Milk IGF-I Research Articles

Gestational Diabetes Mellitus and Colostral Appetite-Regulating Adipokines.

Gestational diabetes mellitus (GDM) is a complex metabolic disorder that has short- and long-term effects on maternal and offspring health. This study aimed to assess the impact of maternal hyperglycemia severity, classified as GDM-G1 (diet treatment) and GDM-G2 (insulin treatment) on colostral appetite-regulating molecules. Colostrum samples were collected from hyperglycemic (N = 30) and normoglycemic (N = 21) mothers, and the concentrations of milk hormones were determined by immunoenzymatic assay. A difference was found for milk ghrelin, but not for molecules such as adiponectin, leptin, resistin, or IGF-I levels, in relation to maternal hyperglycemia. The colostral ghrelin in the GDM-G1 cohort (0.21 ng/mL) was significantly lower than for GDM-G2 (0.38 ng/mL) and non-GDM groups (0.36 ng/mL). However, colostral resistin was higher, but not significantly, for GDM-G1 (13.33 ng/mL) and GDM-G2 (12.81 ng/mL) cohorts than for normoglycemic mothers (7.89 ng/mL). The lack of difference in relation to hyperglycemia for milk leptin, adiponectin, leptin-adiponectin ratio, resistin, and IGF-I levels might be the outcome of effective treatment of GDM during pregnancy. The shift between ghrelin and other appetite-regulating hormones might translate into altered ability to regulate energy balance, affecting offspring's metabolic homeostasis.

Effect of maternal supplementation with essential fatty acids and conjugated linoleic acid on metabolic and endocrine development in neonatal calves

We tested the hypothesis that the maternal supply of essential fatty acids (EFA), especially α-linolenic acid, and conjugated linoleic acid (CLA), affects glucose metabolism, the endocrine regulation of energy metabolism and growth, and the intestinal development of neonatal calves. We studied calves from dams that received an abomasal infusion of 76 g/d coconut oil (CTRL; n = 9), 78 g/d linseed oil and 4 g/d safflower oil (EFA; n = 9), 38 g/d Lutalin (BASF SE) containing 27% cis-9,trans-11 and trans-10,cis-12 CLA (CLA; n = 9), or a combination of EFA and CLA (EFA+CLA; n = 11) during the last 63 d of gestation and early lactation. Calves received colostrum and transition milk from their own dam for the first 5 d of life. Insulin-like growth factor (IGF)-I, leptin, and adiponectin concentrations were measured in milk. Blood samples were taken before first colostrum intake, 24 h after birth, and from d 3 to 5 of life before morning feeding to measure metabolic and endocrine traits in plasma. On d 3 of life, energy expenditure was evaluated by a bolus injection of NaH13CO3 and determination of CO2 appearance rate. On d 4, additional blood samples were taken to evaluate glucose first-pass uptake and 13CO2 enrichment after [13C6]-glucose feeding and intravenous [6,6-2H2]-glucose bolus injection, as well as postprandial changes in glucose, nonesterified fatty acids (NEFA), insulin, and glucagon. On d 5, calves were killed 2 h after feeding and samples of small intestinal mucosa were taken for histomorphometric measurements. The concentrations of IGF-I, adiponectin, and leptin in milk decreased during early lactation in all groups, and the concentrations of leptin in first colostrum was higher in EFA than in CTRL cows. Plasma glucose concentration before first colostrum intake was higher in EFA calves than in non-EFA calves and was lower in CLA calves than in non-CLA calves. Plasma IGF-I concentration was higher on d 1 before colostrum intake in EFA calves than in EFA+CLA calves and indicated an overall CLA effect, with lower plasma IGF-I in CLA than in non-CLA calves. Postprandial NEFA concentration was lowest in EFA and CLA calves. The postprandial rise in plasma insulin was higher in EFA than in non-EFA calves. Plasma adiponectin concentration increased from d 1 to d 2 in all groups and was higher on d 3 in CLA than in non-CLA calves. Plasma leptin concentration was higher on d 4 and 5 in EFA than in non-EFA calves. Maternal fatty acid treatment did not affect energy expenditure and first-pass glucose uptake, but glucose uptake on d 4 was faster in EFA than in non-EFA calves. Crypt depth was lower, and the ratio of villus height to crypt depth was higher in the ilea of CLA than non-CLA calves. Elevated plasma glucose and IGF-I in EFA calves immediately after birth may indicate an improved energetic status in calves when dams are supplemented with EFA. Maternal EFA and CLA supplementation influenced postprandial metabolic changes and affected factors related to the neonatal insulin response.

Update on human health concerns of recombinant bovine somatotropin use in dairy cows

The 20 yr of commercial use of recombinant bovine somatotropin (rbST) in the United States provide the backdrop for reviewing the outcome of use on human health issues by the upcoming 78th meeting of the Joint Food and Agriculture Organization of the United Nations (FAO)/World Health Organization (WHO) Expert Committee on Food Additives. These results and further advancements in scientific knowledge indicate there are no new human health issues related to the use of rbST by the dairy industry. Use of rbST has no effect on the micro- and macrocomposition of milk. Also, no evidence exists that rbST use has increased human exposure to antibiotic residues in milk. Concerns that IGF-I present in milk could have biological effects on humans have been allayed by studies showing that oral consumption of IGF-I by humans has little or no biological activity. Additionally, concentrations of IGF-I in digestive tract fluids of humans far exceed any IGF-I consumed when drinking milk. Furthermore, chronic supplementation of cows with rbST does not increase concentrations of milk IGF-I outside the range typically observed for effects of farm, parity, or stage of lactation. Use of rbST has not affected expression of retroviruses in cattle or posed an increased risk to human health from retroviruses in cattle. Furthermore, risk for development of type 1 or type 2 diabetes has not increased in children or adults consuming milk and dairy products from rbST-supplemented cows. Overall, milk and dairy products provide essential nutrients and related benefits in health maintenance and the prevention of chronic diseases.

Diet influences the content of bioactive peptides in goat milk

Leptin, insulin, ghrelin, and IGF-I are circulating peptide hormones concerned with energy homeostasis and the regulation of GH axis. They are present in human milk, and are thought to promote neonatal development. The aim of the present study was to detect these substances in goat milk and determine whether their levels can be modified by changing the macronutrient content of the lactating animals' diet. Sixteen Saanen goats in mid-lactation were divided into two balanced groups, one given a diet containing 17% starch (LS) and the other a diet of 33% starch (HS). Eighty days later, leptin, insulin, ghrelin, and IGF-I were determined by human radioimmunoassay kits in plasma before and after feeding, and in sonicated milk centrifuged to remove fat from morning and evening milking. The HS diet was associated with higher plasma and milk insulin and IGF-I, and plasma ghrelin. Leptin, insulin, and ghrelin in milk were two-three times higher than in plasma; milk IGF-I was only 5-20% of plasma level. Plasma insulin correlated positively with plasma IGF-I; morning milk IGFI and insulin correlated positively with morning plasma levels. These findings demonstrate that human immuno-activities of bioactive peptides are present in goat milk, and also that levels of insulin and IGF-I in milk can be altered by changing the macronutrient content of the diet. Further research is required to determine whether these substances can be transferred from the milk to suckling animals and humans, and whether they have biological activity in such animals.

Temporal Changes in Insulin-Like Growth Factors I and II and in Insulin-Like Growth Factor Binding Proteins 1, 2, and 3 in Human Milk

Aim: To evaluate the postpartum time course of changes in insulin-like growth factors (IGFs) and their binding proteins (IGFBPs). Methods: Breast milk IGF-I and IGF-II and IGFBP-1, IGFBP-2, and IGFBP-3 levels were determined in 23 women with babies born at term, from day 4 until up to 9 months after birth. Results: The IGFBP-3 levels were highest from day 4 to day 6 and then decreased by days 10–12. In contrast, IGF-I and IGF-II and IGFBP-1 and IGFBP-2 showed little change over the first 2 weeks after birth. Subsequently, all the IGF components showed a moderate decline over approximately the first 1–3 months and then stable levels up to 9 months after birth. Conclusion: Although the possibility cannot be excluded that these changes in levels of IGFs and their binding proteins in human milk represent passive loss from the mammary gland, we speculate that higher early levels of the human milk IGF system contribute to maturation of the infant gut.

Transgenic overexpression of insulin‐like growth factor‐I (IGF‐I) in milk influences intestinal development and gene expression in piglets.

Piglets suckling transgenic sows (TG) that overexpress IGF-I in milk have greater (p<0.05) ileal mucosal weight, protein and DNA content, villus height, disaccharidase activities and type 1 IGF receptor abundance at d21 postpartum than piglets suckling non-TG (CON) sows. Herein, porcine-specific microarrays were used to examine gene expression in ileal crypt and villus cells isolated by laser capture microdissection. Following amplification, mRNA samples were labeled with Cy dyes and hybridized onto microarrays and data were analyzed using the limma package in R. In piglets suckling TG, 2 villus and 3 crypt genes were up-regulated and 1 crypt gene was down-regulated at a FDR-adjusted p<0.05. Five villus and 8 crypt genes tended (p<0.1) to be up-regulated and 4 crypt and 2 villus genes down-regulated. Differentially expressed genes displayed the following biological processes: cell signaling, proliferation, transcription, translation, apoptosis, immune function, metabolism, and structure. Six genes were selected for quantitative real-time PCR and the directionality and fold-change differences were in agreement with microarray results. Coordinate up-regulation of an anti-proliferative gene and down-regulation of a cell cycle regulator in the crypts of piglets suckling TG support reduced proliferation as an adaptation to elevated milk IGF-I. Funded by: AG-00-35206-9537 and IL C-FAR Sentinel Program.

Effect of a short-term fast on intestinal disaccharidase activity and villus morphology of piglets suckling insulin-like growth factor-I transgenic sows1

The objectives of this study were to use transgenic sows that overexpress IGF-I in milk to investigate the effect of a short-term fast on piglet intestinal morphology and disaccharidase activity and to determine how milk-borne IGF-I influences the response to fasting. After farrowing, litters were normalized to 10 piglets. On d 6, piglets (n = 30) suckling IGF-I transgenic (TG) sows and piglets (n = 30) suckling nontransgenic sows (control) were assigned randomly to three treatments: fed piglets (0 h), which remained with the sow until euthanized on d 7, or fasted piglets, which were removed from the sow at either 6 or 12 h before euthanasia on d 7. Serum IGF-I and IGFBP, intestinal weight and length, jejunal protein and DNA content, disaccharidase activity, and villus morphology were measured. Fasting for 12 h resulted in a negative weight change between d 6 and 7 (quadratic response to fasting; P < 0.001). Piglets suckling TG sows tended to have greater intestinal length (P = 0.068), but no effect of IGF-I overexpression was noted for intestinal weight. Fasting, however, resulted in linear (P < 0.001) and quadratic (P = 0.002) decreases in intestinal weight. Serum IGF-I did not differ between control and TG sows, but decreased linearly (P = 0.003) with fasting. Serum IGFBP-4 decreased (linear and quadratic; P < or = 0.02) with fasting, whereas IGFBP-1 increased quadratically (P < 0.001) with fasting. Jejunal villus height, width, and crypt depth were all increased with fasting (linear and quadratic; P < 0.04). Disaccharidase activity was not affected by fed state; however, piglets suckling TG sows had greater jejunal lactase-phlorhizin hydrolase (P < 0.01) and sucrase-isomaltase (P = 0.02) activities than control piglets. In summary, intestinal weight, villus morphology, serum IGF-I, serum IGFBP-1 and -4, and piglet BW change were altered (P < or = 0.02) in response to fasting. Thus, the duration of food deprivation before euthanization should be considered when designing experiments to assess intestinal development or the IGF axis, as the magnitude of differences between the fed and fasted state may exceed those expected as a result of experimental treatment.

Effects of an Enhanced Vitamin A Intake During the Dry Period on Retinoids, Lactoferrin, IGF System, Mammary Gland Epithelial Cell Apoptosis, and Subsequent Lactation in Dairy Cows

Studies in vitro show important interactions among vitamin A, lactoferrin, and insulin-like growth factor (IGF) binding proteins (IGFBP) and, thus, the IGF system. As a consequence, mammary gland epithelial cell proliferation and apoptosis during the bovine dry period and potential milk yield may be affected. We have studied effects of feeding vitamin A (550,000 IU/ d) that exceed daily requirements about 8-fold for up to 2 mo to dairy cows during the dry period on concentrations of retinol and its metabolites in plasma and milk, milk lactoferrin, plasma and milk IGF-I and IGFBP-3, lactoferrin and IGF-I mRNA levels in mammary gland tissue, mammary gland apoptosis, and 100-d milk yield in the ensuing lactation. In the group supplemented with vitamin A, the peripartal decrease of plasma retinol was delayed and attenuated, and colostral retinol plus retinylester concentration was enhanced, but colostral β-carotene concentration decreased. The retinoic acid isomer 9,13-dicis retinoic acid that coeluted with 13-cis retinoic acid, was the predominant circulating retinoic acid and was higher in GrA than the control group. Plasma IGFBP-3 concentrations were positively correlated with plasma retinol concentrations (r=0.51), but there were no group differences. Numbers of apoptotic epithelial cells in mammary epithelium were higher at drying off and parturition than in the middle of the dry period, coinciding with high concentrations of IGF-I and lactoferrin in mammary secretions. At parturition, numbers of apoptotic cells in mammary gland biopsies in cows supplemented with vitamin A were higher than in control cows. In conclusion, supplementation of dairy cows during the dry period with high amounts of vitamin A did not significantly modify concentrations of lactoferrin, IGFBP-3, and IGF-I in plasma and in mammary secretions, but slightly decreased energy-corrected 100-d milk yield and milk fat yield, possibly because of enhanced apoptic rates of mammary cells.

Biological activity of bovine milk: Contribution of IGF-I and IGF binding proteins

The mitogenic activity of milk from different stages of lactation was studied in primary cultures of undifferentiated bovine mammary epithelial cells. The mitogenic activity, measured as DNA synthesis, was 3–4-fold higher in colostrum than in basal medium. The mitogenic activity declined rapidly after calving, and in mid and late lactation the effect was inhibitory, not stimulatory. The content of IGF-I in milk varied with stage of lactation declining from more than 300 ng per ml in colostrum to 1–2 ng per ml in mid lactation and increasing to 20 ng per ml in late lactation. The difference in mitogenic activities between colostrum and mature milk was closely related to the difference in IGF-I content. The changes in IGF-I, however, cannot account for the inhibitory effect of mid and late lactation milk and the difference in the mitogenic effect of colostrum and BPMS (bovine prepartum milk-like secretion). The amounts of IGF binding proteins (24, 28, 34 and 41–44 kDa) in milk followed the same pattern as IGF-I with high content in early lactation and low content in mid lactation. The discrepancies between mitogenic activity and IGF-I content may in some, but not all, cases be related to the content of binding proteins.

Transgenic Over-Expression of Bovine α-Lactalbumin and Human Insulin-Like Growth Factor-I in Porcine Mammary Gland

The first week postpartum is the period of greatest loss for US swine producers, with most morbidity and mortality attributed to malnutrition and scours. Despite the benefit to be gained by improving lactation performance, little progress has been made in this area through conventional means. Transgenic technology provides an important tool for addressing the problem of low milk production and its detrimental impact on swine production. Transgenic swine over-expressing bovine α-lactalbumin (α-LA) and human IGF-I were developed. α-Lactalbumin was selected for its role in lactose synthesis and regulating milk volume. IGF-I regulates mammary development and piglet intestinal development. The IGF-I construct consisted of the IGF-I gene inserted directly behind the α-LA signal peptide coding sequence to allow secretion of IGF-I into milk. Outcomes assessed were milk composition and yield and piglet growth and intestinal development. First parity α-LA gilts (n=8) had higher milk lactose content in early lactation and 20 to 50% greater milk yield on d 3, 6, and 9 of lactation than nontransgenic gilts (n=10). Weight gain of piglets suckling α-LA gilts was greater from d 7 and 21 postpartum than control piglets. Colostral IGF-I was ∼10-fold higher in first-parity IGF-I transgenic gilts (n=5) than non-transgenic gilts (n=4), and elevated milk IGF-I is maintained throughout lactation at ∼0.6mg/L. Milk yield tended to be greater in IGF-I transgenic swine in early lactation. Thus, transgenic over-expression of milk proteins and growth factors may provide a means to improve swine lactation performance.

Dietary Fat during Pregnancy and Lactation Increases Milk Fat and Insulin-Like Growth Factor I Concentrations and Improves Neonatal Growth Rates in Swine

Primiparous (n = 24) and multiparous (n = 24) sows were used to examine the effects of supplemental dietary fat and induction of parturition (d 112) on colostrum and milk composition and suckling piglet growth. Sows were assigned to one of eight treatments on d 90 of gestation that included variables such as parity (1 vs. ≥3), dietary fat (0 vs. 10%), and farrowing (natural vs. induction via lutalyse on d 112). Piglets suckling fat-supplemented dams grew up to 25% faster than control pigs nursing unsupplemented sows (250 vs. 200 g/d; P < 0.01). Improved growth was correlated with elevated milk fat and insulin-like growth factor (IGF) concentrations associated with fat supplementation. Dietary fat elevated milk fat concentration at 48 and 72 h postfarrowing by 21.6 and 22.6%, respectively (P < 0.05). Compared with nonfat-fed controls, multiparous sows fed 10% fat showed a more consistent rise in milk fat concentration, with 26% and 41% elevations for induced or naturally farrowing sows, respectively, vs. a 19% reduction or a 1% elevation in induced or naturally farrowing gilts (P < 0.01). The concentration of milk IGF-I tended to be lower in gilts than in multiparous sows (P < 0.2, 95.7 vs. 117.4 μg/L), and levels were particularly low in milk from induced gilts receiving no additional dietary fat (44.7 μg/L). However, fat supplementation elevated IGF-I to levels (110.6 μg/L) exceeding those measured in unsupplemented, naturally farrowing control sows and gilts (95.8 μg/L). In conclusion, supplemental dietary fat elevates milk fat in multiparous sows more than primiparous gilts regardless of farrowing treatment (induced vs. natural farrowing) and improves piglet growth throughout lactation irrespective of parity or farrowing treatment. The potential of supplemental dietary fat to reverse the reductions in milk IGF-I observed in first-parity females and in dams induced to farrow merits further investigation.

Supplemental protein plus ruminally protected methionine and lysine for primiparous beef cattle consuming annual rye hay.

Primiparous beef cows (n = 35 Bos taurus, average initial BW of 498 kg) were allotted to treatments in a split-plot designed experiment to determine the effects of supplemental ruminally protected amino acids on cow and calf productivity and metabolic changes in the cows. Cows were fed chopped annual rye hay at 1.5% of BW. The following treatments were used: 1) .8 kg soybean hulls, 1.4 kg ground corn, .6 kg soybean meal (CON); 2) 1.4 kg ground corn, 1.4 kg soybean meal (PRO); 3) PRO plus ruminally protected methionine and lysine (supplied 5 and 10 g, respectively; PRO1); and 4) PRO with twice the level of ruminally protected amino acids in PRO1 (PRO2). Cow weight gain was not different (P > .26) among treatments and averaged 1.2 kg/d for the 45 + 6 d before parturition. After parturition, cow weight gain did not differ (P > .47) between CON and PRO treatments, but it decreased quadratically (P < .01) with increasing level of ruminally protected amino acids. Total milk yield, protein, and fat (4 h) were greater (P < .05) for cows consuming PRO supplements than for CON, whereas CON cattle tended (P = .11) to lose less body condition. Total milk protein showed a quadratic increase (P < .05) in response to level of ruminally protected amino acids that was the inverse of the quadratic response noted for cow weight gain. Serum urea N concentration was greater (P = .07) for cattle consuming additional protein. Metabolic hormones were not affected (P > .18) by dietary treatment, but they responded (P < .05) to changes in physiological state. Supplements with additional protein supported greater (P = .0001) milk urea N concentration and output. Milk urea N concentration increased (P < .05) and milk IGF-I decreased (P < .05) as the lactation period progressed. The measurement of CON and PRO diets revealed that supplements with additional soybean meal had greater (P < .05) DM and N degradation; the extent of forage DM and NDF degradation was similar (P > .05) among treatments. Production shifted away from body weight gain to increased milk protein production when daily supplementation of ruminally protected methionine and lysine increased from 5 and 10 to 10 and 20 g, respectively. This shift in production was not reflective of changes in the metabolic regulators measured.

Insulin-like growth factor I in suckling rat gastric contents

The small intestinal mucosa of the neonatal rat expresses primarily lactase activity until just prior to weaning when lactase falls to low levels and a full complement of adult digestive enzymes appears. Insulin-like growth factor 1 (IGF-I) is a normal component of maternal milk of humans and experimental animals. Experiments were performed to examine the concentrations of IGF-I in dam milk and the gastric content of suckling pups. Lactase activity in 1-day-old neonates was 0.66 micromol glucose formed/mg protein/hr (unit) and fell progressively until day 25, whereas sucrase activity at day 1 postpartum was 0.07 units and rose progressively to 0.21 units at day 25. The IGF-I content of dam milk was measured at 1, 5, 10, 15, 18, and 20 days postpartum by radioreceptor assay (RRA). Milk contained 1.02 pmol IGF-I/ml milk at one day postpartum, peaked at day 18 with 5.08 pmol IGF-I/ml, and fell to 2.31 pmol/ml at day 20. By day 25, dams were dry. The IGF-I content of the neonate gastric lumen was also measured by RRA. At day 1 the gastric lumen contained 2.63 pmol IGF-I/ml of luminal contents, fell to 1.06 pmol IGF-I/ml at day 5, and then rose again to peak at 3.37 pmol/ml at day 15 just prior to weaning. Two days after weaning, the level of luminal IGF-I had fallen to 1.15 pmol/ml. These data demonstrate the concentration of IGF-I in maternal milk is reflected in the concentration of the peptide in gastric contents of suckling pups and that the concentration in the gastric lumen may be high enough to affect epithelial cell proliferation and differentiation.

Investigation into the potential physiological sources of rat milk IGF-I and IGF-binding proteins

We have previously reported the presence of IGF-I and IGF-binding proteins (IGFBP-2, -3 and -4) in rat milk. Herein, the potential sources of rat milk IGF-I and IGFBPs were investigated. Lactating dams (day 14 postpartum) were separated from their pups and injected intraperitoneally with 0.45 microCi 125I-IGF-I or 125I-IGFBP-3. After 3 h, serum and milk of rats receiving 125I-IGF-I contained 7642 +/- 3121 and 14,455 +/- 7837 c.p.m./ml respectively. Serum and milk of rats given 125I-IGFBP-3 contained 7232 +/- 1366 and 10,371 +/- 4091 c.p.m./ml respectively. Sephacryl S-200 gel filtration chromatography demonstrated that the 125I-IGF-I in both serum and milk was primarily in the 150 kDa IGF-binding complex, whereas the distribution of 125I-IGFBP-3 differed between serum and milk. In serum, most of the 125I-IGFBP-3 was in the 150 kDa fraction, while most 125I-IGFBP-3 in milk was in the 40 kDa fraction. Northern analysis of liver showed IGFBP-1 and -3 mRNA expression, with variable expression of IGFBP-2 and -4 mRNA. In contrast, mammary tissue expressed only IGFBP-2 and -4 mRNA, suggesting that these IGFBPs in milk may arise from de novo synthesis within the mammary gland. The lack of detectable IGFBP-3 mRNA in mammary tissue and the translocation of 125I-IGFBP-3 from the serum suggest that milk IGFBP-3 arises from the maternal circulation.

Insulin-Like Growth Factors and Insulin-Like Growth Factor Binding Proteins in Porcine Serum and Milk throughout Lactation

IGF-I, IGF-II, and IGF binding proteins (IGFBP) were characterized in porcine serum, colostrum, and milk on d 1-28 postpartum. IGF-I and -II were measured by heterologous RIA. Serum IGFBP were characterized by Western ligand blotting and milk IGF binding activity by [125I]-IGF binding assay. IGF-II accounted for 70-85% of serum IGF and rose 2-fold between d 1 and d 28. Serum IGF-I was unaffected by duration of lactation. Milk IGF-II concentrations were higher than IGF-I concentrations on d 1-7 postpartum. After d 10, milk IGF-I and IGF-II contents were not significantly different. Serum contained IGFBP with M(r) of 43, 39, 34, 28, and 24 kD. Over the course of lactation, the 43- and 39-kD bands increased, the 24-kD band decreased, and the 34- and 28-kD bands were unchanged. Milk IGF binding activity increased between d 1 (28%) and d 3 (44%), then declined until d 28 (7%). Serum and milk were separated by isoelectric focusing into 20 fractions, across a gradient from pH 3 to 10, that were screened for IGFBP by Western ligand blotting. Milk contained six IGFBP of similar M(r) as serum IGFBP; however, the relative amounts of the IGFBP and their apparent isoelectric points differed. In conclusion, porcine milk contains both IGF-I and -II, with IGF-II predominating. Several IGFBP with similar M(r) as those found in serum are present in milk. IGF peptide concentrations were highest in prepartum secretions and colostrum, whereas IGF binding activity peaked on d 4 of lactation.

Nutritional modulation of insulin-like growth factor-I expression in early postnatal piglets.

The roles of intrauterine growth retardation, energy intake, and food composition in determining circulating and hepatic concentrations of IGF-I in early postnatal life have been determined. Intrauterine growth-retarded, small-for-gestational-age piglets were kept at thermal neutrality and fed sow's milk replacement formula to repletion at 6-h intervals between 2 and 14 d of age. When their appropriate-for-gestational-age littermates were pair-fed this intake, there were no significant differences in plasma or hepatic concentrations of IGF-I. Thus, under conditions of controlled food intake, prenatal undernutrition does not affect the postnatal expression of IGF-I. However, when appropriate-for-gestational-age piglets were fed to repletion at 6-h intervals over the 12 d, they had a significantly greater hepatic IGF-I concentration (p < 0.002) and food intake (p < 0.001) than the small-for-gestational-age piglets, indicating a critical role for food intake regulation in catch-up growth. Striking differences in growth rate and IGF-I expression were also found between formula-fed, appropriate-for-gestational-age piglets compared with animals left with the sow. The latter grew much more rapidly (p < 0.0001) and had considerably higher levels of plasma IGF-I (p < 0.0001) despite similar hepatic IGF-I concentrations. Differences in plasma IGF-I may have been caused by the high level of IGF-I in maternal milk, by differences in hepatic synthesis and release, or by altered profiles of IGF binding proteins and hence in altered IGF-I clearance from plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Destripeptide insulin-like growth factor-I in milk from bovine somatotropin-treated cows.

Total somatomedins from milk of bovine somatotropin-treated cows were isolated and characterized to determine the relative amount of the three amino acid N-terminally truncated form of IGF-I (destripeptide IGF-I). The somatomedin fraction was isolated using organic solvent and solid-phase extractions followed by preparative reverse phase HPLC and affinity chromatography. The overall yield of IGF-I was 28%, and destripeptide IGF-I was recovered with similar efficiency. The isolated somatomedins were resolved by capillary zonal electrophoresis and identified using recombinant somatomedin standards. The concentration of destripeptide IGF-I relative to full length IGF-I was determined by amino terminal sequencing and by bioassay. Results from these experiments indicated that the level of destripeptide IGF-I in milk from somatotropin-treated cows was less than 3% of the IGF-I concentration. Destripeptide IGF-I is therefore a minor component of the somatomedins present in milk from treated cows and does not contribute significantly to the proliferative activity of this milk.

Insulin-Like Growth Factors I and II and Their Binding Proteins in Human Milk

Insulin-like growth factors (IGF-I and -II) are peptide growth factors that contribute to the growth-promoting properties of human milk. IGFs in extra cellular fluids are associated with high-affinity binding proteins (IGFBPs). In this study, IGF-I and -II, and IGFBPs in human milk were characterized, and the stability of the IGFs and IGFBPs to heat treatment was investigated. IGF-I and -II were quantified by radioimmunoassays of acid-chromatographed samples, and IGFBPs were characterized using Western ligand blotting. The concentration (mean +/- SD) of IGF-I in human milk was 1.5 +/- 0.5 micrograms/L, compared to 2.7 +/- 0.7 micrograms/L for IGF-II. Heat treatment did not significantly affect either IGF-I or -II content. Human milk contains a single, nonglycosylated, IGFBP, with an apparent Mr of 31 k, which was immunoprecititable by an antibody to IGFBP-2. Stability of the IGFBP to heat treatment was assessed and was not significantly affected by heat treatment. Therefore, both IGF-I and -II, and the IGFBP in human milk appear to be stable under heat treatment conditions routinely used for processing banked human milk.

Radioimmunoassay for insulin-like growth factor-I in bovine milk

This experiment was designed (1) to study the effectiveness of acid-ethanol extraction and gly-gly HCl incubation to dissociate the IGF-binding protein complex before IGF-I RIA measurements in bovine milk, and (2) to determine the influence of freezing/thawing and defatting of milk samples on IGF-I concentration of milk. Acidification of milk with acid-ethanol (acid-ETOH) liberated more IGF-I from its binding proteins than with gly-gly HCl. Milk samples obtained from three control cows and three rbST-treated cows (41–44 wk postpartum) were treated with acid-ethanol and assayed by a radioimmunoassay. IGF-I concentrations in the milk were 3.30 ± 1.40 for the control cows and 2.77 ± 1.36 ng mL−1 for the rbST-treated cows. Fat removal before or after freezing did not affect milk IGF-I measurements. The milk concentration of IGF-I after freezing/thawing twice was not different from that after freezing/thawing once. The radioimmunoassay resulting from this study should provide a tool for monitoring IGF-I concentrations in milk throughout the entire lactation. Key words: Milk, IGF-I, radioimmunoassay, cows

Insulin-Like Growth Factors I and II and Their Binding Proteins in Rat Milk

IGF-I and -II are peptide growth factors that may be important contributors to the growth-promoting properties associated with milk. IGF in extracellular fluids, including serum and milk, are carried by specific high-affinity binding proteins (IGFBP). In this study, the levels of IGF-I and -II in rat serum and milk were quantified by specific RIA, and the IGFBP were characterized using Western ligand blotting and autoradiography throughout lactation. The levels of IGF-I in both milk and maternal serum decreased during lactation. Serum IGF-I decreased from 743 +/- 187 micrograms/L on d 1 to 391 +/- 106 (mean +/- SD) on d 21 of lactation, and milk IGF-I levels fell from 30 +/- 10 to 13 +/- 8 micrograms/L. Levels of IGF-II in serum and milk were much lower than IGF-I, and were unaffected by lactation. In maternal serum, several IGFBP were identified: IGFBP-3, which migrates as four glycosylated bands with apparent Mr from 38 to 42 kD and one to two nonglycosylated bands with apparent Mr of 28 to 29 kD, and an IGFBP with an apparent Mr of 24 kD. In milk, IGFBP-3, the 24-kD binding protein, and a third IGFBP with an apparent Mr of 29 kD were identified. Treatment of milk and serum with Endoglycosidase F reduced the four glycosylated IGFBP-3 bands (38-42 kD) to two bands with apparent Mr of 35 and 32 kD. In rat milk, but not adult rat serum, the IGFBP with an apparent Mr of 29 kD was immunoprecipitable by an antibody that recognizes IGFBP-2.(ABSTRACT TRUNCATED AT 250 WORDS)