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Biomedical subjects

Michael F Holick

Publications and source records attributed to Michael F Holick.

At least 19 recordsLinked to original sources
PubMed2003

Vitamin D: A millenium perspective.

Vitamin D is one of the oldest hormones that have been made in the earliest life forms for over 750 million years. Phytoplankton, zooplankton, and most plants and animals that are exposed to sunlight have the capacity to make vitamin D. Vitamin D is critically important for the development, growth, and maintenance of a healthy skeleton from birth until death. The major function of vitamin D is to maintain calcium homeostasis. It accomplishes this by increasing the efficiency of the intestine to absorb dietary calcium. When there is inadequate calcium in the diet to satisfy the body's calcium requirement, vitamin D communicates to the osteoblasts that signal osteoclast precursors to mature and dissolve the calcium stored in the bone. Vitamin D is metabolized in the liver and then in the kidney to 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. 1,25(OH)(2)D receptors (VDR) are present not only in the intestine and bone, but in a wide variety of other tissues, including the brain, heart, stomach, pancreas, activated T and B lymphocytes, skin, gonads, etc. 1,25(OH)(2)D is one of the most potent substances to inhibit proliferation of both normal and hyperproliferative cells and induce them to mature. It is also recognized that a wide variety of tissues, including colon, prostate, breast, and skin have the enzymatic machinery to produce 1,25(OH)(2)D. 1,25(OH)(2)D and its analogs have been developed for treating the hyperproliferative disease psoriasis. Vitamin D deficiency is a major unrecognized health problem. Not only does it cause rickets in children, osteomalacia and osteoporosis in adults, but may have long lasting effects. Chronic vitamin D deficiency may have serious adverse consequences, including increased risk of hypertension, multiple sclerosis, cancers of the colon, prostate, breast, and ovary, and type 1 diabetes. There needs to be a better appreciation of the importance of vitamin D for overall health and well being.

Adult↗
PubMed2003

Prostatic 25-hydroxyvitamin D-1alpha-hydroxylase and its implication in prostate cancer.

Evidence suggests that vitamin D may have a protective role for prostate cancer. 1alpha,25-Dihydroxyvitamin D [1alpha,25(OH)(2)D] inhibits growth and induces differentiation of prostate cells. 25-Hydroxyvitamin D-1alpha-hydroxylase [1alpha-OHase], the enzyme that is responsible for the synthesis of 1alpha,25(OH)(2)D, is expressed in cultured prostate cells. We observed a marked decrease in 1alpha-OHase activity in prostate cancer cells, suggesting some defect of the 1alpha-OHase in these cells. To investigate whether the defect was due to dysregulation of the enzyme at the promoter level, a series of deletion constructs of the promoter was synthesized and incorporated upstream into the luciferase reporter gene. Two regions were identified with high basal activity in transfected normal prostate cell line (PZHPV-7), -1100 bp (AN2), and -394 bp (AN5) upstream of ATG start site of the 1alpha-OHase gene. When the reporter gene with either AN2 or AN5 was transfected into prostate cancer cell lines, we observed a lower basal promoter activity in PC-3 cells and DU145 cells than that found in PZHPV-7 cells for both constructs, and a loss of promoter activity in LNCaP cells. Thus, the results suggest that the defect in enzyme activity may result from the decreased promoter activity in prostate cancer cells.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed2003

Evolution and function of vitamin D.

It is remarkable that phytoplankton and zooplankton have been producing vitamin D for more than 500 million years. The role of vitamin D in lower non-vertebrate life forms is not well understood. However, it is critically important that most vertebrates obtain an adequate source of vitamin D, either from exposure to sunlight or from their diet, in order to develop and maintain a healthy mineralized skeleton. Vitamin D deficiency is an unrecognized epidemic in most adults who are not exposed to adequate sunlight. This can precipitate and exacerbate osteoporosis and cause the painful bone disease osteomalacia. Once vitamin D is absorbed from the diet or made in the skin by the action of sunlight, it is metabolized in the liver to 25-hydroxyvitamin D [25(OH)D] and then in the kidney to 1,25-dihydroxyvitamin D [1,25(OH)2D]. 1,25(OH)2D interacts with its nuclear receptor (VDR) in the intestine and bone in order to maintain calcium homeostasis. The VDR is also present in a wide variety of other tissues. 1,25(OH)2D interacts with these receptors to have a multitude of important physiological effects. In addition, it is now recognized that many tissues, including colon, breast and prostate, have the enzymatic machinery to produce 1,25(OH)2D. The insights into the new biological functions of 1,25(OH)2D in regulating cell growth, modulating the immune system and modulating the renin-angiotensin system provides an explanation for why diminished sun exposure at higher latitudes is associated with increased risk of dying of many common cancers, developing type 1 diabetes and multiple sclerosis, and having a higher incidence of hypertension. Another calciotropic hormone that is also produced in the skin, parathyroid hormone-related peptide, is also a potent inhibitor of squamous cell proliferation. The use of agonists and antagonists for PTHrP has important clinical applications for the prevention and treatment of skin diseases and disorders of hair growth.

Animals↗
PubMed2003

Regulation of the 25-hydroxyvitamin D-1alpha-hydroxylase gene and its splice variant.

The 25-hydroxyvitamin D-1alpha-OHase (1alpha-OHase) is responsible for producing the active form of vitamin D, 1alpha,25-dihydroxyvitamin D. The enzyme not only is expressed in kidneys, but also is expressed in many nonrenal tissues, including skin. In this study, we compared the regulation of the 1alpha-OHase expression in kidney cells and keratinocytes. Using transfected luciferase reporter gene constructs, we compared the activity and regulatory features of the human 1alpha-OHase gene promoter in C-21 human kidney cells (PTH/PTHrP receptor positive) and cultured human keratinocytes (NHKs). We found that two regions, -1,100 bp and -396 bp from the ATG, were highly sensitive to parathyroid hormone (PTH) in C-21 cells but not in NHK. Furthermore, three CRE-like sequences (CLS) were identified within this PTH-sensitive area of the 1alpha-OHase promoter and when deleted they reduced induction of PTH by 50%-95% in C-21 cells. To further investigate the differential regulation profile, we examined the protein products of 1alpha-OHase in kidney and skin. Western blot analysis of whole cell extracts from these tissues with a 1alpha-OHase-specific antibody revealed the predicted 1alpha-OHase protein product of 56 kDa in kidney and a larger protein product of 59 kDa in skin. Using RT-PCR for the 1alpha-OHase in skin and kidney, we detected an insertion between exons 2 and 3 in skin but not in kidney. These results suggest that the regulation of renal and skin 1alpha-OHase gene expression may be tissue specific and possibly produce different splice variants, and that this specificity is likely conferred by differential expression of CRE-binding proteins in different cell types. In conclusion, the differential tissue expression of 1alpha-OHase gene variants and the tissue-specific regulation profile open up a new paradigm in the understanding of the role of 25-hydroxyvitamin D3 1alpha-hydroxylase gene in the regulation of vitamin D physiology.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed2003

Vitamin D autocrine system and prostate cancer.

25-Hydroxyvitamin D-1alpha-hydroxylase (lalpha-OHase) is expressed in prostate cells. The expression suggests that local production of 1,25-dihydroxyvitamin D could provide an important cell growth regulatory mechanism. However, there is differential expression of 1alpha-OHase activity among the primary cultures of prostate cells derived from cancerous, benign prostatic hypertrophy and normal tissue, and among noncancerous (PZHPV-7) and various cancer cell lines (PC-3, DU145). No activity was found in cancer cell line LNCaP. The observed marked decrease in 1alpha-OHase activity in prostate cancer cells suggests some defect of the 1alpha-OHase in these cells. Using luciferase reporter gene assay, we observed a step-wise decrease in the basal promoter activity in two truncated promoter fragments, AN2 (-1,100 bp) and AN5 (-394 bp), with the highest basal activities found in PZHPV-7 and with loss of promoter activity in LNCaP. In order to understand the mechanism underlying the differential promoter activities among different prostate cells, we investigated the possible role of phosphorylation of cyclic AMP response element binding protein (CREB) on the regulation of 1alpha-OHase promoter activity in the four prostate cell lines. First we compared the levels of CREB phosphorylation among PZHPV-7, DU145, PC-3 and LNCaP cells by Western blot analysis using antibody against phosphorylated CREB. We observed that CREB was phosphorylated to a greater extent in PZHPV-7 than in DU145 cells. No significant phosphorylation of CREB was found in PC-3 and LNCaP cells. Next, we utilized activators and inhibitors of protein kinase A (PKA), protein kinase C (PKC), mitogen-activated protein kinase kinase (MAPKK) and calcium/calmodulin-dependent protein kinase II (CaMKII) to determine which kinases might be involved in phosphorylating the CREB in PZHPV-7 cells. We demonstrated that forskolin (an activator of PKA) increased the AN2 basal promoter activity 50%, whereas H-89 (an inhibitor of PKA) inhibited the basal and forskolin-stimulated AN2 promoter activity 40% and 70%, respectively. We also showed that PD98059 (an inhibitor of MAPKK) decreased the AN2 promoter activity 70%. Phorbol 12-myristate 13-acetate (an activator of PKC), GF109203 (an inhibitor of PKC) and KN-93 (an inhibitor of CaMKII) had no effect on AN2 promoter activity in PZHPV-7 cells. Thus, our results suggest that differential phosphorylation of CREB through PKA and MAPK pathways may be involved in the regulation of 1alpha-OHase promoter activity.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed2003

Analysis of the vitamin D system in cutaneous malignancies.

1,25-dihydroxyvitamin D3, the biological active metabolite of vitamin D, has great impact on keratinocyte growth and differentiation, and consequently has already been successfully used in the therapy of hyperproliferative skin disorders. We have now characterized the key components of the vitamin D system (VDR, 1alpha-OHase, 24-OHase and 25-OHase) in cutaneous basal cell carcinomas (BCC) and squamous cell carcinomas (SCC), using immunohistochemical and quantitative real-time PCR techniques. Additionally, proliferative activity (Ki-67 expression), differentiation status (cytokeratin 10 and transglutaminase K expression), rate of apoptosis (TUNEL assay) and the abundance of the main heterodimerization partners of VDR (RXRs) was determined for these tumours and correlated with the components of the Vitamin D system. Our findings indicate that the Vitamin D system may be of high importance for the growth behaviour of BCCs and SCCs and that new vitamin D analogues that exert less calcaemic side effects may be effective in the prevention or treatment of these tumours.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed2003

Evaluation of vitamin D analogs as therapeutic agents for prostate cancer.

Prostate cancer cells contain specific receptors (VDR) for la,25-dihydroxyvitamin D (1alpha,25(OH)2D), which is known to inhibit the proliferation and invasiveness of these cells. These findings support the use of 1alph,25(OH)2D for prostate cancer therapy. However, because 1alpha,25(OH)2D can cause hypercalcemia, analogs of 1alpha,25(OH)2D that are less calcemic but which exhibit potent antiproliferative activity would be attractive as therapeutic agents. We studied four vitamin D compounds: 25-hydroxyvitaminD3 [25(OH)D3], which is converted to 1alpha,25(OH)2D3 in prostate cells, and three analogs of 1alpha,25(OH)2D3: EB1089, 19-nor-1alpha,25(OH)2D2 and hexafluoro-1alpha,25(OH)2D3 (F6-1alpha,25(OH)2D3). 19-nor-1alpha,25(OH)2D2 has been shown to be less calcemic than 1alpha,25(OH)2D3 in clinical trials. F6-1alpha,25(OH)2D3 has been shown to be 100-fold more active than 1alpha,25(OH)2D3 and to be longer-lasting in inhibiting keratinocyte proliferation in vitro. EB1089 has been shown to be less calcemic than 1alpha,25(OH)2D3 in rats implanted with Leydig cell tumors. For 25(OH)D3, 19-nor-1alpha,25(OH)2D2 and F6-1alpha,25(OH)2D3, we studied the in vitro effects and compared their activity to 1alpha,25(OH)2D3 on cellular proliferation by 3H-thymidine incorporation assay. In addition, we studied transactivation of the VDR in the presence of 25(OH)D3 and 19-nor-1alpha,25(OH)2D2 in prostate cells. For EB1089, we compared its inhibition of prostate cancer metastasis to that induced by 1alpha,25(OH)2D3 in vivo in the rat Dunning MAT LyLu prostate cancer model. We found that 1alpha,25(OH)2D3 and 19-nor-1alpha,25(OH)2D2 caused similar dose-dependent inhibition in 3H-thymidine incorporation into DNA in prostate cells and behaved similarly in the CAT reporter gene transactivation assay in PC-3/VDR cells. F6-1alpha,25(OH)2D3 is 10- to 50-fold more active than 1alpha,25(OH)2D3 in 3H-thymidine incorporation into DNA in the primary cultured prostate cells. Likewise, 25(OH)D3 had comparable antiproliferative activity to la,25(OH)2D3. In the rat model, tumor volumes and the number of metastases in the lungs were significantly reduced by both 1alpha,25(OH)2D3 (10.4 +/- 2.81 tumor foci) and EB1089 (7.7+/-1.29 tumor foci) compared to controls (22.7 +/- 1.98 tumor foci). Although serum calcium levels were significantly elevated in both 1alph,25(OH)2D3- and EB1089-treated rats, EB1089 was significantly less calcemic than 1alpha,25(OH)2D3 (12.59+/-0.21 mg/dl versus 14.47+/-.46 mg/dL; 1 microg/kg; p < 0.001). In conclusion, our data indicate that 25(OH)D3 and the three 1alpha,25(OH)2D analogs represent two different solutions to the problem of hypercalcemia associated with vitamin D-based prostate cancer therapies: 25(OH)D3 requires the presence of 25-hydroxyvitaminD-1alpha-hydroxylase, whereas 19-nor-1alpha,25(OH)2D2, F6-1alpha,25(OH)2D3 and EB1089 do not. These compounds may be good candidates for human clinical trials in prostate cancer.

Animals↗
PubMed2003

Thyroid hormone action on skin: diverging effects of topical versus intraperitoneal administration.

Previously, we demonstrated stimulation of epidermal proliferation and hair growth in triiodothyronine (T(3)) treated mice. To distinguish skin effects of directly applied T(3) from those of systemic hyperthyroidism, we treated CD-1 mice with either intraperitoneally (IP) or topically administered T(3). Relative to controls, mice receiving T(3) IP had 10% thinner epidermis (p < 0.01) and 48% fewer hairs (p < 0.001). By contrast, mice receiving T(3) topically had 78% thicker epidermis (p < 0.01) and 160% more hairs (p < 0.01). To gain insight into factors responsible for the diverging effects, we contrasted T(3) effect on proliferation of isolated keratinocyte cultures versus keratinocytes cocultured with dermal fibroblasts. For keratinocytes grown in the absence of fibroblasts, T(3) stimulated proliferation in a dose-dependent, biphasic pattern with the peak at 0.5 nM T(3) (84 +/- 30%, p < 0.05). Paradoxically, T(3) inhibited proliferation of keratinocytes cocultured with fibroblasts, the nadir at 0.1 nM T(3) (34% +/- 4%, p < 0.001). These studies are the first describing divergent effects of IP and topically administered thyroid hormone. The data suggest that while T(3) stimulated keratinocyte proliferation, T(3) also stimulated proliferation inhibitory factor(s) from skin fibroblasts. Insight into the interplay among the competing factors will be important in understanding thyroid hormone regulation of skin physiology.

Administration, Topical↗
PubMed2003

Vitamin D and bone health in postmenopausal women.

Osteoporosis, a disease of increased skeletal fragility, is becoming increasingly common as the U.S. population ages. Adequate vitamin D and calcium intake is the cornerstone of osteoporosis prevention and treatment. Age-related changes in vitamin D and calcium metabolism increase the risk of vitamin D insufficiency and secondary hyperparathyroidism. Although longitudinal data have suggested a role of vitamin D intake in modulating bone loss in perimenopausal women, studies of vitamin D and calcium supplementation have failed to support a significant effect of vitamin D and calcium during early menopause. There is a clearer benefit in vitamin D and calcium supplementation in older postmenopausal women. Vitamin D intake between 500 and 800 IU daily, with or without calcium supplementation, has been shown to increase bone mineral density (BMD) in women with a mean age of approximately 63 years. In women older than 65, there is even more benefit with vitamin D intakes of between 800 and 900 IU daily and 1200-1300 mg of calcium daily, with increased bone density, decreased bone turnover, and decreased nonvertebral fractures. The decreases in nonvertebral fractures may also be influenced by vitamin D-mediated decreases in body sway and fall risk. There are insufficient available data supporting a benefit from vitamin D supplementation alone, without calcium, to prevent osteoporotic fracture in postmenopausal women.

Age Factors↗
PubMed2003

Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol.

BACKGROUND: The cholecalciferol inputs required to achieve or maintain any given serum 25-hydroxycholecalciferol concentration are not known, particularly within ranges comparable to the probable physiologic supply of the vitamin. OBJECTIVES: The objectives were to establish the quantitative relation between steady state cholecalciferol input and the resulting serum 25-hydroxycholecalciferol concentration and to estimate the proportion of the daily requirement during winter that is met by cholecalciferol reserves in body tissue stores. DESIGN: Cholecalciferol was administered daily in controlled oral doses labeled at 0, 25, 125, and 250 micro g cholecalciferol for approximately 20 wk during the winter to 67 men living in Omaha (41.2 degrees N latitude). The time course of serum 25-hydroxycholecalciferol concentration was measured at intervals over the course of treatment. RESULTS: From a mean baseline value of 70.3 nmol/L, equilibrium concentrations of serum 25-hydroxycholecalciferol changed during the winter months in direct proportion to the dose, with a slope of approximately 0.70 nmol/L for each additional 1 micro g cholecalciferol input. The calculated oral input required to sustain the serum 25-hydroxycholecalciferol concentration present before the study (ie, in the autumn) was 12.5 micro g (500 IU)/d, whereas the total amount from all sources (supplement, food, tissue stores) needed to sustain the starting 25-hydroxycholecalciferol concentration was estimated at approximately 96 micro g (approximately 3800 IU)/d. By difference, the tissue stores provided approximately 78-82 micro g/d. CONCLUSIONS: Healthy men seem to use 3000-5000 IU cholecalciferol/d, apparently meeting > 80% of their winter cholecalciferol need with cutaneously synthesized accumulations from solar sources during the preceding summer months. Current recommended vitamin D inputs are inadequate to maintain serum 25-hydroxycholecalciferol concentration in the absence of substantial cutaneous production of vitamin D.

Administration, Oral↗
PubMed2003

Fortification of orange juice with vitamin D: a novel approach for enhancing vitamin D nutritional health.

BACKGROUND: Fortification of milk with vitamin D may not be adequate for satisfying the vitamin D requirement because of variability in vitamin D content after fortification and because many persons have milk allergy or lactose intolerance. Additional foods need to be fortified with vitamin D. OBJECTIVE: We determined whether vitamin D, a fat-soluble vitamin, is bioavailable in orange juice and skim milk, 2 nonfat beverages. DESIGN: On 3 separate occasions, 18 adults ingested 25 000 IU vitamin D(2) in 240 mL whole milk or skim milk or in 0.1 mL corn oil applied to toast. A separate, double-blind, randomized, controlled trial investigated whether the consumption of orange juice fortified with vitamin D(3) would increase serum 25-hydroxyvitamin D [25(OH)D] concentrations: 14 subjects ingested 240 mL orange juice fortified with 1000 IU vitamin D, and 12 subjects ingested a control orange juice daily for 12 wk. RESULTS: Peak serum vitamin D(2) concentrations did not differ significantly after the ingestion of vitamin D(2) in whole milk, skim milk, or corn oil on toast. After subjects consumed orange juice fortified with 1000 IU vitamin D(3) daily for 12 wk, serum 25(OH)D(3) concentrations increased by 150%, and serum parathyroid hormone concentrations decreased by 25% compared with baseline; control subjects had a seasonal increase of 45% in 25(OH)D and no significant change in serum parathyroid hormone. CONCLUSIONS: The fat content of milk does not affect vitamin D bioavailability. Vitamin D fortification at 1000 IU/240 mL orange juice for 12 wk safely increased 25(OH)D(3) concentrations in adults.

Adult↗
PubMed2002

25-Hydroxyvitamin D-1alpha-hydroxylase activity is diminished in human prostate cancer cells and is enhanced by gene transfer.

The hormone 1alpha,25-dihydroxyvitamin D (1alpha,25(OH)(2)D) inhibits growth and induces differentiation of prostate cells. The enzyme responsible for 1alpha,25(OH)(2)D synthesis, 25-hydroxyvitamin D (25(OH)D)-1alpha-hydroxylase (1alpha-OHase), has been demonstrated in human prostate cells. We compared the levels of 1alpha-OHase activity in prostate cancer cell lines, LNCaP, DU145 and PC-3 and in primary cultures of normal, cancerous and benign prostatic hyperplasia (BPH) prostate cells. We observed a marked decrease in 1alpha-OHase activity in prostate cancer cells, including an undetectable level of activity in LNCaP cells. Transient or stable transfection of 1alpha-OHase cDNA into LNCaP cells increased 1alpha-OHase activity from undetectable to 4.95pmole/mg+/-0.69pmole/mg and 5.8pmole/mg+/-0.7pmole/mg protein per hour, respectively. In response to 25(OH)D, the prohormone of 1alpha,25(OH)(2)D, the transfected LNCaP cells showed a significant inhibition of 3H-thymidine incorporation (37%+/-6% and 56%+/-4% at 10(-8)M for transiently and stably transfected cells, respectively). These findings support an important autocrine role for 1alpha,25(OH)(2)D in the prostate and suggest that the re-introduction of the 1alpha-OHase gene to prostate cancer cells, in conjunction with the systemic administration of 25(OH)D, constitutes an endocrine form of gene therapy that may be less toxic than the systemic administration of 1alpha,25(OH)(2)D.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed2002

Bone mineral density assessment: comparison of dual-energy X-ray absorptiometry measurements at the calcaneus, spine, and hip.

It is widely accepted that bone mineral density (BMD) measurements obtained by dual-energy X-ray absorptiometry (DXA) at the spine, hip, and calcaneus predict fracture risk. Few published studies to date have examined the relationship between pDXA measurements at the calcaneus to those at the hip and spine. It has been demonstrated that T-score-based criteria cannot be universally applied to all skeletal sites and measurement technologies. Our goal was to define the calcaneal T-score threshold equivalent to low bone mass at the hip or spine. A total of 119 female patients between the ages of 33 and 76 yr of age were recruited at Boston University Medical Center for bone densitometry screening. Bone density measurements were obtained at the calcaneus using the portable Norland Apollo Densitometer (Norland Medical Systems, Fort Atkinson, WI) and at the hip and spine using the Norland Eclipse densitometer. By defining a pDXA T-score < or =-1 as a positive test and DXA scores < or =-1 as the presence of low bone mass, we obtained a specificity of 100% and a sensitivity of 73% (positive predictive value 100% and negative predictive value 80%) in detecting low bone mass at the femoral neck in women over age 65 yr. In women between 40 and 65 yr of age, we obtained a sensitivity of 50% and a specificity of 93% (positive predictive value 93% and negative predictive value 50%) in detecting low bone mass at the femoral neck. In women less than 40 yr of age, we obtained a sensitivity of 13% and a specificity of 100% (positive predictive value 100% and negative predictive value 75%) in detecting low bone mass at the femoral neck. From receiver operating characteristic curves, a calcaneal T-score < or =0.0 detects those with a T-score < or =-1 at the femoral neck and lumbar spine with 100% and 85% sensitivity, respectively. Peripheral DXA of the calcaneus is a sensitive and specific test to diagnose low bone mass in women over 65 yr of age. In women under 65 yr of age, this modality, though not as sensitive, is specific in detecting low bone mass. We conclude that a pDXA calcaneal T-score < or =0 is highly sensitive in predicting osteopenia and osteoporosis at the femoral neck and lumbar spine.

Absorptiometry, Photon↗
PubMed2002

Fat soluble vitamins in blood and tissues of free-ranging and captive rhinoceros.

Several disease syndromes in captive rhinoceroses have been linked to low vitamin status. Blood samples from captive and free-ranging black (Diceros bicornis) and white rhinoceros (Ceratotherium simum) and tissue samples of captive individuals from four rhinoceros species were analysed for vitamins A and E. Circulating vitamin A levels measured as retinol for free-ranging versus captive black and white rhinoceros were 0.04 (+/- 0.03 SD) vs. 0.08 (+/- 0.08) and 0.07 (+/- 0.04) vs. 0.06 (+/- 0.02) microgram/ml, respectively. Circulating vitamin E levels measured as alpha-tocopherol were 0.58 (+/- 0.30) vs. 0.84 (+/- 0.96) and 0.62 (+/- 0.48) vs. 0.77 (+/- 0.32) microgram/ml, respectively. In contrast to earlier findings, there was no significant difference in vitamin E concentration between captive and free-ranging black rhinoceros. When the samples of captive black rhinoceros were grouped into those taken before 1990 and after 1990, however, those collected before 1990 had significantly lower (P < 0.001) vitamin E levels (0.46 +/- 0.83 microgram/ml) and those collected in 1990 or later significantly higher (P < 0.001) vitamin E levels (1.03 +/- 1.04 micrograms/ml) than the captive population as a whole. This is probably due to increased dietary supplementation. There were significant differences in circulating vitamin concentrations in black rhinoceroses from different regions in the wild. Serum 25-hydroxy (OH) vitamin D3 averaged 55.7 ng/ml in free-ranging rhinoceroses; no carotenoids were detected in any blood samples. Captive black and white rhinoceroses appear to be adequately supplemented in vitamin A and E. Captive Indian rhinoceroses (Rhinoceros unicornis) had significantly lower vitamin A concentrations in blood (P < 0.001) and higher vitamin A concentrations in liver tissue samples (P < 0.001) than other rhinoceros species. Equine requirements are not recommended as a model for rhinoceros vitamin requirements.

Adipose Tissue↗