Retinoid-Sensitive Steps in Steroidogenesis in Fetal and Neonatal Rat Testes: In Vitro and In Vivo Studies

Retinoic acid (RA) was recently shown to modify testosterone secretion of the fetal testis in vitro. We characterized this effect by culturing rat testes explanted at various ages, from Fetal Day 14.5 to Postnatal Day 3. In basal medium, RA inhibited, in a dose-dependent manner, both basal and acute LH-stimulated testosterone secretion by testes explanted on Fetal Days 14.5, 15.5, and 16.5. It had no effect on testes from older animals. The negative effect of RA did not result from a diminution in the number of Leydig cells but from a decrease in P450c17 mRNA levels and in LH-stimulated cAMP production. However, the RA-induced decrease in P450C17 mRNA levels was also observed with neonatal testes, suggesting that this enzymatic step is no longer rate limiting at this developmental stage. To study the physiological relevance of RA effects, we used fetuses and neonates issued from mothers fed a vitamin A-deficient (VAD) diet, resulting in a threefold decrease of plasma retinol concentration. On Fetal Day 18.5 and on Posnatal Day 3, testosterone secretion by the testis ex vivo was significantly increased in VAD animals. This shows that the endogenous retinol inhibits differentiation and/or function of fetal Leydig cells before Fetal Day 18.5 and is required for the normal regression of fetal Leydig cell function that occurs after Fetal Day 18.5. In conclusion, our results show that retinoids play a negative role on the steroidogenic activity during the differentiation of rat fetal Leydig cells.

Expression of neurogranin and neuromodulin is affected in the striatum of vitamin A-deprived rats

Our previous data showed that vitamin A deficiency (VAD) induces, in whole brain, a reduced amount of mRNA for brain retinoic acid (RA) and triiodothyronine (T3) nuclear receptors (i.e., RAR, RXR, and TR, respectively), which is accompanied by reduced amounts of mRNA and protein of neurogranin (RC3, a neuronal protein involved in synaptic plasticity) as well as selective behavioral impairment. Given the important role of retinoids for optimal brain functioning, the effects of vitamin A depletion and subsequent administration of RA or T3 on the mRNA levels of RA and T3 nuclear receptors and on two target genes' (RC3 and neuromodulin or GAP43) mRNA and protein levels were examined in the hippocampus, striatum, and cerebral cortex. A quantitative real-time polymerase chain reaction (PCR), in situ hybridization, and Western blot analysis demonstrated that the striatal region is the brain site where both RA and T3 signaling pathways are most affected by VAD. Indeed, rats fed a vitamin A-free diet for 10 weeks exhibited decreased expression of RAR, RXR, TR, RC3, and GAP43 in the striatum. The administration of T3 to these vitamin A-deprived rats reversed the reduction in mRNA levels of RA and T3 nuclear receptors and in mRNA and protein levels of target genes in this region. These data suggest that modifications that appear preferentially in the striatum, a region highly sensitive to vitamin A bioavailability, may contribute to neurobiological alterations and the spatial learning impairment that occurs in vitamin A-deprived animals.

Different Testicular Gene Expression Patterns in the First Spermatogenic Cycle of Postnatal and Vitamin A-Deficient Rat Testis1

Spermatogenesis is a complicated process of germ cell differentiation, involving programmatic expression of diverse cell type- and developmental stage-specific genes. To date, the vitamin-A-deficiency (VAD) rats and postnatal rats are two models commonly used to study spermatogenesis. In the present study, we studied the expression of 1185 known genes in the vitamin-A-deficient and retinol-reinitiated spermatogenesis of rat testis using Clontech Atlas rat cDNA expression arrays. The mRNA expression patterns of post-vitamin-A (PVA) testis on Days 15 and 35 were compared with those of the spermatogenic arrested rat testis on Day 0. About 9% (110/1185) of the genes studied were highly expressed. When compared with VAD rat testis on Day 0, 20 and 31 genes were differentially expressed by a factor of twofold or greater on Days 15 and 35, respectively. Four genes (cytochrome P450 17, sulfated glycoprotein 2, protein kinase inhibitor, and cathepsin L) that play important roles in spermatogenesis were selected and their gene expression patterns were confirmed by semiquantitative reverse transcription-polymerase chain reaction. Comparison of the expression patterns of these genes between PVA-VAD and postnatal rat testis in developmentally matched stages revealed substantial differences during the early stages of spermatogenesis. This discrepancy could be caused by either the presence of arrested but mature somatic cells in the PVA-VAD testis that may contribute to a unique gene expression pattern in this model or the direct effect of retinol on spermatogenesis. Therefore, caution is needed in interpreting the gene expression data using the PVA-VAD and postnatal rat models in studying spermatogenesis in rat testes.

Neonatal estrogenization leads to increased expression of cellular retinol binding protein 2 in the mouse reproductive tract

Exposure to estrogenic substances during a time window, the so-called "critical period," in perinatal life causes an irregular development of the genital tract that leads to ovary-independent proliferation and cornification in the vaginal epithelium in mice. We have previously demonstrated that retinol inhibits the irreversible effects of estrogen on the vagina. Here, mice kept in a vitamin-A-deficient condition during perinatal life were shown to be more sensitive to the harmful effects of estrogen. In addition, expression of mRNA for retinol binding protein type 2 (CRBP2), a "small intestine-specific" cytosolic protein that captures intracellular retinal and retinol, was detected in the vaginal epithelium. Induction of increased expression of CRBP2 mRNA by estrogen was also evident in the uterus and epididymis. Both estradiol-17beta and diethylstilbestrol markedly increased the tissue content of CRBP2 mRNA in the vagina and uterus during the neonatal "critical period" but not after 15 days of age. These results taken together imply that estrogen disrupts the local vitamin A balance by an induction of CRBP2 gene expression in the epithelium in the developing mouse genital tract, and that retinoid imbalance may contribute to the genesis of irreversible effects of estrogen on the vagina.

Reversal of liver fibrosis in aryl hydrocarbon receptor null mice by dietary vitamin A depletion

Aryl hydrocarbon receptor (AHR)-null mice display a liver fibrosis phenotype that is associated with a concomitant increase in liver retinoid concentration, tissue transglutaminase type II (TGaseII) activity, transforming growth factor beta (TGF beta) overexpression, and accumulation of collagen. To test the hypothesis that this phenotype might be triggered by the observed increase in liver retinoid content, we induced the condition of retinoid depletion by feeding AHR-null mice a vitamin A- deficient diet with the purpose to reverse the phenotype. Liver retinoid content decreased sharply within the first few weeks on the retinoid-deficient diet. Analysis of TGF beta 1, TGF beta 2, and TGF beta 3 expression revealed a reduction to control levels in the AHR -/- mice accompanied by parallel changes in TGaseII protein levels. In addition, we observed an increase in the TGF beta receptors, TGF beta RI and TGF beta RII, as well as in Smad4, and their reduction to wild-type mouse liver levels in AHR -/- mice fed the retinoid-deficient diet. Reduction of peroxisomal proliferator-activated receptor gamma (PPAR gamma) messenger RNA (mRNA) and protein levels in AHR -/- mice was consistent with the presence of hepatic stellate cell (HSC) activation and liver fibrosis. Vitamin A deficiency normalized PPAR gamma expression in AHR -/- mice. In conclusion, livers from AHR -/- mice fed the vitamin A-deficient diet showed a decrease in collagen deposition, consistent with the absence of liver fibrosis.

Vitamin A deficiency and relational memory deficit in adult mice: relationships with changes in brain retinoid signalling

Vitamin A and its derivatives, the retinoids, have recently been reported to be implicated in the synaptic plasticity of the hippocampus and in cognitive functions. Acting via transcription factors, retinoids can regulate gene expression via their nuclear receptors [retinoic acid receptors (RARs) and retinoid X receptors (RXRs)]. We recently showed that a moderate (about 30%) hypoexpression of brain (and hippocampal) retinoid signalling, like that naturally occurring in the aged brain of mice, might be related to a selective relational memory deficit. To further assess this hypothesis, the present study investigated the effects of Vitamin A deprivation of varying duration both on the brain expression of retinoid receptors (RARbeta and RXRbeta/gamma) and two associated target genes [tissue-type transglutaminase (tTG) and neurogranin, (RC3)], and on radial maze discrimination learning using young adult mice as subjects. We observed that irrespective of its duration (i.e. 31 or 39 weeks), Vitamin A deprivation resulted in a significant reduction (25-30%) in the expression of brain RARbeta, RXRbeta/gamma and tTG mRNAs. Conversely, only the 39-week condition was found to induce a significant decrease in brain RC3 mRNAs contents and a selective relational memory impairment. Finally, daily administration of retinoic acid (RA) failed to reverse the 39-week Vitamin A deficiency (VAD)-related cognitive deficit and to fully normalise the associated brain retinoid hyposignalling. In particular, there was no evidence for an up-regulating effect of RA on whole brain (and hippocampal) RC3 mRNAs of the 39-week-depleted mice. The results show that post-natal VAD may induce a selective memory impairment and give further support to the hypothesis that the fine regulation of retinoid-mediated gene expression is important for optimal brain functioning and higher cognition.

Maturational factors modulate transcription factors CCAAT/enhancer-binding proteins alpha, beta, delta, and peroxisome proliferator-activated receptor-gamma in fetal rat lung epithelial cells

Previous investigations have evidenced the importance of CCAAT/enhancer-binding proteins (C/EBPs) and peroxisome proliferator-activated receptor (PPAR)gamma for lung development, especially for alveolar type II cells (ATII). This prompted us to explore whether ATII maturation-promoting mediators controlled their expression in isolated ATII. In whole rat lung, C/EBPalpha, beta, delta, and PPARgamma mRNAs increased 3-5 times between gestational day 18 and term (Day 22), dropped around birth, then reincreased. C/EBPbeta and delta, but not PPARgamma, displayed similar profile in isolated ATII; C/EBPalpha transcript disappeared and the protein became hardly detectable in isolated cells. In cultured ATII, dexamethasone increased C/EBPbeta and PPARgamma mRNAs 2-4 times, and cyclic AMP increased C/EBPbeta and delta mRNAs approximately 1.5 times. Whereas retinoic acid increased C/EBPbeta and PPARgamma mRNAs 1.5 times in ATII in vitro, vitamin-A deficiency strongly decreased fetal lung C/EBPalpha, beta, and PPARgamma transcripts in vivo. C/EBPbeta, delta, and PPARgamma mRNAs were also increased in vitro by epidermal growth factor and keratinocyte growth factor, whereas they were unchanged by the maturation inhibitor transforming growth factor-beta. C/EBPalpha expression was not reinduced by any mediator. Changes in transcripts were reflected in protein levels analyzed through Western blotting. These results argue for a role of these factors in ATII functional maturation, and indicate a multifactorial control of their ontogeny.

[Vitamin A deficiency and clinical associations: a review]

An important focus of attention in Public Health has been micronutrient deficiency in human being because of the enhanced vulnerability of individuals to the effects of micronutrient deficiency or imbalance. Among all micronutrients deficiencies, vitamin A has been one of the most important public health problems, affecting a large percentage of people in developing countries. Vitamin A is particularly important for its role in the process of organism defense against infections. This article reviews comprehensively vitamin A metabolism, it highlights hypovitaminosis A relationship with pregnancy and human imunodeficiency, showing its repercussions in several clinical conditions.

Vitamin A deficiency alters the bioelectric parameters and RNA content of rat gastric mucosa in vitro

The present study was aimed to investigate the mechanisms by which vitamin A plays a role in maintaining the efficiency of gastric mucosal barrier. Particularly, we measured electrical parameters and the RNA/DNA ratio of gastric mucosa isolated in vitro from the stomach of rats in which vitamin A-deficiency was induced by means of a vitamin A-free diet and then abolished by means of a massive vitamin A supplementation. Pair-fed vitamin A-nondepleted rats and normal rats fed ad libitum on a standard diet served as controls. Vitamin A status was assayed for each group of rats by measuring the hepatic content of vitamin A. We found that in gastric mucosa vitamin A-deficiency induced: 1) a decrease in both transmucosal potential difference and short-circuit current; 2) an increase in transmucosal electrical resistance; 3) a decrease in RNA content resulting in a decreased RNA/DNA ratio. Abolishment of vitamin A-deficiency restored both electrical parameters and RNA content of rat gastric mucosa. Our results stress the role of vitamin A in maintaining the efficiency of the gastric mucosal barrier. Vitamin A seems to act by stabilizing gastric electrical parameters and by controlling the protein synthesis/turnover in the surface gastric mucosal cells.

Vitamin A transport: in vitro models for the study of RBP secretion

Retinol-binding protein (RBP) is the specific plasma carrier of retinol, encharged of the vitamin transport from the liver to target cells. Ligand binding influences the RBP affinity for transthyretin (TTR), a homotetrameric protein involved in the RBP/TTR circulating complex, and the secretion rate of RBP. In fact, in vitamin A deficiency, the RBP release from the hepatocytes dramatically decreases and the protein accumulates in the cells, until retinol is available again. The mechanism is still not clear and new cellular models are needed to understand in detail how the soluble RBP can be retained inside the cell. In fish, a vitamin A transport system similar to that of higher vertebrates is emerging, although with significant differences.

Identification of novel genes expressed during spermatogenesis in stage-synchronized rat testes by differential display

The molecular mechanism regulating spermatogenesis at different developmental stages remains largely unknown. In a vitamin A-deficiency (VAD) rat model, five distinct histologically defined, stage-synchronized testes: (i) resting spermatogonia and preleptotene spermatocytes at Day 0 of post-vitamin A treatment (PVA); (ii) early pachytene spermatocytes at Day 7 PVA; (iii) late pachytene at Day 15 PVA; (iv) round spermatids at Day 25 PVA; and (v) elongated spermatids at Day 35 PVA were used to study gene expression profiles by mRNA differential display. Twenty-four differentially expressed cDNA fragments were identified and cloned; oligonucleotide sequence analyses indicated that there are 12 novel gene sequences, half of which share no apparent match in current GenBank/EMBL databases. Other 12 VAD clones share sequence homology to membrane channel and transport, transcription and translation, cell cycle and morphogenesis, inducer and transducer, surface or secreted glycoproteins or enzymes, and other miscellaneous molecules. Semi-quantitative RT-PCR analyses against different stages of VAD testes demonstrated: (i) restricted expression of VAD1.2 and 1.3 (novel) on Day 25 PVA when round spermatids form; (ii) escalating pattern of VAD12 (Cx43) in Sertoli cells; and (iii) relative constant levels of VAD4 (A5D3), VAD26.1 (ribonuclease), and VAD27 (GRP8) in spermatogenesis.

The effect of retinyl palmitate added to iron-fortified maize porridge on erythrocyte incorporation of iron in African children with vitamin A deficiency

Retinyl palmitate added to Fe-fortified maize bread has been reported to enhance Fe absorption in adult Venezuelan subjects but not in Western Europeans. It is not known to what extent these results were influenced by differences in vitamin A status of the study subjects. The objective of the present study was to evaluate the influence of retinyl palmitate added to Fe-fortified maize porridge on erythrocyte incorporation of Fe in children with vitamin A deficiency, before and after vitamin A supplementation. Erythrocyte incorporation of Fe-stable isotopes was measured 14 d after intake of maize porridge (2.0 mg Fe added as ferrous sulfate) with and without added retinyl palmitate (3.5 micromol; 3300 IU). The study was repeated 3 weeks after vitamin A supplementation (intake of a single dose of 210 micromol retinyl palmitate; 'vitamin A capsule'). Vitamin A status was evaluated by the modified relative dose-response (MRDR) technique. Retinyl palmitate added to the test meal reduced the geometric mean erythrocyte incorporation of Fe at baseline from 4.0 to 2.6 % (P=0.008, n 13; paired t test). At 3 weeks after vitamin A supplementation, geometric mean erythrocyte incorporation was 1.9 and 2.3 % respectively from the test meal with and without added retinyl palmitate (P=0.283). Mean dehydroretinol:retinol molar ratios were 0.156 and 0.125 before and after intake of the single dose of 210 micromol retinyl palmitate; 'vitamin A capsule' (P=0.15). In conclusion, retinyl palmitate added to the labelled test meals significantly decreased erythrocyte incorporation of Fe in children with vitamin A deficiency at baseline but had no statistically significant effect 3 weeks after vitamin A supplementation. The difference in response to retinyl palmitate added to Fe-fortified maize porridge on erythrocyte incorporation of Fe before and after intake of the vitamin A capsule indicates, indirectly, changes in vitamin A status not measurable by the MRDR technique. The lack of conclusive data on the effect of retinyl palmitate on Fe absorption indicates the complexity of the interactions between vitamin A status, dietary vitamin A and Fe metabolism.

Vitamin A depletion is associated with low phosphoenolpyruvate carboxykinase mRNA levels during late fetal development and at birth in mice

Expression of the phosphoenolpyruvate carboxykinase (PEPCK) gene is repressed during fetal liver development and activated at birth. It has been shown that the PEPCK gene is a retinoid-responsive gene, but whether it is regulated by vitamin A in the fetus has not been established. In this study, we found that PEPCK mRNA can be detected in the murine fetal liver as early as gestational d 17. In addition, expression and cAMP induction of the PEPCK gene during late gestation and at birth require vitamin A sufficiency in the fetus and neonate. The PEPCK promoter contains several regulatory elements that bind a diverse array of transcription factors and nuclear coregulators, although it is largely unknown which of these factors are expressed early in liver development. Expression of some of these nuclear factors in livers of fetal mice was investigated by immunohistochemistry (IHC). Fetuses were from dams that were fed from the beginning of gestation diets that were adequate or devoid of vitamin A. Hepatocyte nuclear factor 4alpha (HNF4alpha) was expressed at the earliest stage of liver development on d 11, whereas retinoid X receptor alpha (RXRalpha) and nuclear coactivator CREB-binding protein (CBP) were expressed from d 16 onward. Although expressions of RXRalpha and CBP in livers of vitamin A-sufficient and vitamin A-depleted fetal mice did not differ, the level of HNF4alpha was consistently lower in the latter. Our findings strongly suggest that vitamin A is required during liver development for staged expression of the PEPCK gene and that HNF4alpha may be involved in mediating vitamin A regulation of the PEPCK gene at these critical periods.

Absorption and conversion of a single oral dose of beta-carotene in corn oil to vitamin A in Sprague-Dawley rats with low reserve of vitamin A

This study was carried out to determine how much of a single oral dose of beta-carotene in oil is absorbed and how much of the absorbed dose is converted to retinoids in rats having a vitamin A reserve at the lowest end of adequate status. Weanling rats raised on a vitamin A-deficient diet for four weeks were given a single oral dose of either corn oil or beta-carotene dissolved in corn oil (1.86 mumol). Serum, liver, and the entire digestive tract of the rats were analyzed for carotenoids and retinoids. Results showed that 4 hours after dosing, 1.64 mumol (88%) of the dose of beta-carotene was found intact, with 17.6% found in the stomach, 21% in the small intestine, and 49.3% in the large intestine. A total of 0.28 mumol of newly formed retinoids (expressed as retinyl palmitate) was present in serum, liver, and mucosa of small intestine. The results suggest that a single oral dose of beta-carotene might not be an effective way of raising vitamin A status in rats.

Triiodothyronine administration reverses vitamin A deficiency-related hypo-expression of retinoic acid and triiodothyronine nuclear receptors and of neurogranin in rat brain

Recent studies have revealed that retinoids play an important role in the adult central nervous system and cognitive functions. Previous investigations in mice have shown that vitamin A deficiency (VAD) generates a hypo-expression of retinoic acid (RA, the active metabolite of vitamin A) receptors and of neurogranin (RC3, a neuronal protein involved in synaptic plasticity) and a concomitant selective behavioural impairment. Knowing that RC3 is both a triiodothyronine (T3) and a RA target gene, and in consideration of the relationships between the signalling pathways of retinoids and thyroid hormones, the involvement of T3 on RA signalling functionality in VAD was investigated. Thus, the effects of vitamin A depletion and subsequent administration with RA and/or T3 on the expression of RA nuclear receptors (RAR, RXR), T3 nuclear receptor (TR) and on RC3 in the brain were examined. Rats fed a vitamin A-deficient diet for 10 weeks exhibited a decreased expression of RAR, RXR and TR mRNA and of RC3 mRNA and proteins. RA administration to these vitamin A-deficient rats reversed only the RA hypo-signalling in the brain. Interestingly, T3 is able to restore its own brain signalling simultaneously with that of vitamin A and the hypo-expression of RC3. These results obtained in vivo revealed that one of the consequences of VAD is a dysfunction in the thyroid signalling pathway in the brain. This seems of crucial importance since the down regulation of RC3 observed in the depleted rats was corrected only by T3.

Vitamin A deficiency in the late gastrula stage rat embryo results in a one to two vertebral anteriorization that extends throughout the axial skeleton

Vitamin A and its metabolites are known to be involved in patterning the vertebrate embryo. Study of the effect of vitamin A on axial skeletal patterning has been hindered by the fact that deficient embryos do not survive past midgestation. In this study, pregnant vitamin A-deficient rats were maintained on a purified diet containing limiting amounts of all-trans retinoic acid (12 microg atRA/g diet) and given a daily oral bolus dose of retinol starting at embryonic day 0.5, 8.25, 8.5, 8.75, 9.25, 9.5, 9.75, or 10.5. Embryos were recovered at E21.5 for analysis of the skeleton and at earlier times for analysis of select mRNAs. Normal axial skeletal development and patterning were observed in embryos from pregnant animals receiving retinol starting on or before E8.75. Delay of retinol supplementation to E9.5 or later resulted in a marked increase in both occurrence and severity of skeletal malformations, extending from the craniocervical to sacral regions. Embryos from the groups receiving retinol starting at E9.5 and E9.75 had one-vertebral anterior transformations of the cervical, thoracic, lumbar, and sacral vertebrae. Few embryos survived in the E10.5 group, but these embryos yielded the most severe and extensive anteriorization events. The skeletal alterations seen in vitamin A deficiency are associated with posterior shifts in the mesodermal expression of Hoxa-4, Hoxb-3, Hoxd-3, Hoxd-4, and Hoxa-9 mRNAs, whereas the anterior domains of Hoxb-4 and Cdx2 expression are unaltered. This work defines a critical window of development in the late gastrula-stage embryo when vitamin A is essential for normal axial skeletal patterning and shows that vitamin A deficiency causes anterior homeotic transformations extending from the cervical to lumbosacral regions.

In vivo studies of altered expression patterns of p53 and proliferative control genes in chronic vitamin A deficiency and hypervitaminosis

Several clinical trials have revealed that individuals who were given beta-carotene and vitamin A did not have a reduced risk of cancer compared to those given placebo; rather, vitamin A could actually have caused an adverse effect in the lungs of smokers [Omenn, G.S., Goodman, G.E., Thornquist, M.D., Balmes, J., Cullen, M.R., Glass, A., Keogh, J.P., Meyskens, F.L., Valanis, B., Williams, J.H., Barnhart, S. & Hammar, S. N. Engl. J. Med (1996) 334, 1150-1155; Hennekens, C.H., Buring, J.E., Manson, J.E., Stampfer, M., Rosner, B., Cook, N.R., Belanger, C., LaMotte, F., Gaziano, J.M., Ridker, P.M., Willet, W. & Peto, R. (1996) N. Engl. J. Med. 334, 1145-1149]. Using differential display techniques, an initial survey using rats showed that liver RNA expression of c-H-Ras was decreased and p53 increased in rats with chronic vitamin A deficiency. These findings prompted us to evaluate the expression of c-Jun, p53 and p21WAF1/CIF1 (by RT-PCR) in liver and lung of rats. This study showed that c-Jun levels were lower and that p53 and p21WAF1/CIF1 levels were higher in chronic vitamin A deficiency. Vitamin A supplementation increased expression of c-Jun, while decreasing the expression of p53 and p21WAF1/CIF1. Western-blot analysis demonstrated that c-Jun and p53 showed a similar pattern to that found in the RT-PCR analyses. Binding of retinoic acid receptors (RAR) to the c-Jun promoter was decreased in chronic vitamin A deficiency when compared to control hepatocytes, but contrasting results were found with acute vitamin A supplementated cells. DNA fragmentation and cytochrome c release from mitochondria were analyzed and no changes were found. In lung, an increase in the expression of c-Jun produced a significant increase in cyclin D1 expression. These results may explain, at least in part, the conflicting results found in patients supplemented with vitamin A and illustrate that the changes are not restricted to lung. Furthermore, these results suggest that pharmacological vitamin A supplementation may increase the risk of adverse effects including the risk of oncogenesis.

Vitamin A deficiency leads to increased cell proliferation in olfactory epithelium of mature rats

We have shown previously that vitamin A deficiency (VAD) leads to the decreased expression of gene products that are specifically synthesized by mature neurons in the olfactory epithelium (OE) of adult rats. These results support the hypothesis that retinoic acid, a derivative of vitamin A, is required for neurogenesis and neuron replacement in vivo. VAD does not cause gross degeneration of the OE, raising the question: what types of cells continue to populate VAD OE? In this study, we compared the cell densities of VAD and VA-sufficient (VAS) OE and investigated whether cell proliferation is upregulated in VAD OE. The results show that (1) total cell number in VAD and VAS OE are comparable; (2) localized areas of hyperplasia are present in the basal regions of VAD, but not VAS, OE; (3) there is a substantial increase in the number of PCNA (proliferating cell nuclear antigen) positive cells in the basal region of VAD OE relative to VAS OE; and (4) there is a relative increase in the levels of mRNA encoding the transcription factor, MASH I, in VAD OE. We conclude that reduced availability of vitamin A derivatives, such as retinoic acid, leads to a loss of control over proliferation, hyperplasia, and increased numbers of pro-neural cells in vivo.

Absorption and conversion of 11,12-(3)H-beta-carotene to vitamin A in Sprague-Dawley rats of different vitamin A status

The aim of this study was to determine the bioavailability and bioconversion to vitamin A of a single oral dose in oil or an aqueous dispersion of labeled beta-carotene in rats of different vitamin A status. Weanling Sprague-Dawley rats were fed a vitamin A-deficient diet and supplemented for 4 wk with 0, 7, 21 and 63 micro g/(rat. d) of retinyl acetate. The rats, of different vitamin A status, were then given a single oral dose of 11,12-(3)H-beta-carotene (0.15 micro mol) dissolved in corn oil or dispersed in aqueous Tween 80. The rats were killed 4 or 24 h after the dose, and serum, liver, the entire digestive tract, other tissues, urine and feces were analyzed for carotenoids, retinoids and associated radioactivity. At 4 h after the dose, 85 +/- 9% of the administered radioactivity was recovered. Almost 50% of the dose was present as intact beta-carotene in the large intestine where further absorption and conversion was ruled out. The absorption of beta-carotene was very low, and < 5% of the radioactive dose was converted to retinoids. The absorption and conversion to vitamin A did not differ among rats of different vitamin A status. The results suggest that a single oral dose of beta-carotene might not be an effective way of raising vitamin A stores in the body.

Response of the insulin-like growth factor system to vitamin A depletion and repletion in rats

Vitamin A (VA) and insulin-like growth factors (IGF) are important regulators of a wide range of physiological processes. To investigate the IGF system's involvement in the physiological actions of VA, we examined the effects of VA status on components of the IGF system in rats. Male rats (3-wk-old) fed a VA-deficient diet for 11 wk developed VA deficiency, as confirmed by the depletion of serum retinol and hepatic retinyl palmitate. Rats fed the VA-deficient diet had significantly lower body weight (p < 0.05) and lower serum IGF-I concentrations than the rats fed the control diet. The decreases in serum IGF-I levels were accompanied by approximately 40% lower levels of the IGF-I mRNA in the liver and lungs. With respect to the gene expression of other IGF system components, VA deficiency caused a twofold induction of IGF-I receptor (IGF-IR) mRNA in the heart and a twofold reduction in IGFBP-6 mRNA in the lungs, but did not alter the expression of IGF-II, IGFBP-1, IGFBP-3, IGFBP-4 or IGFBP-5 in all tissues examined. When VA-deficient rats received a single injection of retinoic acid (2 mg/rat), tissue IGF-I and IGF-IR gene expression did not change after 4 or 8 h, while the expression of IGF-II, IGFBP-4, and IGFBP-6 mRNAs in some tissues increased rapidly. These results suggest a possible involvement of the IGF system in mediating the physiological actions of VA, including VA-supported growth, in the rat.

Interaction of zinc and vitamin A on the ocular surface

PURPOSE

The purpose of this study was to assess morphologically the interaction between zinc and vitamin A in their effect on the ocular surface.

METHODS

Three-week-old Wistar Kyoto rats were divided into five groups: group A(+) Zn(+) was fed a diet containing both vitamin A and Zn; group A(-) was fed a vitamin A-deficient diet; group A(-) Zn(+) was given a vitamin A-deficient diet and deionized distilled water with Zn; group Zn(-) and group Zn(-) A(+) were fed a Zn-deficient diet, whereby group Zn(-) A(+) received an intraperitoneal injection of vitamin A. Corneas and conjunctivas of each group were examined by electron microscopy.

RESULTS

The corneas and conjunctivas of group A(-) demonstrated a decrease in the number of microvilli in the epithelium. The corneas and conjunctivas of group A(-) Zn(+) had a decrease in microvilli but more microvilli than those of group A(-). The corneas of group A(-) showed keratinization, but those of group A(-) Zn(+) showed no keratinization. In group Zn(-) the microvilli on the conjunctiva and cornea were sparse. Group Zn(-) A(+) had a decrease in microvilli but more microvilli than group Zn(-). The conjunctivas of group Zn(-) A(+) had more goblet cells with granules than did those of group Zn(-).

CONCLUSION

These results suggest that a synergistic interaction exists between vitamin A and zinc for the maintenance of the corneal and conjunctival epithelium.

[Biochemical mechanisms of radiogenic cytogenetic and somatic disorders in children residing in regions polluted by radionuclides]

Children and adults affected by the Chernobyl accident suffer with lipoperoxic stress coupled with hypovitaminoses A and E, the syndrome and its radiogenic mechanisms described by the authors previously. The relation of these biochemical disturbances to somatic consequences on mutagenic and teratogenic levels caused by chronic low-dose irradiation of children into radiopolluted regions has been investigated. Either the rational approaches to prevent or/and to treat all pathologies indicated were tested. The radionuclide polluted regions had 1-5, 5-15 and 15-40 Ci/km2 by 137Cs. Unprotected newborns (without the therapy) had vA and vE levels about one third of normal ones for minimal radioloads, the vitamins lowered further for higher Da and/or Dm up to the deep hypovitaminoses or even avitaminoses. Increasing of LPC catabolites levels for children were correlated significantly with their stigmation levels. The therapy-protected newborns had normal ranges of all indices. However, unprotected newborns showed dramatic increase for all of radiogenic indices along with fall of vA and vE, and significant inverse correlations of the indices with retinol levels. The values of radiogenic indices showed hyperbolic-like rise along with growing of vA and vE deficits below their lower limits. The combination of radiogenic biochemical deviations evaluated for Chernobyl contingents is supposed to be the primary molecular mechanisms of somatic mutations and irreversible stigmation. The peroral polyvitamin therapy is proposed as the method of choice for prevention or normalization of revealed pathologies.

Lecithin:retinol acyltransferase expression is regulated by dietary vitamin A and exogenous retinoic acid in the lung of adult rats

Lecithin:retinol acyltransferase (LRAT), a retinol esterifying enzyme, plays a major role in the metabolism and storage of vitamin A in several animal tissues. Groups of vitamin A (VA)-adequate (control) and VA-deficient rats were treated with vehicle or 5 mg of all-trans-retinoic acid (RA); an additional group of VA-deficient rats were fed 100 microg of RA. In control rats, lung LRAT mRNA and LRAT specific activity were approximately 50% of the levels expressed in the liver. In the lung of VA-deficient rats, LRAT mRNA and specific activity levels were <10% of those in the control group. Treatment of VA-deficient rats with 100 microg RA increased lung LRAT mRNA (P < 0.005) and specific activity (P < 0.0001), and treatment with 5 mg of RA increased LRAT mRNA level and specific activity more than approximately 15- and 6-fold above those in control lung, respectively (both P < or = 0.001). The lung tissue of VA-adequate rats contained retinyl ester (approximately 3 nmol/g tissue), whereas none was detected in the lung tissue of VA-deficient rats. These results show that LRAT expression and vitamin A storage are regulated by vitamin A status and by treatment with all-trans-RA in the adult lung. These results suggest that the regulated storage of vitamin A may be important for maintaining the integrity and physiologic functions of the lung.