Neuroprotective effects of melanocortins in CNS injury.

New compounds having affinity to various melanocortin receptors have recently been identified as possible neuroprotective agents. This review is focused on the role of neuroprotective effects of melanocortins in CNS injury and repair mechanisms. Using selective non-peptidic compounds with varying affinity to melanocortin receptors, our laboratory has shown their anti-edematous effects in the spinal cord injury. This effect of the compounds is related with their ability to attenuate blood-spinal cord barrier permeability. The functional significance and possible therapeutic strategies of these compounds in CNS injury are discussed.

Neuroprotective effects of melanocortins in experimental spinal cord injury. An experimental study in the rat using topical application of compounds with varying affinity to melanocortin receptors.

The possibility that local administration of low molecular weight non-peptide compounds with varying affinities at melanocortin receptors in the spinal cord will influence pathophysiological outcome of spinal cord injury (SCI) was examined in a rat model. Five new Melacure compounds ME10092, ME10354, ME10393, ME10431 and ME10501 were used in this investigation. Each compound was dissolved in saline and tested at 3 different doses, i.e. 1 microg, 5 microg and 10 microg total dose in 10 microl applied topically 5 min after SCI. The animals were allowed to survive 5 h and trauma induced edema formation, breakdown of the blood-spinal cord barrier (BSCB) and cell injuries were examined and compared with untreated injured rats. A focal SCI inflicted by an incision into the right dorsal horn of the T10-11 segments resulted in marked edema formation, breakdown of the BSCB to Evans blue albumin and caused profound nerve cell injury in the T9 and the T12 segments. Topical application of ME10501 (a compound with high affinity at melanocortin, MC-4 receptors) in high doses (10 microg) resulted in most marked neuroprotection in the perifocal spinal cord (T9 and T12) segments. On the other hand, only a mild or no effect on spinal cord pathology was observed in the traumatized animals that received ME10092, ME10354, ME10393 and ME10431 at 3 different doses. These observations suggest that non-peptide compounds with varying affinity to melanocortin receptors are able to influence the pathophysiology of SCI. Furthermore, compounds acting at melanocortin, MCR4 receptors are capable to induce neuroprotection in spinal cord following trauma.

Anti-inflammatory potential of melanocortin receptor-directed drugs.

Melanocortin receptor-based drug discovery is particularly active in the field of neuroendocrine systems and is mostly related to food intake and novel obesity therapies. The immunomodulatory and anti-inflammatory effects of nonpeptidic, low molecular weight compounds activating the melanocortin-1 receptor (MC1R) provide a new principle for treating various types of inflammation, such as dermal, joint, and gastrointestinal, probably by virtue of the effects acting through modulation of proinflammatory and anti-inflammatory cytokines. Several reports demonstrate that alpha-MSH, for example, has anti-inflammatory effects in different models. The aim of our study was to design, synthesize, and characterize compounds that bind to and activate the MC1R in vitro. The binding affinities are submicromolar to this receptor, and activation of the receptor (cAMP assay) varies from full agonists to partial agonists as well as antagonists. In vivo, the compounds exert prominent anti-inflammatory effects, with efficacy in the same range as that of dexamethasone, for example. The potential advantages of MC1R-based anti-inflammatory effects versus glucocorticosteroids, for example, are that the latter, albeit exerting prominent anti-inflammatory effects, also have many side effects that most likely will not characterize an MC1R-based anti-inflammatory drug.

Low molecular weight compounds with affinity to melanocortin receptors exert neuroprotection in spinal cord injury--an experimental study in the rat.

The possibility that five new low molecular weight compounds with varying affinity and selectivity to the melanocortin receptors will exert neuroprotective effects in the spinal cord injury (SCI) induced edema formation and cell damage was examined in a rat model. A focal trauma of the rat spinal cord made by an incision into the right dorsal horn (T10-11) resulted in profound edema formation, leakage of Evans blue albumin and cell injury of the T9 segment at 5 h. Topical application of the Melacure compound ME10501 in high doses (10 microg in 10 microl) given 5 min after SCI resulted in most significant neuroprotection of the T9 segment of the cord compared to other compounds. Thus, marked reduction in water content, leakage of Evans blue albumin, and cell injury were observed in ME10501 treated traumatised rats. These observations suggest that the non-peptide compound ME10501 with affinity to the melanocortin receptor MC4 is capable to induce neuroprotection in the spinal cord following trauma not reported earlier.

New aspects on the melanocortins and their receptors.

Knowledge of melanocortins and their receptors has increased tremendously over the last few years. The cloning of five melanocortin receptors, and the discovery of two endogenous antagonists for these receptors, agouti and agouti-related peptide, have sparked intense interest in the field. Here we give a comprehensive review of the pharmacology, physiology and molecular biology of the melanocortins and their receptors. In particular, we review the roles of the melanocortins in the immune system, behaviour, feeding, the cardiovascular system and melanoma. Moreover, evidence is discussed suggesting that while many of the actions of the melanocortins are mediated via melanocortin receptors, some appear to be mediated via mechanisms distinct from melanocortin receptors.

Insulin-like growth factor-I, but not growth hormone, is dependent on a high protein intake to increase nitrogen balance in the rat.

The aim of the present study was to investigate the influence of dietary protein level on the protein anabolic effects of growth hormone (GH) and insulin-like growth factor-I (IGF-I). Female growing rats were fed on either a high- or a low-protein diet with crude protein contents of 222 and 83 g/kg respectively. The diets contained the same amount of metabolizable energy (15.1 MJ/kg) and were given during a 14 d period. During the same time, three groups of rats (n 8) on each diet received subcutaneous infusions of either saline, recombinant human GH (rhGH) or recombinant human IGF-I (rhIGF-I). rhGH and rhIGF-I were given in doses of 360 and 500 micrograms/d respectively. The low-protein diet alone reduced significantly (P < 0.05) IGF-I concentrations in serum and in tissue taken from the gastrocnemius muscle as well as IGF-I mRNA from the same muscle. The responses to rhGH and rhIGF-I in terms of muscle IGF-I and its mRNA were variable. However, when rhIGF-I was infused into rats on the high-protein diet, significantly elevated levels of IGF-I in muscle tissues could be observed. This was associated with a significantly (P < 0.05) increased N balance, whereas rhGH significantly (P < 0.05) enhanced the N balance in rats on the low-protein diet. Thus, it can be concluded that the level of dietary protein ingested regulates not only the effect of IGF-I on whole-body N economy but also the regulation of IGF-I gene expression in muscles. The exact mechanism by which GH exerts its protein anabolic effect, however, remains to be elucidated.

Effects of human growth hormone on the porto-arterial concentration differences of glucose and amino acids in the newborn piglet.

It is known that growth hormone (GH) increases the mitotic index of duodenal crypt cells. In early life, such an effect could be of particular importance for the functional development of the intestine in terms of absorptive capacity. In this study, osmotic mini pumps were introduced into the abdominal cavity of newborn piglets. The pumps permitted a continuous infusion of either recombinant human growth hormone (rhGH) at a rate of 0.1 IU GH x kg(-1) x 24 h(-1) or of vehicle. After 7 days of treatment, a bolus of amino acids and glucose was infused into the duodenum. Following this bolus, there was a prompt rise in the plasma concentration of both amino acids and glucose, especially in blood withdrawn from the portal vein. Thus, when the differences in concentrations of both amino acids and glucose between portal and arterial blood plasma were calculated, these differences reached maximum values between 30 and 60 minutes after the bolus. In animals treated with GH, maximum values occurred at a lower level than in control animals. These reductions were in the order of 60% (P > 0.01) if calculated over the first hour of absorption. From this study, it might be concluded that GH does not improve the absorptive capacity of the small intestine in newborn piglets. Instead, GH seems to reduce the absorption dynamics of glucose and amino acids. The reason for this is obscure, but could imply a specific effect of GH on enterocyte function.

Exogenous insulin-like growth factor-I increases weight gain in intrauterine growth-retarded neonatal pigs.

Many cases of intrauterine growth retardation (IUGR) are the result of placental insufficiency, suggesting that potential therapies should focus on the neonate rather than the pregnant female. We wished to determine whether IGF-I could be used therapeutically to stimulate normal rates of growth in these neonates. Eight sows received 2.3 kg/d of either a control (13% protein) or protein-restricted (0.5% protein) diet from d 63 of pregnancy to parturition. Litters were reduced to 6 pigs at 3 d of age, and IUGR neonates were fostered onto a control sow. Three pigs/ litter received an osmotic minipump containing either saline or recombinant human IGF-I, delivered at 4 microg/h from d 3 to d 10 of age. Tissue protein synthesis was measured in all pigs using a flooding dose of [3H]phenylalanine. At birth, both body weight (10%) and circulating IGF-I concentration (30%) were significantly lower in IUGR than in control newborns. The infusion of IGF-I to IUGR neonates significantly increased the circulating concentration of IGF-I, growth rate, and protein and fat accretion to control levels. The infusion of IGF-I did not alter concentrations of insulin, glucose, IGF-II, or the thyroid hormones. Our results suggest that IGF-I may be a potential therapy to restore normal growth in IUGR infants.

Effects of constant infusion with insulin-like growth factor-I (IGF-I) to immature female rats on body weight gain, tissue growth and sexual function. Evidence that such treatment does not affect sexual maturation of fertility.

Plasma levels for insulin-like growth factor-I (IGF-I) steadily increase in female rats between 20 and 40 d of life, and this increase is intimately related to the wellknown growth spurt occurring at this age. Since specific actions of IGF-I related to sexual function have been described at the ovarian and hypothalamic levels, an endocrine role of rising circulating IGF-I levels during sexual maturation cannot be excluded. Therefore, the impact of adult-type plasma IGF-I levels during the juvenile age, on body weight (BW) gain, growth of several organs, sexual development, and fertility has been evaluated. Female Sprague-Dawley rats were infused with rhIGF-I (2 and 4 micrograms/g BW/d, using Alzet minipumps), between 20 and 41 d of life. When infusing 2 micrograms/g BW/d, plasma levels for IGF-I were increased 1.5- to 2-fold over controls at all ages studied. They were further increased with the higher dosage, but only after 35 d of age. Plasma levels for insulin-like growth factor binding protein (IGFBP)-1 to -3 were clearly increased. BW gain was significantly increased, but only with the higher dosage. Tail length was never modified. In contrast, a growth acceleration for spleen, kidneys, adrenals, and ovaries was observed with both dosages. The ovarian weight of treated animals represented approx 140% of control animals with the 4 micrograms/g BW/d dosage. Histology of the enlarged ovaries did not reveal any abnormalities. No meaningful modification of the timing of vaginal opening was observed, and fertility was not comprised by previous rhIGF-I infusion during 20-41 d age period. In summary, early exposure to increased (adult-like) plasma IGF-I levels did not modify BW gain or tail length, but affected the development of spleen, kidneys, adrenals, and ovaries. Exposure to supraphysiological plasma IGF-I levels (> 1200 ng/mL), accelerated BW gain and increased the weight of all organs studied. No signs of precocious sexual maturation were seen and fertility was normal. In conclusion, prematurely increased plasma IGF-I levels affected somatotropic parameters, but not the onset of sexual function.

The role of insulin, insulin-like growth factor-I and growth hormone in counteracting dexamethasone induced nitrogen wasting in rats.

Administration of glucocorticoids is associated with decreased nitrogen balance. The main aim of the present study was to elucidate whether this could be counteracted by subcutaneous infusions of rhGH (360 micrograms/d), rhIGF-1 (500 micrograms/d) or insulin (39 micrograms/d). During a study period of 8 days one out of 10 groups of rats received dexamethasone (dex, 26 micrograms/d) alone, whereas 7 groups were given one or more of the three peptides in combination with dex. One group was given saline alone and one was food restricted to match the average food intake among dex groups. Food restriction and saline alone produced relative nitrogen balances, retained N/ingested N (x100) of 44 (SE 3) and 36% (SE 4), respectively. This was decreased (p < 0.001) to 7% (SE 3) with dex alone. However, if either insulin/rhGH/rhIGF-1, rhIGF-1 alone or insulin/rhIGF-1 were given together with dex, the relative nitrogen balances increased significantly (p < 0.03) up to 16, 22 and 24% (SE 3), respectively. Insulin or rhGH alone were without effect as was rhGH combined with either rhIGF-I or insulin. Although the relative nitrogen balances associated with insulin/rhIGF-1 and rhIGF-1 alone were not found to be significantly different, the former infusion regimen produced a significantly (p < 0.02) lower plasma urea. It is concluded that in the rat, rhIGF-1 has a potential to counteract the decrease in nitrogen balance induced by potent glucocorticoids, whereas rhGH as administered in this experiment does not have this effect.

A quantitative in-vivo MR imaging study of brain dehydration in diabetic rats and rats treated with peptide hormones.

The main aim of the study was to evaluate the combination of quantitative diffusion, T2 and Magnetisation Transfer Imaging of brain water homeostasis using untreated diabetes as an animal model of brain dehydration. In addition, experimental groups of diabetic rats treated with insulin and insulin-like growth factor (IGF-I) and normal rats treated with IGF-I and growth hormone were studied using the same MR imaging protocol. Untreated diabetes caused weight reduction and an increase in water intake, indicating a general body dehydration linked to chronic blood hyperosmolarity. In the investigated cortical gray matter untreated diabetes caused a significant reduction in the apparent diffusion coefficient of water (ADC) and an increase in T2 relaxtivity (R2) when compared to a control group. No significant changes were observed for the calculated magnetisation transfer parameters Kfor and T1sat. Both ADC and R2 normalized after appropriate insulin treatment whereas only ADC was normalized after IGF-I treatment. IGF-I treatment of normal rats caused significantly higher rate of increase in body weight compared to normal controls. There were, however, no significant changes in ADC, R2 nor the magnetisation transfer parameters measured in the cortical gray matter of the IGF-I treated normal rats. In conclusion, we found that changes in brain water homeostasis during diabetes were detected by quantitative MR imaging, and that the dehydration induced by diabetes was normalized by insulin treatment but not by IGF-I.

Reliability of the western ligand blot method for the simultaneous relative estimations of serum insulin-like growth factor binding proteins (IGFBPs).

It is well established that nutrition is an important regulator of both serum insulin-like growth factor-I (IGF-1) and its binding proteins (IGFBPs). The Western ligand blot method (WLB) for simultaneous determinations of IGFBPs in serum or plasma samples was evaluated and validated with emphasis on its reproducible capabilities. After electrophoretic separation and transfer, the membranes were incubated with a mixture of recombinant labeled human (GF-I/IGF-II(rhIGF-I/rhlGF-II) and band intensities measured by autoradiography. The typical electrophoretic profile for pig serum, as determined with molecular weight markers, showed four mainbands of approximately 42-39, 32, 30-28 and 24 kDa which seemed to correspond to IGFBP-3, IGFBP-2, IGFBP-1 and IGFBP-4 respectively. Likewise, a triplet of approximately 42-39 kDa (IGFBP-3), a broad area called IGFBP-30 region (most probably IGFBP-1, -2 and -3 variants) and a third band of approximately 24 kDa (IGFBP-4) were seen in rat samples. Determination of IGFBP-2 and -1 in rat serum samples, as two separate bands on 12% gels was difficult due to their close electrophoretic migration and possibly to the reported lower levels of IGFBP-2 in adult rat serum. Dilutions tested on 0.2 micron nitrocellulose membranes with samples volumes between 0.25 to 1.5 microliters (1:10-1:60 dilutions), showed IGFBPs curves with good linearity which suggest first, that there exist a quantitative relation between the amount of each protein and the densitometric response and second, that the transfer of the proteins was linear across the range of 0.25 to 1.5 microliters (1:10-1:60 dilutions). Moreover, the results also suggest that losses were equally spread and that the proteins retained their binding properties after the transfer process. Reproducibility showed intraassay coefficients of variation (CVs) of 15% or lower using either a transfer device without cooling system or a combination of a transfer device with cooling system and manually defined band boundaries. In summary, it was shown that the optimized experimental conditions here described for the WLB method, allow reliable simultaneous measurements of the main pig and rat serum IGFBPs and therefore, could be utilised to detect changes in the serum profile after dietary manipulations.

Effects of recombinant human growth hormone and insulin-like growth factor-I, with or without 17 beta-estradiol, on bone and mineral homeostasis of aged ovariectomized rats.

This study aimed to evaluate whether recombinant human growth hormone (rhGH) or insulin-like growth factor-I (rhIGF-I) can reverse or prevent further bone loss in aged osteopenic ovariectomized (OVX) rats and to compare their effects with those of 17 beta-estradiol (E2). Twelve-month-old rats were OVX, remained untreated for 8 weeks, and subsequently received daily subcutaneous (SC) injections of rhGH (75 micrograms/day), rhIGF-I (250 micrograms/day), E2 (1.5 micrograms/day), and their respective combinations during 8 weeks, and were then compared with sham-operated, pretreatment OVX, and saline-treated OVX rats. A single sc injection of rhGH resulted in peak hGH concentrations after 90 minutes, with a half-life of 124 minutes; the highest plasma IGF-I concentrations were reached 45 minutes after rhIGF-I injection (+57% vs. baseline) with a gradual decline thereafter. Measurements included: biochemical parameters of bone remodeling (plasma osteocalcin and urinary pyridinolines); histomorphometry of proximal tibial metaphysis; DXA of femur; biomechanical analysis of femur and fifth lumbar vertebra (L5); plasma 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), and calbindin-D9K in duodenal mucosa. Whereas all E2-treated OVX rats had much suppressed bone remodeling, rhGH or rhIGF-I had no effect on any biochemical or histomorphometrical parameter of remodeling. The bone mineral density (BMD) at the distal femoral metaphysis as well as parameters of strength at L5 were maintained at pretreatment values in OVX rats treated with E2, GH, or IGF-I, but not in saline-treated OVX rats; their effects were not additive, however. Trabecular bone volume in the tibial metaphysis was also higher in rats treated with these agents than in saline-treated rats, but this was more apparent at the primary than at the secondary spongiosa, suggesting that their mechanism of action is on primary spongiosa formation or breakdown. E2 alone was ineffective to augment the BMD at the femoral diaphysis; however, the diaphyseal BMD was 12-14% higher (p < 0.01) after 8 weeks of GH treatment than in pretreatment or saline-treated OVX rats and sham-operated rats, while IGF-I was less effective than GH, GH or IGF-I treatment had no effect on plasma 1,25(OH)2D3 or duodenal calbindin-D9K concentrations, but the combination of GH or IGF-I with E2 potentiated the effect of E2 to stimulate calbindin-D9K concentrations and urinary calcium excretion, indicating "hyperabsorption hypercalciuria." In conclusion, the administration of rhGH and rhIGF-I, like that of E2, into aged OVX rats prevents further loss of bone mass and strength at sites containing trabecular bone. In addition, rhGH increases cortical bone mass above pretreatment values.

Effects of insulin-like growth factor I (IGF-I) on the porto-arterial concentration differences of amino acids and glucose: a comparison between oral and intraperitoneal administration in the newborn piglet.

It is established that insulin-like growth factor I (IGF-I) influences cell differentiation and proliferation. Less is known, however, if such changes also influence the flow of nutrients from the intestinal lumen to the portal circulation. In the present study, we tested if IGF-I treatment (0.3 mg IGF-I/24 hr and kg) during 7 days affects the porto-arterial concentration differences of amino acids and glucose in piglets. Two routes of administration, oral and intraperitoneal, were compared. Following the IGF-I treatment, a bolus of nutrients was administered to the proximal duodenum and the porto-arterial concentration differences of amino acids and glucose were determined. We found that intraperitoneal administration of IGF-I significantly increased the difference in concentration between portal and arterial plasma for amino acids, whereas no such effect was seen with glucose. This might suggest that IGF-I has a specific effect on amino acid transporters in the intestinal wall. The same dose of IGF-I given orally did not exhibit the same effect on the absorption of amino acid as the animals which were given the peptide intraperitoneally.

New aspects of lactate metabolism: IGF-I and insulin regulate mitochondrial function in cultured brain cells during normoxia and hypoxia.

Using 13C nuclear magnetic resonance spectroscopy in combination with conventional biochemical techniques, effects of insulin and IGF-I on energy metabolism and cell viability were studied in cerebral cortical neurons, astrocytes and cocultures thereof during normoxia and hypoxia. Lactate dehydrogenase leakage was used to monitor the cytoprotective effects of IGF-I and insulin. Thus, during normoxia both peptides decreased LDH leakage from neurons. During hypoxia, however, this protection was only observed when insulin was present. Interestingly, neurons showed much less LDH leakage during hypoxia than astrocytes or cocultures. A possible explanation could be an increased glycolysis in neurons. Thus, lactate production and glucose consumption were increased severalfold in neurons during hypoxia whereas astrocytes and cocultures only showed a slight increase. Both insulin and IGF-I increased glucose metabolism during normoxia in astrocytes but not in neurons, whereas during hypoxia this increase was less pronounced. Using [1-13C]glucose it could be demonstrated that production of lactate from mitochondrial precursors was, in the presence of insulin or IGF-I, down regulated in astrocytes but increased in neurons during normoxia. This route for lactate production was not used during hypoxia and incorporation into the C-3 position of lactate approached the theoretical maximum of 50%.

A comparison of the effects of insulin-like growth factor-I, insulin and combined infusions of insulin and insulin-like growth factor-I on glucose metabolism in dogs.

The effect of infusions of recombinant insulin-like growth factor-I (IGF-I) (34, 103 or 688 pmol kg-1 min-1), insulin (3.4, 10.3 or 68.8 pmol kg-1 min-1) or combined infusions (34 pmol IGF-I + 3.4 pmol kg-1 min-1 insulin or 103 pmol IGF-I + 3.4 pmol kg-1 min-1 insulin) on glucose metabolism was investigated in dogs using a [3-3H]-glucose infusion and euglycaemic clamp. All insulin doses decreased glucose production rate (Ra) in a dose-dependent manner (P < 0.05). All IGF-I doses decreased glucose Ra (P < 0.05) but this decrease was not dose dependent. The decrease in glucose Ra with the combined infusion of 34 pmol kg-1 min-1 IGF-I + 3.4 pmol kg-1 min-1 insulin was greater than 34 pmol kg-1 min-1 IGF-I (P < 0.05) but not different from 3-4 pmol kg-1 min-1 insulin. All insulin and IGF-I doses increased glucose utilization rate (Rd) in a dose-dependent manner (P < 0.01). The increase in glucose utilization was greater following both combined infusions than with either component infused alone (P < 0.05). Although at the doses selected, insulin and IGF-I had similar effects on glucose utilization with additive effects when the two peptides were combined, IGF-I was less effective than insulin in suppressing glucose production.

Insulin-like growth factor I does not inhibit insulin secretion in adult human pancreatic islets in tissue culture.

Insulin-like growth factor I (IGF-I) has been found to increase insulin sensitivity and suppress insulin secretion, thereby having a potential interest as a therapeutic agent for non-insulin-dependent diabetes mellitus (NIDDM). The aim of the present study was to investigate the direct actions of IGF-I (400 ng/ml) on human pancreatic islets, or on rat pancreatic islets, during a 48 h period in tissue culture. Insulin-like growth factor I did not affect medium insulin accumulation, DNA or insulin content or short-term glucose-induced insulin release of human islets. However, in rat islets the peptide induced a significant decrease in the insulin increase ratio in response to 16.7 mmol/l glucose. In conclusion, the present data suggest that IGF-I does not directly affect the function of human pancreatic beta-cells. If this in vitro data can be extrapolated to the in vivo situation, it suggests that the observed inhibitory effects of IGF-I on serum insulin levels may be secondary to peripheral effects of the peptide.

13C NMR study of IGF-I- and insulin-effects on mitochondrial function in cultured brain cells.

Development of differential cell culture systems has facilitated the study of cellular and physiological actions of growth factors. Here we report the novel effects of insulin and insulin-like growth factor (IGF)-I on energy metabolism in cerebral cortical neurones, astrocytes and co-cultures thereof. Incorporation of label from [1-13C]glucose into lactate has been shown to involve both glycolysis and the tricarboxylic acid cycle in astrocytes. Thus 13C nuclear magnetic resonance spectroscopy was used to monitor mitochondrial function by measuring 13C labelling of the C-2 position of lactate. It could be demonstrated that insulin and IGF-I have similar effects on mitochondria but individual effects on cytosolic glucose metabolism. Evidence is presented that IGF-I and insulin stimulate neurones to release factors affecting astrocytic lactate production. Furthermore, lactate released from neuronal-astrocytic co-cultures was mostly of astrocytic origin, implicating the importance of lactate for neuronal metabolism.

Effects of insulin-like growth factor-I and growth hormone on the net flux of amino acids across the hind limbs in the surgically traumatized pig.

1. After surgery three groups of six female pigs weighing on average 52.2 kg (SD 3.5) received vehicle, recombinant insulin-like factor-1 (364.4 micrograms day-1 kg-1) or recombinant human growth hormone (467.7 m-i.u. day-1 kg-1) for two post-operative days. Vehicle and peptides were infused intravenously together with total parenteral nutrition providing 129 kJ day-1 kg-1 non-protein calories and 0.35 g N day-1 kg-1. 2. On both post-operative days the mean concentration of insulin-like growth factor-1 in arterial blood samples was clearly below presurgical levels in animals receiving vehicle or recombinant human growth hormone, whereas recombinant human insulin-like growth factor-1 infusions more than restored insulin-like growth factor-1 concentrations. These last samples, however, contained significantly (P < 0.05) less insulin than those from other animals. 3. Infusion of recombinant human growth factor was often associated with higher circulating levels of amino acids compared with recombinant human insulin-like growth factor-1 infusions. Despite this, both hormones significantly (P < 0.05) increased the hind limb net balance of total amino acids on post-operative day 1. Net balances of -44.2, +69.5 and +100.9 mumol/min (pooled SE 35.3) were associated with infusion of vehicle, recombinant human insulin-like growth factor-1 and recombinant human growth hormone respectively. This response was also closely reflected in the group of non-essential amino acids. 4. The net efflux of alanine from the hind limbs was also significantly (P < 0.002) reduced, whereas glutamine was less affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Human growth hormone does not cross the placenta of the pregnant rat.

The purpose of this study was to investigate if human growth hormone (hGH) crosses the placenta to the fetus of the pregnant rat. Pregnant rats were injected i.v. with 125I-hGH alone or co-injected with unlabelled hormone on gestational day 20 or 21. The rats were sacrificed 10 min after injection, and the distribution of the radioactivity was determined by direct measurement in brain, thymus, liver, kidney, rectus femoris muscle, placenta and fetus. Free iodine was determined in samples from maternal liver, placental and fetal tissue homogenates after precipitation of proteins by trichloroacetic acid. Two animals were injected with a higher dose of radioactivity. One of them was co-injected with a high dose of unlabelled hormone. They were sacrificed after 10 min, frozen, and sections of 20 microns were cut sagittally for autoradiography. A small amount of radioactivity was detected in the fetal tissue. However, this activity was shown to be free iodine, and no inhibition of that uptake was found by unlabelled hGH. No radioactivity was detected in the fetuses of either rat exposed to autoradiography. Therefore, we conclude that there is no transfer of hGH from the mother to the fetus of the pregnant rat. Our result is in agreement with some early observations in humans and rabbits but disagrees to some extent with recent results found in rats, where a small passage of 125I-hGH from mother to fetus was reported.