Biomedical subjects

E R Froesch

Publications and source records attributed to E R Froesch.

At least 91 records · Page 5Linked to original sources

PubMed1989

Production of carrier proteins for insulin-like growth factors (IGFs) by rat osteoblastic cells. Regulation by IGF I and cortisol.

A bone-derived rat cell line, PyMS, releases IGF I and IGF carrier proteins which are similar to those found in rat serum. Western blot analysis of culture media conditioned by hormone-treated cells shows that growth hormone and IGF I stimulate and cortisol inhibits production of IGF carrier proteins in vitro. A glycosylated carrier protein species of 49-42 kDa is closely related to the subunits of the growth hormone-dependent carrier protein complex found in rat serum. In addition, rhIGF I rapidly induces a 32 kDa, non-glycosylated IGF-binding protein whose accumulation is markedly increased by cortisol.

Alkaline Phosphatase↗

PubMed1989

Phenol red mimics biological actions of estradiol: enhancement of osteoblast proliferation in vitro and of type I collagen gene expression in bone and uterus of rats in vivo.

Since osteoblasts are direct targets for estradiol in vitro, and Phenol Red has been reported to bear estrogen-like bioactivity, we investigated whether the pH indicator also mimicked the biological effects of estradiol on bone cells in vitro. We then asked whether estrogenic effects of Phenol Red could be observed in vivo, firstly on the uterus, and if so, whether Phenol Red could also effect bone in vivo. The proliferation of calvarial osteoblasts was stimulated by commercially available preparations of Phenol Red in a dose-dependent manner at 1.5-50 microM. This effect was not abolished in the presence of an antibody against insulin-like growth factor I. In addition, Phenol Red increased alpha 1 (I) collagen mRNA levels of osteoblasts in vitro. 17 beta-estradiol (1.5 micrograms) or Phenol Red (10 mg) administration to immature female rats (45-50 g) resulted in a weight gain of the uterus, and alpha 1(I) procollagen transcripts were more abundant in RNA prepared from uterus of drug-treated rats than observed in the control rats. Similarly, higher procollagen mRNA steady-state levels were observed in RNA prepared from parietal bones of Phenol Red or estradiol-treated rats compared to RNA from control rats. The data extend previous findings in vitro by demonstrating that Phenol Red also exerts estrogen-like effects in vivo. Moreover, we show that Phenol Red stimulates bone cells and, therefore, is likely to interfere at least in experiments designed to investigate estrogen effects on osteoblasts.

Animals↗

PubMed1989

Recombinant human insulin-like growth factor I induces its own specific carrier protein in hypophysectomized and diabetic rats.

The physiology of the specific serum binding proteins which constitute the main storage pool for insulin-like growth factors (IGFs) in mammals is still incompletely understood. We have, therefore, investigated the regulation of these proteins in (i) hypophysectomized (hypox) rats infused with recombinant human growth hormone (rhGH) or recombinant human IGF 1 (rhIGF I) and (ii) streptozotocin-diabetic rats infused with insulin or rhIGF I. The main carrier protein, a GH-dependent complex of apparent molecular mass 200 kDa, contains N-glycosylated IGF-binding subunits (42, 45, and 49 kDa) that differ in their glycosyl but not in their protein moiety. These subunits are lacking in hypox and diabetic rats. They are induced by GH and insulin, respectively, and appear in the 200-kDa complex. Infusion of rhIGF I induces the subunits in both states; however, only in diabetic, not in hypox, rats do they form the 200-kDa complex. Glycosylated carrier protein subunits do not appear before 8 hr of rhIGF I infusion. During that period, hypox rats may become severely hypoglycemic. After 16 hr, glycosylated subunits are clearly induced, and blood sugar values are normal. We conclude: (i) The N-glycosylated subunits of the 200-kDa complex reflect the IGF I status. (ii) IGF I may mediate the induction of these subunits by GH. (iii) Significant association to the 200-kDa complex occurs only in the presence of GH. It is likely that GH, but not IGF I, induces a component, which itself does not bind IGF, but associates with the glycosylated IGF-binding subunits. (iv) The glycosylated subunits protect against IGF-induced hypoglycemia and may be involved in tissue-specific targeting of IGFs.

Animals↗

PubMed1989

Effects of recombinant insulin-like growth factor I on insulin secretion and renal function in normal human subjects.

Insulin-like growth factor I (IGF-I) is an important mediator of growth hormone (GH) action and it appeared tempting to evaluate possible clinical applications. Recombinant IGF-I was infused s.c. at a dose of 20 micrograms/kg of body weight per hour during 6 days in two healthy adult subjects. Blood glucose and fasting insulin levels remained within normal limits and IGF-II levels were suppressed. In contrast to insulin, fasting C peptide levels were decreased. GH secretion was also suppressed by IGF-I. Our preliminary data allow us to distinguish between the effects of GH per se and those of IGF-I: GH causes hyperinsulinism, whereas IGF-I leads to decreased insulin secretion. Glomerular filtration rate, as estimated by creatinine clearance, increased to 130% of preinfusion values during the IGF-I infusion. Total creatinine and urea excretion remained unchanged. We conclude that IGF-I influences kidney function and, in contrast to GH, exerts an insulin-sparing effect. It may be speculated that the therapeutic spectrum of IGF-I is quite different from that of GH.

Adult↗

PubMed1989

Insulin-like growth factor I regulates type I procollagen messenger ribonucleic acid steady state levels in bone of rats.

RNA extracted from parietal bones of rats was analyzed for the abundance of type I procollagen mRNA by a dot hybridization assay using specific cDNA probes. Hypophysectomized rats, deficient in IGF I, have 4.1-fold lower steady state levels of mRNA encoding the alpha 1 chain of type I collagen when compared to normal rats of the same weight (120 g). Administration of recombinant human insulin-like growth factor I (IGF I) for 6 days restores bone collagen mRNA levels to normal, and a single sc injection of 100 micrograms IGF I results in a 1.9-fold increase of both alpha 1(I) and alpha 2 (I)chain mRNAs after 8 h. Studies with calvaria cells in primary culture and with a bone-derived cell line, PyMS, yielded similar results: IGF I treatment of these osteoblast-like cells for 24 h increased steady state levels of type I procollagen mRNAs. Thus, IGF I appears to contribute to osteoblast mRNA expression for both chains of type I collagen.

Animals↗

PubMed1989

Insulin-like growth factor I increase glomerular filtration rate and renal plasma flow in man.

Recombinant IGF-I was infused seal at a dose of 20 micrograms-kg 1-h 1 to 2 healthy subjects during a total of 79 h. Serum levels of IGF-I rose from 93 and 177 to 502 and 616 micrograms/l, respectively. Fasting blood glucose remained normal. During the infusion glomerular filtration rate increased by 31%, in subject No. 1 and by 32% in subject No.2. Concomitantly, renal plasma flow increased by 26% and 22%, respectively. Proximal and distal tubular reabsorption of fluid and sodium as determined by lithium clearance was elevated to a similar extent. When determined again one week after the end of the IGF-I infusion, all parameters of renal function had returned to baseline. Sodium excretion, body weight and blood pressure did not change. We conclude that IGF-I infused at pharmacological doses has marked effects on kidney function. Future studies will necessary to define the clinical potential of recombinant IGF-I in the treatment of diseases characterized by impaired renal perfusion and filtration.

Adult↗

PubMed1989

Inhibition of insulin degradation by insulin-like growth factors I and II in human hepatoma (HepG2) cells.

IGF-I infused at pharmacological doses in healthy men markedly decreases C-peptide levels, whereas insulin levels remain within the normal range. One possible explanation is decreased insulin removal. As the liver is the major site of insulin degradation, we studied insulin degradation by HepG2 cells in the presence of IGF. We found that IGF-I at a concentration of 130 nmol/l inhibits insulin degradation by HepG2 cells when the initial insulin concentration is 0.34 nmol/l. The effect of IGF-I on insulin degradation is dose-dependent and the rate of insulin degradation is dependent on the insulin concentration. IGF-II is 6 to 10 times more potent than IGF-I in inhibiting 125I-insulin binding to HepG2 cells and in protecting insulin from being degraded. Thus, IGF-I and IGF-II inhibit insulin degradation most likely by competing for binding at insulin binding sites of liver cells.

Carcinoma, Hepatocellular↗

PubMed1989

Small stature and insulin-like growth factors: prolonged treatment of mini-poodles with recombinant human insulin-like growth factor I.

The short stature of mini-poodles is associated with low serum levels of IGF-I. Standard poodles are taller and have considerably higher serum levels of IGF-I. Low IGF-I serum levels may be a symptom or the cause of small stature. We, therefore, undertook a study in which serum IGF-I levels of mini-poodles were elevated over a prolonged period of time by a constant infusion of rhIGF-I and the growth rate of the mini-poodles was followed. We infused four mini-poodles from day 91 to day 221 of age with 6 mg/day of recombinant human insulin-like growth factor I (rhIGF-I). Serum levels of IGF-I rose from about 160 to about 500 micrograms/l. Blood glucose remained within normal limits. Stimulation tests with clonidine and with GHRH revealed suppression of endogenous GH secretion during the IGF-I infusion. Serum levels of IGF-II and of creatinine were lower in the IGF-I-infused animals. Radial length and body weight did not increase to a greater extent in the IGF-I infused dogs than in controls. However, 'adapted body mass index' (aBMI = gram body weight/(mm radial length)2) decreased in each of the IGF-I infused animals, whereas it increased in each of the control dogs (p less than 0.05). We conclude that long-term infusion of IGF-I does not stimulate growth in young mini-poodles, but may change body composition.

Animals↗

PubMed1989

The role of insulin-like growth factor I in growth of diabetic rats.

Insulin-deficient, streptozotocin-diabetic rats show severe metabolic disturbances and stop growing. Besides insulin, these animals also lack growth hormone and insulin-like growth factor-I. We examined whether or not growth parameters correlate with IGF-I serum levels in young rats with streptozotocin-diabetes of different severity. In the diabetic rats, blood glucose varied between 18.4 and 38.6 mmol/l (healthy controls between 6.1 and 9.3), IGF-I serum levels between 2.6 and 15.6 nmol/l (controls between 19.6 and 26.5), and serum insulin levels between 0.05 and 0.14 nmol/l (controls between 0.36 and 0.55). We found a highly significant linear correlation between IGF-I serum levels and the two investigated growth parameters, tibial epiphyseal width and longitudinal tibial bone growth. The finding that these indices of growth are strongly correlated with IGF-I serum levels in young rats with diabetes of different severity, suggests that IGF-I is a major determinant of growth. This is in keeping with our earlier demonstration that exogenously infused IGF-I promotes growth in diabetic rats.

Animals↗

PubMed1989

Insulin-like growth factors I and II in healthy man. Estimations of half-lives and production rates.

IGF-I and -II share specific serum carrier proteins which elute on neutral Sephadex G-200 gel permeation chromatography at apparent molecular masses of 50 and 200 kD. The half-lives of free and carrier protein-bound 125I-IGF-I and -II were determined after bolus injections of the tracers into two normal adults. Labelled IGF-I and -II migrated first with the 50-kD and later with the 200-kD complex. In these complexes their apparent half-lives were 20-30 min and 12-15 h, respectively. The apparent half-life a free 125I-IGF-I and -II was 10-12 min. In a second set of experiments, recombinant human insulin-like growth factor I was infused during 6 days in two healthy adults at a dose of 20 micrograms.kg-1.h-1 (corresponding to around 30 mg/day). Serum obtained before and during the infusion was subjected to neutral Sephadex G-200 gel permeation chromatography and fractions were pooled according to the apparent molecular masses at which the carrier protein complexes elute. IGF-I and -II in these pools were determined by RIA. Before the IGF-I infusion, 92 and 272 micrograms/l of IGF-I and -II were found in the 200-kD complex, 45 and 91 micrograms/l in the 50-kD complex, and 15 and 5 micrograms/l were present in the free form. Corresponding figures during the IGF-I infusion were 389 and 18 micrograms/l for the 200-Kd complex, 201 and 54 micrograms/l for the 50-kD complex, and 80 and less than 1 microgram/l for free IGF-I and -II. Using the half-lives of the tracer studies and the levels of the different molecular weight forms of IGF in serum, the production rates for IGF-I and -II were calculated to be 10 mg and 13 mg per day.

Chromatography, Gel↗

PubMed1988

Isolation and NH2-terminal amino acid sequences of rat serum carrier proteins for insulin-like growth factors.

Three N-glycosylated carrier proteins (CP) for insulin-like growth factors (apparent molecular weights 30-32, 42 and 45 kDa) were isolated from adult rat serum. They share the same amino terminus (up to amino acid 31) and are constituents of the growth hormone-dependent native 150-200 kDa IGF carrier complex. Residues 12-31 display 60 and 50% sequence homology, respectively, to residues 2-21 of fetal rat and to residues 4-22 of a human amniotic fluid IGF carrier protein. No homology exists with the type I or II IGF receptors. Adult rat serum also contains a fourth IGF CP (24 kDa) whose 9 NH2-terminal amino acids are identical to those of the fetal form. Our findings suggest that the three N-glycosylated components originate from the same IGF carrier protein (adult form) and that the 24 kDa protein is a separate (fetal) species.

Age Factors↗

PubMed1988

Growth hormone dependent stimulation of osteoblast-like cells in serum-free cultures via local synthesis of insulin-like growth factor I.

Gene-recombinant human growth hormone (rhGH) elicited a dose-dependent stimulation of the proliferation of osteoblast-like cells (OB), when grown in strictly serum-free longterm cultures. A half-maximal effect was observed at concentrations of 15-20 ng/ml and the maximal stimulation was 160% of hormone-free controls. The rhGH-induced effect on proliferation could be inhibited dose-dependently by the addition of an insulin-like growth factor (IGF) I-antiserum to the medium. Moreover, IGF I and rhGH had additive effects only when the exogenous IGF I concentration exceeded that of endogenously produced IGF I by a large margin. Thus, direct stimulation of OB proliferation by rhGH is, at least in part, mediated by IGF I-like immunoreactivity.

Animals↗

PubMed1988

Recombinant human insulin-like growth factor I stimulates growth and has distinct effects on organ size in hypophysectomized rats.

Recombinant human insulin-like growth factor I (rhIGF-I) was infused subcutaneously into hypophysectomized rats for as long as 18 days. Three hundred micrograms (39 nmol) of rhIGF-I per day and 200 milliunits (4.5 nmol) of human growth hormone (hGH) per day increased body weight, tibial epiphyseal width, longitudinal bone growth, and trabecular bone formation similarly. Weight gains of the kidneys and spleen, however, were greater with rhIGF-I than with hGH, whereas the weight of the epididymal fat pads was reduced with rhIGF-I. The weight of the thymus was increased by rhIGF-I treatment. Thus, IGF-I administered over a prolonged period of time mimics GH effects in hypophysectomized rats. Quantitative differences between rhIGF-I and hGH treatment with respect to organ weights may be related to different forms of circulating IGF-I or may be due to independent effects of GH and IGF-I. The results support the somatomedin hypothesis, but they also stress the role of GH as a modulator of IGF-I action.

Animals↗

PubMed1988

Insulin-like growth factor I stimulates erythropoiesis in hypophysectomized rats.

Stimulation of erythropoiesis during growth is necessary to ensure proportionality between erythrocyte mass and body mass. However, the way by which erythrocyte formation is adapted to body growth is still unknown. Growth arrest in hypophysectomized rats is accompanied by decreased erythropoiesis. We have, therefore, examined whether insulin-like growth factor I (IGF-I), the mediator of growth hormone effects on body growth, is able to restore erythropoiesis in these animals. Subcutaneous infusions of 120 micrograms of recombinant human IGF-I per day in hypophysectomized rats led to increases in body weight, 59Fe incorporation into erythrocytes, and the number of reticulocytes that were similar to increases caused by infusions of 28 milliunits of human growth hormone per day. Body weight gain and 59Fe incorporation were linearly correlated. Like growth hormone, IGF-I also caused a significant rise in serum erythropoietin concentrations. However, the stimulatory effect on erythropoiesis occurred before serum erythropoietin levels had risen. These results demonstrate that IGF-I mediates the stimulatory effect of growth hormone on erythropoiesis in vivo and thus further support the somatomedin concept. They also show that IGF-I can stimulate erythropoiesis in an endocrine manner, and they suggest two possible routes of action: a direct one and an indirect one by means of enhanced erythropoietin production.

Animals↗

PubMed1988

Enhanced osteoblast proliferation and collagen gene expression by estradiol.

Estrogens play a crucial role in the development of postmenopausal osteoporosis. However, the mechanism by which estrogens exert their effects on bone is unknown. To examine possible direct effects of 17 beta-estradiol on bone-forming cells, we used pure rat osteoblast-like cells in vitro as a model. Osteoblast-like cells prepared from calvaria of newborn rats were cultured serum-free in methylcellulose-containing medium for 21 days. Osteoblast-like cells proliferate selectively into clonally derived cell clusters of spherical morphology. 17 beta-Estradiol at concentrations of 0.1 nM and 1 nM enhanced osteoblast-like cell proliferation by 41% and 68% above vehicle-treated controls. The biologically inactive stereoisomer 17 alpha-estradiol (same concentrations) had no effect. Moreover, the antiestrogen tamoxifen abolished the stimulation of osteoblast-like cell proliferation by 17 beta-estradiol. After 21 days of culture, RNA was prepared and analyzed in a dot-hybridization assay for the abundance of pro alpha 1(I) collagen mRNA. Steady-state mRNA levels were increased in cultures treated with 17 beta-estradiol in a dose-dependent manner with maximal stimulation at 1 nM and 10 nM. At the same concentrations, the percentage of synthesized protein (labeled by [3H]proline pulse) that was digestible by collagenase was increased, indicating that 17 beta-estradiol acts at pretranslational levels to enhance synthesis of bone collagen. These data show that the osteoblast is a direct target for 17 beta-estradiol.

Animals↗

PubMed1988

Spontaneous postoperative normalization of growth hormone levels in two patients with acromegaly not cured by transsphenoidal surgery.

Postoperative persistence of elevated growth hormone (GH) levels in patients with acromegaly usually suggests residual adenoma tissue secreting GH and is an indication for further treatment. In rare cases, spontaneous normalization of serum GH levels in patients with acromegaly has been reported to occur as a consequence of intratumoral hemorrhage (pituitary apoplexy). We report two patients in whom persisting acromegaly was documented 1 and 2 weeks, respectively, after transsphenoidal operation and who experienced spontaneous normalization of GH levels. In one patient, this favorable outcome was found 1.5 years after the operation and followed a pregnancy. The other patient, whose GH values normalized 3 months after operation, had received preoperative treatment with a new, long-acting somatostatin analog.

Acromegaly↗

PubMed1988

Insulin-like growth factors in the Göttinger miniature-pig.

IGF I was determined by a radioimmunoassay and IGF II by a radioreceptorassay in 20 Göttinger miniature (mini)-pigs and 13 domestic pigs of different weight and age. Immunoreactive IGF I serum levels of mini-pigs were similar to those of domestic pigs in corresponding age-classes (150-250 and 100-270 micrograms/l, respectively). No differences were detectable between receptor-reactive IGF II serum levels in mini-pigs (150-200 micrograms/l) and domestic pigs (110-270 micrograms/l) nor did the biological insulin-like activities (measured in the rat fat cell assay) differ in mini- and domestic pigs (81-100 and 71-98 mU insulin/l, respectively). IGF I and IGF II decreased drastically after hypophysectomy in one of the mini-pigs. Intravenous bolus injections of 30 micrograms/kg of recombinant human IGF I in 4 mini-pigs caused a similar degree of hypoglycemia (nadir of blood glucose 1.33 +/- 0.61 mmol/l) as 0.15 IU insulin/kg, followed by a sharp growth hormone peak. We conclude that the marked difference between mini- and domestic pigs regarding body size is unrelated to serum levels of IGF I and II, a lack of response of tissues to IGF I or a reduced growth hormone secretory capacity in the mini-pig.

Animals↗

PubMed1987

Triiodothyronine stimulates proliferation of osteoblast-like cells in serum-free culture.

Primary rat osteoblast-like cells (Ob) were grown under strictly serum-free conditions for up to 20 days. In the presence of triiodothyronine (T3) at concentrations of 0.01 and 0.1 nM, Ob proliferation was enhanced. Moreover, a decrease of alkaline phosphatase (AP) activity, a differentiation marker for Ob, was prevented, whereas protein synthesis (collagen and noncollagen protein) was decreased. T3 at much higher concentration (10 nM) had no significant effect on cell proliferation and matrix formation but decreased AP activity disproportionately. Thus, T3 at close to physiological concentrations stimulates growth and maintains differentiation of Ob.

Alkaline Phosphatase↗