Increased circulating concentrations of bioactive PTH 1-84 in patients with heart failure.

BACKGROUND: PTH is related to left ventricular hypertrophy and its circulating levels are associated with worse prognosis in patients with heart failure (HF). The objectives of our study were to measure the circulating levels of bioactive PTH 1-84 through third-generation assay in HF patients, to determine their association with the disease severity as well as their relation with recognized biomarkers of HF worsening and prognosis. METHODS: PTH 1-84 concentrations were determined in 76 HF patients and in 49 healthy volunteers. Circulating levels of amino-terminal proatrial natriuretic peptide (Nt-proANP), B-type natriuretic peptide (BNP), Nt-proBNP, proBNP, and big endothelin-1 (Big ET-1) were also measured. RESULTS: HF patients had in- creased PTH 1-84 levels in comparison to controls. A significant increase of the PTH 1-84 circulating concentrations was observed according to the New York Heart Association functional classes. PTH 1-84 circulating concentrations were also significantly correlated with Nt-proANP, BNP, Nt-proBNP, proBNP, and Big ET-1. CONCLUSIONS: PTH 1-84 circulating levels are significantly increased in HF patients in comparison to healthy individuals. Our study has also demonstrated that circulating concentrations of bioactive PTH are related to HF severity and well-established biomarkers of the worsening of the disease.

Role of Akt/GSK-3beta/beta-catenin transduction pathway in the muscle anti-atrophy action of insulin-like growth factor-I in glucocorticoid-treated rats.

Decrease of muscle IGF-I plays a critical role in muscle atrophy caused by glucocorticoids (GCs) because IGF-I gene electrotransfer prevents muscle atrophy caused by GCs. The goal of the present study was to identify the intracellular mediators responsible for the IGF-I anti-atrophic action in GC-induced muscle atrophy. We first assessed the IGF-I transduction pathway alterations caused by GC administration and their reversibility by local IGF-I overexpression performed by electrotransfer. Muscle atrophy induced by dexamethasone (dexa) administration occurred with a decrease in Akt (-53%; P<0.01) phosphorylation together with a decrease in beta-catenin protein levels (-40%; P<0.001). Prevention of atrophy by IGF-I was associated with restoration of Akt phosphorylation and beta-catenin levels. We then investigated whether muscle overexpression of these intracellular mediators could mimic the IGF-I anti-atrophic effects. Overexpression of a constitutively active form of Akt induced a marked fiber hypertrophy in dexa-treated animals (+175% of cross-sectional area; P<0.001) and prevented dexa-induced atrophy. This hypertrophy was associated with an increase in phosphorylated GSK-3beta (+17%; P<0.05) and in beta-catenin content (+35%; P<0.05). Furthermore, overexpression of a dominant-negative GSK-3beta or a stable form of beta-catenin increased fiber cross-sectional area by, respectively, 23% (P<0.001) and 29% (P<0.001) in dexa-treated rats, preventing completely the atrophic effect of GC. In conclusion, this work indicates that Akt, GSK-3beta, and beta-catenin probably contribute together to the IGF-I anti-atrophic effect in GC-induced muscle atrophy.

Nutritional regulation of the insulin-like growth factors.

Nutrition is one of the main regulators of circulating IGF-I. In humans, serum IGF-I concentrations are markedly lowered by energy and/or protein deprivation. Both energy and proteins are critical in the regulation of serum IGF-I concentrations. Indeed, after fasting, optimal intake of both energy and protein is necessary for the rapid restoration of circulating IGF-I. We believe, however, that in adult humans energy may be somewhat more important than protein in this regard. While the lowest protein intake is able to increase IGF-I in the presence of adequate energy, there is a threshold energy requirement below which optimal protein intake fails to raise IGF-I after fasting. When energy intake is severely reduced, the carbohydrate content of the diet is a major determinant of responsiveness of IGF-I to GH. The essential amino acid content of the diet is also critical for the optimal restoration of IGF-I after fasting, when protein intake is reduced. The exquisite sensitivity of circulating IGF-I to nutrients, the nycthemeral stability of its concentrations and its relative short half-life constitute the basis for its use as a marker of both nutritional status and adequacy of nutritional rehabilitation. For these indications, IGF-I measurement is more sensitive and more specific than measurement of the other nutrient-related serum proteins (albumin, prealbumin, transferrin, retinol-binding protein). Animal models have been developed to investigate the mechanisms responsible for the nutritional regulation of IGF-I. There is no doubt that many mechanisms are involved (Fig. 12). Decline of serum IGF-I in dietary restriction is independent of the diet-induced alterations in pituitary GH secretion. The role of the liver GH receptors is dependent on the severity of the nutritional insult. In severe dietary restriction (fasting), a marked decrease of the number of somatogenic receptors supports the role of a receptor defect in the decline of circulating IGF-I. In contrast, in less severe forms of dietary restriction (protein restriction), the decline of IGF-I results from a postreceptor defect in the GH action at the hepatic level. Nutritional deprivation decreases hepatic IGF-I production by diminishing IGF-I gene expression. Decline in IGF-I gene expression is mainly caused by nutrient deficiency and less importantly by the nutritionally induced hormonal changes (insulin and T3). Diet restriction also increases the clearance and degradation of serum IGF-I through changes in the levels of circulating IGFBPs.(ABSTRACT TRUNCATED AT 400 WORDS)

Reference values of IGF-I in children from birth to 5 years of age, in Burkina Faso, using blood samples on filter paper.

OBJECTIVES: The aims of this study were to validate the use of filter paper to measure insulin-like growth factor-I (IGF-I) and to establish normal levels of IGF-I in children appearing healthy, from birth to 5 years of age in an African population. METHODS: We determined IGF-I from blood collected on filter paper. We validated this method by comparing the IGF-I values from dried blood spots on filter paper (kept at 4 degrees C and ambient temperature) and from serum among 13 children under 5. IGF-I were measured by the classical IGF-I RIA, after separation of the IGF-I from its binding proteins, using Sep-Pak chromatography. To establish normal levels of IGF-I, we conducted a cross-sectional study and collected blood samples with filter paper among 360 children in Ouagadougou (Burkina Faso). RESULTS: IGF-I determined from dried blood spots on filter paper were in good agreement with IGF-I levels obtained from blood serum, whether the filter papers were kept at 4 degrees C or at ambient temperature. The results of IGF-I-levels in apparently healthy children showed that geometric mean IGF-I ranged from 27 microg/l in boys younger than five months to 31 microg/l in 5-year-old boys. In girls, mean IGF-I ranged from 29 microg/l for girls younger than five months to 45 microg/l at the age of 5. From birth to 24 months, IGF-I decreased by 0.32+/-0.08 microg/l/month in boys and by 0.27+/-0.06 microg/l/month in girls and these decreases were not significantly different (p=0.95). After the age of 24 months, there was an increase in IGF-I of 4.9+/-1.3 microg/l/year in boys and of 8.4+/-0.8 microg/l/year in girls. This increase was indeed significantly different (p<0.001). CONCLUSIONS: Reference values of IGF-I for African boys and girls were determined. They will be used for endocrine evaluations and nutritional monitoring.

Myostatin gene deletion prevents glucocorticoid-induced muscle atrophy.

Glucocorticoids mediate muscle atrophy in many catabolic states. Myostatin expression, a negative regulator of muscle growth, is increased by glucocorticoids and myostatin overexpression is associated with lower muscle mass. This suggests that myostatin is required for the catabolic effects of glucocorticoids. We therefore investigated whether myostatin gene disruption could prevent muscle atrophy caused by glucocorticoids. Male myostatin knockout (KO) and wild-type mice were subjected to dexamethasone treatment (1 mg/kg.d for 10 d or 5 mg/kg.d for 4 d). In wild-type mice, daily administration of low-dose dexamethasone for 10 d resulted in muscle atrophy (tibialis anterior: -15%; gastrocnemius: -13%; P < 0.01) due to 15% decrease in the muscle fiber cross-sectional area (1621 +/- 31 vs. 1918 +/- 64 microm(2), P < 0.01). In KO mice, there was no reduction of muscle mass nor fiber cross-sectional area after dexamethasone treatment. Muscle atrophy after 4 d of high-dose dexamethasone was associated with increased mRNA of enzymes involved in proteolytic pathways (atrogin-1, muscle ring finger 1, and cathepsin L) and increased chymotrypsin-like proteasomal activity. In contrast, the mRNA of these enzymes and the proteasomal activity were not significantly affected by dexamethasone in KO mice. Muscle IGF-I mRNA was paradoxically decreased in KO mice (-35%, P < 0.05); this was associated with a potentially compensatory increase of IGF-II expression in both saline and dexamethasone-treated KO mice (2-fold, P < 0.01). In conclusion, our results show that myostatin deletion prevents muscle atrophy in glucocorticoid-treated mice, by blunting the glucocorticoid-induced enhanced proteolysis, and suggest an important role of myostatin in muscle atrophy caused by glucocorticoids.

Thyroid-stimulating activity and chorionic gonadotropin.

The nature of the substance with thyroid-stimulating activity (TSA) present in human chorionic gonadotropin (hCG) prepared from pregnancy urine was investigated. In the mouse thyrotropin bioassay, the characteristic maximum of blood radioactivity obtained with the TSA in hCG preparations occurred after that obtained with pituitary thyrotropin (hTSH) but before that obtained with long-acting thyroid stimulator. Antiserum to the alpha subunit of hCG produced significant neutralization of the TSA in hCG. Significant antagonism of hTSH biologic activity was achieved with certain doses of hCG, suggesting that the TSA in hCG was a partial agonist of hTSH. This antagonism was neutralized by antiserum to the beta subunit of hCG. These immunologic results suggest that the substance with TSA in hCG preparations contains antigenic determinants similar to those of both the alpha and the beta subunit of hCG. Amounts of highly purified hCG and crude commercial hCG of equal immunologic activity were biologically indistinguishable in the bioassay for TSA. Both hCG immunoreactivity and the TSA in hCG adsorbed to concanavalin A and eluted with 0.2 M methyl alpha-D-glucopyranoside. These results are consistent with the hypothesis that TSA is an intrinsic property of hCG or of a glycoprotein molecule physicochemically, biologically, and immunologically similar to hCG.

Combined baseline and one-month changes in big endothelin-1 and brain natriuretic peptide plasma concentrations predict clinical outcomes in patients with left ventricular dysfunction after acute myocardial infarction: Insights from the Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study (EPHESUS) study.

OBJECTIVE: Increased levels of neuro-hormonal biomarkers predict poor prognosis in patients with acute myocardial infarction (AMI) complicated by left ventricular systolic dysfunction (LVSD). The predictive value of repeated (one-month interval) brain natriuretic peptides (BNP) and big-endothelin 1 (BigET-1) measurements were investigated in patients with LVSD after AMI. METHODS: In a sub-study of the Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study (EPHESUS trial), BNP and BigET-1 were measured at baseline and at 1month in 476 patients. RESULTS: When included in the same Cox regression model, baseline BNP (p=0.0003) and BigET-1 (p=0.026) as well as the relative changes (after 1month) from baseline in BNP (p=0.049) and BigET-1 (p=0.045) were predictive of the composite of cardiovascular death or hospitalization for worsening heart failure. Adding baseline and changes in BigET-1 to baseline and changes in BNP led to a significant increase in prognostic reclassification as assessed by integrated discrimination improvement index (5.0%, p=0.01 for the primary endpoint). CONCLUSIONS: Both increased baseline and changes after one month in BigET-1 concentrations were shown to be associated with adverse clinical outcomes, independently from BNP baseline levels and one month changes, in patients after recent AMI complicated with LVSD. This novel result may be of clinical interest since such combined biomarker assessment could improve risk stratification and open new avenues for biomarker-guided targeted therapies. KEY MESSAGES: In the present study, we report for the first time in a population of patients with reduced LVEF after AMI and signs or symptoms of congestive HF, that increased baseline values of BNP and BigET-1 as well as a further rise of these markers over the first month after AMI, were independently predictive of future cardiovascular events. This approach may therefore be of clinical interest with the potential of improving risk stratification after AMI with reduced LVEF while further opening new avenues for biomarker-guided targeted therapies.

Circulating urotensin II levels in moderate to severe congestive heart failure: its relations with myocardial function and well established neurohormonal markers.

Urotensin II (UII) is a potent vasoactive cyclic peptide thought to play a role in myocardial hypertrophy and remodelling. We therefore determined UII plasma levels in congestive heart failure (CHF) patients and its relationship with the severity of the disease and well-established markers of left ventricular function. UII was significantly higher in CHF patients (n = 57) than in controls (n = 48) [geometric mean (pg/ml), 95% PI: 1.32 (0.67-2.59) versus 0.84 (0.31-1.61), p < 0.0001], was related to the functional class of the disease and correlated negatively with left ventricular ejection fraction (r = -0.316, P = 0.016). Furthermore, UII correlated significantly with Big-ET1 (r = 0.32, p = 0.03), BNP (r = 0.42, p = 0.005) but poorly with Nt-proANP (r = 0.28, p = 0.07). Our results suggest that UII could play a role in worsening the course of congestive heart failure and is associated with established markers of cardiovascular dysfunction.

Follitropin receptors in rat testis. Characterization with enzymatically 125I-labeled human follitropin.

The interaction between enzymatically radioiodinated human follitropin and the follitropin receptors in testis homogenate was investigated in immature and adult rats. The 125I-labeled human follitropin exhibited high binding activity with specific binding of up to 17% in the presence of an excess of testis homogenate. Approx. 50% of the bound hormone could be eluted at pH 5, and the receptor purified tracer exhibited a 3.6-fold increase in binding activity when compared with the original tracer preparation. Quantitative analysis of equilibrium binding data was performed with corrections for the measured specific activity and maximum binding activity of the tracer hormone. The equilibrium association constants (Ka) determined 24 degrees C were not significantly different in immature and adult rat testis, and the mean value for Ka was 3.9 . 10(9) M-1. At 37 degrees C, the Ka value obtained using immature rat testis was 1.3 . 10(10) M-1. The association of 125I-labeled human follitropin with immature rat testis homogenate was time and temperature dependent. In the presence of an excess of unlabeled hormone, 30--60% of the preformed hormone . receptor complex was dissociated after 24 h incubation. A specific and sensitive radioligand-receptor assay for follitropin was developed using immature rat testis homogenate. The minimum detectable dose of purified human follitropin was 0.6 ng, and human urinary and pituitary follitropin, ovine follitropin and pregnant mare serum gonadotropin reacted in the assay with equivalent slopes. The potencies of highly purified pregnent mare serum gonadotropin and highly purified human follitropin were similar in the radioligand-receptor assay, consistent with the follitropin bioactivity of the equine gonadotropin.

Insulin-like growth factor-I gene transfer by electroporation prevents skeletal muscle atrophy in glucocorticoid-treated rats.

Catabolic states caused by injury are characterized by a loss of skeletal muscle. The anabolic action of IGF-I on muscle and the reduction of its muscle content in response to injury suggest that restoration of muscle IGF-I content might prevent skeletal muscle loss caused by injury. We investigated whether local overexpression of IGF-I protein by gene transfer could prevent skeletal muscle atrophy induced by glucocorticoids, a crucial mediator of muscle atrophy in catabolic states. Localized overexpression of IGF-I in tibialis anterior (TA) muscle was performed by injection of IGF-I cDNA followed by electroporation 3 d before starting dexamethasone injections (0.1 mg/kg.d sc). A control plasmid was electroporated in the contralateral TA muscle. Dexamethasone induced atrophy of the TA muscle as illustrated by reduction in muscle mass (403 +/- 11 vs. 461 +/- 19 mg, P < 0.05) and fiber cross-sectional area (1759 +/- 131 vs. 2517 +/- 93 mum(2), P < 0.05). This muscle atrophy was paralleled by a decrease in the IGF-I muscle content (7.2 +/- 0.9 vs. 15.7 +/- 1.4 ng/g of muscle, P < 0.001). As the result of IGF-I gene transfer, the IGF-I muscle content increased 2-fold (15.8 +/- 1.2 vs. 7.2 +/- 0.9 ng/g of muscle, P < 0.001). In addition, the muscle mass (437 +/- 8 vs. 403 +/- 11 mg, P < 0.01) and the fiber cross-sectional area (2269 +/- 129 vs. 1759 +/- 131 mum(2), P < 0.05) were increased in the TA muscle electroporated with IGF-I DNA, compared with the contralateral muscle electroporated with a control plasmid. Our results show therefore that IGF-I gene transfer by electroporation prevents muscle atrophy in glucocorticoid-treated rats. Our observation supports the important role of decreased muscle IGF-I in the muscle atrophy caused by glucocorticoids.

Low plasma somatomedin-C in streptozotocin-induced diabetes mellitus. Correlation with changes in somatogenic and lactogenic liver binding sites.

To determine the mechanism for the decrease of somatomedin levels in insulin-dependent diabetes, the relationships among plasma immunoreactive somatomedin-C (Sm-C), plasma growth hormone (GH) and prolactin (PRL), and the somatogenic and lactogenic binding sites in liver were assessed in rats with nonketotic diabetes mellitus of different duration (1 wk or 1 mo) and severity (50 or 60 mg streptozotocin/kg BW). One week after administration of 60 mg streptozotocin (STZ)/kg, plasma Sm-C concentrations were significantly decreased (0.23 +/- 0.03 versus 0.43 +/- 0.03 U/ml in controls; mean +/- SEM, P less than 0.01). In contrast, plasma GH concentrations, bovine GH (bGH) binding, and human GH (hGH) binding were not significantly changed. After 1 mo of diabetes, no further decrease in plasma Sm-C content was observed despite a reduction in plasma GH and PRL concentrations and reduced hepatic bGH binding capacity (5 +/- 2 versus 38 +/- 4 fmol/mg protein; P less than 0.01). In the group of rats injected with 50 mg STZ/kg, the Sm-C was reduced at 1 mo but hepatic GH binding was not. In a second study, diabetic rats (75 mg STZ/kg) were treated after 3 wk with insulin (10 U lente per day for 7 days). This treatment normalized Sm-C levels and partially restored the GH binding capacity (treated: 49 +/- 4 fmol/mg protein versus untreated diabetics: 28 +/- 6 fmol/mg protein; P less than 0.01 and versus controls: 68 +/- 4 fmol/mg protein; P less than 0.05).2+ suggest that in an early phase of nonketotic diabetes, the low plasma Sm-C is not due primarily to reduced GH receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastric acid and pancreatic polypeptide responses to sham feeding are impaired in diabetic subjects with autonomic neuropathy.

To assess the relationship between cardiac and extra-cardiac dysfunction in diabetic autonomic neuropathy, the gastric acid output and the pancreatic polypeptide (hPP) secretion in response to sham feeding were evaluated in diabetic patients with (group 1) and without (group 2) cardiac autonomic neuropathy (CAN), and in normal subjects (group 3). All patients assigned to the group with CAN exhibited an impaired beat-to-beat heart rate variation during deep breathing. The basal gastric acid output was comparable in the three groups (1.3 +/- 0.5, 2.8 +/- 1.5, and 3.9 +/- 1.5 mmol/h, respectively). In contrast, the gastric acid output stimulated by sham feeding was significantly lower in patients with CAN (5.3 +/- 1.3 mmol/h) than in diabetic subjects without CAN (14.0 +/- 3.5 mmol/h; P less than 0.01) and in controls (10.9 +/- 3.1; P less than 0.05). The maximal gastric acid secretion capacity, determined after pentagastrin injection, was similar in all patients. Mean basal hPP concentrations were comparable in the three groups (185 +/- 53 pg/ml, 131 +/- 29 pg/ml, and 116 +/- 19 pg/ml). In the controls and diabetic subjects without CAN, a significant mean 60% increase of the hPP levels above basal values was observed during sham feeding. In contrast, no significant hPP response occurred in the group with CAN. These data suggest that diabetic CAN is associated with dysfunctions of the vagal pathways controlling the gastric acid output and the hPP secretion. Moreover, the results demonstrate a strong association between cardiac autonomic neuropathy and gastric vagal neuropathy (P less than 0.001).

Contributions of growth hormone receptor and postreceptor defects to growth hormone resistance in malnutrition.

Malnutrition results in poor growth and is associated with resistance to growth hormone (GH) action. The mechanisms involved in the GH resistance depend on the severity and the timing of the nutritional insult. Stringent dietary restrictions such as fasting may produce GH resistance by reducing the number of GH receptors. Less severe nutritional deprivation such a short-term protein restriction may cause GH insensitivity mainly through postreceptor mechanisms.

Comparison of plasma glucose and plasma free insulin during CSII and intensified conventional insulin therapy.

The plasma glucose and plasma free insulin profiles of six totally insulin-dependent diabetic patients were compared during periods of 4 days in hospital under a conventional insulin therapy (ICIT) comprising 4 daily injections of regular insulin and under continuous subcutaneous insulin infusion (CSII). Two profiles of prandial insulin administration with CSII were compared: a rectangular (R) and an exponential wave (E) in which 50% of the dose was given rapidly followed by an exponential decrease. In both cases, the basal infusion rate was increased by 30-50% between 5 a.m. and 8 a.m. Mean circadian blood glucose was equally good with ICIT: R and E: 7.0 +/- 0.9, 7.3 +/- 1.0, and 7.1 +/- 1.0 mmol/L, respectively. In five patients, fasting plasma glucose was higher with ICIT than with R and E (12.7 +/- 1.8 versus 6.9 +/- 1.0 and 6.8 +/- 0.8 mmol/L, respectively; t test: P less than 0.05; Wilcoxon: P = 0.06). Mean plasma free insulin level was significantly higher (t test: P less than 0.005; Wilcoxon: P less than 0.05) with ICIT (0.46 +/- 0.04 nmol/L) than with R (0.37 +/- 0.04 nmol/L) or E (0.36 +/- 0.05 nmol/L), although the daily doses were similar. In conclusion, CSII leads to a better glycemic control than ICIT, since it appears to prevent the morning rise of blood glucose.

Impaired gastric emptying in diabetic patients with cardiac autonomic neuropathy.

The aim of our study was to measure the gastric emptying rate for a solid meal in diabetic patients who had no gastrointestinal complaints with (group 1, n = 12) or without (group 2, n = 10) cardiac autonomic neuropathy and in normal controls comparable in age and sex (group 3, n = 10). Gastric emptying rate was assessed with a sequential scintiscanning method. The percentages of the initial isotope activity remaining in the stomach at different times (20, 40, 60, 80, 100, and 120 min) after the ingestion of a Tc-99m-labeled test meal and the emptying half-time were calculated. Cardiac autonomic neuropathy was determined by the beat-to-beat variations in heart rate during deep breathing. A significant reduction of the gastric emptying rate was observed in group 1. Indeed, at 80, 100, and 120 min the percentage of residual isotope activity was 73 +/- 4, 60 +/- 6, and 50 +/- 6% (mean +/- SE), respectively, in group 1 versus 61 +/- 3 (P less than .05), 45 +/- 4 (P less than .05), and 32 +/- 4% (P less than .02) in group 2. In group 3, residual isotope activity was 57 +/- 4 (P less than .05 vs. group 1), 41 +/- 4 (P less than .05), and 29 +/- 4% (P less than .02), respectively. Emptying half-time was also longer in group 1 (121 +/- 9 min) than in group 2 (95 +/- 6 min, P less than .05) or group 3 (90 +/- 4 min, P less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise and posture-related changes of atrial natriuretic factor and cardiac function in diabetes.

To study whether the release of atrial natriuretic factor (ANF) was altered in diabetic cardiac autonomic neuropathy (CAN), we determined plasma ANF concentrations during exercise and changes of posture in three groups of age- and sex-matched subjects (9 healthy subjects, 7 diabetic patients with CAN, and 7 diabetic patients without CAN). During exercise, plasma ANF concentrations rose threefold (P less than .001), and this increase was similar in the three groups. However, heart-rate response to exercise was impaired in the two groups of diabetic patients (P less than .004 vs. healthy subjects) but was more severely impaired in patients with CAN (P less than .03 vs. patients without CAN). In healthy subjects and patients without CAN, the increases of ANF during exercise correlated significantly with those of heart rate, systolic blood pressure, and rate-pressure product (P less than .01). In patients with CAN, the correlation was found exclusively with heart rate (P less than .01). An increase of ventricular ejection fraction occurred in all groups (P less than .001) but without showing statistical differences between groups. After 30 min of standing, a similar postural drop of plasma ANF concentrations (P less than .002) was observed in all subjects, reflecting preserved sympathetic control of vessels. In conclusion, exercise induces an increase of plasma ANF in diabetic patients with CAN. This increase, occurring similarly to healthy subjects, indicates that autonomic activation plays a minor role in ANF release during exercise. Impaired heart-rate response to exercise in patients without CAN suggests early damage of autonomic function, undetected by conventional rest tests.

Low serum somatomedin-C in insulin-dependent diabetes: evidence for a postreceptor mechanism.

In insulin-dependent diabetic rats, plasma somatomedin (Sm) levels are low and are not corrected by GH treatment, suggesting GH resistance. To define the mechanism of this GH-resistant state, the number and affinity constant of bovine liver GH-binding sites and the serum Sm-C responses to injections of bovine GH were determined in control (diluent-injected) and diabetic (streptozotocin-injected; 40 mg/kg BW) hypophysectomized rats. The affinity constants (Ka) of the GH-binding sites of control (0.92 +/- 0.07 X 10(9) M-1) and diabetic animals (0.68 +/- 0.04 X 10(9) M-1) were not significantly different (P less than 0.1). Likewise, there were no significant differences in the liver GH-binding capacities between control and diabetic hypophysectomized rats, whether these capacities were expressed as picomoles per liver (26.99 +/- 3.43 vs. 22.27 +/- 2.55, controls vs. diabetics), picomoles per mg DNA (1.26 +/- 0.15 vs. 1.10 +/- 0.12), or femtomoles per mg protein (30.95 +/- 4.08 vs. 29.98 +/- 2.70). Despite the absence of alterations in liver GH-binding sites, the Sm-C responses 24 h after sc injections of graded doses of bovine GH were severely blunted in the diabetic animals. The maximal serum Sm-C response in the controls was 0.81 +/- 0.12 U/ml, but was only 0.09 +/- 0.01 U/ml in the diabetics (P less than 0.01). The dose of GH required to achieve the half-maximal Sm-C response (ED50) was similar in diabetic and nondiabetic rats (700-900 micrograms). The absence of significant alterations in liver GH binding and the decreased maximal serum Sm-C response without changes in the ED50 suggest that the GH-resistant state in insulin-dependent diabetes is due to a postreceptor defect.

Acute down-regulation of the somatogenic receptors in rat liver by a single injection of growth hormone.

Prolonged continuous administration of GH induces somatogenic receptors in rat liver. However, because GH secretion is pulsatile and the effect of acute changes in serum GH concentrations on liver GH receptors is unknown, we measured total (MgCl2-treated homogenates) and free (water-treated homogenates) GH-binding sites in the livers of hypophysectomized (hypox) rats killed between 1 and 24 h after a single sc injection of rat GH (100 micrograms/100 g BW; n = 29). Control hypox rats (n = 10) were studied immediately or 3 h after injection of vehicle. GH injection caused profound decreases in both total and free liver GH receptors, but these changes followed different kinetic patterns. Free receptors declined rapidly (to 17% of control), reaching a nadir at the same time (1 h) as the maximal GH concentration in serum. These free receptors then increased, returning to normal 12 h after GH injection. In contrast, total GH receptors were slightly increased at 1 h, decreased to their minimal value at 6 h (53% of control), and returned to normal at 12 h. Serum immunoreactive somatomedin-C/insulin-like growth factor I concentrations peaked 12 h after GH injection. Total and free liver GH receptors were quantitated in hypox rats that had been injected 3 h previously with doses of rat GH from 2.5-500 micrograms/100 g BW or with vehicle. Both total and free binding sites decreased in a dose-dependent manner; the maximal responses were 40% and 90% below control values, respectively. Half-maximal reductions in GH binding were achieved when 10 micrograms GH/100 g BW were given. These data suggest that a surge of GH in serum leads to a time- and dose-dependent down-regulation of the liver somatogenic binding sites and are consistent with ligand-induced internalization and degradation of the receptor.

Detection and identification of endothelin-1 immunoreactivity in rat and porcine thyroid follicular cells.

Endothelin-1 immunoreactivity (irET-1) was observed in rat and porcine thyroid glands. Using a radioimmunoassay for endothelin-1, the mean concentration in extracts of rat and porcine thyroid glands were 0.75 pg/mg +/- 0.03 (n = 4) and 1.5 pg/mg +/- 0.2 (n = 8) (mean +/- SE) respectively. Gel-filtration and reverse-phase HPLC showed that ir ET-1 eluted in a position identical to synthetic endothelin-1. In addition, immunohistochemical study showed that irET-1 is located within epithelial follicular cells. No immunostaining was seen in parafollicular C-cells nor in parathyroid.

Ontogeny of liver somatotropic and lactogenic binding sites in male and female rats.

Developmental changes in liver somatotropic (GH) and lactogenic (PRL) binding sites were evaluated in male and female rats from birth to sexual maturity, and compared with growth velocity, plasma GH, PRL, testosterone, and estrogens. The affinity (Ka) and the concentration of these sites were determined from the analysis of equilibrium saturation curves with [125I]bovine GH and [125I]ovine PRL, incubated with liver homogenates. GH receptors rose from 6.4 fmol/mg protein at 8 days of age to 30.3 fmol/mg protein in males and 39.4 fmol/mg protein in females at 28 days. This surge occurred concomitant with the fall of plasma GH observed after birth. It preceded by about 1 week the acceleration of growth velocity and the increase of plasma GH seen at puberty. After the peak of growth velocity (42 days), GH receptors increased steadily until 120 days in females (63.8 fmol/mg protein), whereas in males they reached a concentration of 33.5 fmol/mg protein after a transient decrease to a nadir of 13.3 fmol/mg protein a day 50. From day 8 to day 35, PRL receptors in males remained at a constant level of 10.3 fmol/mg protein, whereas in females they increased progressively from 4.8 to 21.5 fmol/mg protein. Thereafter, in most pubertal males, they became undetectable, whereas plasma testosterone was rising. In contrast, PRL receptors in females increased 3-fold between day 42 (18.9 fmol/protein) and day 50 (50.2 fmol/mg protein). Between days 8 and 120, the Ka of GH and PRL receptors showed no significant changes with age and sex (GH: 0.66 X 10(9) M-1; PRL: 0.97 X 10(9) M-1). In conclusion, the rise of liver GH receptors occurring before puberty in male and female rats may be of importance for the initiation of the pubertal growth spurt. The inverse relationship between plasma testosterone and liver PRL receptors in pubertal male rats suggests that physiological concentrations of testosterone may inhibit PRL receptors. In contrast, in female rats an opposite change of PRL receptors is observed during puberty.