Milking frequency alters the milk yield and mammary blood flow response to intra-mammary infusion of insulin-like growth factor-I in the goat.

The milk yield and mammary blood flow responses to close-arterial, intra-mammary infusion of IGF-I were investigated in five Saanen goats milked frequently or normally the day before. Animals were infused for 6 h with recombinant human IGF-I (1.3 nmol/min) and milked hourly following i.v. injection of oxytocin beginning 2 h before infusion and then every 2 h. On one occasion animals were milked five times (after i.v. injection of oxytocin) on the day before infusion and on the other they were milked twice, without oxytocin. The ratio of milk yield from the infused to that from non-infused gland increased by 17 +/- 4% (mean +/- S.E.M.) in goats milked twice the day before infusion and by 6 +/- 2% when the infusion was preceded by frequent milking. Maximal responses were obtained 4 h after the start of the infusion and differed significantly (P < 0.05), according to pretreatment milking. Blood flow through the infused gland rose in parallel to the milk yield response. At 5 h, when maximal levels were achieved, blood flow was 182 +/- 23% of the pre-infusion flow rate following twice-daily milking and 139 +/- 3% of the pre-infusion flow rate following more frequent milk removal. Thus, more frequent milk removal on the day before close-arterial infusion of IGF-I attenuated both the milk yield and mammary blood-flow response to the infusion of IGF-I.     

Mechanism of secretion of plasma insulin-like growth factor-I into milk of lactating goats.

125I-Labelled insulin-like growth factor-I (IGF-I) was infused as the free form directly into the pudic artery supplying one gland of lactating goats (n = 6). The infusion was for 60 min and 0.4 +/- 0.09% (S.E.M.) of the infusate was secreted into milk from the infused gland during its first passage through that gland. A large proportion of the 125I-labelled IGF-I escaped into the systematic circulation and was secreted into milk of both glands. A total of 5.2 +/- 0.4% of infused radioactivity was recovered in milk from both glands from 0 to 720 min. Radioactivity consisted of trichloroacetic acid (TCA)-precipitable and -soluble counts which were shown by gel filtration to be authentic IGF-I and degraded products of the peptide. The amount and time course of TCA-soluble radioactivity in milk from both glands was similar, suggesting degradation of 125I-labelled IGF-I at extramammary sites. Maximum specific activity for 125I-labelled IGF-I in milk from the infused gland was reached 80-120 min after the start of infusion and was 2.5-fold greater than milk from the non-infused gland. The time course of appearance of 125I-labelled IGF-I in milk suggests that transfer was via the transcellular pathway and this was further supported by comparing the pattern of transfer of [14C]sucrose and [14C]amino acids. When excess unlabelled IGF-I was included in the infusate, specific activity in milk from the infused gland was reduced to that of the non-infused gland, indicating a competitive and saturable mechanism of secretion for 125I-labelled IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)     

Progesterone stimulates mammary gland ductal morphogenesis by synergizing with and enhancing insulin-like growth factor-I action

Progestins have been implicated in breast cancer development, yet a role for progesterone (Pg) in ductal morphogenesis (DM) has not been established. To determine whether Pg could cause DM, we compared relative effects of Pg, estradiol (E2) and IGF-I on anatomical and molecular biological parameters of IGF-I-related DM in oophorectomized female IGF-I(-/-) mice. Pg had little independent effect on mammary development, but together with IGF-I, in the absence of E2, Pg stimulated an extensive network of branching ducts, occupying 92% of the gland vs. 28.3% with IGF-I alone, resembling pubertal development (P < 0.002). Its major effect was on enhancing duct length and branching (P < 0.002). Additionally, Pg enhanced phosphorylation of IRS-1, increased cell division, and increased the antiapoptotic effect of IGF-I. Pg action was inhibited by RU486 (P < 0.01). E2 also stimulated DM by enhancing IGF-I action but had a greater effect on terminal end bud formation and side branching (P < 0.002). In contrast to previous findings, long-term exposure to E2 alone, without IGF-I, caused formation of ducts and side branches, a novel finding. Both IGF-I and E2 were found necessary for Pg-induced alveolar development. In conclusion, Pg, through Pg receptor can enhance IGF-I action in DM, and E2 acts through a similar mechanism; E2 alone caused formation of ducts and side branches; there were differences in the actions of Pg and E2, the former largely affecting duct formation and extension, and the latter side branching; and both IGF-I and E2 were necessary for Pg to form mature alveoli.     

Non-lactogenic effects of growth hormone on growth and insulin-like growth factor-I messenger ribonucleic acid of rat mammary gland

In contrast to established dogma that PRL is central in mammary development, and GH mimics PRL in affecting growth because of structural similarities, we found that both hGH, which is lactogenic, and rGH, which is non-lactogenic, were significantly more potent than hPRL and rPRL in stimulating mammary growth in rats. Additionally, hGH was more potent than hPRL in increasing mammary IGF-I mRNA content. These data indicate that GH has separate effects on parameters of mammary gland growth, suggesting an independent role for GH in mammary growth.     

Reversal of diet-induced catabolism by infusion of recombinant insulin-like growth factor-I in humans.

Treatment of catabolic conditions with insulin-like growth factor I (IGF-I), the peptide that mediates some of the anabolic growth-promoting effects of GH, offers potential advantages of avoiding the hyperglycemia caused by treatment with GH. A state of moderate catabolism was produced in six normal, young adult volunteers by restricting their daily dietary intake to 20 kilocalories/kg/day. During the last 6 days of two 2-week diet-study periods, they received either IGF-I (12 micrograms/kg/h by i.v. infusion over 16 h) or GH (0.05 mg/kg/day by sc injection). IGF-I improved nitrogen balance from -236 +/- 45 mmol/day (+/- SE) during diet alone, to -65 +/- 40 mmol/day (P less than 0.001) during the last 4 days of IGF-I infusion. A similar effect was produced by GH. IGF-I infusion decreased fasting blood glucose from 4.94 +/- 0.91 mmol/L to 3.13 +/- 0.44 mmol/L (P less than 0.001), while GH raised blood glucose values (4.75 +/- 1.01 mmol/L on diet alone, to 5.48 +/- 1.00 during the period of GH treatment; P less than 0.05). Despite these differences in blood glucose, IGF-I infusions decreased serum insulin (74.9 +/- 26.8 pmol/L on diet alone, to 16.7 +/- 1.5 pmol/L during IGF-I) and serum connecting-peptide concentrations (2.14 +/- 0.89 mmol/L on diet alone, to 0.97 +/- 0.14 during IGF-I), while GH raised insulin (109.4 +/- 31.3 pmol/L, P less than 0.05 during GH) and connecting-peptide (3.12 +/- 0.59 mmol/L, P less than 0.02). At the dose of each hormone used, the attenuation of nitrogen wasting produced by infusions of IGF-I was similar in magnitude and timing to that produced by injections of GH. The reduction in serum glucose concentrations produced by IGF-I compared with the increase in glucose noted during GH treatment, could benefit hyperglycemic catabolic patients.     

Insulin secretion and insulin-like growth factor-I levels in active and controlled acromegaly

OBJECTIVE: We examined the contributions of growth hormone (GH) and insulin-like growth factor-I (IGF-I) to insulin sensitivity and beta-cell function in acromegaly. DESIGN: A cross-sectional study was used with continuous infusion of glucose with model assessment to determine insulin sensitivity and beta-cell function. PATIENTS: Ten patients with active acromegaly, seven with controlled disease and 22 normal individuals were studied. MEASUREMENTS: Glucose and insulin levels were measured fasting and at the end of the one-hour glucose infusion to calculate insulin sensitivity and beta-cell function. Random GH and IGF-I were recorded. Most patients had values of GH taken after a 100-g oral glucose tolerance test and K values from intravenous glucose tolerance tests. RESULTS Patients with active acromegaly had significantly decreased insulin sensitivity compared to the normal population (P less than 0.001), while those with controlled disease did not. There was a significant negative correlation between IGF-I and insulin sensitivity in those with active disease (P less than 0.05). Beta-cell function in both active and controlled patient groups was elevated compared to the normal population (P less than 0.05, P less than 0.01 respectively) and this was significantly related to IGF-I in the active group (P less than 0.05). GH levels did not correlate with fasting insulin, glucose, insulin sensitivity or beta-cell function in either group. CONCLUSIONS: Patients with active acromegaly have decreased insulin sensitivity and increased beta-cell function that are significantly related to IGF-I but not GH levels. When the disease is controlled, beta-cell function remains elevated but insulin sensitivity improves.     

Epithelial-specific and stage-specific functions of insulin-like growth factor-I during postnatal mammary development

Postnatal development of the mammary gland requires interactions between the epithelial and stromal compartments, which regulate actions of hormones and growth factors. IGF-I is expressed in both epithelial and stromal compartments during postnatal development of the mammary gland. However, little is known about how local expression of IGF-I in epithelium or stroma regulates mammary growth and differentiation during puberty and pregnancy-induced alveolar development. The goal of this study was to investigate the mechanisms of IGF-I actions in the postnatal mammary gland and test the hypothesis that IGF-I expressed in stromal and epithelial compartments has distinct functions. We established mouse lines with inactivation of the igf1 gene in mammary epithelium by crossing igf1/loxP mice with mouse lines expressing Cre recombinase under the control of either the mouse mammary tumor virus long-terminal repeat or the whey acidic protein gene promoter. Epithelial-specific loss of IGF-I during pubertal growth resulted in deficits in ductal branching. In contrast, heterozygous reduction of IGF-I throughout the gland decreased expression of cyclins A2 and B1 during pubertal growth and resulted in alterations in proliferation of the alveolar epithelium and milk protein levels during pregnancy-induced differentiation. Reduction in epithelial IGF-I at either of these stages had no effect on these indices. Taken together, our results support distinct roles for IGF-I expressed in epithelial and stromal compartments in mediating growth of the postnatal mammary gland.     

Testosterone blunts feedback inhibition of growth hormone secretion by experimentally elevated insulin-like growth factor-I concentrations

The present study tests the hypothesis that a high dose of testosterone (Te) drives GH and IGF-I production, in part, by blunting autonegative feedback by the end-product peptide. To this end, we infused saline or recombinant human IGF-I (10 microg/kg.h iv for 6 h) in seven healthy men ages 51-72 yr after administration of placebo (Pl) and Te in randomized order. GH release was quantitated fasting before and after injection of GHRH (1 microg/kg). Statistical analyses disclosed that Te vs. Pl: 1) increased the mean concentration of GH from 0.15 +/- 0.045 to 0.48 +/- 0.11 microg/liter (P = 0.007) and IGF-I from 108 +/- 5.0 to 124 +/- 4.1 (P = 0.047) without altering GHRH-induced GH release; 2) elevated the GH nadir from 0.13 +/- 0.03 to 0.23 +/- 0.06 microg/liter (P < 0.05) in the control session and from 0.06 +/- 0.02 to 0.14 +/- 0.04 microg/liter (P = 0.038) during IGF-I infusion; 3) augmented GHRH-stimulated GH release from 3.0 +/- 0.56 (Pl) to 3.7 +/- 0.52 microg/liter (Te) (P < 0.05) during IGF-I infusion; and 4) did not influence estimated IGF-I kinetics. In summary, supplementation of a high dose of Te in middle-aged and older men attenuates IGF-I feedback-dependent inhibition of nadir and peak GH secretion. Both effects of Te differ from those reported recently for estradiol in postmenopausal women. Accordingly, we postulate that Te and estrogen modulate IGF-I negative feedback differentially.     

The galactopoietic effect of bovine growth hormone in goats is associated with increased concentrations of insulin-like growth factor-I in milk and mammary tissue

Lactating goats exhibiting widely divergent responses to short-term (4 days) treatment with bovine GH (bGH) were retrospectively divided into two groups based on the magnitude of this response. There was no difference between groups in terms of the pretreatment milk yield, but by day 4 of treatment milk secretion had increased by 4.99 +/- 2.5 (S.E.M.) ml/h (P greater than 0.05 compared with pretreatment) for group 1 and 22.9 +/- 2.4 ml/h (P less than 0.001) for group 2. Plasma GH increased in both groups, but concentrations were significantly higher both before and during treatment in group 1 compared with group 2. Plasma concentrations of insulin-like growth factor-I (IGF-I) increased significantly during bGH treatment for both groups and there was no significant difference between the two until day 4 of treatment when levels of IGF-I in group 1 began to decline, whereas those from group 2 were maintained. Concentrations of IGF-I in milk from goats in group 1 were not significantly altered by GH administration, whereas those in goats in group 2 were increased by 40% (P less than 0.01 compared with pretreatment). Levels of IGF-I in mammary secretory tissue from four animals from group 1 were not altered by bGH (2.8 +/- 0.2 and 2.77 +/- 0.08 nmol/kg tissue before and after treatment respectively), but were significantly (P less than 0.05) increased in four animals from group 2 (2.80 +/- 0.2 and 9.9 +/- 1.1 nmol/kg tissue).(ABSTRACT TRUNCATED AT 250 WORDS)     

Spontaneous growth hormone and somatomedin-C/insulin-like growth factor-I secretion in obese subjects during puberty

It has been reported that adult obese subjects present a reduced growth hormone secretion. As no data are available in the pubertal period, which is characterized in lean subjects by an increased spontaneous growth hormone secretion, the growth hormone circadian concentration was studied in a group of 18 obese male subjects in different pubertal stages, and compared to 26 age-matched control subjects. The data observed evidenced no statistically relevant differences regarding LH and FSH circadian secretion and morning testosterone concentration. On the contrary a statistically significant (p less than 0.02) difference in growth hormone 24 h integrated concentration was evident, particularly in prepubertal subjects; the sleep-related peak was evident in 28% of obese subjects and in 85% of controls. Sm-C/IGF-I concentration was similar to the concentration observed in controls in the prepubertal stage, but did not show the expected increase in the late puberty. Auxological data, performed on a sample of 80 subjects, showed both advanced height and bone age at beginning of puberty, and a trend toward a reduction of percentile for height in parallel with the pubertal maturation, suggesting that pubertal growth spurt in obese subjects is at least less pronounced than in lean subjects. It is concluded that GH and Sm-C/IGF-I secretion is impaired during puberty in obese subjects, leading to a reduced growth rate, while in the prepubertal period factors other than GH may replace or even potentiate its action.     

Human growth hormone and insulin-like growth factor-I inhibit erythropoietin secretion from the kidneys of adult rats

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) play important roles in erythropoiesis and erythro-poietin (EPO) secretion. We examined the effects of GH and IGF-I on EPO production in adult rat kidney and liver in vivo and in vitro. Male Wistar rats aged 8-10 weeks were used. Recombinant human GH (hGH) was continuously infused (20 mug/kg per h) subcutaneously for 48 h using a micro-osmotic infusion pump. Octreotide (10 mug/kg) was subcutaneously injected every 12 h beginning 12 h before the hGH treatment. GH increased plasma EPO levels earlier than it increased plasma IGF-I levels. At 24 h, the IGF-I content in the liver and kidney was increased from 172.8+/-14.6 to 232.6+/-17.8 ng/g tissue (means+/-S.E.) and from 53.8+/-3.1 to 112.8+/-7.2 ng/g tissue, respectively. The EPO content in the liver was increased from 7.5+/-1.2 to 15.1+/-1.4 mIU/g tissue at 48 h, whereas the EPO content in the kidney was decreased at 12, 24, and 48 h after the start of hGH treatment. When the kidneys were organ-cultured, hGH considerably decreased EPO levels in the culture medium in a dose-related manner. The addition of anti-hGH IgG blunted the GH-induced inhibition of EPO secretion from the kidneys. IGF-I also decreased EPO levels in the medium in a dose-related manner. The addition of anti-IGF-I IgG blunted the IGF-I-induced inhibition of EPO secretion from the kidneys, whereas the GH-induced inhibition of EPO secretion was not affected. These findings suggest that both hGH and IGF-I have direct inhibitory effects on EPO secretion from adult rat kidneys.     

Effects of alpha-interferon on insulin-like growth factor-I, insulin-like growth factor-II and insulin-like growth factor binding protein-3 secretion by a human lung cancer cell line in vitro

The aim of our study was to evaluate the effect of alpha-interferon (alpha-IFN) on cell growth and on the different IGF system components in a human non-small cell lung cancer line (Calu-6) in vitro. Our results confirm the release of IGF-I and IGF-II by these cells. The amount of IGF-II in conditioned media (10.25 +/- 3.95 nM/10(6) cells, mean +/- SE) was more than 10-fold higher than that of IGF-I. alpha-IFN treatment reduced IGF-II levels in the media, with a maximal effect between 1 and 10 U/ml (delta% of control: -31 and -55%, respectively, p < 0.05). IGF-I was significantly reduced at 0.5 U/ml (p < 0.01). No difference, however, was observed in IGF mRNA expression between untreated and alpha-IFN treated cells. An increase in IGF-I and IGF-II intracellular levels in alpha-IFN treated cultures was observed, suggesting that alpha-IFN can regulate the transfer of these peptides into the cells. Furthermore, IGF type-I and particularly type-lI receptor expression was increased after alpha-IFN treatment. IGFBP-3 was detected only in trace amounts in the conditioned media; however, it showed an increase after alpha-IFN treatment (+110% at 1 U/ml). IGFBP-3 mRNA expression showed a slight increase after treatment with 1 and 10 U/ml. alpha-IFN (1-10 U/ml) reduced the stimulatory effect of IGF-I on cell replication (p < 0.01), inhibited (p < 0.01) cell replication in untreated and in fetal calf serum (FCS)-stimulated cells, and increased apoptosis in Calu-6 cells. Our data suggest that alpha-IFN may exert its effects at the cellular level in part through modification of the local IGF system.     

Stimulation of choleresis by insulin-like growth factor-I in rats

Insulin-like growth factor-I (IGF-I) is an endogenous growth factor which is mainly produced in the liver. The functions of IGF-I can be summarized as growth-promoting and insulin-like metabolic actions. In the present study, the effect of IGF-I on bile flow and bile acid secretion was investigated in rats. In normal rats bile flow was significantly increased by single exogenous administration of IGF-I, and by 1 week treatment of IGF-I, both bile flow and bile acid secretion were significantly increased. Moreover, to further understand the relationship between IGF-I and bile acid secretion, hypophysectomized rats were next used. We found that the decreases in bile flow and bile acid secretion observed in rats after hypophysectomy, as well as the decrease in the endogenous level of IGF-I in the blood, were partially reversed by 1 week exogenous IGF-I treatment. Overall, this study showed that IGF-I stimulates choleresis associated with an elevation of bile acid secretion in both normal and hypophysectomized rats when exogenously administered, suggesting the importance of IGF-I in the stimulation of choleresis in vivo.     

Liver-derived insulin-like growth factor-I is involved in the regulation of blood pressure in mice

IGF-I has been suggested to be of importance for cardiovascular structure and function, but the relative role of locally produced and liver-derived endocrine IGF-I remains unclear. Using the Cre-LoxP recombination system, we have previously created transgenic mice with a liver-specific, inducible IGF-I knockout (LI-IGF-I-/-). To examine the role of liver-derived IGF-I in cardiovascular physiology, liver-derived IGF-I was inactivated at 4 wk of age, resulting in a 79% reduction of serum IGF-I levels. At 4 months of age, systolic blood pressure (BP) was increased in LI-IGF-I-/- mice. Echocardiography showed increased posterior wall thickness in combination with decreased stroke volume and cardiac output, whereas other systolic variables were unchanged, suggesting that these cardiac effects were secondary to increased peripheral resistance. Acute nitric oxide-synthase inhibition increased systolic BP more in LI-IGF-I-/- mice than in control mice. LI-IGF-I-/- mice showed impaired acetylcholine-induced vasorelaxation in mesenteric resistance vessels and increased levels of endothelin-1 mRNA in aorta. Thus, the increased peripheral resistance in LI-IGF-I-/- mice might be attributable to endothelial dysfunction associated with increased expression of endothelin-1 and impaired vasorelaxation of resistance vessels. In conclusion, our findings suggest that liver-derived IGF-I is involved in the regulation of BP in mice.     

Human growth hormone (hGH) secretion in milk of goats after direct transfer of the hGH gene into the mammary gland by using replication-defective retrovirus vectors.

Mammary-specific promoters have been used in transgenic animals to limit transgene expression to the mammary gland. Gene therapy techniques to target just one organ for introduction of a foreign gene have also been demonstrated. We have directly infused replication-defective retroviruses encoding hGH into the mammary gland of goats via the teat canal during a period of hormone-induced mammogenesis. This resulted in the secretion of hGH into the milk when lactation commenced on day 14 of the regime. Levels of hGH in the milk were highest on the first day of lactation, averaging approximately 60 ng/ml, and declined to a plateau of 12 ng/ml from day 9 to day 15 of lactation. Thus we report targeting of replication-defective retroviruses to the mammary secretory epithelial cells to produce foreign proteins in the milk of ruminants.     

Intrafetal insulin-like growth factor-I infusion stimulates adrenal growth but not steroidogenesis in the sheep fetus during late gestation

We investigated the effects of an intrafetal infusion of IGF-I on adrenal growth and expression of the adrenal steroidogenic and catecholamine-synthetic enzyme mRNAs in the sheep fetus during late gestation. Fetal sheep were infused for 10 d with either IGF-I (26 microg/kg.h; n = 14) or saline (n = 10) between 120 and 130 d gestation, and adrenal glands were collected for morphological analysis and determination of the mRNA expression of steroidogenic and catecholamine-synthetic enzymes. Fetal body weight was not altered by IGF-I infusion; however, adrenal weight was significantly increased by 145% after IGF-I infusion. The density of cell nuclei within the fetal adrenal cortex (the zona glomerulosa and zona fasciculata), and within the adrenaline synthesizing zone of the adrenal medulla, was significantly less in the IGF-I-infused fetuses compared with the saline-infused group. Thus, based on cell-density measurements, there was a significant increase in cell size in the zona glomerulosa and zona fasciculata of the adrenal cortex and in the adrenaline-synthesizing zone of the adrenal medulla. There was no effect of IGF-I infusion on the adrenal mRNA expression of the steroidogenic or catecholamine-synthetic enzymes or on fetal plasma cortisol concentrations. In summary, infusion of IGF-I in late gestation resulted in a marked hypertrophy of the steroidogenic and adrenaline-containing cells of the fetal adrenal in the absence of changes in the mRNA levels of adrenal steroidogenic or catecholamine-synthetic enzymes or in fetal plasma cortisol concentrations. Thus, IGF-I infusion results in a dissociation of adrenal growth and function during late gestation.     

Effects of estrogen and recombinant human insulin-like growth factor-I on ghrelin secretion in severe undernutrition

Ghrelin is a nutritionally regulated gut peptide that increases with fasting and chronic undernutrition and decreases with food intake. Sex steroid levels change in chronic undernutrition and might signal changes in ghrelin. At the same time, chronic undernutrition is characterized by low IGF-I that might also influence ghrelin, either directly or through changes in the GH axis. Little is known regarding sex steroid regulation of ghrelin and the effects of IGF-I on ghrelin in severe undernutrition. We investigated the effects of sex steroids and IGF-I on ghrelin in 78 female subjects with anorexia nervosa simultaneously randomized to receive estrogen (Ovcon 35, 35 microg ethinyl estradiol, and 0.4 mg norethindrone) as well as recombinant human (rh)IGF-I (30 microg/kg sc twice a day) in a two-by-two factorial model, in which the individual effects of estrogen (E) and rhIGF-I on ghrelin could be determined. Subjects were 24.9 +/- 0.7 (mean +/- sem) yr of age and had low weight (body mass index, 16.7 +/- 0.2 kg/m(2)). At baseline, ghrelin was inversely correlated with body mass index (r = -0.39, P = 0.0005) and IGF-I (r = -0.30, P = 0.01). IGF-I increased significantly more in subjects receiving rhIGF-I alone (Delta 23.0 +/- 5.8 nmol/liter) and rhIGF-I and E (Delta 34.9 +/- 6.3 nmol/liter) compared with subjects receiving E alone (Delta -3.2 +/- 1.9 nmol/liter) or control (C; rhIGF-I placebo and no E) (Delta 0.4 +/- 2.0 nmol/liter) (overall P < 0.0001 by multivariate analysis of variance, P < 0.0001 for rhIGF-I vs. C, P < 0.0001 for rhIGF-I and E vs. C). Ghrelin increased significantly more over 6 months in response to E alone (Delta 150 +/- 86 pg/ml), rhIGF-I alone (Delta 198 +/- 116 pg/ml), and the combination (E and rhIGF-I) (Delta 441 +/- 214 pg/ml) compared with C (Delta -39 +/- 48 pg/ml) (overall P = 0.02 by multivariate analysis of variance, P = 0.01 for E vs. C, P = 0.04 for rhIGF-I vs. C, and P = 0.001 for rhIGF-I and E vs. C). Weight, caloric intake, and morning GH levels did not change significantly between the groups, but the change in ghrelin was inversely related to the change in GH among all subjects (r = -0.27, P = 0.03).Our data demonstrate that, in a model of severe undernutrition, rhIGF-I and E individually increase ghrelin levels. The mechanisms of these effects are unknown and may relate to direct effects on ghrelin or changes in GH. Further studies are needed to determine the mechanisms by which rhIGF-I and E increase ghrelin in human physiology.