Insulin-like Growth factor-I Treatment Research Articles

Response of young broiler chickens to chronic injection of recombinant-derived human insulin-like growth factor-I

The purpose of this study was to determine if exogenous insulin-like growth factor-I (IGF-I) would improve growth rate or body composition of young broiler chickens. Broiler cockerels were given a daily intramuscular ( im) injection of sodium acetate buffer (buffer control), 100 or 200 μg recombinant-derived human IGF-I (rhIGF-I) per kg body weight from 11 to 24 days of age. Exogenous IGF-I did not affect the average daily gain, average daily feed consumption, or the gain-to-feed ratio of broiler chickens. Although daily injection of 200 μg/kg of rhIGF-I reduced (P<0.05) body ash content, there was no significant effect of IGF-I treatment on either body fat or protein content. Plasma GH levels were depressed (P<0.05) by chronic treatment with rhIGF-I. In contrast, plasma levels of T 3 and T 4 were not affected by rhIGF-I treatment. The half-life of rhIGF-I in plasma was determined at 25 days of age in naive control or chronically-injected chickens after a single intravenous dose of 50 μg rhIGF-I/kg. We found a single compartment, first-order disappearance pattern of rhIGF-I from chicken plasma. The half-life ( t 1 2 ) of rhIGF-I in plasma was similar ( t 1 2 = 32.5 min ) for naive controls (injected once) or chronically-treated chickens which had received a daily injection of rhIGF-I (100 or 200 μg/kg) for 14 d. These data indicate that daily injection of IGF-I cannot be used to enhance growth performance or body composition of broiler chickens when given during the early growth period. The depression of plasma GH levels in rhIGF-I-injected chickens supports a negative-feedback role of IGF-I on pituitary GH secretion.

Effects of full-length and truncated insulin-like growth factor-I on nitrogen balance and muscle protein metabolism in nitrogen-restricted rats

The ability of insulin-like growth factor-I (IGF-I) to protect against losses of body protein during periods of dietary nitrogen restriction has been evaluated in young rats. Recombinant human IGF-I was administered by osmotic pumps at dose rates of 0, 1.2 or 2.9 mg/kg per day over a 7-day period beginning with the transfer of animals from an 18% to a 4% protein diet. A fourth group received the potent truncated IGF-I analogue, des(1-3)IGF-I, at a dose of 1.2 mg/kg per day over a comparable 7-day period. Plasma IGF-I levels were reduced by 60% following nitrogen restriction, a reduction that was partly prevented by IGF-I administration, especially at the higher dose, but not measurably by des(1-3)IGF-I. The major IGF-binding protein circulating in blood, IGFBP-3, demonstrated a similar pattern of change. A significant (P less than 0.05) protection of body weight was achieved in the low dose IGF-I and des(1-3)IGF-I groups, but only after differences in food intake had been eliminated by analysis of covariance. Nitrogen balances were not significantly different unless analysis of covariance was used to adjust for the nitrogen intakes, whereupon all treatment groups showed improved balance, especially the animals treated with the low IGF-I dose and des(1-3)IGF-I (both P less than 0.01). The rate of muscle protein breakdown calculated from the urinary excretion of 3-methyl-histidine was not significantly altered by the treatments, but fell progressively throughout the 7 days. The fractional rate of muscle protein synthesis measured on the final day was increased by 31,26 and 21% respectively by the low and high doses of IGF-I and by des(1-3)IGF-I. Organ weights (g/kg body weight) showed no effects of IGF-I treatment except for 16% increases in the weight of kidneys in the high dose IGF-I and the des(1-3)IGF-I groups. Carcass analyses demonstrated higher water and lower fat contents (all P less than 0.01) in the same groups. These results suggest that exogenous IGF-I and especially des(1-3)IGF-I can partly protect body protein reserves during nitrogen restriction.

Repopulation of the atrophied thymus in diabetic rats by insulin-like growth factor I.

Atrophy of the thymus is one of the consequences of severe insulin deficiency. We describe here that the weight and the architecture of the thymus of diabetic rats is restored towards normal not only by insulin but also by insulin-like growth factor I (IGF-I) treatment. In contrast to insulin, this effect of IGF-I occurs despite persisting hyperglycemia and adrenal hyperplasia. We also investigated the in vivo effect of IGF-I on replication and differentiation of thymocytes from streptozotocin-induced diabetic rats. Thymocytes from diabetic rats incorporated less [3H]thymidine than did thymocytes from healthy rats. Insulin, as well as IGF-I treatment of diabetic rats increased [3H]thymidine incorporation by thymocytes. Flow cytometry of thymocytes labeled with monoclonal antibodies revealed a decreased expression of the Thy-1 antigen in diabetic rats compared with control rats. In addition, a major deficiency of thymocytes expressing simultaneously the W3/25 and the Ox8 antigens (corresponding to immature human CD4+/CD8+ thymocytes) was observed. These changes were restored towards normal by insulin as well as by IGF-I treatment. The antibody response to a T cell-dependent antigen (bovine serum albumin) was comparable in normal and diabetic rats. We conclude that IGF-I has important effects on the thymocyte number and the presence of CD4+/CD8+ immature cells in the thymus of diabetic rats despite persisting hyperglycemia. However, helper T-cell function for antibody production appears to be preserved even in the severely diabetic state.

Studies on the Effect of Insulin‐Like Growth Factor‐I on Catecholamine Secretion from Chromaffin Cells

Chromaffin cells cultured in serum-free medium secreted a smaller percentage of their catecholamine stores in response to stimulation by high K+ (55 mM) than did cells cultured in serum-containing medium. Addition of insulin-like growth factor-I (IGF-I) to serum-free medium restored high K(+)-stimulated catecholamine secretion to the levels seen in serum-treated cultures. In contrast, addition of IGF-I to serum-containing medium had little effect on catecholamine secretion. These results suggest that serum contains IGF-I or another factor that maintains the secretory responsiveness of chromaffin cells. IGF-I not only enhanced high K(+)-stimulated catecholamine secretion, but also augmented secretion elicited by the nicotinic agonist dimethyl-phenylpiperazinium, the dihydropyridine agonist Bay K 8644, and Ba2+. IGF-I did not affect the dependence of catecholamine secretion on extracellular Ca2+ concentration nor did it affect the time course of secretion. Experiments using 45Ca2+ demonstrated that IGF-I treatment enhanced Ca2+ uptake into the cells. When cells were permeabilized by treatment with digitonin, Ca2(+)-dependent catecholamine secretion was slightly, but consistently, greater from IGF-I-treated cells than from untreated cells. Our results suggest that IGF-I may enhance catecholamine secretion partly by increasing Ca2+ entry into the cells and partly by affecting a step distal to Ca2+ entry.

Insulin-Like Growth Factor-I Action on Growth Hormone Secretion and Messenger Ribonucleic Acid Levels: Interaction with Somatostatin*

Insulin-like growth factor I (IGF-I) suppresses GH gene transcription and GH secretion, while somatostatin (SRIF) only suppresses GH secretion. The interaction of these inhibitors of GH was, therefore, tested in primary rat pituitary cells grown in serum-free medium. Maximal inhibition of GH secretion (to 30% of the control value) was achieved by 13 nM IGF-I, while 5 nM SRIF suppressed GH to 36% of control secretion. The respective ED50 values for IGF-I and SRIF inhibition of GH secretion were similar (approximately 2.5 nM). Treatment of cells with the two agents together resulted in a further inhibition of basal GH secretion to 18% of control untreated cells (P less than 0.005). Increasing doses of SRIF (2.5-10 nM) in the presence of IGF-I caused a dose-dependent suppression of GH secretion. PRL levels were not altered by these treatments, indicating a selective effect on GH. GRH-induced GH secretion was further attenuated by combined IGF-I and SRIF treatment compared to the effect of either of these two agents alone. Northern analysis showed that IGF-I suppressed GH mRNA transcripts, while SRIF did not alter GH mRNA levels. The results indicate that physiological concentrations of both IGF-I and SRIF suppress long term basal GH secretion. Only IGF-I alters GH mRNA levels. These two peptides, therefore, appear to attenuate in vitro GH secretion by different mechanisms.

Effects of epidermal growth factor and insulin-like growth factor I on the levels of mRNA encoding aromatase cytochrome P-450 of human ovarian granulosa cells

The effects of growth factors to regulate the activity of aromatase, as well as the synthesis of aromatase cytochrome P-450 ( P-450 AROM) have been studied in human ovarian granulosa cells obtained from women undergoing oocyte retrieval. Insulin-like growth factor I (IGF-I) increased aromatase activity as well as the synthesis of P-450 AROM, in a concentration-dependent fashion. The levels of hybridizable mRNA species encoding cytochrome P-450 AROM were also increased with IGF-I treatment. By contrast, epidermal growth factor (EGF) had no effect on these parameters when added alone, but markedly inhibited the action of follicle-stimulating hormone (FSH) to stimulate aromatase activity, and the synthesis of cytochrome P-450 AROM as well as lts ability to increase the levels of mRNA encoding the enzyme. It is concluded that these growth factors have opposite effects on aromatase activity, and that these actions reflect, in part, changes in the synthesis of cytochrome P-450 AROM which in turn are the consequence of changes in the levels of mRNA encoding this enzyme.

Modulation of aromatase and P450 cholesterol side-chain cleavage enzyme activities of human placental cytotrophoblasts by insulin and insulin-like growth factor I.

The placenta is the primary source of estrogens and progesterone during pregnancy. Because pregnant diabetic women are reported to have lower serum estrogen and higher progesterone concentrations than nondiabetic pregnant women, we studied the roles of insulin and insulin-like growth factor I (IGF-I) in the regulation of human cytotrophoblastic aromatase and P450 side-chain cleavage enzyme (P450 SCC) activities. Incubation of cytotrophoblasts with insulin or IGF-I for 24 h significantly inhibited the conversion of androstenedione to estrogens by approximately 20-40%. Insulin and IGF-I suppressed aromatization at doses as low as 20 and 10 ng/ml, respectively. Insulin's suppressive effect was demonstrable only after 18-22 h of incubation, suggesting an effect of insulin on aromatase protein mass rather than on aromatase activity. Cytotrophoblasts pretreated with insulin for 24 h possessed 23-30% less aromatase activity than control cells, as quantitated directly by the specific release of 3H2O from [3H]androstenedione, indicating that insulin inhibited estrogen synthesis rather than increased estrogen catabolism. Insulin's suppressive effect on aromatase was not due to a toxic effect of insulin, since incubates exposed to insulin for 24 h showed no decrease in cell number, cellular DNA content, or cellular protein content compared to control incubates. Also, insulin's suppression of aromatization was not due to increased cAMP phosphodiesterase activity, since cotreatment with 1 mM (Bu)2cAMP did not alter insulin's suppressive effect. Blockade of the IGF-I receptor of cytotrophoblasts with alpha IR-3, a monoclonal anti-IGF-I receptor antibody, prevented the suppression of aromatase activity by IGF-I, but did not alter insulin's inhibitory effect. This suggests that the two hormones inhibit aromatization via activation of their specific receptors and not by cross-association. Insulin treatment did not affect P450 SCC activity, whereas IGF-I treatment significantly stimulated P450 SCC activity by 19-36%, as measured by the conversion of 25-hydroxycholesterol to progesterone. These studies indicate that insulin exerts a selective inhibitory effect on cytotrophoblastic aromatase activity, whereas IGF-I inhibits aromatase activity but stimulates P450 SCC activity. Since pregnant diabetic women manifest peripheral hyperinsulinemia, and IGF-I levels in fetal cord sera from diabetic pregnancies are elevated, these observations may help explain the lower serum estrogen and elevated progesterone levels associated with diabetic pregnancy.

Insulinlike growth factor I regulation of growth hormone gene transcription in primary rat pituitary cells.

We have previously shown that insulinlike growth factor I (IGF-I) inhibits growth hormone (GH) secretion and messenger RNA (mRNA) levels in pituitary cells. The effects of IGF-I on new GH mRNA synthesis rates in primary monolayer rat pituitary cells were therefore examined by nuclear runoff transcription assays. IGF-I (1.3 nM) treatment for 1 h inhibited GH gene transcription to 60% of controls. IGF-I (3.25 nM) maximally suppressed GH gene transcription to 30% of control values after 4 h. After 24 h treatment, GH transcription was suppressed to 48% of controls by 3.25 nM IGF-I. IGF-I (3.25 nM) also inhibited the twofold growth hormone-releasing hormone (GHRH) (10 nM)-stimulated GH gene transcription by 30% after 4 h. Transcription of the prolactin (PRL) gene was not suppressed in these cells by IGF-I. Relatively high doses of insulin (200 nM) also suppressed GH gene transcription, but epidermal growth factor and fibroblast growth factor did not change GH mRNA synthesis. The results show that IGF-I exerts a rapid and selective suppression of basal and GHRH-stimulated GH gene transcription. These data indicate a role for IGF-I in negative feedback of GH gene expression and provide evidence for the direct transcriptional regulation of the GH gene by IGF-I in primary rat anterior pituitary cells.

&lt;I&gt;In vivo&lt;/I&gt; Effects of Insulin-Like Growth Factor I in Rats

The scarcity of somatomedin/insulin-like growth factor (SM/IGF) has prevented investigation of the mechanism of SM/IGF action. Recently insulin-like growth factor I (IGF-I) has been synthesized by recombinant DNA technology. With the availability of large quantities of the biosynthetic IGF-I, we undertook a study of biological effects of IGF-I in vivo in rats. 120μg/day of IGF-I was administered continuously for 7 days via subcutaneous implanted osmotic minipump to hypophysectomized (hypox), normal, and diabetic rats. The body weights and tibial epiphyseal widths after 7 day treatment of IGF-I in both hypox and normal rats were significantly greater than those for untreated rats. Blood urea nitrogen levels in both hypox and normal rats treated with IGF-I were significantly lower than those for untreated rats, suggesting that IGF-I has anabolic action in vivo. In contrast to hypox and normal rats, in diabetic rats, IGF-I treatment did not stimulate growth in vivo, but, had a little anabolic and insulin-like effects in vivo.This study demonstrates that IGF-I has growth promoting, anabolic and insulin-like effects in vivo and suggests that IGF-I might be useful in the treatment of growth retardation but not that for diabetes mellitus.

Comparison of the effect of plasmapheresis and penicillamine on the level of circulating rheumatoid factor.

It has been shown previously that slight elevations in serum levels of insulin-like growth factor-I (IGF-I) are correlated with an increased risk for developing prostate, breast, colon, and lung cancer. The aim of this study was to determine the role of serum IGF-I levels in the process of stimulating tumor growth and metastasis in a mouse model of colon cancer. Colon 38 adenocarcinoma tissue fragments were orthotopically transplanted by attachment to the surface of the cecum in control and liver-specific IGF-I-deficient (LID) mice in which serum IGF-I levels are 25% of that in control mice. A total of 156 male mice at 5 weeks of age (74 control mice and 82 LID mice) received tumor transplants. Mice were divided randomly into two groups; one group was injected i.p. with recombinant human IGF-I (2 mg/kg) twice daily for 6 weeks, and the other group received saline injections. IGF-I treatment increased the serum levels of IGF-I and IGFBP-3 in both control and LID mice. In the saline-injected group, the incidence of tumor growth on the cecum as well as the frequency of hepatic metastasis was significantly higher in control mice as compared with LID mice. Both control and LID mice treated with recombinant human IGF-I displayed significantly increased rates of tumor development on the cecum and metastasis to the liver, as compared with saline-injected mice. The number of metastatic nodules in the liver was significantly higher in control mice as compared with LID mice. The expression of vascular epithelial growth factor (VEGF) as well as vessel abundance in the cecum tumors was dependent on the levels of serum IGF-I. This study supports the hypothesis that circulating IGF-I levels play an important role in tumor development and metastasis.