Immunohistochemical techniques to detect PCNA confirmed cell proliferation in the basal stratum of the adenomer cells. The lipids and glycoconjugates secreted by the uropygial gland serve numerous functions including protection against microorganisms.     

Uropygial gland volume and malaria infection are related to survival in migratory house martins

Pathogens such as bacteria, fungi and malaria and related haemosporidians provoke negative effects on the fitness of their hosts. Animals have developed a range of defensive mechanisms to resist or eliminate these parasitic infections and their negative fitness costs. The uropygial gland secretion has been proposed to act as defensive barrier of skin and plumage in the fight against bacteria and fungi, and may prevent birds from acquiring haemosporidian infections. Thus, the secretion of uropygial glands of birds may favour survival of individuals. However, whether uropygial gland secretion influence survival remains unknown. Here we explore if the size of the uropygial gland and malaria infection influence survival of house martins Delichon urbica. We showed, for the first time, that the volume of the uropygial gland positively predicted survival prospects of malaria infected house martins. Malaria infected birds had the lowest probability of survival, with the effect of gland size on survival prospects depending on infection: infected house martins with larger uropygial glands were better able to survive to the next breeding season, while infected birds with small uropygial glands were not. These results highlight the importance of uropygial gland secretion in the life history of wild birds.     

Down-regulation of endodermal Shh is required for gland formation in chicken stomach

During the development of the proventriculus (glandular stomach) of the chicken embryo, the endodermal epithelium invades into the surrounding mesenchyme and forms glands. The glandular epithelial cells produce pepsinogen, while the non-glandular (luminal) epithelial cells secrete mucus. Sonic hedgehog is expressed uniformly in the proventricular epithelium before gland formation, but its expression ceases in gland cells. Here we present evidence that down-regulation of Sonic hedgehog is necessary for gland formation in the epithelium using a specific inhibitor of Sonic hedgehog signaling and virus mediated overexpression of Sonic hedgehog. We also show that gland formation is not induced by down-regulation of Sonic hedgehog alone; a mesenchymal influence is also required.     

Epidermal growth factor inhibits morphogenesis of the embryonic quail uropygial gland cultured in vitro

Formation of the uropygial papilla and glandular lumena was inhibited when the uropygial rudiment of a day 8 1/3 quail embryo was cultured for 2 days in a chemically defined medium in the presence of 50 ng/mL of epidermal growth factor (EGF). The epithelium of EGF-treated explants remained at the placode stage, or underwent minor invagination into the mesenchyme and became stratified like that of a 12- or 13-day-old embryo. EGF promoted cellular proliferation in the uropygial epithelium and the epidermis adjacent to the gland and it shortened the lag phase of proliferation and markedly stimulated epithelial DNA synthesis, detected immunocytochemically by labeling explants with 5-bromodeoxyuridine (BrdU). The maximal labeling index in EGF-treated uropygial epithelium was 55% higher than in the control. Electron microscopic observation revealed that the basal lamina had become irregular in the EGF-treated explants and that epithelial cytoplasmic processes penetrated through the basal lamina toward the mesenchyme. These same phenomena are observed in vivo when the glandular buds are formed during day 12–13. Some precocious changes occurred in the uropygial epithelium when the rudiment was cultured in the presence of EGF.     

From preen secretions to plumage: the chemical trajectory of blue petrels' Halobaena caerulea social scent

Petrel seabirds heavily rely on their olfactory sense and are thus appropriate models for the study of avian chemical communication. The uropygial secretions of blue petrels Halobaena caerulea, for instance, have been shown to encapsulate elaborate sociochemical information including species, gender and identity. Yet, it is the plumage, and not preening secretions per se, which acts as the final substrate of avian scents. Importantly, the chemical relationship between secretions from the uropygial gland, located at the dorsal base of the tail, and plumage lipids has been considered in only a handful of studies which reported large qualitative differences. The emission process of avian scents, and the possible participation of the uropygial gland in particular, are therefore not elucidated. In the present study, we examine the early chemical trajectory of blue petrels' social chemosignals by comparing secretion and feather samples using Gas‐Chromatography Mass‐Spectrometry (GC/MS) and recently developed multivariate statistics. Our results indicate that (1) 85% of the feather lipids come from the uropygial secretions, (2) chemical differentiation between secretions and feather lipids includes qualitative and quantitative variations, which both have interesting implications for scent production, (3) the sociochemical information contained within the secretions (i.e. a sex‐specific signal and individual chemical signatures) are present in very conserved forms on the plumage. In the light of these results, it is apparent that the uropygial gland plays a critical role for chemical communication in petrels and possibly other avian groups.     

Action of the collagenase on the morphogenesis of the duck embryonic urophygial gland cultured in vitro]

Collagenase prevents in vitro the uropygial invaginations differentiation and the ectodermal glandular buds development. The basal lamina and the extracellular material disappear. These data suggest that collagen is essential to preen gland morphogenesis.     

Ultrastructural changes in the uropygial gland of the male Japanese quail,Coturnix coturnix,after testosterone treatment

Summary The ultrastructure of the uropygial gland of the male quail was compared to that of the sebaceous gland of the male rat after castration and testosterone treatment of both species. In intact animals, the differentiating cells of these glands displayed almost the same pattern as regards their smooth endoplasmic reticulum, an organelle involved in lipogenesis in both cases. Castration reduced the volume of this organelle, while testosterone administration restored cell morphology to a normal or supranormal level. Finally, this study showed that at ultrastructural level, there is a close functional analogy between the uropygial gland of quail and the sebaceous glands of rats as regards their androgen dependency. Consequently, the uropygial gland might be an attractive model for study of action of androgens on sebaceous-like glands.     

Body‐mass‐dependent trade‐off between immune response and uropygial gland size in house sparrows Passer domesticus

Parasites greatly impact host fitness. The immune system is fundamental to combat endoparasites, and survival increases with greater investment in immunity. Some ectoparasites, by contrast, are reportedly combated by the use of the uropygial gland, an organ exclusive to birds, which secretes an oily substance (preen oil) that is spread on plumage. However, both mounting an immune response against a parasite and producing uropygial gland secretion depend on the same resources, a situation which may induce trade‐offs between the two antiparasitic functions. In this study, I experimentally test whether immune response is traded off against uropygial gland size in the house sparrow Passer domesticus. In the experiment, a group of sparrows were injected with an antigen (lipopolysaccharide, LPS), which stimulates the immune system, while the other group received a sham injection. The uropygial gland of LPS‐treated birds decreased significantly more than that of the control birds after treatment. Nevertheless, the effect of the treatment was limited to house sparrows with low body mass, suggesting that heavy house sparrows were able to produce an immune response while maintaining a relatively large uropygial gland. Given that uropygial gland size is strongly related to production of preen oil, these results suggest that preen oil production declines in birds in poor body condition when resources are preferentially diverted to other demanding functions, such as the immune system. Considering that the uropygial gland is involved in several fitness‐related processes in birds, the trade‐off between immune response and uropygial gland size may have important consequences for bird life histories.     

Differentiation in culture of cells from an avian holocrine secretory gland: preparation of isolated cells and conditions which induce accumulation of malic enzyme

Mammalian sebaceous glands contain cells which are constantly going through a process of cell division, differentiation, and destruction. Birds have an analogous holocrine secretory gland, the uropygial gland, which is an excellent model for mammalian sebaceous glands and for analysis of the regulation of differentiation. Isolated uropygial cells were purified in good yield, and with high viability, after enzymatic digestion of the duck uropygial gland. Almost exclusively progenitor (basal) cells are recovered after separation of isolated cells on a Percoll density gradient; mature uropygial cells are destroyed during preparation of isolated cells. In primary culture, uropygial gland cells grow to confluence and partially duplicate the in vivo differentiation pathway. Malic enzyme activity increases 30-fold during 4 wks in culture, but there is little, if any, accumulation of fatty acid synthase and only a modest deposition of fat droplets. Medium conditioned by chick embryo fibroblasts inhibits the accumulation of malic enzyme without affecting cell growth. The basement membrane components, collagen, laminin, and Matrigel, which stimulate differentiation in other cell systems, were without effect on uropygial gland cultures. Triiodothyronine, cyclic AMP, and dexamethasone together with isobutylmethylxanthine had no effect on cell growth or malic enzyme activity. Epidermal growth factor, which stimulates cell division, increased cell number with no increase in malic enzyme accumulation. Factors which would stimulate further differentiation are missing from our culture system, but may include components of the basal lamina and/or factors secreted by mesenchymal cells.     

Evidence for the holocrine nature of lipoid secretion by avian epidermal cells: A histochemical and fine structural study of rictus and the uropygial gland

Cells of the avian epidermis (rictus of the chicken), when examined under the light microscope following suitable fat staining, show similarities to epithelial cells of the uropygial gland of chicken and pigeon, an organ which is recognized both morphologically and functionally as a holocrine gland. Evidence thus far from electron microscopic studies strongly suggests that the skin of the bird is also a holocrine gland, although details of cytogenesis and secretion differ somewhat in the two organs.     

Malic enzyme and fatty acid synthase in the uropygial gland and liver of embryonic and neonatal ducklings. Tissue-specific regulation of gene expression

Malic enzyme [L-malate-NADP oxidoreductase (decarboxylating), EC 1.1.1.40] and fatty acid synthase activities were barely detectable in the uropygial gland of duck embryos until 4 or 5 days before hatching, when they began to increase. These activities increased about 30- and 140-fold, respectively, by the day of hatching. Malic enzyme and fatty acid synthase activities were also very low in embryonic liver. However, hepatic malic enzyme activity did not increase until the newly hatched ducklings were fed. Hepatic fatty acid synthase began to increase the day before hatching and the rate of increase in enzyme activity accelerated markedly when the newly hatched ducklings were fed. Starvation of newly hatched or 12-day-old ducklings had no effect on the activities of malic enzyme and fatty acid synthase in the uropygial gland but markedly inhibited these activities in liver. Changes in the concentrations of both enzymes and in the relative synthesis rates of fatty acid synthase correlated with enzyme activities in both uropygial gland and liver. Developmental patterns for sequence abundance of malic enzyme and fatty acid synthase mRNAs in uropygial gland and liver were similar to those for their respective enzyme activities. Starvation of 4-day-old ducklings had no significant effect on the abundance of these mRNAs in uropygial gland but caused a pronounced decrease in their abundance in liver. It is concluded that developmental and nutritional regulation of these enzymes is tissue specific and occurs primarily at a pretranslational level in both uropygial gland and liver.     

Dual sites of occurrence of malonyl-CoA decarboxylase and their possible functional significance in avian tissues.

1. Uropygial glands of domestic goose and mallard which synthesize methyl-branched fatty acids, contain large quantities of cytosolic malonyl-CoA decarboxylase and a small quantity of mitochondrial enzyme. 2. Uropygial glands of chicken and the liver of geese which generate little methyl-branched acids, contain only small quantities of malonyl-CoA decarboxylase and in such cases the enzyme is in the mitochondria. 3. The mitochondrial decarboxylase from the uropygial gland and liver of goose is immunologically similar to the cytosolic decarboxylase of the uropygial gland. 4. The mitochondrial enzyme probably protects the mitochondrial enzymes which are susceptible to inhibition by malonyl-CoA, whereas the cytosolic enzyme promotes the synthesis of methyl-branched acids.     

The role of uropygial gland on sexual behavior in domestic chicken Gallus gallus domesticus

Recent studies have indicated that avian social behavior is influenced by olfactory cues. During the reproductive season a change in the chemical composition of uropygial gland secretion has been reported in some species and the hypothesis that olfactory signals may be produced by this gland has been proposed. To examine this hypothesis we performed two behavioral experiments to determine whether a female’s uropygial gland produce chemical signals that stimulate mating behaviors in domestic chickens. In Experiment 1 the role of the female’s uropygial gland in male mating behavior was examined by removing and examining the female’s uropygial gland. The frequency of mounts and copulations of intact male birds with sham-operated female birds was significantly higher than with uropygial glandectomized female birds. With respect to the number of waltzing that is one of the courtship displays intact males showed no significant difference between sham-operated female birds and uropygial glandectomized female birds. In Experiment 2 the relationship between male olfaction and the female’s uropygial gland was investigated using olfactory bulbectomized male birds. The number of mounts and copulations of sham-operated male birds with sham-operated female bird was significantly higher than with uropygial glandectomized female birds. In contrast olfactory bulbectomized male birds showed no significant differences in the number of mounts and copulations between sham-operated female birds and uropygial glandectomized female birds. These results indicate that intact and sham-operated male birds prefer to mate with female birds with the uropygial gland. The number of courtship waltzing of sham-operated male birds showed no significant difference. However olfactory bulbectomized male birds significantly courted to uropygial glandectomized female birds. Summarizing our results show that while anosmic males did not have any preference both intact and sham-operated male birds chose to mate with female birds having an intact uropygial gland suggesting that mate preference involves in male olfaction and that the female’s uropygial gland acts as a source of social odor cues in domestic chickens.     

Removal of the uropygial gland does not affect serum lipids, cholesterol and calcium levels in the rock pigeon Columba livia

The uropygial gland is an organ typical of birds, over which no agreement regarding its function has been attained yet. Authors attribute to the gland an hydrophobic action. The function of the gland is herein explored in rock pigeon, Columba livia, was used as experimental model for trials. The study was focused on the physiological role of the gland in relation to biochemical parameters. Pigeons were separated in groups of six birds each: a) intact control, b) surgical control, c) ablationed. Comparing control specimens with gland-removed specimens, recorded serum levels after 32 days were the following (mean+/-SD): cholesterol (g/l), 3.7+/-0.6 vs. 4.1+/-0.6; total lipids (g/l), 15.7+/-2.0 vs. 13.7+/-2.7; calcium (mg/l), 100.5 +/- 24.3 vs. 99.1 +/- 9.2. None of the differences were statistically significant. Thus, no alterations of basic biochemical parameters associated with metabolism of lipids were registered. In one group of birds the calcium and cholesterol levels were determined 122 days after surgery; in this case values remained unchanged related to the beginning of the trials. Results suggest that the uropygial gland is not physiologically related to either the homeostasis of total lipids, cholesterol or the regulation of calcium metabolism.     

Stereospecificity of malonyl-CoA decarboxylase, acetyl-CoA carboxylase, and fatty acid synthetase from the uropygial gland of goose

Malonyl-CoA decarboxylase from the uropygial gland of goose decarboxylated (R,S)-methylmalonyl-CoA at a slow rate and introduced 3H from [3H]2O into the resulting propionyl-CoA. Carboxylation of this labeled propionyl-CoA by propionyl-CoA carboxylase from pig heart and acetyl-CoA carboxylase from the uropygial gland completely removed 3H. Repeated treatment of (R,S)-[methyl-14C]methylmalonyl-CoA with the decarboxylase converted 50% of the substrate into propionyl-CoA, whereas (S)-methylmalonyl-CoA, generated by both carboxylases, was completely decarboxylated. Radioactive (R)- (S), and (R,S)-methylmalonyl-CoA were equally incorporated into fatty acids by fatty acid synthetase from the uropygial gland. The residual methylmalonyl-CoA remaining after fatty acid synthetase reaction on (R,S)-methylmalonyl-CoA was also racemic. These results show that: (a) the decarboxylase is stereospecific, (b) replacement of the carboxyl group by hydrogen occurs with retention of configuration, (c) acetyl-CoA carboxylase of the uropygial gland generates (S)-methylmalonyl-CoA from propionyl-CoA, and (d) fatty acid synthetase is not stereospecific for methylmalonyl-CoA.