Insulin-like growth factors I and II. Peptide, messenger ribonucleic acid and gene structures, serum, and tissue concentrations.

There is currently widespread interest in the IGFs (IGF-I and IGF-II) and their roles in the regulation of growth and differentiation of an ever increasing number of tissues are being reported. This selective review focused on the current state of our knowledge about the structure of mammalian IGFs and the multiple forms of mRNAs which arise from alternative splicing and promoter sites which arise from gene transcription. Current progress in the immunological measurement of the IGF is reviewed including different strategies for avoiding binding protein interference. The results of measurements of serum IGF-I and IGF-II in fetus and mother and at various stages of postnatal life are described. Existing knowledge of the concentration of these peptides in body fluids and tissues are considered. Last, an attempt is made to indicate circumstances in which the IGFs are exerting their actions in an autocrine/paracrine mode and when endocrine actions predominate. In the latter context it was concluded that an important role for GH action on skeletal tissues via hepatic production of IGF-I and endocrine action of IGF-I on growth cartilage is likely.

Human placental lactogen: studies of its acute metabolic effects and disposition in normal man.

The acute metabolic effects and disposition of human placental lactogen (HPL) have been studied in 15 men and 8 women during continuous intravenous infusions. The mean plasma half-life, metabolic pool size, and turnover rate of HPL are comparable to the values previously reported for human growth hormone (HGH). From the data presented, we calculate that the placenta secretes approximately 290 mg HPL daily at term. After 12-hour infusions of HPL in physiologic amounts, impairment of glucose tolerance despite increased plasma insulin responses to glucose was observed in 7 of 8 subjects tested. However, HPL, unlike HGH, did not produce significant changes in blood glucose, plasma insulin, or plasma free fatty acid concentrations in fasting subjects before glucose administration or in carbohydrate tolerance or plasma insulin responses to glucose during 5-hour infusions. These findings are compatible with the thesis that HPL is a physiologic antagonist to insulin during pregnancy.

Growth hormone secretion during sleep.

Plasma growth hormone (GH), insulin, cortisol, and glucose were measured during sleep on 38 nights in eight young adults. Blood was drawn from an indwelling catheter at 30-min intervals; EEG and electrooculogram were recorded throughout the night. In seven subjects, a plasma GH peak (13-72 mmug/ml) lasting 1.5-3.5 hr appeared with the onset of deep sleep. Smaller GH peaks (6-14 mmug/ml) occasionally appeared during subsequent deep sleep phases. Peak GH secretion was delayed if the onset of sleep was delayed. Subjects who were awakened for 2-3 hr and allowed to return to sleep exhibited another peak of GH secretion (14-46 mmug/ml). Peak GH secretion was not correlated with changes in plasma glucose, insulin, and cortisol. The effects of 6-CNS-active drugs on sleep-related GH secretion were investigated. Imipramine (50 mg) completely abolished GH peaks in two of four subjects, whereas chlorpromazine (30 mg), phenobarbital (97 mg), diphenylhydantoin (90 mg), chlordiazepoxide (20 mg), and isocarboxazid (30 mg) did not inhibit GH peaks. Altered hypothalamic activity associated with initiation of sleep results in a major peak of growth hormone secretion unrelated to hypoglycemia or changes in cortisol and insulin secretion.

Concentration of myo-inositol in skeletal muscle of the rat occurs without active transport.

The cellular uptake of nonphosphorylated myo-inositol (MI) and its incorporation into phosphoinositide in the rat epitrochlearis muscle was measured. Cellular uptake of [2-(3)H]MI was determined by the difference between total uptake and [2-(3)H]MI present in the extracellular fluid determined with [1-(14)C]mannitol. Cellular uptake was parabolic and directly proportional to medium MI concentrations between 25 and 3,200 muM. Saturation of a MI carrier was not evident. Moreover, uptake was not inhibited by 2 mM ouabain, 0.3 mM 2,4-dinitrophenol, or 22 mM glucose. Insulin, 100 mU/ml, was without effect on either cellular uptake of [2-(3)H]MI or its incorporation into phosphoinositides. In muscles that were preloaded with [2-(3)H]MI and then incubated in media that contained a constant amount of MI but no [2-(3)H]MI, 44.3% of the [2-(3)H]MI was released after 10 min increasing to 62.5% by 120 min. Cellular MI concentrations were 0.18 mumol/g wet tissue (four times plasma levels) in rapidly isolated and frozen epitrochlearis muscle. When muscle was incubated without MI, 48% of endogenous MI was lost rapidly. Restoration of cellular MI in 50 muM MI media occurred in two phases, a rapid uptake phase lasting 10 min and a subsequent slow phase of MI uptake. It is concluded that MI enters and leaves skeletal muscle cells freely by a process that does not involve active transport. Neither insulin nor hyperglycemia affected MI transport nor its incorporation into phosphoinositides. The intracellular to medium concentration gradient may be dependent on reversible binding to tubulin and possibly to other intracellular components.

Thyroid hormone inhibition of the prolactin response to thyrotropin-releasing hormone.

The influence of serum triiodothyronine (T(3)) and thyroxine (T(4)) concentrations on the release of prolactin in man was studied by determining the prolactin response to synthetic thyrotropin-releasing hormone (TRH) in hypothyroid and hyperthyroid patients before and after correction of their serum thyroid hormone abnormalities. The maximum increment in serum prolactin above the basal level (maximum Delta prolactin) was used as the index of response to TRH. In 12 patients with primary hypothyroidism, the maximum Delta prolactin in response to TRH fell from 100.5+/-29.1 ng/ml (mean +/-SEM) before treatment to 36.1+/-6.0 ng/ml (P < 0.01) during the 4th wk of treatment with 30 mug T(3) + 120 mug T(4) daily. The mean serum T(3) level increased from 57+/-8 to 138+/-10 ng/100 ml, and the mean serum T(4) level increased from 3.0+/-0.4 to 7.2+/-0.4 mug/100 ml during this treatment. In eight normal subjects the maximum Deltaprolactin in response to TRH was not significantly different during the 4th wk of treatment with 30 mug T(3) + 120 mug T(4) daily from the response before treatment. In 10 patients with hyperthyroidism, the maximum Deltaprolactin in response to TRH increased from 14.2+/-2.9 ng/ml before treatment to 46.9+/-6.7 ng/ml (P < 0.001) during antithyroid treatment. The mean serum T(3) level fell from 313+/-47 to 90+/-8 ng/100 ml, and the mean serum T(4) level fell from 20.8+/-2.5 to 6.8+/-0.6 mug/100 ml during this treatment. These results show that changes from normal serum levels of T(3) and T(4) are associated with changes in prolactin responses to TRH; subnormal serum levels of T(3) and T(4) increase TRH-induced prolactin release, whereas substantially higher than normal serum levels of T(3) and T(4) inhibit this release.

Effects of glucose and parathyroid hormone on the renal handling of myoinositol by isolated perfused dog kidneys.

The effects of glucose and parathyroid hormone (PTH) on the transport and metabolism of myoinositol (MI) and [2-(3)H]MI were studied in isolated perfused dog kidneys. Studies during perfusion of kidneys with normal and elevated glucose concentrations demonstrated that under normal conditions the isolated kidney reabsorbed 94.7+/-0.2% of the filtered MI, and the renal production of (3)H-metabolities of MI was 117.9+/-6% of the filtered MI load. This indicated that entry of MI into tubular cells by reabsorption was not the sole pathway for entry into the pool of MI within the kidney undergoing catabolism. High glucose perfusate decreased MI reabsorption to 68.6+/-4.7% and thus decreased delivery of [2-(3)H]MI into the catabolic pool from the reabsorptive pathway. In the high glucose experiments, the rate of [2-(3)H]MI catabolism exceeded [2-(3)H]MI reabsorption by the same fraction as in normal glucose experiments, which indicates that high glucose did not affect nonreabsorptive access of MI to the catabolic site. In contrast to the effects of glucose, PTH administration resulted in an increase in perfusate MI concentration and a decrease in the perfusate [2-(3)H]MI specific activity. Concomitantly, urinary MI and [2-(3)H]MI concentrations were increased, again with a decrease in [2-(3)H]MI specific activity. These results indicate that PTH caused a release of MI into the urine (not the same as decreased MI reabsorption, which would not affect urinary [(3)H]MI specific activity) and into the perfusate of the isolated kidneys. These effects on MI release were about coincidental with the increase in urinary cyclic 3',5'-AMP after PTH and preceded the peak phosphaturic effect of PTH. There was no detectable effect of PTH on MI synthesis from glucose as a source of the MI released into the urine and perfusate. However, PTH temporarily halted accumulation of tritiated MI catabolites. There was no effect of inactivated PTH on urinary cyclic 3',5'-AMP or on MI transport, which indicates that the PTH effect on MI handling was a specific hormonal effect. These studies clarify the renal metabolism of MI, and they demonstrate heretofore unknown effects of PTH on the renal handling and metabolism of MI. The effects of PTH on renal MI metabolism have important implications in renal carbohydrate metabolism and phospholipid turnover.

Endogenous insulin-like growth factor (IGF) binding proteins cause IGF-1 resistance in cultured fibroblasts from a patient with short stature.

The ED50 of insulin-like growth factor (IGF)-I-stimulated alpha-aminoisobutyric acid (AIB) uptake (mean +/- SD) in cultured fibroblasts from a child with short stature that we have reported (1.40 +/- 0.24 nM), is significantly higher than the ED50 of IGF-I-stimulated AIB uptake in fibroblasts from 11 normal subjects (0.42 +/- 0.12 nM) and from 127 short children (0.35 +/- 0.11 nM). Similarly, the ED50 of IGF-I-stimulated thymidine incorporation in fibroblasts from this child is 2.8 times higher than that in fibroblasts from four normal subjects. To minimize potential modulation of IGF-I action by endogenous IGF binding proteins in these assays, fibroblast responsiveness to [Q3,A4,Y15,L16]IGF-I, an IGF-I variant that has a 600-fold reduced affinity for serum IGF binding proteins, has been examined. The biological activity of this variant is comparable in the patient's and normal fibroblasts, suggesting that the resistance to IGF-I action cannot be attributed to a defective IGF-I receptor. To investigate directly the possibility that IGF-I sensitivity in the patient's fibroblasts is reduced by endogenous IGF binding proteins (IGFBP), binding proteins that are secreted into AIB assay buffer during a 3-h collection and that are cell-associated at the end of the collection have been analyzed. Ligand blot analysis of conditioned AIB assay buffer demonstrates that fibroblasts from the patient secrete 1.3-2.2 times more of Mr 46,400/42,900, 32,000, and 26,800 binding proteins than normal fibroblasts. The major difference between fibroblasts from the patient and from normal subjects is a striking 10-fold increase in the amount of a cell surface Mr 32,000 binding protein in the patient's fibroblasts. The Mr 32,000 binding protein is similar in size to IGFB-1 and different from IGFBP-2 and IGFBP-3, but it does not cross-react with an antibody against IGFBP-1. We conclude that the resistance to IGF-I action in the patient's fibroblasts is caused by an abnormal production and/or cell association of IGF binding proteins.

Suppression of sleep-related prolactin secretion and enhancement of sleep-related growth hormone secretion.

Methysergide, a clinically-used blocker of serotonin receptors, was administered to 10 normal young men at a dose of 2 mg every 6 h for 48 h. After drug treatment, serum levels of growth hormone during sleep were 41.9% higher than placebo values (less than 0.001). In contrast, drug treatment was associated with a 36.4% decrease in stimulated growth hormone secretion during insulin tolerance testing (P less than 0.01). These opposite effects of methysergide suggest that different mechanisms are responsible for sleep-related and insulin-induced growth hormone secretion. Accordingly, data obtained with pharmacologic stimuli may lead to erroneous inferences regarding physiologic growth hormone control mechanisms. Administration of methysergide profoundly suppressed sleep-related prolactin secretion; overall nocturnal mean prolactin fell by 70.3% from 4.30+/-0.19 to 1.28+/-0.06 ng/ml (P less than 0.0001). It appears that serotonin may be significant modulating neurotransmitter for the control of growth hormone secretion, limiting sleep-related release, and enhancing insulin-induced release. It seems likely from these data that the role of serotonin in the control of prolactin secretion is relatively more important, since serotonin receptor blockade dramatically reduced sleep-related prolactin secretion.

Human prolactin and thyrotropin concentrations in the serums of normal and hypopituitary children before and after the administration of synthetic thyrotropin-releasing hormone.

Synthetic thyrotropin-releasing hormone (TRH) was administered to normal children and hypopituitary patients in a dose of 7 mug/kg i.v. over 30-60 sec. Serum thyrotropin (TSH) and prolactin (HPr) concentrations were measured by radioimmunoassay before and at 15-min intervals for 2 hr after TRH. In 20 normal children HPr rose from a mean baseline value of 7.0+/-1.2 (SEM) ng/ml to a mean peak value of 39.5+/-5 ng/ml. In 11 patients with growth hormone (GH) deficiency without TSH deficiency. HPr values rose from a mean baseline of 3.6+/-0.8 ng/ml to a mean peak value of 13.9+/-2.8, a significantly less peak response as compared with normal children (P < 0.005). The TSH responses to TRH, however, were statistically indistinguishable from those of normal children. In 10 patients with GH and TSH deficiency both the mean baseline HPr levels (25.0+/-5 ng/ml) and the mean peak HPr levels after TRH (68.5+/-10 ng/ml) were significantly higher (P < 0.005 and < 0.025) than those of normal children. Similar comparisons were also true for the peak TSH responses (P < 0.05). Two panhypopituitary patients released no TSH and only small amounts of HPr after TRH. After thyroid replacement therapy in eight of the patients with GH and TSH deficiency, the mean HPr baseline levels (7.6+/-1.0 ng/ml) and peak levels (23.3+/-4.6 ng/ml) after the same dose of TRH were significantly less than their pretreatment levels (P < 0.001 and < 0.01) and were within the range for normal children. Synthetic TRH stimulates the simultaneous release of TSH and HPr in normal children and most hypopituitary patients. When the concentrations of thyroxine (T4) and triiodothyronine (T3) are low, the levels of HPr before and after TRH are elevated. After thyroid replacement therapy, HPr levels decrease to normal. T4 and/or T3 may condition the production or effects of prolactin-inhibiting factor (PIF) activity. The TSH and HPr responses after TRH in hypopituitary patients will determine whether the primary defect resides in the pituitary or hypothalamus, but cannot delineate the hypothalamic defect as a deficiency of hypothalamic hormone production or neurohumoral transmission.

Demonstration and partial characterization of insulin receptors in human platelets.

Recently, evidence has been reported to suggest that human platelets like several other circulating blood cells may bind insulin. To examine whether human platelets contain specific insulin receptors, washed human platelets suspended in Hepes buffer were incubated at 24 degrees C with 125I-insulin in the presence and absence of unlabeled insulin and specific insulin binding was determined. Insulin binding by platelets increased progressively with time of incubation to reach a maximum at 3 h and was proportional to the number of platelets in the incubation mixture. Maximum insulin binding was observed at pH 8. Insulin degradation by platelets as assessed by TCA precipitability and reincubation studies was minimal. Scatchard analysis of the binding data and dissociation studies revealed evidence of negative cooperativity of the platelet insulin receptor. A high affinity dissociation constant of approximately equal to 3 X 10(9) M-1 was determined and the concentration of platelet insulin receptors was estimated as 25 binding sites/micron2 platelet surface area. Binding of 125I-insulin by platelets was inhibited by unlabeled porcine insulin and to a lesser extent by catfish insulin and porcine proinsulin but not by glucagon, prolactin, growth hormone, and thrombin. The findings indicate that human platelets contain specific insulin receptors. The significance of the platelet insulin receptor, particularly with respect to altered platelet function in diabetes mellitus, remains to be determined.

Current concepts of somatomedin and other biologically related growth factors.

Since the discovery 20 years ago that the growth-promoting effects of somatotropin are mediated through a serum factor(s), research in this area has rapidly expanded. It is the purpose of this review to bring this area of scientific endeavor into perspective. The first part of this review will deal with aspects of total serum somatomedin activity and its biologic actions and measurements in health and disease. The last part of this review will summarize some of the physical and biologic characteristics of the recently purified "somatomedin-like" substances: somatomedin A, B, and C, NSILA-S (nonsuppressible insulin-like activity-soluble in acid ethanol) and MSA (multiplication-stimulating activity).

Marked hyperthermia as a manifestation of hypoglycemia in long-standing diabetes mellitus.

Hyperthermia has recently been recognized as a manifestation of hypoglycemia. We describe two episodes of hypoglycemia associated with nausea, vomiting, chills, and impaired consciousness which were followed by marked hyperthermia. We suggest that the hyperthermia may result from excessive reaction to preceding hypothermia caused by the hypoglycemia. We would like to alert the clinician to the possibility of a previous, severe hypoglycemic episode in any diabetic patient with hyperthermia and coma.

The Jewish Hospital of St. Louis therapeutic grand rounds no. 9. Diagnosis and therapy of acromegaly.

Acromegaly, the clinical expression of chronic hypersecretion of growth hormone, develops insidiously and is too often not recognized until the disease is advanced. However, a useful screening procedure, the measurement of serum growth hormone after an oral glucose load, is available. Though evidence suggesting that acromegaly may be a disorder of defective hypothalamic regulation of pituitary growth hormone secretion has accumulated, the pathogenesis of the diease is not sufficiently understood to permit consistently effective medical therapy. Current therapy, therefore, is directed toward destruction of growth hormone producing pituitary tissue. Patients with major suprasellar extension and chiasmal compression usually require transfrontal surgery. Patients without major suprasellar extension can be treated with external irradiation or with transsphenoidal surgery. It is our current practice to limit the former to young patients withe relatively modest elevation of the serum growth hormone concentration.

Release of growth hormone binding protein from IM-9 lymphocytes by endopeptidase is dependent on sulfhydryl group inactivation.

The hydrophilic GH-binding protein of serum is a derivative of the GH receptor. Little is known how this GH binding protein is released from the receptor which is firmly anchored in the plasma membrane. The IM-9 lymphocytes provide a useful laboratory model for studying this process because they are richly endowed with GH receptors and, under special conditions, are able to shed these receptors during incubation. Incubation of IM-9 cells for 90 min at 30 C did not result in the appearance of significant [125I]hGH binding in conditioned medium as determined with an ultrogel AcA 44 minicolumn. When iodoacetamide, 20 mM, or N-ethylmaleimide, 5 mM, was added during incubation, the conditioned medium bound 20-35% of [125I]human(h)GH. p-Chloromercuriphenyl sulfonic acid was less effective in promoting shedding of GH-binding protein. In contrast, aprotinin, phenylmethylsulfonylfluoride (PMSF), bacitracin, leupeptin, pepstatin, phosphoramidon, or chloroquine did not promote release of GH binding protein and did not affect iodoacetamide-induced release. Release was not inhibited by the addition of serum lacking GH binding protein. GH binding protein release was markedly temperature sensitive and practically ceased at 4 C. GH binding protein incubated with [125I] hGH was cross-linked with disuccinimidyl suberate. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of dithiothreitol the complex migrated with an estimated molecular weight of 100,000 whereas [125I]hGH cross-linked to the membrane-bound GH receptor of the IM-9 cells migrated with an estimated molecular weight of 135,000. The smaller size of the binding protein is consistent with its derivation from the extracellular domain of the GH receptor. Because the release of this GH binding is greatly augmented by iodoacetamide and N-ethylmaleimide, two known sulfhydryl reactive reagents, we suggest that a free sulfhydryl group, either on the GH receptor or on a neighboring protein normally maintains the integrity of the receptor. The loss of this sulfhydryl group destabilizes the receptor and permits a membrane endopeptidase to release the GH binding protein. Cleavage is not dependent on lysosomal action and is not inhibited by protease inhibitors.

Maintenance of serum somatomedin activity in hypophysectomized pregnant rats.

Pregnant female rats were hypophysectomized on the 14th day of pregnancy without fetal loss or premature delivery. Completeness of hypophysectomy was confirmed by measurements of serum growth hormone and prolactin. Serum somatomedin activities were measured by the hypophysectomized rat costal cartilage in vitro assay using a human serum standard. In this assay somatomedin activity of normal rat serum is about four times that of normal human serum. Forty-eight hours after hypophysectomy serum somatomedin was maintained at 3.9 +/- 1.0 units/ml. At this time after operation somatomedin activity of nonpregnant hypophysectomized rat serum would be virtually undetectable. Somatomedin concentrations were still maintained on the 18th and 20th day of pregnancy. However, within 24 hours after delivery somatomedin had fallen to less than 0.6 units/ml and by three days post delivery were less than 0.2 units/ml. These observations indicate that the fetal-placental unit, probably by secreting a chorionic somatomammotropin, can maintain the concentration of growth hormone-dependent somatomedin in tha absence of the pituitary.

Insulin-like growth factors I and II in maternal and fetal guinea pig serum.

The role of insulin-like growth factors (IGFs) in fetal development has been the subject of much speculation. We undertook studies of maternal and fetal IGF I and II in the guinea pig because the long gestation period and greater size of the fetuses permitted blood sampling over a longer period of gestation and maturation than is possible in the rat. Acid gel filtrates of fetal and maternal serum were prepared, and the IGF I was measured by RIA; IGF II was measured by rat placental membrane radioreceptor assay. Fetal IGF I levels were lower than maternal levels from the 33rd day of estimated gestation to term. Fetal IGF II levels from the 33rd day to the 49th day of gestation were not significantly different from those of maternal serum [1597 +/- 377 (SE) ng/ml vs. 1295 +/- 224] ng/ml. Very high levels of IGF II, in excess of 5000 ng/ml, were observed in fetuses at 50, 55, and 60 days of gestation. Thereafter, fetal IGF II levels fell markedly before term. Fetal and maternal IGFs after 49, 50, 60, and 65 days of pregnancy were compared by isoelectric focusing. The guinea pig normally has two major basic peaks of IGF I, which were present both in maternal and fetal serum. Most maternal and fetal guinea pig sera contained only a single, slightly acidic peak of IGF II. No evidence of a unique fetal IGF was detected by our methods. The very high levels of IGF II reached in fetal guinea pig sera suggest that it may have a role in fetal development.

The effect of hypophysectomy on rat chorionic somatomammotropin as measured by prolactin and growth hormone radioreceptor assays: possible significance in maintenance of somatomedin generation.

We have previously reported that serum somatomedin concentrations are maintained in pregnant rats after hypophysectomy. Because rat chorionic somatomammotropin (rCS) might replace pituitary GH during pregnancy, the concentration of rCS was measured at intervals after hypophysectomy on day of pregnancy. By day 16 of pregnancy, the serum rCS of hypophysectomized (hypox) rats was actually higher than that of normal pregnant rats when measured by a lactogenic radioreceptor assay. Increased levels of lactogenic radioreceptor activity (L-RRA) were maintained in the serum of hypox rats throughout the remainder of pregnancy. The GH radioreceptor activity (GH-RRA) of serum of hypox pregnant rats was also greater than that of normal rats during the last days of pregnancy, but the activity was only about 1/20th that of the L-RRA with the assays employed. There was no significant difference between placental L-RRA and GH-RRA of normal and hypox pregnant rats. The difference in concentration could not be attributed to differences in the number of fetuses. We conclude that the high levels of rCS were sufficient to maintain serum somatomedin concentration in hypox pregnant rats. This effect of rCS could have been due to binding by GH or PRL receptors of the maternal liver.

Release of insulin-like growth factors and binding protein activity into serum-free medium of cultured human fibroblasts.

We have studied insulin-like growth factors (IGFs) and IGF-binding proteins released by human fibroblasts. Conditioned medium was obtained after incubation of 2 X 10(6) cells in 2 ml serum-free medium for 72 h. IGF binding protein was identified in aliquots of conditioned medium at 4 C for 16 h with [125]IGF II after charcoal separation. After gel filtration in neutral phosphate buffer through Sephadex G-150, the binding activity eluted with an apparent size greater than 100,000 daltons. After gel filtration through Bio-Rad P-100 in 1 M acetic acid, binding activity had a molecular size of about 50,000 daltons. When [125I]IGF-II bound to conditioned medium binding protein was cross-linked with disuccimidyl suberate and subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis, the complex had an estimated molecular size of 67,000 daltons. Competitive binding studies with labeled and unlabeled IGF-I and IGF-II showed that IGF-II was preferentially bound by fibroblast binding protein. The above findings are characteristic of serum binding protein but not shed IGF surface receptors. To eliminate possible interference from binding proteins in the IGF-I RIA and the IGF-II radioreceptor assay, conditioned medium was subjected to acid gel filtration, and the peptide fractions were pooled. We found that conditioned medium of seven fibroblast lines contained 0.20 +/- 0.06 ng/ml IGF-I. After the addition of 20 ng/ml human GH (hGH), the conditioned medium contained 0.48 +/- 0.09 ng/ml. These results are lower than those previously reported. One of the two lines of fibroblasts from patients apparently resistant to GH had a minimal increase in IGF-I in conditioned medium after hGH addition. We were able to detect IGF-II in fibroblast conditioned medium in concentrations of 4.4 to 21 ng/ml but there was no consistent response to GH either in the normal fibroblast lines or in fibroblasts obtained from children with short stature.

Stimulation of supranormal growth in prepubertal, adult plateaued, and hypophysectomized female rats by large doses of rat growth hormone: physiological effects and adverse consequences.

A supranormal rate of growth in intact, prepubertal, 26-day-old female rats was evoked by administration of large doses of highly purified rat GH (rGH). In response to daily doses of 1 and 5 mg/rat (13.6 mg/kg BW and 68 mg/kg BW), sc, for 20 days, body weight (BW) gain increased 51% and 73%, and skeletal growth increased 27% and 40%, respectively. Serum rGH in treated rats rose as much as 69-fold greater than that of controls. Feed efficiency, the ratio of weight gained to feed consumed, increased from 19.8% to 32.0%. This rGH treatment depleted pituitary GH content as much as 58% and caused hepatomegaly. These effects, as well as the accelerated growth rate, reverted to normal after cessation of rGH treatment. Onset of puberty in rGH-treated rats was delayed an average of 2.7 days. A similar stimulatory effect on BW gain, but not skeletal growth, as well as depletion of pituitary GH content, and hepatomegaly, was elicited by rGH treatment in adult, plateaued female rats. These effects in plateaued rats reverted to normal after cessation of GH treatment, and 50% of the body weight gain was rapidly lost. The largest dose of rGH used, 5 mg/day, was apparently toxic, resulting in a 20% higher mortality rate in treated prepubertal and plateaued female rats. Antibody formation was not the cause of the toxicity, since antibodies against rGH were undetectable at the lowest dilutions of serum tested. Serum rat insulin-like growth factor I (RIA), 3.5 U/ml in untreated intact prepubertal rats, increased to 4.7 and 5.0 U/ml, respectively, after 20 days of rGH treatment. In hypophysectomized rats, serum rat insulin-like growth factor I (RIA), undetectable in controls, was increased to 1.63 U/ml after 14 days treatment with 1 mg rGH/day. This study demonstrates that greater than normal growth can be stimulated in normal female rats by administration of large doses of homologous GH, but at the risk of serious adverse effects. Possible implications for the administration of GH to non-GH-deficient children, to promote taller stature, are clear.

Retinoic acid regulates insulin-like growth factor II expression in a neuroblastoma cell line.

Insulin-like growth factors (IGF-I and IGF-II) are mitogenic polypeptides that play an important role in normal growth and development. IGF-II has been shown to stimulate the growth of neuroblastoma tumors in an autocrine and paracrine fashion. Critical in determining the role of IGF-II in tumorigenesis is the necessity to delineate factors affecting the transcription of IGF-II in normal and tumor tissues. To date such factors are poorly characterized. In this study we find that retinoic acid (RA), a naturally occurring morphogen, that has been shown to be indispensable in the development of the chick limb bud, stimulates an increase in IGF-II messenger RNA (mRNA) in the Lan-1-15N neuroblastoma cell line. This increase in IGF-II is coincident with RA mediated inhibition of DNA synthesis. An increase in the steady state levels of IGF-II mRNA is detectable within 2 h of RA treatment and maximal by 24 h. In RA-treated Lan-1-15N cells, IGF-II mRNA levels are regulated at the level of new gene transcription and result in an increase in IGF-II protein in the culture supernatant. These studies suggest one mechanism affecting the production of IGF-II in vivo may be mediated by RA and detail a model system by which transcriptional regulation of IGF-II mRNA can be analyzed.