Effect of electroacupuncture on the kisspeptin system in a pubertal rat model of polycystic ovary syndrome.

OBJECTIVE: To explore the effects and mechanism of action of electroacupuncture (EA) in a rat model of pubertal polycystic ovary syndrome (PCOS). METHODS: Female offspring of Sprague-Dawley rats receiving dihydrotestosterone (DHT) during pregnancy (days 16-19), as a model of prenatal androgenization, were divided randomly into three groups: model group (M), EA group, and sham acupuncture (SA) group (n = 8 each). A normal (N) group comprising female offspring of healthy pregnant rats not receiving DHT (n = 8) was added. EA was administered at CV6 and bilateral SP6/ST36 with 2 Hz frequency and 2 mA intensity. SA consisted of superficial needling at different locations without electrical stimulation. RESULTS: EA improved the disturbed estrous cycles, while it could not be concluded that SA was effective in this respect. EA improved ovarian morphology including the number of corpora lutea and area of the ovary, whereas SA did not. However, both EA and SA attenuated the increased luteinizing hormone and decreased estradiol and gonadotropin-releasing hormone levels in the serum of PCOS model rats. Levels of testosterone, follicle-stimulating hormone, and progesterone did not significantly differ between groups. EA and SA alleviated the upregulation of kisspeptin protein and mRNA levels in the hypothalamus and kisspeptin protein level in the arcuate nucleus (ARC). No differences were found between groups in protein or mRNA expression of dynorphin (DYN) or neurokinin B (NKB) in the hypothalamus. Co-expression of kisspeptin, NKB, and DYN were observed in ARC. The GnRH level in the median eminence decreased and could be rescued by EA and SA. Intriguingly, kisspeptin levels in the granulosa cells of the ovary decreased in the model group and could be rescued by EA but not SA. Levels of kisspeptin, NKB, and DYN protein and mRNA in the ovary did not differ between any groups. CONCLUSION: Both EA and SA appeared to improve symptoms of PCOS at puberty by modulating the kisspeptin system in the hypothalamus. EA also had an effect on ovarian kisspeptin expression and a more comprehensive effect with respect to improving PCOS at puberty than SA.

Soy Intake Since the Prepubertal Age May Contribute to the Pathogenesis of Endometriosis in Adulthood.

High prevalence of endometriosis was reported in Asian women as a result of their traditionally high intake of soy foods during infancy. Soy is widely used in infant feeding after weaning from breast milk or cow milk. This study thus aimed to determine to what extent soy intake before puberty may contribute to the development of endometriosis. For this purpose, immature (6-week old) female rats were fed with various soy formulas (0%, 10%, 20%, 30%, 40%, 50%, and 60%). Normal control animals were fed with a soy-free diet. At 13 weeks of age, animals (except the normal control) underwent a transplantation surgery to establish endometriosis. Estradiol valerate and oxytocin were used to induce pelvic pain. Endometrial implant levels of glutathione (GSH) and malondialdehyde (MDA) allowed estimating tissue oxidative status. Physiological ovarian function was assessed by histological analysis of ovaries. Results showed that soy-fed animals grew faster than animals receiving a soy-free diet (P < .001). In animals supplemented with more than 10% of soy, the intensity of pelvic pain increased (P < .001) as well as the volume of ectopic foci. In addition, tissue levels of MDA and GSH increased (P < .001). The ovarian function was altered and the number of luteinized unruptured follicles increased. In conclusion, although animals supplemented with soy at the prepubertal stage displayed a good growth performance, regular soy consumption may promote the development and progress of endometriosis in adulthood, especially when soy content in food is more than 10%.

Influences of manganese on pubertal development.

The onset of puberty is the result of complex neuroendocrine interactions within hypothalamic region of the brain, as well as from genetic and environmental influences. These interactions ultimately result in the increased synthesis and release of luteinizing hormone-releasing hormone (LHRH). Manganese (Mn) is an essential environmental element known for years to be involved in numerous mammalian physiological processes, including growth and reproductive function. Studies in recent years have shown the ability of Mn to cross the blood-brain barrier and act within the hypothalamus to influence the timing of puberty. This review will depict research showing the molecular and physiological actions of Mn in the control of prepubertal LHRH and discuss the potential for the element to cause either helpful or harmful outcomes on the developmental process depending upon the age and accumulation of Mn within the hypothalamus.

The roles of kisspeptin revisited: inside and outside the hypothalamus.

Kisspeptin, encoded by KISS1/Kiss1 gene, is now considered a master regulator of reproductive functions in mammals owing to its involvement in the direct activation of gonadotropin-releasing hormone (GnRH) neurons after binding to its cognate receptor, GPR54. Ever since the discovery of kisspeptin, intensive studies on hypothalamic expression of KISS1/Kiss1 and on physiological roles of hypothalamic kisspeptin neurons have provided clues as to how the brain controls sexual maturation at the onset of puberty and subsequent reproductive performance in mammals. Additionally, emerging evidence indicates the potential involvement of extra-hypothalamic kisspeptin in reproductive functions. Here, we summarize data regarding kisspeptin inside and outside the hypothalamus and revisit the physiological roles of central and peripheral kisspeptins in the reproductive functions of mammals.

Metabolic control of female puberty: potential therapeutic targets.

INTRODUCTION: The onset of puberty in females is highly sensitive to the nutritional status and the amount of energy reserves of the organism. This metabolic information is sensed and transmitted to hypothalamic GnRH neurons, considered to be ultimately responsible for triggering puberty through the coordinated action of different peripheral hormones, central neurotransmitters, and molecular mediators. AREAS COVERED: This article will review and discuss (i) the relevant actions of the adipose hormone leptin, as a stimulatory/permissive signal, and the gut hormone ghrelin, as an inhibitory factor, in the metabolic control of female puberty; (ii) the crucial role of the hypothalamic kisspeptin neurons, recently emerged as essential gatekeepers of puberty, in transmitting this metabolic information to GnRH neurons; and (iii) the potential involvement of key cellular energy sensors, such as mTOR, as molecular mediators in this setting. EXPERT OPINION: The thorough characterization of the physiological roles of the above elements in the metabolic control of female puberty, along with the discovery of novel factors, pathways, and mechanisms involved, will promote our understanding of the complex networks connecting metabolism and puberty and, ultimately, will aid in the design of target-specific treatments for female pubertal disorders linked to conditions of metabolic stress.

The role of kisspeptin signalling in the hypothalamic-pituitary-gonadal axis--current perspective.

The discovery of kisspeptins in the recent past remoulded current understanding of the neuroendocrine axis relating to the regulation of human puberty and reproduction. Kisspeptins have been recognised to act upstream of GnRH and have been shown to play a vital role in the control of the hypothalamic-pituitary-gonadal axis via regulation of gonadotrophin secretion, onset of puberty, and control of fertility. KNDy (kisspeptin/neurokinin-B/dynorphin) neurons have been suggested to modulate GnRH pulsatile secretion, which is required to support reproductive function in both sexes. They have also been involved in mediating both positive and negative sex steroid feedback signals to GnRH neurons and serve as a vital connection between reproduction and metabolic status of the body. When kisspeptin is administered to healthy humans, and in patients with reproductive disorders, it strongly and directly stimulates GnRH and subsequent LH secretion and enhances LH pulse frequency. These observations suggest that kisspeptins are a potential novel therapeutic approach for treating disorders with either pathologically reduced or augmented gonadotrophins pulsatile secretion and is currently a focus of translational research. Kisspeptins have also been identified in several peripheral reproductive organs, indicating their role in modulation of ovarian function, embryo implantation, and placentation, but a great deal of work remains to be done to explore further in this regard, and the evidence is only available from studies done on animal models. In this review we will mainly focus on current available evidence related to the role of kisspeptins in controlling GnRH pulse frequency, specifically their role in puberty, fertility, and reproduction. We will also be appraising other factors that regulate the kiSS1/Kisspeptin/GPR-54 system.

Delayed pubertal onset and prepubertal Kiss1 expression in female mice lacking central oestrogen receptor beta.

Ovarian oestradiol is essential for pubertal maturation and adult physiology of the female reproductive axis. It acts at central and peripheral sites through two main oestrogen receptors (ER) α and ß. Here we investigate the role of ERß on central effects of oestradiol, by generating a mouse line specifically lacking the ERß gene in neuronal and glial cells. Central ERß deletion delays the age at vaginal opening and first oestrous and reduces uterine weight without affecting body growth. Analysis of factors necessary for pubertal progression shows reduced levels of Kiss1 transcripts at postnatal (P) day 25 in the preoptic area, but not in the mediobasal hypothalamus (MBH) of mutant females. In agreement with these data, the number of kisspeptin-immunoreactive neurons was decreased by 57-72% in the three subdivisions of the rostral periventricular area of the third ventricle (RP3V), whereas the density of kisspeptin-immunoreactive fibres was unchanged in the arcuate nucleus of mutant mice. These alterations do not involve changes in ERα mRNAs in the preoptic area and protein levels in the RP3V. The number and distribution of GnRH-immunoreactive cells were unaffected, but gonadotropin-releasing hormone (GnRH) transcript levels were higher in the P25 preoptic area of mutants. At adulthood, mutant females have normal oestrous cyclicity, kisspeptin system and exhibit unaltered sexual behaviour. They display, however, reduced ovary weight and increased anxiety-related behaviour during the follicular phase. This argues for the specific involvement of central ERß in the regulation of pubertal onset in female reproduction, possibly through prepubertal induction of kisspeptin expression in the RP3V.

Female puberty acceleration by male odour in mice: neural pathway and behavioural consequences.

In female mice, exposure to male chemosignals results in early puberty onset characterized by advanced vaginal opening and higher uterine weight. Evidence suggests that the male chemosignals responsible for acceleration of female puberty are androgen-dependent, but not all of the compounds that contribute to puberty acceleration have been identified. The male chemosignals are primarily detected and processed by the vomeronasal system including the vomeronasal organ, the accessory olfactory bulb and the medial amygdala. By contrast, the mechanism by which this olfactory information is integrated in the hypothalamus is poorly understood. In this context, the recent identification of the neuropeptide kisspeptin as a gatekeeper of puberty onset may provide a good candidate neuropeptide system for the transmission of chemosensory information to the gonadotrope axis.

Hypothalamic mTOR: the rookie energy sensor.

Optimal cellular function and therefore organism's survival is determined by the sensitive and accurate convergence of energy and nutrient abundance to cell growth and division. Among other factors, this integration is coupled by the target of rapamycin (TOR) pathway, which is able to sense nutrient, energy and oxygen availability and also growth factor signaling. Indeed, TOR signaling regulates cell energy homeostasis by coordinating anabolic and catabolic processes for survival. TOR, named mTOR in mammals, is a conserved serine/threonine kinase that exists in two different complexes, mTORC1 and mTORC2. Recently, studies are suggesting that alterations of those complexes promote disease and disrupted phenotypes, such as aging, obesity and related disorders and even cancer. The evidences linking mTOR to energy and metabolic homeostasis included the following. At central level mTOR regulates food intake and body weight being involved in the mechanism by which signals such as leptin and ghrelin exert its effects. At peripheral level it influences adipogenesis and lipogenesis in different tissues including the liver. Noteworthy chronic nutritional activation of mTOR signaling has been implicated in the development of beta cell mass expansion and on insulin resistance. Understanding of mTOR and other molecular switches, such as AMP-activated protein kinase (AMPK), as well as their interrelationship is crucial to know how organisms maintain optimal homeostasis. This review summarizes the role of hypothalamic TOR complex in cellular energy sensing, evidenced in the last years, focusing on the metabolic pathways where it is involved and the importance of this metabolic sensor in cellular and whole body energy management. Understanding the exact role of hypothalamic mTOR may provide new cues for therapeutic intervention in diseases.

Kisspeptin and the hypothalamic control of reproduction: lessons from the human.

The hypothalamic hormone GnRH is a central driver of pituitary gonadotropin secretion, controlling pulsatile gonadotropin secretion, modulating gonadal steroid feedback, and bringing about full fertility in the adult. Thus, understanding GnRH neuronal regulation is essential to understanding the neurohumoral control of human reproduction. Genetic tools were used in patients with GnRH deficiency (i.e. idiopathic hypogonadotropic hypogonadism), a clinical syndrome that results from the failure of a normal pattern of pulsatile GnRH, to discover upstream modulators of GnRH secretion (1). In 2003, homozygosity mapping of two consanguineous pedigrees led to the identification of loss of function mutations in KISS1R (a G protein coupled receptor) by two groups (2, 3). In parallel, the Kiss1r(-/-) mouse was shown to be a phenocopy of the human GnRH-deficient state, demonstrating that the function of KISS1R/Kiss1r is conserved across mammalian species (4). Just before these human genetic discoveries, the ligand for kisspeptin-1 receptor [KISS1R; also known as G protein coupled receptor 54 (GPR54)], was discovered to be kisspeptin. Soon thereafter a large array of experimental studies began assembling genetic, expression, physiologic, transgenic, knockdown, and electrophysiological data to characterize the physiology of kisspeptin and its seminal role in modulating GnRH release.

Prenatal stress and peripubertal stimulation of the endocannabinoid system differentially regulate emotional responses and brain metabolism in mice.

The central endocannabinoid system (ECS) and the hypothalamic-pituitary-adrenal-axis mediate individual responses to emotionally salient stimuli. Their altered developmental adjustment may relate to the emergence of emotional disturbances. Although environmental influences regulate the individual phenotype throughout the entire lifespan, their effects may result particularly persistent during plastic developmental stages (e.g. prenatal life and adolescence). Here, we investigated whether prenatal stress--in the form of gestational exposure to corticosterone supplemented in the maternal drinking water (100 mg/l) during the last week of pregnancy--combined with a pharmacological stimulation of the ECS during adolescence (daily fatty acid amide hydrolase URB597 i.p. administration--0.4 mg/kg--between postnatal days 29-38), influenced adult mouse emotional behaviour and brain metabolism measured through in vivo quantitative magnetic resonance spectroscopy. Compared to control mice, URB597-treated subjects showed, in the short-term, reduced locomotion and, in the long term, reduced motivation to execute operant responses to obtain palatable rewards paralleled by reduced levels of inositol and taurine in the prefrontal cortex. Adult mice exposed to prenatal corticosterone showed increased behavioural anxiety and reduced locomotion in the elevated zero maze, and altered brain metabolism (increased glutamate and reduced taurine in the hippocampus; reduced inositol and N-Acetyl-Aspartate in the hypothalamus). Present data further corroborate the view that prenatal stress and pharmacological ECS stimulation during adolescence persistently regulate emotional responses in adulthood. Yet, whilst we hypothesized these factors to be interactive in nature, we observed that the consequences of prenatal corticosterone administration were independent from those of ECS drug-induced stimulation during adolescence.

Kisspeptins and reproduction: physiological roles and regulatory mechanisms.

Procreation is essential for survival of species. Not surprisingly, complex neuronal networks have evolved to mediate the diverse internal and external environmental inputs that regulate reproduction in vertebrates. Ultimately, these regulatory factors impinge, directly or indirectly, on a final common pathway, the neurons producing the gonadotropin-releasing hormone (GnRH), which stimulates pituitary gonadotropin secretion and thereby gonadal function. Compelling evidence, accumulated in the last few years, has revealed that kisspeptins, a family of neuropeptides encoded by the Kiss1 gene and produced mainly by neuronal clusters at discrete hypothalamic nuclei, are pivotal upstream regulators of GnRH neurons. As such, kisspeptins have emerged as important gatekeepers of key aspects of reproductive maturation and function, from sexual differentiation of the brain and puberty onset to adult regulation of gonadotropin secretion and the metabolic control of fertility. This review aims to provide a comprehensive account of the state-of-the-art in the field of kisspeptin physiology by covering in-depth the consensus knowledge on the major molecular features, biological effects, and mechanisms of action of kisspeptins in mammals and, to a lesser extent, in nonmammalian vertebrates. This review will also address unsolved and contentious issues to set the scene for future research challenges in the area. By doing so, we aim to endow the reader with a critical and updated view of the physiological roles and potential translational relevance of kisspeptins in the integral control of reproductive function.

High-fat diet increases LH pulse frequency and kisspeptin-neurokinin B expression in puberty-advanced female rats.

To investigate whether the advancement of puberty in response to high-fat diet (HFD) results from a concomitant increase in LH pulse frequency and kisspeptin (Kiss1) and neurokinin B (NKB) signaling in the hypothalamus, blood samples were collected on postnatal day (pnd) 28, 32, or 36 for LH measurement and vaginal opening monitored as a marker of puberty in female rats fed with HFD or standard chow from weaning. Quantitative RT-PCR was used to determine Kiss1 and kisspeptin receptor (Kiss1r) mRNA levels in brain punches of the medial preoptic area and the arcuate nucleus (ARC), and NKB and NKB receptor (NK3R) mRNA levels in the ARC. There was a gradual increase in LH pulse frequency from pnd 28, reaching significance by pnd 36 in control diet-fed rats. The advancement of puberty by approximately 6 d (average pnd 34) in rats fed HFD was associated with an earlier onset of the higher LH pulse frequency that was already extant on pnd 28. The increased levels of expression of Kiss1 in the medial preoptic area and ARC, and NKB in the ARC, associated with pubertal onset were similarly advanced in HFD-fed rats. These data suggest that the earlier accelerated GnRH pulse generator frequency and advanced puberty with obesogenic diets might be associated with premature up-regulation of kisspeptin and NKB signaling in the hypothalamus of the female rat.

Sex steroids and the control of the Kiss1 system: developmental roles and major regulatory actions.

Kisspeptins, encoded by the Kiss1 gene, and their canonical receptor, GPR54 (also termed Kiss1R), are unanimously recognised as essential regulators of puberty onset and gonadotrophin secretion. These key reproductive functions stem from the capacity of kisspeptins to stimulate gonadotrophin-releasing hormone (GnRH) secretion in the hypothalamus, where discrete populations of Kiss1 neurones have been identified. In rodents, two major groups of hypothalamic Kiss1 neurones exist: one present in the arcuate nucleus (ARC) and the other located in the anteroventral periventricular area (AVPV/RP3V). In recent years, numerous signals have been identified as putative modulators of the hypothalamic Kiss1 system. Among them, the prominent role of sex steroids as being important regulators of Kiss1 neurones has been documented in different species and developmental stages, such as early brain sex differentiation, puberty, adulthood and senescence. These regulatory actions are (mainly) conducted via oestrogen receptor (ER)α, which is expressed in almost all Kiss1 neurones, and likely involve both classical and nonclassical pathways. The regulatory effects of sex steroids are nucleus-specific. Thus, sex steroids inhibit the expression of Kiss1/kisspeptin at the ARC, as a mechanism to conduct their negative-feedback actions on gonadotrophin secretion. By contrast, oestrogens enhance Kiss1 expression at the AVPV/RP3V in rodents, suggesting the involvement of this population in the positive-feedback actions of oestradiol to generate the preovulatory surge of gonadotrophins. In addition, sex steroids have been shown to act post-transcriptionally, modulating GnRH/gonadotrophin responsiveness to kisspeptin. Finally, sex steroids also regulate the expression of co-transmitters of Kiss1 neurones, such as neurokinin B, whose mRNA content in the ARC fluctuates in parallel to that of Kiss1 in response to changes in the circulating levels of sex steroids, therefore suggesting the contribution of this neuropeptide in the feedback control of gonadotrophin secretion. In sum, compelling experimental evidence obtained in different mammalian (and non-mammalian) species, including primates, demonstrates that sex steroids are essential regulators of hypothalamic Kiss1 neurones, which in turn operate as conduits for their effects on GnRH neurones. The physiological relevance of such regulatory phenomena is thoroughly discussed.

Transcriptional regulation of the human KiSS1 gene.

Kisspeptin, the product of the KiSS1 gene, has emerged as a key component of the mechanism by which the hypothalamus controls puberty and reproductive development. It does so by stimulating the secretion of gonadotropin releasing hormone (GnRH). Little is known about the transcriptional control of the KiSS1 gene. Here we show that a set of proteins postulated to be upstream components of a hypothalamic network involved in controlling female puberty regulates KiSS1 transcriptional activity. Using RACE-PCR we determined that transcription of KiSS1 mRNA is initiated at a single transcription start site (TSS) located 153-156bp upstream of the ATG translation initiation codon. Promoter assays performed using 293 MSR cells showed that the KiSS1 promoter is activated by TTF1 and CUX1-p200, and repressed by EAP1, YY1, and CUX1-p110. EAP1 and CUX-110 were also repressive in GT1-7 cells. All four TFs are recruited in vivo to the KiSS1 promoter and are expressed in kisspeptin neurons. These results suggest that expression of the KiSS1 gene is regulated by trans-activators and repressors involved in the system-wide control of mammalian puberty.

Reproductive dysfunction and decreased GnRH neurogenesis in a mouse model of CHARGE syndrome.

CHARGE is a multiple congenital anomaly disorder and a common cause of pubertal defects, olfactory dysfunction, growth delays, deaf-blindness, balance disorders and congenital heart malformations. Mutations in CHD7, the gene encoding chromodomain helicase DNA binding protein 7, are present in 60-80% of individuals with the CHARGE syndrome. Mutations in CHD7 have also been reported in the Kallmann syndrome (olfactory dysfunction, delayed puberty and hypogonadotropic hypogonadism). CHD7 is a positive regulator of neural stem cell proliferation and olfactory sensory neuron formation in the olfactory epithelium, suggesting that the loss of CHD7 might also disrupt development of other neural populations. Here we report that female Chd7(Gt/+) mice have delays in vaginal opening and estrus onset, and erratic estrus cycles. Chd7(Gt/+) mice also have decreased circulating levels of luteinizing hormone and follicle-stimulating hormone but apparently normal responsiveness to gonadotropin-releasing hormone (GnRH) agonist and antagonist treatment. GnRH neurons in the adult Chd7(Gt/+) hypothalamus and embryonic nasal region are diminished, and there is decreased cellular proliferation in the embryonic olfactory placode. Expression levels of GnRH1 and Otx2 in the hypothalamus and GnRHR in the pituitary are significantly reduced in adult Chd7(Gt/+) mice. Additionally, Chd7 mutant embryos have CHD7 dosage-dependent reductions in expression levels of Fgfr1, Bmp4 and Otx2 in the olfactory placode. Together, these data suggest that CHD7 has critical roles in the development and maintenance of GnRH neurons for regulating puberty and reproduction.

Effect of zinc supplementation on markers of insulin resistance, oxidative stress, and inflammation among prepubescent children with metabolic syndrome.

OBJECTIVE: This trial aimed to evaluate the effects of zinc sulfate in comparison with placebo on markers of insulin resistance, oxidative stress, and inflammation in a sample of obese prepubescent children. METHODS: This triple-masked, randomized, placebo-controlled, crossover trial was conducted among 60 obese Iranian children in 2008. Participants were randomly assigned to two groups of equal number; one group received 20 mg of elemental zinc and the other group received placebo on a regular daily basis for 8 weeks. After a 4-week washout period, the groups were crossed over. In addition to anthropometric measures and blood pressure, fasting plasma glucose, lipid profile, insulin, apolipoproteins A-1 (ApoA-I) and B, high-sensitivity C-reactive protein (hs-CRP), leptin, oxidized low-density lipoprotein (ox-LDL), and malondialdehyde were determined at all four stages of the study. RESULTS: Irrespective of the order of receiving zinc and placebo, in both groups, significant decrease was documented for Apo B/ApoA-I ratio, ox-LDL, leptin and malondialdehyde, total and LDL-cholesterol after receiving zinc without significant change after receiving placebo. In groups, hs-CRP and markers of insulin resistance decreased significantly after receiving zinc, but increased after receiving placebo. In both groups, the mean body mass index (BMI) Z-score remained high, after receiving zinc, the mean weight, BMI, BMI Z-score decreased significantly, whereas these values increased after receiving placebo. CONCLUSION: These results are particularly important in light of the deleterious consequences of childhood obesity and early changes in markers of inflammatory and oxidative stress. We suggest exploring the direct clinical application of zinc supplementation in childhood obesity in future studies.

Vitamin D status and calcium metabolism in adolescent black and white girls on a range of controlled calcium intakes.

BACKGROUND: There are limited data in adolescents on racial differences in relationships between dietary calcium intake, absorption, and retention and serum levels of calcium-regulating hormones. OBJECTIVES: The aim of this study was to investigate these relationships cross-sectionally in American White and Black adolescent girls. METHODS: Calcium balance studies were conducted in 105 girls, aged 11-15 yr, on daily calcium intakes ranging from 760-2195 mg for 3-wk controlled feeding periods; 158 observations from 52 Black and 53 White girls were analyzed. RESULTS: Black girls had lower serum 25-hydroxyvitamin D [25(OH)D], higher serum 1,25-dihydroxyvitamin D, and higher calcium absorption and retention than White girls. Calcium intake and race, but not serum 25(OH)D, predicted net calcium absorption and retention with Black girls absorbing calcium more efficiently at low calcium intakes than White girls. The relationship between serum 25(OH)D and serum PTH was negative only in White girls. Calcium intake, race, and postmenarcheal age explained 21% of the variation in calcium retention, and serum 25(OH)D did not contribute further to the variance. CONCLUSIONS: These results suggest that serum 25(OH)D does not contribute to the racial differences in calcium absorption and retention during puberty.