Relations of prolactin and thyroid hormone to molting, skin texture, and cutaneous secretion in the red-spotted newt

A short review on the role of thyroxine in fast wound healing and tissue regeneration

Wound healing is a multiplex interaction process that involves extracellular matrix, blood vessels, proteases, cytokines, and chemokine. So far, a number of studies have been performed to understand the basis of the wound-healing process and multiple wound-healing products have been designed. However, significant morbidity and mortality incidents still occurred due to poor wound healing. Thus, there is a dire need to understand the effects of topical applications of various therapeutic options that lead to fast wound healing. Thyroxine is one great panacea for wound healing that has been vigorously mooted throughout the years but a conclusive result regarding its effectiveness is still not achieved. This review is intended to find a rational basis for its positive role in wound healing. To accomplish the objective, this review highlights the different aspects of thyroxine's role in wound healing like keratin synthesis, skin thickening, and pro-angiogenesis, the basis of controversy on its wound healing ability and its potential to be used as a wound healing agent. This study will be helpful for researchers and surgeons to assess the importance of thyroxine as a candidate to comprehensively research to develop a potent, effective, and affordable wound healing drug.

Calcineurin/Nfatc1 signaling links skin stem cell quiescence to hormonal signaling during pregnancy and lactation

In most tissues, the prevailing view is that stem cell (SC) niches are generated by signals from within the nearby tissue environment. Here, we define genetic changes altered in hair follicle (HF) SCs in mice treated with a potent SC activator, cyclosporine A (CSA), which inhibits the phosphatase calcineurin (CN) and the activity of the transcription factor nuclear factor of activated T cells c1 (Nfatc1). We show that CN/Nfatc1 regulates expression of prolactin receptor (Prlr) and that canonical activation of Prlr and its downstream signaling via Jak/Stat5 drives quiescence of HF SCs during pregnancy and lactation, when serum prolactin (Prl) levels are highly elevated. Using Prl injections and genetic/pharmacological loss-of-function experiments in mice, we show that Prl signaling stalls follicular SC activation through its activity in the skin epithelium. Our findings define a unique CN-Nfatc1-Prlr-Stat5 molecular circuitry that promotes persistent SC quiescence in the skin.

Integument structure and function in juvenile Xenopus laevis with disrupted thyroid balance

The skin is the largest organ in the body and is a barrier between the internal and external environment. The present study evaluates how PTU, a goitrogen, that is used to treat hyperthyroidism affects the structure and electrical properties of the frog (Xenopus laevis) skin. The results are considered in the context of the two-membrane model established in the seminal work of Ussing and collegues in the 1940s and 1950s. In vitro experiments with skin from Xenopus adults revealed that PTU can act directly on skin and causes a significant increase (p<0.05, One-way ANOVA) in short circuit current (Isc) via an amiloride-insensitive mechanism. Juvenile Xenopus exposed to waterborne PTU (5 mg/L) had a significantly bigger and more active thyroid gland (p<0.01, Student's t-test) than control Xenopus. The bioelectric properties of skin taken from Xenopus juveniles treated with PTU in vivo had a lower Isc, (3.05±0.4, n=13) and Rt (288.2±39.5) than skin from control Xenopus (Isc, 4.19±1.14, n=14; Rt, 343.3±43.3). A histological assessment of skin from PTU treated Xenopus juveniles revealed the epidermis was significantly thicker (p<0.01, Student's t-test) and had a greater number of modified exocrine glands (p<0.01, Student's t-test) in the dermis compared to control skin. Modifications in skin structure are presumably the basis for its changed bioelectric properties and the study highlights a site of action for environmental chemicals which has been largely neglected.

Prolactin: Fishy Tales of Its Primary Regulator and Function

Prolactin (PRL) is an important regulator of multiple biological functions, and the control of PRL expression integrates a wide spectrum of molecules throughout vertebrates. PRL-releasing peptide (PrRP) seems to be an essential stimulator of PRL transcription and secretion in teleost pituitary and peripheral organs. In the amphibious euryhaline mudskipper, the localization of mRNA levels of PrRP and PRL as well as their regulation during acclimation to different environments are closely related. The presence of PrRP-PRL axes in the peripheral organs might suggest an ancient history of this axis prior to the evolution of the hypothalamus-pituitary, and it is possible that the PrRP is an original and primary regulator of PRL. In the euryhaline fishes, the permeability of gut of seawater-acclimated fish is generally greater than that of the freshwater (FW)-acclimated fish. The modification in the epithelial cell renewal system may play an important role in regulation of the permeability. PRL induces the cell proliferation during FW acclimation, whereas cortisol stimulates both cell proliferation and apoptosis. Indeed, a large proportion of the various actions of PRL seem to be associated directly or indirectly with cell proliferation and/or apoptosis, which might be a primary function of PRL.

Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice

PRL is an anterior pituitary hormone that, along with GH and PLs, forms a family of hormones that probably resulted from the duplication of an ancestral gene. The PRLR is also a member of a larger family, known as the cytokine class-1 receptor superfamily, which currently has more than 20 different members. PRLRs or binding sites are widely distributed throughout the body. In fact, it is difficult to find a tissue that does not express any PRLR mRNA or protein. In agreement with this wide distribution of receptors is the fact that now more than 300 separate actions of PRL have been reported in various vertebrates, including effects on water and salt balance, growth and development, endocrinology and metabolism, brain and behavior, reproduction, and immune regulation and protection. Clearly, a large proportion of these actions are directly or indirectly associated with the process of reproduction, including many behavioral effects. PRL is also becoming well known as an important regulator of immune function. A number of disease states, including the growth of different forms of cancer as well as various autoimmune diseases, appear to be related to an overproduction of PRL, which may act in an endocrine, autocrine, or paracrine manner, or via an increased sensitivity to the hormone. The first step in the mechanism of action of PRL is the binding to a cell surface receptor. The ligand binds in a two-step process in which site 1 on PRL binds to one receptor molecule, after which a second receptor molecule binds to site 2 on the hormone, forming a homodimer consisting of one molecule of PRL and two molecules of receptor. The PRLR contains no intrinsic tyrosine kinase cytoplasmic domain but associates with a cytoplasmic tyrosine kinase, JAK2. Dimerization of the receptor induces tyrosine phosphorylation and activation of the JAK kinase followed by phosphorylation of the receptor. Other receptor-associated kinases of the Src family have also been shown to be activated by PRL. One major pathway of signaling involves phosphorylation of cytoplasmic State proteins, which themselves dimerize and translocate to nucleus and bind to specific promoter elements on PRL-responsive genes. In addition, the Ras/Raf/MAP kinase pathway is also activated by PRL and may be involved in the proliferative effects of the hormone. Finally, a number of other potential mediators have been identified, including IRS-1, PI-3 kinase, SHP-2, PLC gamma, PKC, and intracellular Ca2+. The technique of gene targeting in mice has been used to develop the first experimental model in which the effect of the complete absence of any lactogen or PRL-mediated effects can be studied. Heterozygous (+/-) females show almost complete failure to lactate after the first, but not subsequent, pregnancies. Homozygous (-/-) females are infertile due to multiple reproductive abnormalities, including ovulation of premeiotic oocytes, reduced fertilization of oocytes, reduced preimplantation oocyte development, lack of embryo implantation, and the absence of pseudopregnancy. Twenty per cent of the homozygous males showed delayed fertility. Other phenotypes, including effects on the immune system and bone, are currently being examined. It is clear that there are multiple actions associated with PRL. It will be important to correlate known effects with local production of PRL to differentiate classic endocrine from autocrine/paracrine effects. The fact that extrapituitary PRL can, under some circumstances, compensate for pituitary PRL raises the interesting possibility that there may be effects of PRL other than those originally observed in hypophysectomized rats. The PRLR knockout mouse model should be an interesting system by which to look for effects activated only by PRL or other lactogenic hormones. On the other hand, many of the effects reported in this review may be shared with other hormones, cytokines, or growth factors and thus will be more difficult to study. (ABSTRACT TRUNCATED)

Prolactin alters the expression of integumental glycoconjugates in the red-spotted newt, Notophthalmus viridescens

Prolactin (PRL)-mediated changes in the texture and secretory activity of the skin in adult red-spotted newts may involve alterations in the distribution and/or expression of structural and secretory epidermal glycoconjugates. To explore this possibility, skin samples were obtained from groups of conditioned animals that had received injections of either ovine prolactin or amphibian saline over a 14-day period. Glycoconjugates within the epidermis and cutaneous glands were examined by means of lectin histochemistry using a panel of eight HRP-labelled lectins. PRL increased levels of sialic acid and n-acetylglucosamine in the stratum corneum. In contrast, glycoconjugates containing fucose, galactose, n-acetylgalactosamine, and galactose-(1,3)-n-acetylgalactosamine were decreased by PRL within both glands and epidermis. These results suggest that the integumental effects associated with prolactin in the red-spotted newt are mediated, at least in part, through the alteration of epidermal and glandular glycoconjugates.

Morphology and glycoconjugate histochemistry of the palpebral glands of the adult newt, Notophthalmus viridescens

The eyelids of the newt were studied in 10 microns serial paraffin and 1-2 microns plastic sections using standard histological stains and special stains for glycoconjugates. The eyelids contain four different glands. Simple acinar serous and simple acinar mucous glands occur in the skin; unicellular mucous glands occur in the conjunctiva; and convoluted tubular seromucous glands are present in connective tissue beneath the conjunctiva. The first two are identical to cutaneous glands found elsewhere on the head and body. The simple acinar serous glands are surrounded by myoepithelial cells and release their secretion, which is composed largely of proteins with minimal glycoconjugate content, by a holocrine mechanism. The secretory product of the simple acinar mucous glands is composed of neutral glycoconjugates with a minor content of acidic glycoconjugates; the mucin exhibits strong PAS and PAPD staining and weak staining by AB and PAPS methods. The unicellular conjunctival mucous glands secrete both neutral and acidic glycoconjugates as shown by positive reactions with PAS, PAPD, PAPS, and AB methods. Convoluted tubular seromucous glands in the ventral eyelid synthesize both proteins and neutral glycoconjugates. The mucous secretions of the conjunctival glands probably provide lubrication and protection for the cornea.

Amphibian prolactins: activity in the eft skin transepithelial potential bioassay

The effects of purified prolactins isolated from frogs (fPRL; Rana catesbeiana) and newts (nPRL; Cynops pyrrhogaster) were compared with those of ovine prolactin (oPRL) and thyrotropin releasing hormone (TRH) in the eft (Notophthalmus viridescens) skin transepithelial potential (TEP) bioassay. At total doses as low as 0.4 micrograms/animal, both fPRL and nPRL were as effective as oPRL in reducing eft skin TEP. By contrast, TRH at total doses as high as 400 micrograms/animal was ineffective in altering eft skin TEP. These data provide the first direct evidence that amphibian PRLs can exert significant physiological control over salamandrid integumental sodium transport.

Unequal activities of the two tilapia prolactins in the whole-animal transepithelial potential bioassay using the red eft

The cichlid fish tilapia (Oreochromis mossambicus) produces two forms of prolactin (tPRL177 and tPRL188) at equal rates. The primary sequences of this prolactin pair share only 69% identity. In these experiments, the whole-animal transepithelial potential (TEP) in the eft stage of the red-spotted newt (Notophthalmus viridescens) was measured in response to two injections totaling about 2 μg of tPRL177, tPRL188, ovine PRL, or tilapia growth hormone (tGH), or distilled water (5 μL/injection). This investigation was undertaken in order to locate prolactin receptors which discriminate between the two molecular forms of tilapia prolactin. The salamandrid integumental bioassay for prolactin was found to respond to tPRL177 as it does to ovine PRL. The more mainline tPRL188 was without effect at this dose and thus behaved more similarly to growth hormone (tilapia and ungulate) in this bioassay. The suspected magnitude of differences in the molecular surface characteristics between the two prolactins seem to be adequate to allow the binding of tPRL177 and to hinder the binding of tPRL188 to prolactin specific receptors in eft epithelial tissues.

Induction of cloacal and dermal skin glands of tiger salamander larvae, (Ambystoma tigrinum): effects of testosterone and prolactin

Treatment of male and female tiger salamander larvae with testosterone (0.3 micrograms/g body weight/day) induced precocious formation of ventral cloacal glands and stimulated proliferation and differentiation of mucous and granular (serous) glands in the ventral dermis of the skin. Lower doses of testosterone produced no visible glandular effects but did cause hyperemia and edema in the cloacal region. Prolactin (0.5 micrograms/g body weight/day) enhanced the action of testosterone on the cloacal glands, increasing both the amount of gland induced and the degree of glandular secretion. There was no apparent effect of prolactin alone on cloacal glands or any effect of prolactin with or without testosterone on the dermal glands. The possible homology of the amphibian ventral cloacal gland to the mammalian prostate gland is discussed.

Electrophysiology of newt skin: effects of prolactin

Integumental transepithelial potential (TEP) was measured by both in vivo and in vitro (Ussing chamber) techniques in the same adult terrestrial-phase California newts (Taricha torosa). In both types of preparation, TEP showed a logarithmic relation to external sodium (as Na2SO4) concentrations between 0.1 and 10 meq/liter, with in vivo values exceeding in vitro values at all points. KM was ca. 1 and 5 meq/liter for the in vivo and in vitro preparations, respectively. When terrestrial-phase newts were treated with prolactin (PRL; 50 mIU/g/day), in vivo TEP declined significantly within 3 days. In vivo TEP versus [Na+]ext curves of recently collected aquatic-phase newts were found to be not significantly different from those of PRL-treated terrestrial-phase animals. Current/voltage (I/V) plots likewise showed that skin from aquatic-phase and PRL-treated terrestrial-phase newts was electrophysiologically alike. Estimates and calculations based on the I/V relationship suggest that PRL acts primarily to increase the epithelial electrical resistance in the transcellular pathway, with no effect on the electromotive force of the sodium pump.

Thyroid function in adult rough-skinned newts (Taricha granulosa): effects of hypophysectomy and hormone replacement

This study examines the regulation of thyroid activity in adult rough-skinned newts, Taricha granulosa. Aquatic, breeding-condition newts were hypophysectomized and were injected for 23 days with the mammalian adenohypophysial hormones: ACTH, PRL, and GH. During a fourth week of treatment, these newts also received TSH. Plasma T4 concentrations were lower in hypophysectomized newts than in sham-hypophysectomized newts 23 days after surgery. Both ACTH and PRL increased T4 titers above these in saline-injected control newts; GH alone had no effect. TSH effectively increased the plasma T4 concentrations in newts from all five groups. GH, and possibly PRL, depressed the response to TSH. Plasma T4 concentration was positively correlated with body fluid loss, suggesting that hormone concentration/dilution effects may occur generally in animals such as these that undergo substantial seasonal changes in degree of hydration.

Sensitivity and specificity of salamandrid integumental transepithelial potential to prolactin

The effects of ovine prolactin (oPRL), bovine growth hormone (bGH) and human placental lactogen (hPL) on in vivo integumental transepithelial potential (TEP) were examined in two salamandrid urodeles, adult terrestrial-phase Taricha granulosa and the juvenile red-eft stage of Notophthalmus viridescens. TEP in efts treated with 1.0 microgram oPRL/2 days fell from 73.3 +/- 6.1 to 15.2 +/- 5.5 mV by Day 7 (P less than 0.001), whereas the TEP of efts treated with either 1.0 or 10 micrograms bGH/2 days remained at control levels for as long as 24 days. TEP in efts treated with a single dose of 10 micrograms oPRL dropped from 65.74 +/- 4.1 to 23.0 +/- 3.4 mV (P less than 0.01) in 3 days. Efts treated with various doses of oPRL showed a linear log total dose response over the range of 0.05 to 10.0 micrograms oPRL/animal, with a minimum detectable total dose of 0.4 micrograms/g (0.01 IU/g). In the same experiments, tail height increased by Day 7 in efts treated every other day with 10.0 micrograms oPRL, but not 1.0 microgram oPRL or either 1.0 or 10.0 micrograms bGH/2 days. In Oregon newts injected every other day with 10 micrograms oPRL, TEP decreased by 33% in 8 days (P less than 0.05), whereas in animals treated with 10 micrograms bGH/2 days, TEP did not change from control values even after 23 days. TEP in Oregon newts receiving a single dose of 100 micrograms oPRL dropped to 68% of initial values within 2 days (P less than 0.05), but subsequently recovered to control values 3 weeks after the last injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Osmoregulatory changes during the aquatic-to-terrestrial transition in the rough-skinned newt, Taricha granulosa: the roles of temperature and ACTH

Aquatic breeding-condition newts kept at 5, 11, or 18 degrees showed temperature-dependent changes in body weight (BW), tail height, plasma [Na+], hematocrit, integumental osmotic permeability, urine production, and transepithelial potential. Net urine production could account for the change in weight observed in animals kept at 11 and 18 degrees, suggesting that initial weight change results from a reduction in extracellular volume. Weight loss was correlated with increased hematocrit and plasma [Na+]. In another experiment, newts were sham-hypophysectomized (sham-HX) or hypophysectomized (HX) and injected with saline, ovine prolactin (PRL), ovine growth hormone (GH), or porcine adrenocorticotropic hormone (ACTH) and maintained at 5 degrees for 13 days. All animals lost 3-7% of their initial BW. Plasma [Na+] was reduced in animals injected with hormone compared with both sham-operated and saline-injected controls. Following an increase in water temperature to 11 degrees for 13 days, weight loss in sham-operated and ACTH-injected newts increased to 16% of BW compared with a total of 4-8% in newts injected with PRL, GH, or saline. In this experiment also, loss of body weight was correlated with increased plasma [Na+]. Although measurements of plasma Na+ concentrations indicated that ACTH caused "sodium retention," estimates of changes in total extracellular Na+ revealed that both sham-operated and ACTH-injected newts experienced a net sodium loss. In Taricha granulosa, warm temperatures and ACTH (presumably acting via interrenal hormones) appear necessary for the fluid and electrolyte loss which accompanies the transition from the aquatic to the terrestrial condition.

The effects of thyroidectomy on androgen and prolactin receptors in the dorsal skin and caudal fin of Triturus cristatus carnifex

The interactions between thyroid hormones and receptors for steroid hormones and prolactin in dorsal skin and caudal fin of Triturus cristatus carnifex were studied during the annual cycle. Thyroidectomy induces an increase of prolactin binding in the dorsal skin and caudal fin in the animals captured in March. In these thyrodectomized animals the androgen receptors became undetectable. Results indicate that in Triturus cristatus carnifex the thyroid induces an increase of androgen receptors and a decrease, that is removed by thyroidectomy, of prolactin receptors.

Breeding condition, temperature, and the regulation of salt and water by pituitary hormones in the red-spotted newt, Notophthalmus viridescens

In vivo integumental transepithelial potential (TEP) in the Eastern red-spotted newt (Notophthalmus viridescens) increases linearly with external [Na+] from 0.1 to 10 mM and is anion independent. Both integumental TEP and osmotic permeability are higher in laboratory-conditioned (LC, terrestrial) than in breeding-condition (BC, aquatic) newts at temperatures of 5-25 degrees. Prolactin (PRL) treatment of LC newts decreased both TEP and rate of water uptake. Arginine vasotocin (AVT) treatment resulted in a substantial increase in water uptake in LC newts, while little or no AVT response was seen in PRL-treated or BC newts. Hypophysectomy (HX) or ergocryptine treatment increased TEP in BC newts, whereas HX + PRL maintained TEP at control levels. Although ergocryptine and HX were without effect on water uptake in BC newts kept at 5 degrees for 9 days, HX + ACTH increased water uptake. HX produced a substantial fall in serum [Na+] in BC newts, while either PRL or ACTH replacement elevated serum [Na+]. Combined ACTH and PRL treatment returned serum [Na+] to control levels. These data suggest that high endogenous prolactin plays a significant role in maintaining serum [Na+] and integumental permeability and transport characteristics in breeding-condition N. viridescens. Although PRL and ACTH are both sodium retaining in the aquatic breeding stage, these two hormones promote opposite effects on the integument; PRL decreases both water uptake and integumental TEP, whereas ACTH (presumably acting through the adrenals) increases water uptake and possibly TEP.

Has prolactin an intermedin-like activity on the integument of the Axolotl?

Skin explants of the neotenic form of Ambystoma tigrinum (Axolotl) have been kept in culture during several days. When alpha-MSH or prolactin are added to the medium, a dispersion of melanin in melanosomes is observed. The reaction is reversible in the case of prolactin when the explants are transferred in the medium without hormones. Furthermore with prolactin, expansion of melanin in dermal melanophores is a more permanent and highly reproducible phenomenon, compared with the action of alpha-MSH in the same conditions. The type of action of prolactin could be different of the one of alpha-MSH.

Hyperpigmented patches in the skin of the newt Notophthalmus viridescens

In the integument of the red-spotted newt there occasionally appear patches of skin which are at the same time melanistic and iridescent. Such hyperpigmented patches have been found on the back, on the tail and on the dorsal surface of both fore and hind limbs. Cytological examination of several such areas revealed the presence of large numbers of chromatophores distributed throughout the dermis. The majority of the chromatophores consisted of atypically large and dendritic melanophores, which contained typical pigment granules. The iridescence resulted from a high incidence of iridophores. Xanthophores also were found in considerable abundance. This extensive and apparently random intermingling of melanophores, iridophores and xanthophores in limited areas constitutes a striking exception to the usual distributional patterns of pigment cells in this animal.

Effects of hormones on differentiation of parotid glands of suckling mice in vitro

The hormonal requirements for functional differentiation of mouse parotid glands were investigated using organ cultures in chemically defined medium. The hormones tested were insulin, thyroxine and prednisolone, and the parameters examined were alpha-amylase activity and the ultrastructure of the tissue. It is found that most of the amylase in the cultures (80%) was released into the culture medium after 5 days of cultivation. Prednisolone (5 . 10(-3) mg/ml) alone resulted in a 3--4-fold increase in specific activity of amylase (total amylase activity in the medium and culture) over that in its absence, but neither insulin nor thyroxine alone induced the enzyme. Prednisolone plus thyroxine (over 1 . 10(-7) mg/ml) or insulin (over 1 . 10(-3) unit/ml) induced markedly the enzyme, amylase specific activity being as much as 4- or 6-fold that with prednisolone alone. Moreover the enzyme specific activity was dependent on the prednisolone concentration (5 . 10(-7) - 5 . 10(-3) mg/ml) in the presence of thyroxine (1 . 10(-2) mg/ml) or insulin (1 . 10(-2) unit/ml). Morphological differentiation was also observed in explants cultivated in medium containing prednisolone plus thyroxine or insulin. These results suggest that besides glucocorticoids, insulin and thyroxine are involved in increase in amylase activity in mouse parotid glands during the late suckling period.

The morphology of the mucous gland and its responses to prolactin in the skin of the red-spotted newt

The mucous gland of the red-spotted newt, Notophthalamus viridescens viridescens, Rafinesque was examined by histochemical and ultrastructural techniques and its cytological responses to various hormonal conditions were studied. Its secretory epithelial cells produce and release in merocrine fashion a neutral, unsulphated mucosubstance. The secretory epithelium is bounded peripherally by a thin, but apparent non-functional, myoepithelium. The duct of this mucous gland consists of a single keratinized tubular cell that extends from the neck region of the gland to the surface of the epidermis. Mucous secretion is absent or greatly reduced on the skins of newts maintained under laboratory conditions for a few weeks but reappears after injection of ovine prolactin. Mucous glands in laboratory conditioned animals show a 4-fold increase in volume brought about by the engorgement of their epithelial cells with secretory granules. Ovine prolactin reduces the volume of the glands to unconditioned levels with a corresponding reduction in granular content, suggesting that prolactin functions in the release of the granules. This view is reinforced by the findings that autotransplantation of the pituitary gland prevents the conditioning effect and that glandular volume increases in autotransplanted animals given ergocornine. Granular accumulation begins also in hypophysectomized newts but ceases after a week, indicating the need for some hypophyseal factor in the synthesis as well as the release of the granules. Ovine prolactin restores mucous glands of hypophysectomized newts to the unconditioned state. Contrary to earlier findings, ovine prolactin induces a reduction in the volume of the mucous gland in thyroidectomized newts.