Intestinal transport of insulin-like growth factor-I (igf-I) in the suckling rat

Components of human breast milk: from macronutrient to microbiome and microRNA

Human breast milk (HBM) is essential for the infant's growth and development right after birth and is an irreplaceable source of nutrition for early human survival. Various infant formulas have many similarities to HBM in many components, but there is no perfect substitute for HBM. Recently, various breast milk components and their roles have been studied according to the development of various analysis techniques. As is already well known, HBM contains about 87%-88% water, and 124- g/L solid components as macronutrients, including about 7% (60-70 g/L) carbohydrates, 1% (8-10 g/L) protein, and 3.8% (35-40 g/L) fat. The composition may vary depending on the environmental factors, including maternal diet. Colostrum is low in fat but high in protein and relatively rich in immuneprotective components. Although HBM contains enough vitamins to ensure normal growth of the infant, vitamins D and K may be insufficient, and the infant may require their supplementation. Growth factors in HBM also serve as various bioactive proteins and peptides on the intestinal tract, vasculature, nervous system, and endocrine system. In the past, HBM of a healthy mother was thought to be sterile. However, several subsequent studies have confirmed the presence of rich and diverse microbial communities in HBM. Some studies suggested that the genera Staphylococcus and Streptococcus may be universally predominant in HBM, but the origin of microbiota still remains controversial. Lastly, milk is the one of most abundant body fluid of microRNAs, which are known to play a role in various functions, such as immunoprotection and developmental programming, through delivering from HBM and absorption by intestinal epithelial cells. In conclusion, HBM is the most important source of nutrition for infants and includes microbiomes and miRNAs for growth, development, and immunity.

Production-related contaminants (pesticides, antibiotics and hormones) in organic and conventionally produced milk samples sold in the USA

OBJECTIVE

Consumption of cow's milk, which is associated with diet and health benefits, has decreased in the USA. The simultaneous increase in demand for more costly organic milk suggests consumer concern about exposure to production-related contaminants may be contributing to this decline. We sought to determine if contaminant levels differ by the production method used.

DESIGN

Half-gallon containers of organic and conventional milk (four each) were collected by volunteers in each of nine US regions and shipped on ice for analysis. Pesticide, antibiotic and hormone (bovine growth hormone (bGH), bGH-associated insulin-like growth factor 1 (IGF-1)) residues were measured using liquid or gas chromatography coupled to mass or tandem mass spectrometry. Levels were compared against established federal limits and by production method.

SETTING

Laboratory analysis of retail milk samples.

RESULTS

Current-use pesticides (5/15 tested) and antibiotics (5/13 tested) were detected in several conventional (26-60 %; n 35) but not in organic (n 34) samples. Among the conventional samples, residue levels exceeded federal limits for amoxicillin in one sample (3 %) and in multiple samples for sulfamethazine (37 %) and sulfathiazole (26 %). Median bGH and IGF-1 concentrations in conventional milk were 9·8 and 3·5 ng/ml, respectively, twenty and three times that in organic samples (P < 0·0001).

CONCLUSIONS

Current-use antibiotics and pesticides were undetectable in organic but prevalent in conventionally produced milk samples, with multiple samples exceeding federal limits. Higher bGH and IGF-1 levels in conventional milk suggest the presence of synthetic growth hormone. Further research is needed to understand the impact of these differences, if any, on consumers.

Effect of Early Breast Milk Nutrition on Serum Insulin-Like Growth Factor-1 in Preterm Infants

BACKGROUND:

Insulin-like growth factor 1 (IGF-1) is one of the essential intrauterine hormonal mediators of growth, and its serum values are often low after preterm delivery.

AIM:

To evaluate the influence of immediate breast milk feeding on serum IGF-1 in preterm newborns.

SUBJECTS AND METHODS:

This prospective, observational cohort study included 60 premature infants born < 32 weeks of gestation, divided into group A and B regarding breastfeeding or formula feeding. Growth measurements were taken at birth. The standard deviation of each measurement was calculated. Serum IGF-I was measured one day postnatal and at a time equivalent to 40 weeks of gestation.

RESULTS:

Significant higher level of mean serum IGF-1 was detected in group A than B at postnatal age equivalent to 40 weeks of gestation. In group A, the higher significant level was detected in mean serum IGF-1 at an age equivalent to 40 weeks of gestation than at birth (25.21 ± 6.69 and 20.13 ± 5.46 p < 0.05). Multiple linear regression analysis showed that high birth weight, increased age of gestation and breastfeeding were correlated to the elevated serum level of IGF-1 at a postnatal age corresponding to 40 weeks gestational age.

CONCLUSION:

Immediate breast milk feeding was accompanied by elevated IGF-1 in the serum of preterm infants.

Associations of Calcium, Vitamin D, and Dairy Product Intakes with Colorectal Cancer Risk among Older Women: The Iowa Women's Health Study

Calcium and, to a lesser extent, dairy products are consistently modestly inversely associated with colorectal cancer (CRC). Dairy products may contain components other than calcium and fat, such as insulin-like growth factor-1, that may affect CRC risk. In the prospective Iowa Women's Health Study, calcium, dairy product, and vitamin D intakes were assessed using a semiquantitative food frequency questionnaire. To investigate dairy products independent of their calcium components, we estimated residuals from linear regression models of their associations with dietary calcium. Of the 35,221 55-69-year-old cancer-free women at baseline in 1986, 1,731 developed CRC during follow-up through 2012. For those in the highest relative to the lowest intake quintiles, the adjusted hazards ratios and 95% confidence intervals from multivariable Cox proportional hazards regression models for overall and distal CRC were 0.81 (0.67-0.98; P_trend = 0.004) and 0.59 (0.44-0.80; P_trend = 0.003), respectively, for total calcium; and 0.79 (0.66-0.94; P_trend = 0.01) and 0.69 (0.53-0.90; P_trend = 0.003) for total dairy products, respectively. The various dairy product residuals were not associated with CRC. These results support that, among women, calcium and dairy products may be inversely associated with CRC-perhaps primarily distal CRC-but suggest that the non-calcium, non-fat component of dairy products may not be associated with CRC.

Diseases of Civilization - Cancer, Diabetes, Obesity and Acne - the Implication of Milk, IGF-1 and mTORC1

Nutrition and food are one of the most complex aspects of human lives, being influenced by biochemical, psychological, social and cultural factors. The Western diet is the prototype of modern dietary pattern and is mainly characterized by the intake of large amounts of red meat, dairy products, refined grains and sugar. Large amounts of scientific evidence positively correlate Western diet to acne, obesity, diabetes, heart disease and cancer, the so-called "diseases of civilization". The pathophysiological common ground of all these pathologies is the IGF-1 and mTORC pathways, which will be disscussed further in this paper.

Functional analysis of the IGF-system in milk

The development of milk during evolution is considered a more recent step to provide the neonate with adequate amounts of energy, nutrients, and specific hormonal signals thereby, granting a fast and efficient rate of postnatal growth and development. Since the insulin- or the insulin-like growth factor (IGF) systems were evolved much earlier, it can be assumed that the functionality of the IGF-system has been integrated into the novel matrix milk containing casein and whey proteins from the beginnings. In fact, IGFs and IGF-binding proteins (IGFBPs) are abundantly present in milk, which is particularly true for fore-milk or colostrum and the potential effects of milk-borne IGF-compounds on the consuming organisms have in fact been addressed by several studies. Those studies examined, if orally administered IGFs can be absorbed by the consumer's gastro-intestinal tract and thus contribute e.g. to the somatic growth of infants. A second line of studies assessed local effects of milk-borne IGFs on growth and development of the gastro-intestinal tract itself. Finally, distinct functions of isolated IGF-compounds for growth and involution of the mammary gland have also been provided in the past. While the consumption of milk seems not to represent a major source of endogenous IGFs, accumulating evidence indicates secondary effects of milk on the endogenous IGF-system, which may be mediated by micronutrients such as branched amino acids and metabolic programming. By contrast, direct effects on growth and development of oesophageal and intestinal cells have been observed if IGFs were administered orally.

Associations of Calcium and Milk Product Intakes with Incident, Sporadic Colorectal Adenomas

Calcium intake has been consistently, modestly inversely associated with colorectal neoplasms, and supplemental calcium reduced adenoma recurrence in clinical trials. Milk products are the major source of dietary calcium in the United States, but their associations with colorectal neoplasms are unclear. Data pooled from three colonoscopy-based case-control studies of incident, sporadic colorectal adenoma (n = 807 cases, 2,185 controls) were analyzed using multivariable unconditional logistic regression. Residuals from linear regression models of milk with dietary calcium were estimated as the noncalcium, insulin-like growth factor 1-containing component of milk. For total, dietary, and supplemental calcium intakes, the adjusted odds ratios (ORs) comparing the highest to the lowest intake quintiles were 0.94 (95% confidence interval [CI] 0.69-1.30), 0.86 (CI 0.62-1.20), and 0.99 (CI 0.77-1.27), respectively. The corresponding ORs for consumption of total milk products, total milk, nonfat milk, total milk product residuals, and nonfat milk residuals were, respectively, 0.99, 0.90, 0.92, 0.94, and 0.95; all CIs included 1.0. For those who consumed any whole milk relative to those who consumed none, the OR was 1.15 (CI 0.89-1.49). These results are consistent with previous findings of modest inverse associations of calcium intakes with colorectal adenoma, but suggest that milk products may not be associated with adenoma.

Effect of Early Expressed Human Milk on Insulin-Like Growth Factor 1 and Short-Term Outcomes in Preterm Infants

Aims

Preterm breast milk contains high levels of bioactive components, including insulin-like growth factor 1 (IGF-1), that are reduced by Holder pasteurization. Animal studies have shown that milk-borne IGF-1 is likely absorbed intact in a bioactive form by the intestines. The aim of this study was to assess if early non-pasteurized expressed breast milk nutrition may affect IGF-1 plasma levels in premature infants. We also investigated the possible association between early expressed milk nutrition and short-term outcomes.

Methods

Fifty-two preterm infants with gestational age < 31 weeks were divided into two groups according to expressed breast milk intake (< or ≥ 50 mL/Kg/day) until 32 weeks of postmenstrual age when blood sampling for IGF-1 analysis was performed.

Results

In our population, early expressed breast milk does not affect IGF-1 plasma levels (p 0.48). An association was observed between early expressed milk nutrition and a lower incidence of bronchopulmonary dysplasia, sepsis, feeding intolerance, need for parenteral nutrition and length of hospitalization.

Conclusions

Contrary to the results in some animal studies, our results did not seem to show that early expressed breast milk can help to maintain postnatal IGF-1 near foetal levels in preterm infants. The observed protective effect of expressed breast milk on short-term outcomes can be the starting point for further study of the effects of non-pasteurized human milk in preterm infants.

Maternally Administered Cyclic Glycine-Proline Increases Insulin-Like Growth Factor-1 Bioavailability and Novelty Recognition in Developing Offspring

Cyclic glycine-proline (cGP), a metabolite of IGF-1, is an endogenous neuropeptide that improves memory in adult rats. The presence and concentrations of endogenous cGP, and its association with IGF-1 and IGF binding protein-3 (IGFBP-3) in rat milk and plasma, were evaluated during postnatal development. Maternal-infantile transfer of cGP during lactation and its efficacy on the memory of developing offspring were also investigated. Dams were gavaged with either cGP (3 mg/kg) or saline daily from postnatal days 8-22. Concentrations of cGP were measured in dams' milk, and concentrations of cGP, IGF-1, and IGFBP-3 were measured in the plasma of dams, pups, and young adults. The recognition memory, locomotor function, and anxiety-like behavior of offspring were evaluated using behavioral tests. Endogenous cGP was detected in rat milk, and its concentration was higher during peak lactation compared with late lactation. Comparisons within control groups showed low endogenous IGF-1 and IGFBP-3 and high endogenous cGP concentrations in the plasma of male pups. The reduced IGFBP-3 and increased cGP may be a response to increase the bioavailability of IGF-1 during infancy. Exogenous cGP showed oral bioavailability and effective maternal-infantile transfer through milk. Maternally transferred cGP also led to improved recognition memory in the developing offspring, possibly through increased IGF-1 bioavailability, with no effect on locomotor activity and anxiety-like behavior. These results show that cGP is an essential endogenous peptide during early postnatal development as it improves the bioavailability of IGF-1 during infancy. Furthermore, maternal cGP supplementation offers an effective and natural route of administration for improving memory in the developing offspring.

Milk Consumption after Age 9 Years Does Not Predict Age at Menarche

BACKGROUND

Regular milk consumption during childhood and adolescence is recommended for bone health. However, milk consumption increases circulating insulin-like growth factor I concentrations, and may also accelerate puberty.

OBJECTIVE

We prospectively investigated the association between milk consumption and age at menarche in the Growing Up Today Study.

METHODS

Study participants were 5583 US girls who were premenarcheal and ages 9-14 y in 1996. Girls were followed through 2001, at which time 97% of noncensored participants had reported menarche. Frequency of milk and meat consumption was calculated with the use of annual youth/adolescent food frequency questionnaires from 1996-1998. Intake of related nutrients was also measured. Age at menarche was self-reported annually through 2001.

RESULTS

During follow-up, 5227 girls attained menarche over 10,555 accrued person-years. In models adjusted for dietary and sociodemographic predictors of menarche, frequency of milk consumption did not predict age at onset of menarche (for >3 glasses of milk/d vs. 1.1-4 glasses/wk, HR: 0.93; 95% CI: 0.83, 1.04). After additional adjustment for body size, premenarcheal girls consuming >3 glasses of milk daily were 13% less likely (95% CI: -3%, -23%; P-trend: <0.01) to attain menarche in the next month relative to those consuming 1.1-4 glasses/wk. Neither total meat nor red meat consumption was associated with age at menarche.

CONCLUSIONS

Our findings suggest that regular consumption of milk in girls aged ≥9 y is unlikely to substantially affect age at onset of menarche. Studies assessing associations between diet in early childhood and pubertal timing may be more illuminating.

Reducing blood glucose levels in TIDM mice with an orally administered extract of sericin from hIGF-I-transgenic silkworm cocoons

In previous studies, we reported that the blood glucose levels of mice with type I diabetes mellitus (TIDM) was reduced with orally administered silk gland powder from silkworms transgenic for human insulin-like growth factor-I (hIGF-I). However, potential safety hazards could not be eliminated because the transgenic silk gland powder contained heterologous DNA, including the green fluorescent protein (gfp) and neomycin resistance (neo) genes. These shortcomings might be overcome if the recombinant hIGF-I were secreted into the sericin layer of the cocoon. In this study, silkworm eggs were transfected with a novel piggyBac transposon vector, pigA3GFP-serHS-hIGF-I-neo, containing the neo, gfp, and hIGF-I genes controlled by the sericin-1 (ser-1) promoter with the signal peptide DNA sequence of the fibrin heavy chain (Fib-H) and a helper plasmid containing the piggyBac transposase sequence under the control of the Bombyx mori actin 3 (A3) promoter, using sperm-mediated gene transfer to generate the transformed silkworms. The hIGF-I content estimated by enzyme-linked immunosorbent assay was approximately 162.7 ng/g. To estimate the biological activity of the expressed hIGF-I, streptozotocin-induced TIDM mice were orally administered sericin from the transgenic silkworm. The blood glucose levels of the mice were significantly reduced, suggesting that the extract from the transgenic hIGF-I silkworm cocoons can be used as an orally administered drug.

Human milk composition: nutrients and bioactive factors

This article provides an overview of the composition of human milk, its variation, and its clinical relevance. The composition of human milk is the biological norm for infant nutrition. Human milk also contains many hundreds to thousands of distinct bioactive molecules that protect against infection and inflammation and contribute to immune maturation, organ development, and healthy microbial colonization. Some of these molecules (eg, lactoferrin) are being investigated as novel therapeutic agents. Human milk changes in composition from colostrum to late lactation, within feeds, by gestational age, diurnally, and between mothers. Feeding infants with expressed human milk is increasing.

Lactation Biology Symposium: role of colostrum and colostrum components on glucose metabolism in neonatal calves

In neonatal calves, nutrient intake shifts from continuous glucose supply via the placenta to discontinuous colostrum and milk intake with lactose and fat as main energy sources. Calves are often born hypoglycemic and have to establish endogenous glucose production (eGP) and gluconeogenesis, because lactose intake by colostrum and milk does not meet glucose demands. Besides establishing a passive immunity, colostrum intake stimulates maturation and function of the neonatal gastrointestinal tract (GIT). Nutrients and nonnutritive factors, such as hormones and growth factors, which are present in high amounts in colostrum of first milking after parturition, affect intestinal growth and function and enhance the absorptive capacity of the GIT. Likely as a consequence of that, colostrum feeding improves the glucose status in neonatal calves by increasing glucose absorption, which results in elevated postprandial plasma glucose concentrations. Hepatic glycogen concentrations rise much greater when colostrum instead of a milk-based colostrum replacer (formula with same nutrient composition as colostrum but almost no biologically active substances, such as hormones and growth factors) is fed. In contrast, first-pass glucose uptake in the splanchnic tissue tended to be greater in calves fed formula. The greater plasma glucose rise and improved energy status in neonatal calves after colostrum intake lead to greater insulin secretion and accelerated stimulation of anabolic processes indicated by enhanced maturation of the postnatal somatotropic axis in neonatal calves. Hormones involved in stimulation of eGP, such as glucagon and cortisol, depend on neonatal diet, but their effects on eGP stimulation seem to be impaired. Although colostrum feeding affects systemic insulin, IGF-I, and leptin concentrations, evidence for systemic action of colostral insulin, IGF-I, and leptin in neonatal calves is weak. Studies so far indicate no absorption of insulin, IGF-I, and leptin from colostrum in neonatal calves, unlike in rodents where systemic effects of colostral leptin are demonstrated. Therefore, glucose availability in neonatal calves is promoted by perinatal maturation of eGP and colostrum intake. There may be long-lasting effects of an improved colostrum supply and glucose status on postnatal growth and development, and colostrum supply may contribute to neonatal programming of performance (milk and growth) in later life, but data proving this concept are missing.

Insulin-like growth factors in the gastrointestinal tract and liver

The liver is a major source of insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) that are present in the circulation and have important endocrine activities relating to energy metabolism, body size, carcinogenesis, and various organ-specific functions. Although IGFs have only minor effects on the normal liver itself, production of IGFs and IGFBPs in a tissue-specific manner in the gastrointestinal tract exert important regulatory effects on cellular proliferation, survival, and apoptosis. IGFs and IGFBPs play important regulatory roles in the response of both the liver and the gastrointestinal tract to inflammation and in the development of neoplasia.

Effects of oxidative stress on intestinal type I insulin-like growth factor receptor expression

INTRODUCTION

Oxidative stress activates multiple signaling transduction pathways, including the phosphatidylinositol 3-kinase (PI3-K), in an injured intestine as occurs in necrotizing enterocolitis (NEC). We have previously shown that hydrogen peroxide (H2O2)-induced PI3-K activation is significantly enhanced with exogenous insulin-like growth factor (IGF)-1 in intestinal epithelial cells. However, the effects of oxidative stress on IGF receptor type I (IGF-IR) activation and expression in the neonatal intestine during NEC are unknown.

MATERIAL AND METHODS

Intestinal sections from neonates undergoing bowel resections (control = 3, NEC = 20) were analyzed for IGF-IR expression. NEC was induced in newborn mouse pups using hypoxia and hyperosmolar feeds, and distal small bowel segments were analyzed for IGF-IR expression (control = 3, NEC = 7). H2O2 was used to induce oxidative stress in rat (RIE-1) and fetal human (FHs74 Int) intestinal epithelial cells. Phosphorylation of IGF-IR, Akt, a downstream effector of PI3-K, and IGF-IR levels were determined by Western blotting. Flow cytometry, immunofluorescence, immunohistochemistry, IGF-IR tyrosine phosphorylation array, cell death enzyme-linked immunosorbent assay, and Western blotting were used to determine the IGF-IR expression.

RESULTS

An increased IGF-IR expression was noted in intestinal sections from NEC as well as murine model of NEC. H2O2 treatment rapidly activated IGF-IR and increased the expression in RIE-1 and FHs74 Int cells. Inhibition of IGF-IR resulted in significant RIE-1 cell apoptosis during oxidative stress. IGF-IR tyrosine phosphorylation array showed the recruitment of several key SH2 domain-containing proteins and oncogenes to the IGF-IR tyrosine kinase domain in H2O2-treated RIE-1 cells.

CONCLUSION

IGF-IR-mediated activation of intracellular signaling may play a critical role during oxidative stress-induced apoptosis in NEC.

Expression of the hIGF-I gene driven by the Fhx/P25 promoter in the silk glands of germline silkworm and transformed BmN cells

The expression of the human insulin-like growth factor (hIGF-I) gene driven by the Fhx/P25 promoter in the silk glands of transgenic silkworms (Bombyx mori) and in transformed silkworm cells, was achieved using BmN cells transfected with a piggyBac vector, pigA3GFP-Fhx/P25-hIGF-ie-neo containing a neomycin-resistance gene (neo), a green fluorescent protein gene (gfp), an hIGF-I gene, and a helper plasmid containing the piggyBac transposase sequence under the control of the B. mori actin 3 (A3) promoter. We selected stably transformed BmN cells expressing hIGF-I using the antibiotic G418. The expression level of hIGF-I was about 450 pg in 3 × 10(6) cells, determined by ELISA. The piggyBac vector was transferred into the silkworm eggs using sperm-mediated gene transfer. The expression level of hIGF-I per gram fresh posterior silk glands of G4 transgenic silkworms was approx. 150 ng.

Milk consumption and circulating insulin-like growth factor-I level: a systematic literature review

Studies suggest that the circulating insulin-like growth factor I (IGF-I) level is positively associated with the prostate cancer risk. The association of milk consumption and circulating IGF-I level has been examined in epidemiological studies with inconsistent results. We conducted a systematic literature review to summarize and quantify the current evidence for milk or dairy product consumption and the circulating IGF-I level. We searched relevant papers published in English up to March 2009 in various databases. Fifteen cross-sectional studies and eight randomized controlled trials were finally identified. Ten cross-sectional studies showed statistically positive correlation between milk consumption and the circulating IGF-I level. Randomized controlled trials indicated that the circulating IGF-I level was significantly higher in the milk intervention group. After meta-analysis, the weighted mean difference of the circulating IGF-I level was 13.8 ng/ml (95% confidence interval: 6.1-21.5 ng/ml) comparing the intervention group with the control group. The current evidence suggests that milk consumption may increase the circulating IGF-I level.

Conditioned polarized Caco-2 cell monolayers allow to discriminate for the ability of gut-derived microorganisms to modulate permeability and antigen-induced basophil degranulation

BACKGROUND

Food allergy is a common allergic disorder--especially in early childhood. The avoidance of the allergenic food is the only available method to prevent further reactions in sensitized patients. A better understanding of the immunologic mechanisms involved in this reaction would help to develop therapeutic approaches applicable to the prevention of food allergy.

OBJECTIVE

To establish a multi-cell in vitro model of sensitized intestinal epithelium that mimics the intestinal epithelial barrier to study the capacity of probiotic microorganisms to modulate permeability, translocation and immunoreactivity of ovalbumin (OVA) used as a model antigen.

METHODS

Polarized Caco-2 cell monolayers were conditioned by basolateral basophils and used to examine apical to basolateral transport of OVA by ELISA. Activation of basophils with translocated OVA was measured by beta-hexosaminidase release assay. This experimental setting was used to assess how microorganisms added apically affected these parameters. Basolateral secretion of cytokine/chemokines by polarized Caco-2 cell monolayers was analysed by ELISA.

RESULTS

Basophils loaded with OVA-specific IgE responded to OVA in a dose-dependent manner. OVA transported across polarized Caco-2 cell monolayers was found to trigger basolateral basophil activation. Microorganisms including lactobacilli and Escherichia coli increased transepithelial electrical resistance while promoting OVA passage capable to trigger basophil activation. Non-inflammatory levels of IL-8 and thymic stromal lymphopoietin were produced basolaterally by Caco-2 cells exposed to microorganisms.

CONCLUSION

The complex model designed in here is adequate to learn about the consequence of the interaction between microorganisms and epithelial cells vis-a-vis the barrier function and antigen translocation, two parameters essential to mucosal homeostasis. It can further serve as a direct tool to search for microorganisms with anti-allergic and anti-inflammatory properties.

Milk consumption and the prepubertal somatotropic axis

BACKGROUND

Nutrients, hormones and growth factors in dairy foods may stimulate growth hormone (GH), insulin-like growth factor I (IGF-I), and raise the ratio of IGF-I to its binding protein, IGFBP-3. We conducted pilot studies in Mongolia and Massachusetts to test the extent to which milk intake raised somatotropic hormone concentrations in prepubertal children.

METHODS

In Ulaanbaatar, we compared plasma levels before and after introducing 710 ml daily whole milk for a month among 46 10-11 year old schoolchildren. In a randomized cross-over study in Boston, we compared plasma hormone levels of 28 6-8 year old girls after one week of drinking 710 ml low fat (2%) milk with their hormone levels after one week of consuming a macronutrient substitute for milk.

RESULTS

After a month of drinking whole milk, Mongolian children had higher mean plasma levels of IGF-I (p < 0.0001), IGF-I/IGFBP-3 (p < 0.0001), and 75th percentile of GH levels (p = 0.005). After a week of drinking low fat milk, Boston girls had small and non-significant increases in IGF-1, IGF-1/IGFBP-3 and GH.

CONCLUSION

Milk drinking may cause increases in somatotropic hormone levels of prepubertal girls and boys. The finding that milk intake may raise GH levels is novel, and suggests that nutrients or bioactive factors in milk may stimulate endogenous GH production.

The effect of bovine whey protein on ectopic bone formation in young growing rats

The beneficial effect of bovine whey protein (WP) on bone metabolism has been shown in adult human subjects and ovariectomised rats. However, its effect on bone formation in earlier life, particularly during periods of bone mineral accrual, has not been investigated. Twenty-one male rats (4 weeks old, Wistar strain) were randomised by weight into three groups of seven rats each and fed ad libitum on a semi-purified low-Ca diet (3.0 g Ca/kg diet) containing 0 (control), 10 (diet WP1) or 20 (diet WP2) g bovine WP/kg for 47 d. On day 34 of the dietary intervention, all rats had two gelatine capsules containing demineralised bone powder implanted subcutaneously in the thorax region (a well-established in vivo model of ectopic bone formation). At 14 d after implantation, alkaline phosphatase activity (reflective of bone formation) in the bone implants from animals fed WP1 and -2 diets was almost 2-fold (P<0.01) that of control animals. Insulin-like growth factor (IGF)-I mRNA levels were about 3-fold (P<0.05) higher in implants from animals fed the WP diets compared with those from control animals. Serum- and urine-based biomarkers of bone metabolism and bone mineral composition in intact femora were unaffected by WP supplementation. In conclusion, the present findings suggest that bovine WP can enhance the rate of ectopic bone formation in young growing rats fed a Ca-restricted diet. This effect may be mediated by an increased synthesis of IGF-I in growing bone. The effect of WP on bone formation warrants further investigation.