Vitamin A-deficient Diet Research Articles

Vitamin A Deficiency in Rats Induces Langerhans Cells in the Iliac Lymph Nodes Draining to the Squamous Metaplastic Urinary Bladder

We previously observed Langerhans cells (LC) in the squamous metaplastic urinary bladder in rats fed a vitamin A-deficient diet. Here we report the finding of LC in the iliac lymph nodes, one of the abdominal lymph nodes draining to the urinary bladder. LC had previously only been observed in the superficial and hilar lymph nodes, but never in the abdominal lymph nodes. This is also the first observation of Birbeck granule (BG)-positive LC in the iliac lymph nodes. LC were not found in the transitional mucosa of the urinary bladder. In the present experiments, the LC were observed in both the squamous metaplastic mucosa and lamina propria of the urinary bladder, and also in the iliac lymph nodes, which drain into the urinary bladder. BG-positive LC may mature not only in the squamous epithelia, but also in squamous metaplastic mucosa. LC in the lamina propria of the urinary bladder might migrate to the iliac lymph nodes, which are regional lymph nodes, where they could function in antigen presentation. LC in the skin play a role in antigen-antibody interactions, and the squamous metaplastic mucosa of the urinary bladder may be a similar environment, in which LC in the mucosa can migrate to the regional lymph nodes.

Retinoic acid inhibits rat XY gonad development by blocking mesonephric cell migration and decreasing the number of gonocytes.

Vitamin A (also called retinol) and its derivatives, retinoic acids (RAs), are required for postnatal testicular function. Abnormal spermatogenesis is observed in rodents on vitamin A-deficient diets and in retinoic acid receptor alpha (RARalpha) knockout mice. In contrast, RA has an inhibitory effect on the XY gonad development in embryos. To characterize this inhibitory effect of RA, we investigated the cellular events that are required for the XY gonad development, including cell migration from the adjacent mesonephros into the gonad, fetal Sertoli cell differentiation, and survival of gonocytes. In organ cultures of Embryonic Day 13 (E13) XY gonads from rats, all-trans-retinoic acid (tRA) inhibited mesonephric cell migration into the gonad. Moreover, treatment with tRA decreased the expression of Müllerian-inhibiting substance in Sertoli cells and dramatically reduced the number of gonocytes. Increased apoptosis was detected in the XY gonads cultured with tRA, suggesting that the loss of gonocytes could be due to increased apoptosis. In addition, Am580, a synthetic compound that exhibits RARalpha-specific agonistic properties, mimicked the inhibitory effects of tRA on the XY gonad development including mesonephric cell migration and gonocyte survival. Conversely, a RARalpha-selective antagonist, Ro 41-5253, suppressed the inhibitory ability of tRA on the XY gonad development. These results suggest that retinoic acid acting through RARalpha negatively affects fetal Sertoli cell differentiation and gonocyte survival and blocks the migration of mesonephric cells, thereby leading to inhibition of the XY gonad development.

Relief effect of vitamin A on the decreased motility of sperm and the increased incidence of malformed sperm in mice exposed neonatally to bisphenol A.

Administration of 50 microg of bisphenol A (BPA) for the first 5 days after birth resulted in a decrease in the percentage of moving sperm, and an increase in the incidence of malformed sperm, in the epididymides of mice at 10 weeks of age, although no marked changes were found in the testicular histology between BPA-treated and vehicle-treated control mice. The deteriorating effects of 50 microg of BPA were ameliorated by the concurrent administration of 100 IU of retinol acetate (RA). Neonatal treatment with 0.5 microg of BPA for 5 days resulted in an increase in the incidence of malformed sperm, whereas the BPA effect became more severe in mice nursed by mothers fed a vitamin A-deficient (VAD) diet only a few days before and after parturition. On the other hand, neonatal treatment with 20 microg of estrogen for the first 5 days after birth resulted in an increase in the number of estrogen receptor alpha (ERalpha)-positive cells in the epithelium of the vas deferens, whereas only a few epithelial cells showed weak ERalpha-positive signals in the vehicle-treated control mice at 18 days after birth. This increase, however, was suppressed by the concurrent administration of RA. Although five daily treatments with 50 microg BPA led to no significant increase in the number of ERalpha-positive cells, it may have been due to the weak estrogenic activity of BPA, as discussed. These findings clearly showed that in mice, neonatal exposure to a relatively large dose of BPA causes damage to the motility and morphology of sperm, but the BPA effect is, to some extent, inhibited by a supplement of VA, and enhanced under a VAD condition.

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.

Absorption and Conversion of 11,12-3H-β-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.

Interaction of zinc and vitamin A on the ocular surface.

The purpose of this study was to assess morphologically the interaction between zinc and vitamin A in their effect on the ocular surface. 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. 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(-). These results suggest that a synergistic interaction exists between vitamin A and zinc for the maintenance of the corneal and conjunctival epithelium.

Drosophila Crumbs Is Required to Inhibit Light-Induced Photoreceptor Degeneration

Mutations in the human transmembrane protein CRB1 are associated with severe forms of retinal dystrophy, retinitis pigmentosa 12 (RP12), and Leber's congenital amaurosis (LCA) [1–3]. The Drosophila homolog, crumbs, is required for polarity and adhesion in embryonic epithelia [4–6] and for correct formation of adherens junctions and proper morphogenesis of photoreceptor cells [7, 8]. Here, we show that mutations in Drosophila crumbs result in progressive, light-induced retinal degeneration. Degeneration is prevented by expression of p35, an inhibitor of apoptosis, or by reduction of rhodopsin levels through a vitamin A-deficient diet. In the dark, rhabdomeres survive but exhibit morphogenetic defects. We demonstrate that it is the extracellular portion of the Crumbs protein that is essential to suppress light-induced programmed cell death, while proper morphogenesis depends on the intracellular part. We conclude that human and Drosophila Crumbs proteins are functionally conserved to prevent light-dependent photoreceptor degeneration. This experimental system is now ideally suited to study the genetic and molecular basis of RP12- and LCA-related retinal degeneration.

Changes of adiposity in response to vitamin A status correlate with changes of PPAR gamma 2 expression.

To gain insight into the in vivo modulation of the expression of the adipogenic transcription factors PPAR gamma 2, C/EBP alpha, and ADD1/SREBP1c by retinoids and its relationship with whole-body adiposity. Three-week-old mice were fed with standard chow or a vitamin A-deficient diet for 10 weeks. During the 4 days immediately before they were killed, the animals were treated either with all-trans retinoic acid (tRA; 100 mg/kg per day, subcutaneously) or vehicle. The specific levels of the mRNAs for the three transcription factors were analyzed in epididymal white adipose tissue (eWAT) and inguinal white adipose tissue and in brown adipose tissue (BAT). Other parameters determined were leptin and UCP2 levels in white adipose tissue depots, total cholesterol and triglyceride serum levels, energy intake, body weight, and adiposity. Vitamin A-deficient diet feeding led to a marked increase of adiposity and to a small increase of body weight. Hypertrophy of white adipose tissue depots correlated with enhanced PPAR gamma 2 expression. Hypertrophy of BAT, in contrast, correlated with a decrease of PPAR gamma 2 expression that may contribute to the known reduced thermogenic potential of BAT under conditions of vitamin A restriction. Treatment with tRA triggered a reduction of adiposity and body weight that correlated with a down-regulation of PPAR gamma 2 expression in all adipose tissues. The effects of tRA were more pronounced in eWAT, where C/EBP alpha and ADD1/SREBP1c levels were also reduced. The response to tRA was impaired in the eWAT and BAT of animals fed the vitamin A-deficient diet. The results emphasize the importance of retinoids as physiological regulators of adipose tissue development and function in intact animals.

Vitamin A Insufficiency Accelerates the Decrease in the Number of Sperm Induced by an Environmental Disruptor, Bisphenol A, in Neonatal Mice

Exposure of neonatal mice to an estrogenic endocrine disruptor, bisphenol A, resulted in a malfunction of the testes when the animals became adults. The effect of bisphenol A was cancelled out by concurrent administration of retinol acetate, a naturally occurring metabolite of vitamin A. In contrast, the effect of endocrine disruption became more severe in mice neonatally exposed to bisphenol A and nursed by mothers fed a vitamin A-deficient diet only a few days before and after parturition. These results clearly show that maternal vitamin A is important for relieving in a baby the effect of endocrine disruption caused by environmental xenoestrogens, and suggest that the changes in the content of vitamin A and similar physiological factors in the habitat may be worth considering in studies on environmental disruptors.

Vitamin A Deficiency Reduces Insulin-Like Growth Factor (IGF)-I Gene Expression and Increases IGF-I Receptor and Insulin Receptor Gene Expression in Tissues of Japanese Quail (Coturnix coturnix japonica)

The insulin-like growth factor (IGF) system is regulated by various stimuli, including hormones, growth factors and nutritional status. We examined the effects of vitamin A on components of the IGF system in Japanese quail. Male quail (1 d old) fed a vitamin A-deficient diet for 14 or 21 d developed vitamin A deficiency, as confirmed by a depletion of serum retinol and hepatic retinyl palmitate. Consuming the vitamin A-deficient diet for 14 d did not affect growth rate, but decreased the serum IGF-I concentrations by 22% compared with the control group. The decreased serum IGF-I levels were accompanied by 21-52% lower levels of IGF-I mRNA in the testis, lung, liver and heart, whereas IGF-I receptor (IGF-IR) and insulin receptor (IR) gene expressions were unaffected in these tissues. Continuous feeding of the vitamin A-deficient diet for 21 d retarded growth and further decreased the levels of serum IGF-I and tissue IGF-I mRNA. Serum IGF-I levels were reduced by approximately 50%; IGF-I mRNA levels were > 90% lower in the liver and lung and approximately 60% lower in the heart and testis. In contrast, levels of the IGF-IR and IR mRNAs were approximately 100% greater in some tissues examined. When vitamin A-deficient quail received a single injection of retinol or retinoic acid (0.1 mg/bird), tissue IGF-I, IGF-IR and IR gene expressions did not change after 4 h. These results suggest a possible physiologic role of the IGF system in mediating vitamin A-supported growth of Japanese quail.

Effects of vitamin A deficiency on mitochondrial function in rat liver and heart

The aim of this study was to investigate comparative effects of vitamin A deficiency on respiratory activity and structural integrity in liver and heart mitochondria. Male rats were fed a liquid control diet (control rats) or a liquid vitamin A-deficient diet (vitamin A-deficient rats) for 50 days. One group of vitamin-A deficient rats was refed a control diet for 15 days (vitamin A-recovered rats). To assess the respiratory function of mitochondria the contents of coenzyme Q (ubiquinone, CoQ), cytochrome c and the activities of the whole electron transport chain and of each of its respiratory complexes were evaluated. Chronic vitamin A deficiency promoted a significant increase in the endogenous coenzyme Q content in liver and heart mitochondria when compared with control values. Vitamin A deficiency induced a decrease in the activity of complex I (NADH-CoQ reductase) and complex II (succinate-CoQ reductase) and in the levels of complex I and cytochrome c in heart mitochondria. However, NADH and succinate oxidation rates were maintained at the control levels due to an increase in the CoQ content in accordance with the kinetic behaviour of CoQ as an homogeneous pool. On the contrary, the high CoQ content did not affect the electron-transfer rate in liver mitochondria, whose integrity was preserved from the deleterious effects of the vitamin A deficiency. Ultrastructural assessment of liver and heart showed that vitamin A deficiency did not induce appreciable alterations in the morphology of their mitochondria. After refeeding the control diet, serum retinol, liver and heart CoQ content and the activity of complex I and complex II in heart mitochondria returned to normality. However, the activities of both whole electron transfer chain and complex I in liver were increased over the control values. The interrelationships between physiological antioxidants in biological membranes and the beneficial effects of their administration in mitochondrial diseases are discussed.

Vitamin A Status Assessment in Rats with 13C4-Retinyl Acetate and Gas Chromatography/Combustion/Isotope Ratio Mass Spectrometry

Vitamin A assessment methods that indirectly determine liver reserves are still in development. The deuterated vitamin A assay has been successfully applied in several population groups, but large doses of vitamin A must be used and the gas chromatography/mass spectrometry analysis is not very sensitive. Therefore, 10,11,14,15-(13)C(4)-retinyl acetate was synthesized using a modified Wittig-Horner procedure. Thereafter, female Sprague-Dawley rats (n = 47) were fed a vitamin A-deficient diet and divided into three groups: low (L), moderate (M) and high (H) vitamin A. Groups L, M and H were supplemented with 35, 70 and 350 nmol of unlabeled retinyl acetate/d for 17 d. On d 18, three rats from each group were killed to determine baseline (13)C levels. Serum was prepared, and livers were collected and stored at -70 degrees C until analyzed with HPLC and gas chromatography/combustion/isotope ratio mass spectrometry. The remaining rats were supplemented with 52 nmol of (13)C(4)-retinyl acetate. Rats were killed on d 1, 2, 4 and 10. The calculated and measured values of total body reserves (TBR) of vitamin A were within 7% of each other overall, and the relationship was linear (r = 0.98, P < 0.0001). The calculated mean TBR were 0.49 +/- 0.03, 0.82 +/- 0.007 and 3.72 +/- 0.40 micromol, and the measured mean TBR were 0.50 +/- 0.045, 0.69 +/- 0.10 and 3.6 +/- 0.29 micromol for groups L, M and H, respectively. In contrast, serum retinol concentrations did not show a difference among the dietary groups: 1.32 +/- 0.14, 1.35 +/- 0.17 and 1.28 +/- 0.15 micromol/L for groups L, M and H, respectively (P = 0.25). In conclusion, this method offers more sensitivity than traditional methods and may be applicable to human vitamin A status assessment when TBR estimations are desired.

Vitamin a deficiency modifies antioxidant defenses and essential element contents in rat heart

Oxidative stress in the heart of male rats fed on a vitamin A-deficient diet for three months from 21 days of age was evaluated. Vitamin A restriction produced subclinical plasma retinol concentration (0.7 μmol/l), negligible liver retinol stores and a significant decrease of heart retinol concentration, as determined by HPLC, compared with the control group receiving the same diet with 4000 IU of vitamin A (8 mg retinol as retinyl palmitate) per kg of diet. Vitamin A-deficient rats had lower body weight than control rats. No change in the heart weights was observed. In serum of rats fed the vitamin A-deficient diet the concentrations of thiobarbituric acid-reactive substances (TBARS) and reduced glutathione (GSH) increased by ∼65% and 60%, respectively, compared with those fed on the control diet. In hearts of vitamin A-deficient rats the concentration of TBARS and the glutathione peroxidase activity significantly increased. The activity of catalase decreased by ∼30%, while the superoxide dismutase did not change. Additionally, vitamin A-deficient rats showed lower heart concentrations of the trace elements selenium, manganese and chromium. Heart iron, copper and zinc concentrations were not affected. Vitamin A deprivation for 3 months decreased the plasma and heart retinol concentrations associated with changes in non-enzymatic and enzymatic antioxidant defense system components.

Effect of Vitamin A Palmitate on Vitamin A-Deficient Rabbits

Purpose: We examined the effects of vitamin A palmitate (VA pal) eyedrops on the symptoms caused by vitamin A-deficiency in rabbits. Methods: Three-week-old rabbits were raised on a vitamin A-deficient diet, and were examined for the quantity of retinol in the serum and the condition of the anterior segment of the eye. The vitamin A-deficient animals were treated with VA pal eyedrops. Results: The retinol in the serum began to decrease 7 months after the animals were placed on the vitamin A-deficient diet. After 10 months, superficial punctate keratitis and the loss of conjunctival goblet cells were observed. Treatment of the disease in the anterior segment of the eyes with VA pal eyedrops resulted in restoration of normal condition within 3 weeks. The treatment increased the goblet cells in the ocular conjunctiva and the retinol in the serum. Conclusions: These results show the efficacy of topical VA pal treatment for vitamin A-deficient rabbits.

Nutritional vitamin A deficiency alters antioxidant defenses and modifies the liver histoarchitecture in rat

Oxidative stress and morphologic changes in the liver of female rats fed on a vitamin A-deficient diet for 3 months from 21 days of age were evaluated. Vitamin A restriction produced subclinical plasma retinol concentration (0.6 μmol–L) and negligible liver retinol stores, as determined by high-performance liquid chromatography, compared to the control group, which received the same diet with 4000 IU of vitamin A (8 mg retinol as retinyl palmitate) per kg of diet. Vitamin A-deficient rats had lower body weight than control rats. No change in the liver weights was observed. In the liver of rats fed the vitamin A-deficient diet, the concentrations of thiobarbituric acid-reactive substances increased by ∼50%, and the activities of catalase and glutathione peroxidase increased by 30% and 40%, respectively, compared with those fed on the control diet. Liver superoxide dismutase activity did not change. Additionally, vitamin A-deficient rats showed higher liver concentrations (μg/g tissue) of iron (316.03 ± 12.1 vs 203.12 ± 9.5) and lower concentrations of the antioxidant trace elements zinc (15.50 ± 1.03 vs 26.63 ± 0.25) and copper (2.27 ± 0.22 vs 4.25 ± 0.37) than those of control. Liver selenium concentration was not affected. Morphologically, livers from vitamin A-deficient rats showed a partial hepatic cord disarrangement and an increased number of hepatocytes in process of involution with piknotic nuclei and condensed cytoplasm. A reduced number of fat-hepatocytes distributed at random was observed. Portal spaces showed evidence of edema and a marked infiltration by mononuclear as well as polimorphonuclear cells. Loose portal connective tissue increased, as did the number of fibroblast-like cells in portal spaces. Vitamin A deprivation for 3 months decreased the liver retinol concentration associated with marked histological alterations in the organ, which could be due, at least in part, to the increase in oxidative stress. J. Trace Elem. Exp. Med. 13:343–357, 2000. © 2000 Wiley-Liss, Inc.

Ovariectomy increases squamous metaplasia of the uterine horns and survival of SENCAR mice fed a vitamin A–deficient diet

Retinoic acid is necessary for the growth and differentiation of organisms and exerts its molecular actions by binding to specific nuclear receptors that belong to the thyroid-steroid hormone receptor superfamily. Steroids and retinoids control the differentiation of the female reproductive epithelia: estrogen maintains the squamous differentiation of vaginal and ectocervical epithelia, whereas retinoic acid maintains the simple columnar endocervical and uterine epithelia. These lining epithelia transform into a squamous metaplastic phenotype in vitamin A-deficient animals. Furthermore, mortality due to vitamin A deficiency is usually attributed to infection resulting in part from dysfunction of the protective epithelia. Our objective was to test the hypothesis that estrogen depletion might change the squamous metaplastic response to vitamin A deficiency and affect animal survival. We used female SENCAR mice maintained on a purified vitamin A-deficient diet containing either 0 or 3 microg retinoic acid/g diet. Mice were either ovariectomized or intact. Squamous cells arising in the normally simple columnar epithelium of the endocervix and uterine cavity were monitored by keratin 5 expression with immunohistochemistry. Ovariectomy did not change the time to onset of vitamin A deficiency. It increased the number of squamous metaplastic cells and prolonged survival in mice consuming a vitamin A-deficient diet by as much as 40%. Factors other than epithelial differentiation per se control survival outcome of vitamin A-deficient mice. The results also show a significant increase in longevity of vitamin A- deficient mice when ovariectomized.

Impaired retinal function and vitamin A availability in mice lacking retinol-binding protein.

Retinol-binding protein (RBP) is the sole specific transport protein for retinol (vitamin A) in the circulation, and its single known function is to deliver retinol to tissues. Within tissues, retinol is activated to retinoic acid, which binds to nuclear receptors to regulate transcription of >300 diverse target genes. In the eye, retinol is also activated to 11-cis-retinal, the visual chromophore. We generated RBP knockout mice (RBP(-/-)) by gene targeting. These mice have several phenotypes. Although viable and fertile, they have reduced blood retinol levels and markedly impaired retinal function during the first months of life. The impairment is not due to developmental retinal defect. Given a vitamin A-sufficient diet, the RBP(-/-) mice acquire normal vision by 5 months of age even though blood retinol levels remain low. Deprived of dietary vitamin A, vision remains abnormal and blood retinol declines to undetectable levels. Another striking phenotype of the mutant mice is their abnormal retinol metabolism. The RBP(-/-) mice can acquire hepatic retinol stores, but these cannot be mobilized. Thus, their vitamin A status is extremely tenuous and dependent on a regular vitamin A intake. Unlike wild-type mice, serum retinol levels in adult RBP(-/-) animals become undetectable after only a week on a vitamin A-deficient diet and their retinal function rapidly deteriorates. Thus RBP is needed for normal vision in young animals and for retinol mobilization in times of insufficient dietary intake, but is otherwise dispensable for the delivery of retinol to tissues.

Ligand-dependent regulation of retinoic acid receptor alpha in rat testis: in vivo response to depletion and repletion of vitamin A.

Male animals are sterile due to testicular degeneration in the absence of retinoic acid (RA) or functional retinoic acid receptor-alpha (RAR alpha). This degeneration can be reversed by injecting retinol, a precursor of RA, into vitamin A-deficient (VAD) rats. To determine the relationship between this ligand-dependent testicular degeneration and regeneration and the expression levels of RAR alpha messenger RNA and protein, testes were depleted and then replenished with retinol in vivo. Results showed that RAR alpha messenger RNA and protein levels declined to VAD amounts after 7 weeks on a VAD diet. This decline was due to decreased RAR alpha levels in early meiotic spermatocytes and the loss of advanced germ cells. Interestingly, the advanced germ cells still contained RAR alpha, but the protein was primarily cytoplasmic instead of nuclear, indicating inactivity as a transcription factor. In VAD testis, RAR alpha levels were low and then increased primarily in Sertoli cells after retinol replenishment. TUNEL analyses showed that most germ cells at the basal aspect of seminiferous tubules were undergoing apoptosis during degeneration. These results indicate that RAR alpha is either down-regulated or inactivated in RA-deficient testis and coincident with that, testes degenerate by apoptosis or selective loss of germ cells.

Ligand-Dependent Regulation of Retinoic Acid Receptor in Rat Testis: In Vivo Response to Depletion and Repletion of Vitamin A

Male animals are sterile due to testicular degeneration in the absence of retinoic acid (RA) or functional retinoic acid receptor-α (RARα). This degeneration can be reversed by injecting retinol, a precursor of RA, into vitamin A-deficient (VAD) rats. To determine the relationship between this ligand-dependent testicular degeneration and regeneration and the expression levels of RARα messenger RNA and protein, testes were depleted and then replenished with retinol in vivo. Results showed that RARα messenger RNA and protein levels declined to VAD amounts after 7 weeks on a VAD diet. This decline was due to decreased RARα levels in early meiotic spermatocytes and the loss of advanced germ cells. Interestingly, the advanced germ cells still contained RARα, but the protein was primarily cytoplasmic instead of nuclear, indicating inactivity as a transcription factor. In VAD testis, RARα levels were low and then increased primarily in Sertoli cells after retinol replenishment. TUNEL analyses showed that most germ cells at the basal aspect of seminiferous tubules were undergoing apoptosis during degeneration. These results indicate that RARα is either down-regulated or inactivated in RA-deficient testis and coincident with that, testes degenerate by apoptosis or selective loss of germ cells.