Insulin-like growth factors and insulin: comparative aspects

Insulin-like material from the digestive tract of the tunicate Pyura pachydermatina (sea tulip)

Gut tissue from the tunicate Pyura pachydermatina (sea tulip) was found to contain a compound or compounds which react with anti-porcine insulin antibodies, but not anti-hag-fish insulin antibodies, and which also stimulate lipogenesis in isolated rat fat cells. The insulin-like material is present in two immunologically active forms, a species of Mr 6000 apparently similar to mammalian insulin, and a high Mr form which expresses biological activity only after further purification by reverse-phase HPLC. The bioactivity of both species is suppressed in the presence of anti-porcine insulin antibodies.

Effect of insulin-like growth factor-I on metabolism in bovine mesenteric arteries

The effect of insulin-like growth factor-I (IGF-I) on glucose accumulation, amino acid uptake and incorporation of amino acid into protein was studied in arterial smooth muscle. Accumulation of [14C]glucose, uptake of [14C]alpha-aminoisobutyric acid (AIB) and incorporation of [14C]phenylalanine into protein were measured in intima-media preparations of bovine mesenteric arteries (BMA) incubated with IGF-I for 2, 4 or 6 h. IGF-I (2.2 nmol l-1) increased the accumulation of glucose into BMA after 4 h (P = 0.0079) and 6 h incubation (P = 0.0027) and in a concentration of 22 nmol l-1) also after 2 h (P = 0.015). The uptake of AIB and the incorporation of phenylalanine were increased after 4 h incubation with 2.2 nmol l-1) IGF-I (P = 0.0045 and P = 0.026, respectively). The effects of IGF-I on all of the metabolic parameters were dependent on incubation time and concentration of IGF-I. Concentration-effect curves were determined for the effect of IGF-I and also for insulin on glucose accumulation in BMA incubated for 6 h. The concentration-effect relationships for IGF-I and insulin were very similar with pD2 values of 7.6 +/- 0.2 (EC50 = 27 nmol l-1) and 7.5 +/- 0.2 (EC50 = 34 nmol l-1), respectively. No additive effect of IGF-I and insulin in supra-physiological concentrations (1.0 mumol l-1) could be demonstrated. These results show that IGF-I has metabolic effects which are similar to the effects of insulin in vascular smooth muscle and suggest that IGF-I may be of importance for the metabolism in vascular smooth muscle.

Dynamic changes in insulin-like growth factor I immunoreactivity correlate to repair events in rat ear after freeze-thaw injury

The distribution of the trophic peptide insulin-like growth factor I (IGF-I) in the rat ear was mapped after freeze-thaw injury. Immunocytochemical methods and antisera specific to human IGF-I were used. In the ear of normal adult rats scattered basal epidermal cells and a few cells in the underlying connective tissue and elastic cartilage expressed IGF-I immunoreactivity. Within 1 day after injury and reaching maximum in 3 days, all epidermal cells became stained as did invading macrophages and some of the other inflammatory cells. Concomitantly, there were hypertrophic changes. The staining leveled off after 1-2 weeks. Perichondrial cells became IGF-I immunoreactive in increasing frequency during the first week, reached maximal intensity and frequency in 2 weeks, and remained stained for at least 4 weeks. New cartilage was formed concomitantly on both sides of the old one. It is proposed that IGF-I is a substance of general importance for cell maintenance and tissue repair.

Short-term metabolic effects of recombinant human insulin-like growth factor I in healthy adults

Insulin-like growth factor I (IGF I) is structurally similar to insulin and shares many of its biologic properties. We compared the short-term metabolic effects of recombinant IGF I (100 micrograms [13.3 nmol] per kilogram of body weight) and insulin (0.15 IU [1 nmol] per kilogram) in eight healthy volunteers (four men and four women). The hypoglycemic responses to both hormones were nearly identical in the doses used. The lowest blood glucose levels were reached after 30 minutes: 1.98 +/- 0.44 mmol per liter after IGF I and 1.78 +/- 0.29 after insulin. On a molar basis, IGF I was only 6 percent as potent as insulin in the production of hypoglycemia. Insulin also inhibited lipolysis more effectively than IGF I. Levels of epinephrine, norepinephrine, growth hormone, glucagon, and cortisol responded similarly to both agents. The hypoglycemia produced by IGF I is probably due to the supraphysiologic concentrations of the free peptide that result from its rapid intravenous injection. Fifteen minutes after injection, the serum level of IGF I increased from 144 +/- 38 ng per milliliter at base line to 424 +/- 56, of which 80 percent was free in the plasma (not bound to IGF carrier proteins). The determination of whether any of the short-term metabolic effects of IGF I have any clinical application will require further investigation.

IGF-I expression in blood vessels varies with vascular load

The present study was designed to investigate if the immunoreactivity of insulin-like growth factor I (IGF-I, somatomedin C) in blood vessels was changed in relation to the vascular load in adult rats. Occlusion of the right femoral artery resulted within 24 h in a strongly increased IGF-I immunoreactivity in the media of the contralateral, left, femoral artery and a significant decrease in the IGF-I expression in the right femoral artery distal to the occlusion. The increased labelling of the smooth muscle cells persisted for at least 21 days. Inactivity of the right hind limb, secondarily to an ischaemic insult, likewise induced a significant increase in IGF-I immunoreactivity, within 24 h, in the femoral vessels of the undamaged, contralateral left hind limb. It is concluded that IGF-I immunoreactivity varies with the dynamic load in the vascular walls. It is proposed that IGF-I may serve as a parahormone exerting its effect by paracrine and/or autocrine mechanisms, taking part in regulating the structural adaption of blood vessels in response to stress.

Sequences of liver cDNAs encoding two different mouse insulin-like growth factor I precursors

Complementary DNAs encoding mouse liver insulin-like growth factor I (IGF-I) have been isolated and sequenced. Alternative RNA splicing results in the synthesis of two types of mouse IGF-I precursor that differ in the size and sequence of the COOH-terminal peptide. The sequences of the signal peptides, IGF-I moieties and the first 16 amino acids of the COOH-terminal peptides or E-domains of the two precursors are identical. The sequence difference results from the presence in preproIGF-IB mRNA of a 52 base insertion which introduces a 17 amino acid segment into the COOH-terminal peptide of preproIGF-IB and also causes a shift in the reading frame of the mRNA. As a consequence of this insertion, the COOH-terminal 19 and 25 amino acids of mouse preproIGF-IA and -IB, respectively, are different. The sequences of mouse and human preproIGF-IA are highly conserved and possess 94% identity. In contrast, the sequences of mouse and human preproIGF-IB are quite different in the region of the COOH-terminal peptide. A comparison of the sequences of mouse and human preproIGF-IB mRNA indicates that they are generated by different molecular mechanisms.

Sequence of a placental cDNA encoding the mouse insulin-like growth factor II precursor

cDNAs encoding the mouse insulin-like growth factor II (IGF-II) precursor have been isolated from a placental library and sequenced. Mouse prepro-IGF-II is predicted to be 180 amino acids and has 84% and 97% identity with human and rat IGF-II precursors, respectively. There are two prepro-IGF-II transcripts in mouse placenta; the major transcript is 3850 bases and the minor one is 4800 bases. Prepro-IGF-II mRNA cannot be detected in adult mouse liver, but it is readily detected in adult human liver, indicating that there are differences in the regulation of expression of the IGF-II gene in the liver of adult mice and human beings.

Growth restoration of insulin-deficient diabetic rats by recombinant human insulin-like growth factor I

Insulin-like growth factor I (IGF-I) and insulin stem from a common precursor, are structural homologues, act through similar receptors and elicit insulin-like and growth-promoting effects in vitro and in vivo. Serum IGF-I levels are controlled by growth hormone, insulin and nutrition. Insulin-deficient growth-arrested diabetic animals have reduced serum IGF-I levels which are restored towards normal by insulin but not by growth-hormone treatment. Here we show that normal growth of diabetic rate is restored by infusion of recombinant human (rh)IGF-I without normalization of the blood sugar level and that insulin acts via an increase of IGF-I synthesis on growth of diabetic rats. We describe a new mechanism of endocrine control of growth in which IGF-I is the major stimulator at the cellular level. Growth hormone and insulin act mainly by modulating the hepatic synthesis of IGF-I.

Insulin-like growth factor I (IGF I) receptor autophosphorylation and kinase activity. Effect of a human polyclonal antibody (pIgG)

IGF I receptor is a tyrosine kinase capable of phosphorylating the receptor itself and other substrates. A high degree of homology does exist in tyrosine kinase domain among receptors for several polypeptide growth factor receptors and this enzymic activity has been indicated as a possible mediator of biological action. Nevertheless growth factor receptors possess peculiar specificities both in their functions and tissue distribution. A human polyclonal IgG (pIgG), previously characterized as anti insulin receptor antibody, able to inhibit insulin receptor kinase activity, was used to further investigate subunit homologies and differences in antigenicity and functional regulation between IGF I and insulin receptors, IGF I receptor tyrosine kinase was stimulated by a IGF I analog (aIGF I), produced by DNA recombinant technology, pIgG was able to inhibit IGF I receptor kinase activity, thus revealing antigenic homologies between the kinase domains of insulin and IGF I receptors. However the more pronounced inhibition of IGF I receptor-compared with insulin receptor kinase activity by pIgG suggests the existence of different regulatory mechanisms.