Differential changes in free and total insulin-like growth factor I after major, elective abdominal surgery: the possible role of insulin-like growth factor-binding protein-3 proteolysis

Major surgery is accompanied by extensive proteolysis of insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3). Proteolysis of IGFBP-3 is generally believed to increase IGF bioavailability due to a diminished affinity of the IGFBP-3 fragments for IGFs. We have investigated 18 patients undergoing elective ileo-anal J-pouch surgery. Patients were randomized to treatment with GH (12 IU/day; n = 9) or placebo (n = 9) from 2 days before to 7 days after operation. Free IGF-I and IGF-II were measured by ultrafiltration of serum, and IGFBP-3 proteolytic activity was determined by a [125I]recombinant human IGFBP-3 degradation assay. In the GH-treated group, total IGF-I increased preoperatively by 99%. Postoperatively, total IGF-I decreased by 48% (placebo) and 52% (GH). Immunoassayable IGFBP-3 decreased by 27% (placebo) and 26% (GH). In the placebo-treated group, free IGF-I was unchanged throughout the study. In the GH-treated group, free IGF-I increased by 277% preoperatively and remained elevated after operation. IGFBP-3 proteolytic activity increased by 63-73% after operation. The relative elevations of free IGF-I levels despite decreased total IGF-I levels could thus relate to augmented IGFBP-3 proteolysis.

[Substrate metabolism in untreated and treated thyrotoxicosis]

Accelerated metabolism is a hallmark of thyrotoxicosis, but the underlying biochemical mechanisms are incompletely understood. In order to elucidate these metabolic events further, we studied 12 patients with newly diagnosed diffuse (10 patients) or nodular (two patients) toxic goitre (ten women, two men; age 42.8 +/- 3.2 yr; BMI: 21.6 +/- 0.7 kg/m2) before ("TOX") and after ("TRE") 11.2 +/- 1.0 weeks treatment with methimazole and compared these patients to a control group ("CTR") of 11 subjects (nine women, two men; age 40.5 +/- 3.9 yr; BMI 22.5 +/- 1.0 kg/m2). All were studied for three hours in the basal state, using indirect calorimetry, isotope dilution for measurement of glucose turnover and the forearm technique for assessment of muscle metabolism. Prior to treatment patients with thyrotoxicosis were characterized by: Increased (p < 0.05) levels of T3 (3.75 +/- 0.23 [TOX], 1.89 +/- 0.08 [TRE] and 1.75 +/- 0.11 [CTR] nmol/l), resting energy expenditure (130.5 +/- 3.5 [TOX], 107.7 +/- 2.7 [TRE] and 106.3 +/- 3.1 [CTR] percent of predicted), protein oxidation (0.67 +/- 0.03 [TOX], 0.54 +/- 0.06 [TRE] and 0.46 +/- 0.05 [CTR] mg/kg/min), lipid oxidation (1.34 +/- 0.08 [TOX], 1.00 +/- 0.06 [TRE] and 1.02 +/- 0.04 [CTR] mg/kg/min), endogenous glucose production (2.51 +/- 0.13 [TOX], 1.86 +/- 0.12 [TRE] and 1.85 +/- 0.12 [CTR] mg/kg/min), non-oxidative glucose turnover (1.28 +/- 0.16 [TOX], 0.75 +/- 0.18 [TRE] and 0.71 +/- 0.11 [CTR] mg/kg/min) and a 50% increase in total forearm blood flow. Glucose oxidation (1.23 +/- 0.09 [TOX], 1.13 +/- 0.10 [TRE] and 1.13 +/- 0.09 [CTR] mg/kg/min), exchange of substrates in the muscles of the forearm and circulating levels of insulin, C-peptide, growth hormone or glucagon were not influenced by hyperthyroidism. Propranolol (20 mg thrice daily) given to seven of the patients for two days did not affect circulating levels of thyroid hormones, energy expenditure or glucose turnover rates. These results suggest that all major fuel sources contribute to the hypermetabolism of thyrotoxicosis and that augmented non-oxidative glucose metabolism may further aggravate the condition. All abnormalities recede with medical treatment of the disease.

[Insulin resistance among relatives of patients with NIDDM. Significance of physical fitness and muscle metabolism]

To explore the possible role of a reduced physical fitness for the diminished insulin sensitivity in first-degree relatives of NIDDM patients, 21 relatives and 22 matched control subjects were examined employing a hyperinsulinaemic (insulin infusion rate 0.6 mU/kg/min) euglycaemic clamp combined with the isotope dilution technique (3-3H-glucose), the forearm technique and indirect calorimetry. During hyperinsulinaemia glucose disposal (Rd) was significantly diminished in the relatives (p < 0.01). Maximal oxygen uptake (VO2 max) was 15% lower in the relatives than in the controls (p = 0.03). There was a highly significant correlation between Rd and VO2 max in both groups. In multiple linear regression analyses with Rd as the dependent variable VO2 max significantly determined the level of Rd (p < 0.01), whereas forearm blood flow and anthropometric data did not. We concluded that the insulin resistance in healthyfirst degree relatives of patients with NIDDM is associated with a diminished physical work capacity. Whether this finding is ascribable to environmental or genetic factors remains to be determined.

[Polycystic ovary syndrome II. Endocrinology and metabolism]

The polycystic ovary syndrome (PCOS) is diagnosed by the simultaneous presence of polycystic ovaries by ultrasound together with clinical and biochemical signs of hyperandrogenaemia. Recently, it has been shown that a majority of PCO patients exhibit metabolic abnormalities, i.e. android obesity, insulin resistance and dyslipidaemia, all of which dispose to "civilized" life-style diseases such as cardiovascular disease and non-insulin dependent diabetes. PCOS is therefore not merely a gynaecological curiosity, but an endocrinopathy with multisystem sequelae. The endocrinological and metabolic aspects of the disease are discussed.

[Polycystic ovary syndrome I. Clinical presentation and treatment]

Polycystic ovary syndrome (PCOS) is probably the most prevalent endocrinopathy in women and the most common cause of menstrual disturbances during the reproductive age. It is characterised by the presence of polycystic ovaries on ultrasound examination together with clinical and biochemical signs of hyperandrogenaemia. The majority of patients will seek medical advice because of menstrual disturbances, infertility or signs of hyperandrogeneamia (hirsutism, acne, alopecia). In obese patients the therapeutic mainstay is weight reduction. Anovulatory infertility is treated by stimulation of ovulation, laparoscopic electrocautery or IVF, while patients with menstrual disturbances without a wish to conceive should be treated with cyclic gestagen therapy or oral contraceptives in order to reduce the increased life-long risk of endometrial cancer. Additionally, hirsutism may be treated by epilation or antiandrogen therapy. PCOS is a common disease with an increased risk of NIDDM, hypertension, cardiovascular disease and endometrial cancer. Polycystic ovary syndrome is thus a disease which needs attention from the health system.

Metabolic effects and pharmacokinetics of a growth hormone pulse in healthy adults: relation to age, sex, and body composition

The acute effects of a single GH pulse have previously been studied in young males. It is, however, likely that both the metabolic effects and the pharmacokinetics of GH may differ between age groups and sexes. We studied 36 healthy, clinically nonobese adults of both sexes, who were divided into a young group (mean age, 29.6 yr) and an older group (mean age, 51.0 yr). On 2 separate occasions, they received an i.v. bolus of either GH (200 micrograms) or saline followed by blood sampling for 5 h. Glucose turnover was estimated by infusion of [3-3H]glucose, and indirect calorimetry was performed before and 2 h after the bolus infusions. Body composition (computed tomography scan and dual energy x-ray absorptiometry) was performed at baseline. Baseline levels of serum insulin-like growth factor I (IGF-I) was lower in older subjects, whereas circulating IGF-binding protein-1 and lipid intermediates were lower in males than in females. The area under the GH curve was lower in older subjects (young, 3978 +/- 1532 micrograms/L.24 h; older, 1144 +/- 79; P = 0.001), whereas the elimination half-life did not differ with age (young, 18.1 +/- 0.9 min; older, 16.4 +/- 0.8; P = NS). The MCR and apparent distribution volume of GH were higher in older subjects [MCR: young, 0.11 +/- 0.02 min/L; older, 0.19 +/- 0.01; P = 0.001; apparent distribution volume: young, 2.5 +/- 0.4 L; older, 4.5 +/- 0.3; P < 0.001). Both MCR and Vd correlated inversely with age and positively with indexes of adiposity. GH significantly increased lipid intermediates, but the response was higher in young subjects and males. By contrast, the ability of GH to acutely suppress IGF-binding protein-1 was more pronounced in older subjects and females. Serum levels of insulin and IGF-I did not differ significantly between GH and saline treatment groups. GH decreased the respiratory exchange ratio and increased resting energy expenditure, with no age or gender differences. A gradual decline over time in plasma levels and rate of turnover of glucose was recorded after both GH and saline. The following conclusions were reached. 1) The MCR and Vd of GH increase with age and correlate positively with fat mass. 2) Older subjects are responsive to the acute lipolytic effects of GH, but the response is higher in young subjects and in males. 3) Adipose tissue may be actively involved in the distribution and clearance of GH. 4) Age, sex, and body composition interact with GH in a complex manner, involving clearance, distribution, and metabolic actions of the hormone.

Insulin resistance in cardiac syndrome X and variant angina: influence of physical capacity and circulating lipids

Insulin resistance has been demonstrated in patients with angina pectoris irrespective of detectable atherosclerosis at coronary angiograms. We compared insulin sensitivity, lipid profiles, and exercise capacity in 20 patients with syndrome X, 15 patients with variant angina, and 20 healthy controls to investigate whether the presentation of the insulin resistance syndrome differs between the two patient groups with disparate vascular abnormalities. All patients had angiographically normal coronary arteries. Maximal oxygen uptake (VO2 max) was determined at bicycle exercise testing. Insulin sensitivity (SI) was assessed by the minimal model analysis of the intravenous glucose tolerance test. Patients with variant angina had significantly lower VO2 max than controls (mean +/- SE, 25.6 +/- 1.5 vs 30.6 +/- 1.4 ml x kg-1 x min-1, p < 0.05), whereas VO2 max in patients with syndrome X was intermediate (27.1 +/- 1.3 ml x kg-1 x min-1). Compared with controls, patients with syndrome X and variant angina had reduced insulin sensitivity (controls, 1.47 +/- 0.16 10(-4) x min-1/per pmol/L vs syndrome X, 0.86 +/- 0.11 10(-4) x min-1 per pmol/L and variant angina, 0.96 +/- 0.15 x 10(-4) x min-1 per pmol/L; analysis of variance, p < 0.05). Only patients with syndrome X exhibited fasting hyperinsulinemia. Patients with syndrome X also had higher fasting concentrations of triglycerides and total cholesterol and lower concentrations of high-density lipoprotein cholesterol than controls. When adjusting SI for variances of VO2 max, differences in SI vanished between controls and patients with variant angina but not between controls and patients with syndrome X. Thus syndrome X and variant angina are both associated with insulin resistance, but lipid abnormalities are only prominent in patients with syndrome X. A variable expression in terms of concomitant disturbances of lipid profiles and disparate influences of physical capacity suggests different underlying mechanisms.

Effects of amylin and the amylin agonist pramlintide on glucose metabolism

Since the discovery of the pancreatic islet hormone amylin in 1987, its metabolic effects have been investigated in a number of studies in animals and humans. Data from some early animal studies suggested that amylin might be associated with the development of insulin resistance, but other studies found that amylin had no effect on insulin sensitivity. More recently, studies performed using the human amylin analogue pramlintide in patients with Type 1 diabetes found that the hormone has no influence on either insulin-stimulated glucose uptake or the restraining effect of insulin on hepatic glucose production during periods of euglycaemia. Furthermore, during insulin-induced hypoglycaemia, pramlintide appears to increase the plasma concentrations of cortisol and growth hormone, and to stimulate the release of the gluconeogenic substrate lactate by the skeletal muscles. Taken together with evidence that, in short-term studies, pramlintide improved glycaemic control in patients with Type 1 diabetes who were also treated with insulin, these data suggest that pramlintide may have a role in the management of patients with diabetes. However, longer-term studies are required to ascertain whether these findings are sustained over time.

Blockade of the renin-angiotensin-aldosterone system prevents growth hormone-induced fluid retention in humans

To test if the renin-angiotensin-aldosterone system (RAAS) is involved in growth hormone (GH)-associated fluid retention, we examined the effect of GH administration in the presence or absence of RAAS blockade at different levels on body fluid homeostasis. Eight subjects were examined in a controlled, randomized double-blinded trial. During four 6-day periods they received subcutaneous GH (6 IU-m-2) or placebo injections and tablets as follows: 1) placebo and placebo, 2) GH and placebo, 3) GH and captopril, and 4) GH and spironolactone. GH increased extracellular volume (liters; placebo 18.87 +/- 0.85; GH + placebo 20.43 +/- 1.01) but this effect was abolished by captopril (GH + captopril 18.82 +/- 0.67) and spironolactone (GH + spironolactone 18.99 +/- 0.85). Correspondingly, the GH-induced reduction in bioimpedance was blocked by captopril and spironolactone. Plasma renin and angiotensin II concentrations increased during all three GH treatment regimens, whereas plasma aldosterone was increased only after GH plus spironolactone. The data demonstrate that GH activates the RAAS and that blockade of the RAAS by two separate mechanisms prevents fluid retention normally encountered after GH exposure. These observations suggest that the RAAS plays a key role in GH-induced regulation of fluid homeostasis.

Effects of growth hormone and insulin-like growth factor-I singly and in combination on in vivo capacity of urea synthesis, gene expression of urea cycle enzymes, and organ nitrogen contents in rats

Improvement of nitrogen balance is desirable in patients with acute or chronic illness. Both growth hormone (GH) and insulin-like growth factor-I (IGF-I) are promising anabolic agents, and their combined administration has been shown to reverse catabolism more efficiently than each of the peptides alone. This is believed to be mediated primarily through increased peripheral protein synthesis, whereas little attention has focused on a possible participation of amino acid metabolism in the liver. Four groups of rats were given: 1) placebo; 2) GH (200 micrograms/d); 3) IGF-I (300 micrograms/d); and 4) both GH and IGF-I. After 3 days, the maximum capacity of urea-nitrogen synthesis was determined by saturating infusion of alanine (n = 8 in each group), together with measurements of liver messenger RNA (mRNA) levels for urea cycle enzymes (n = 5 in each group) and N-contents of muscles, heart, and kidney. Basal plasma alpha-amino acid concentrations were similar in all groups. The capacity of urea-N synthesis [mumol/(min x 100 g body weight)] was reduced in a stepwise manner (placebo: 8.25 +/- 1.2; GH treatment: 6.52 +/- 0.8; IGF-I treatment: 5.5 +/- 0.6; and GH/IGF-I: 4.22 +/- 1.6 [P < .001 by ANOVA]), each step being lower than the former. Serum IGF-I increased stepwise from placebo (699 +/- 40 to 1,579 +/- 96 micrograms/L in the combined GH/IGF-I group), and was correlated negatively with the capacity of urea-nitrogen synthesis (P < .01). mRNA levels for urea cycle enzymes in the liver decreased after GH and IGF-I treatment, and the effect was more pronounced after the combined treatment in which the rate-limiting enzyme, argininosuccinate synthetase, was halved. Nitrogen contents of organs increased after both GH and IGF-I treatment, and even more so after the combination treatment, reaching an increase of 30% (P < .05). Data suggest that GH and IGF-I singly and, even more so in combination, additively inhibit urea synthesis. This is supposed to favor protein buildup in organs. We speculate that this inhibitory effect on the capacity of urea synthesis is caused by a decreased translation rate of the urea cycle enzymes caused by GH and IGF-I's down-regulatory effect on urea cycle enzyme gene transcription. The findings may indicate a novel mechanism of the protein anabolic action of GH and IGF-I.

Increased circulating leptin concentrations in insulin-resistant first-degree relatives of patients with non-insulin-dependent diabetes mellitus: relationship to body composition and insulin sensitivity but not to family history of non-insulin-dependent diabetes mellitus

OBJECTIVE

To explore a possible association between serum concentration of leptin, insulin sensitivity and non-insulin-dependent diabetes mellitus (NIDDM).

DESIGN

Forty first-degree relatives of NIDDM patients and 35 control subjects matched for age, gender and body mass index underwent a hyperinsulinaemic (insulin infusion rate 0.6 mU/kg per min) euglycaemic clamp combined with indirect calorimetry. Serum leptin was measured in fasting blood samples obtained before the clamp.

RESULTS

All subjects had a normal oral glucose tolerance test. Insulin-stimulated glucose uptake (M) was decreased in the relatives compared with the control subjects (4.58 +/- 0.27 versus 6.06 +/- 0.25 mg/kg per min, P < 0.001). Conversely, serum leptin was increased in the relatives (9.6 x/divided by 1.1 versus 6.1 x/divided by 1.2 ng/ml (geometric mean x/divided by antilog S.E.M.), P < 0.05). A positive correlation was observed between circulating levels of leptin and percentage body fat (P < 0.001) and inverse correlations were found between leptin, M (P < 0.01), maximal aerobic capacity (VO2 max) (P < 0.01), and energy expenditure (P < or = 0.01) in both groups. In multiple linear regression analysis, percentage body fat, gender and M significantly determined the level of leptin (r2 = 0.71, P < 0.001) whereas family history of NIDDM and VO2 max did not.

CONCLUSION

Serum leptin is increased in insulin-resistant offspring of NIDDM patients. The association between leptin, anthropometric measures and insulin sensitivity is, however, comparable with that of a control group. The increased concentrations of serum leptin in the relatives appear to be associated with the insulin resistance, but not with a family history of NIDDM.

Hepatic amino nitrogen conversion and organ N-contents in hypothyroidism, with thyroxine replacement, and in hyperthyroid rats

BACKGROUND/AIMS

The role of thyroid hormones in the regulation of hepatic conversions of amino nitrogen to urea is unresolved. The present study was designed to assess ureagenesis in rats with experimentally well-established hypo- and hyperthyroidism. The possible role of propylthiuracil (PTU), used for induction of hypothyroidism, was ascertained during thyroxine replacement of PTU treated hypothyroid rats.

METHODS

Basal blood amino nitrogen concentrations (AAN), the urea nitrogen synthesis rate (UNSR) and the maximal hepatic capacity for urea nitrogen synthesis (CUNS) obtained during alanine infusion were determined together with N-contents in the soleus muscle and kidneys in experimentally hypothyroid rats (n = 19), upon thyroxine replacement (n = 14) and in experimentally hyperthyroid rats (n = 19). Hypothyroidism was induced by adding propylthiouracil (0.05%) to the drinking water for 5 weeks. Hyperthyroidism was induced by thyroxine 100 micrograms/100 g body weight.

RESULTS

During hyperthyroidism, T3 fell to less than 10%, food intake was halved, and body weight fell by 13%. Basal blood AAN fell by 25% (p < 0.01), UNSR more than doubled (p < 0.01), and CUNS rose by 45% (p < 0.05). N-contents of the soleus muscle fell by 13% and by 20% in kidneys, respectively (p < 0.05). Thyroxine replacement normalized AAN, UNSR, CUNS and reduced N-loss to 7% in the soleus muscle (NS) and kidneys (p < 0.05), respectively. During hyperthyroidism, T3 rose five-fold, food intake rose by two thirds, and body weight fell by 10%. Basal AAN rose by 20% (p < 0.05), UNSR doubled (p < 0.01), and CUNS rose by 25% (p < 0.05). N-contents of the soleus muscle decreased by 19%, whereas kidney N-contents increased by 25% (p < 0.05). Overall liver function assessed by galactose elimination capacity did not differ among groups. Both conditions increased the rate of urea synthesis; in the hypothyroid state the hepatic waste of amino-N was limited by low blood concentration of amino-N, probably due to lower proteolysis. In the hyperthyroid state hepatic amino-N loss was aggravated by higher blood concentration of amino-N, probably due to higher proteolysis. This difference may explain the markedly different dietary nitrogen economy between the two groups.

CONCLUSIONS

The findings suggest that distinct hepatic acceleration of urea synthesis may contribute to the protein loss seen in both myxedema and in thyrotoxicosis in humans.

Effects of hyperinsulinaemia and hypoglycaemia on circulating leptin levels in healthy lean males

Current knowledge of the regulatory mechanisms of leptin synthesis and release is limited. To elucidate the role of short-term hyperinsulinaemia and hypoglycaemia on circulating levels of leptin, 7 healthy lean men underwent a 360-min hyperinsulinaemic (insulin infusion rate: 1.5 mU/kg/min) clamp in two conditions: (i) during 360 min of euglycaemia and (ii) during 120 min of euglycaemia followed by 240 min of graded hypoglycaemia (nadir 2.9 +/- 0.1 mmol/l). During hyperinsulinaemic euglycaemia, serum leptin levels were initially stable and then rose gradually after 180 min to a peak value of 147 +/- 7% of baseline (ANOVA, p < 0.01). During the hypoglycaemic clamp, the leptin profile differed from that of euglycaemic conditions (p < 0.01) since the increase was postponed and reduced. In both clamp studies, leptin dynamics contrasted with the changes in a control study performed in 7 other men whose serum leptin fell significantly (p < 0.05) to 77 +/- 4% of baseline values during a 360-min fast (following overnight fasting). It is concluded that hyperinsulinaemia for more than 3 h increases circulating levels of leptin in lean males, whereas hyperinsulinaemia with concomitant hypoglycaemia leads to transient suppression. The exact nature of the underlying mechanisms, e.g. changes in levels of insulin, glucose, various substrates, glucose turnover and/or counterregulatory hormones, remains to be determined.

Is skeletal responsiveness to thyroid hormone altered in primary osteoporosis or following estrogen replacement therapy?

Hyperthyroidism is characterized by increased bone turnover and resorptive activity. Similar changes in remodeling are seen in osteoporosis. To study the pathogenetic role of thyroid hormone in osteoporosis, we measured concentrations of free and total thyroid hormones and investigated the sensitivity of the skeleton toward thyroid hormones in 14 osteoporotic, 16 estrogen-treated, and 15 normal postmenopausal women with comparable thyroid status. Triiodothyronine (T3, 60 microg/day for 7 days) was administered to the three groups. The skeletal response was assessed by monitoring bone alkaline phosphatase (BAP), osteocalcin (BGP), and pyridinium cross-linked telopeptide domain of type I collagen (ICTP) in serum and urinary excretion of hydroxyproline (OHP), pyridinoline (PYR), and deoxypyridinoline (DPR) at days 0, 8, 15, and 57. Women on estrogen replacement therapy exhibited lower bone turnover than the normal postmenopausal women. Markers of bone formation were reduced by 19-43% and markers of resorption by 22-48%. The osteoporotic women displayed lower bone mass at the lumbar spine and the distal forearm (p < 0.01-0.001), but the levels of biochemical markers of bone formation and resorption were comparable to values obtained in the normal postmenopausal women. T3 stimulation caused significant increases (p values ranging between 0.05-0.001) in all three groups of the resorptive markers: ICTP (47%, 47%, 45%), OHP (29%, 30%, 33%), PYR (43%, 27%, 51%), and DPR (42%, 24%, 59%). Of the formative markers, only BGP increased significantly (32%, 40%, 47%) (p < 0.001). At day 57, however, all three formative markers increased compared with day 15 (p < 0.05-0.001). No significant differences in bone markers were demonstrated between groups. In the osteoporotic group, as the only group, serum calcium increased (p < 0.05) and serum PTH fell (p < 0.05). In conclusion, osteoporosis and estrogen substitution are not characterized by altered concentrations of thyroid hormones or responsiveness to thyroid hormones at the level of individual bone cells; however, altered responses pertaining to PTH and calcium were detected.

Skeletal responsiveness to thyroid hormone is not altered at menopause

Hyperthyroidism is characterized by increased bone turnover and resorptive activity. Similar changes in remodeling are seen after menopause. To study the role of thyroid hormone in the menopause-related changes in bone metabolism, we investigated thyroid status and the sensitivity of bone to thyroid hormone in 14 premenopausal and 15 early postmenopausal women. Triiodothyronine (T3) was administered to the two groups as 20 micrograms doses three times daily for 7 days. The skeletal response was assessed by monitoring bone alkaline phosphatase (BAP), osteocalcin (BGP), pyridinium crosslinked telopeptide domain of type I collagen (ICTP) in serum and urinary excretion of hydroxyproline (OHP), pyridinoline (PYR), and deoxypyridinoline (DPR) at days 0, 8, 15, and 57. The early postmenopausal women had increased bone turnover as reflected in sBAP (p < 0.05), sBGP (p < 0.05), and uOHP (p < 0.01) when compared with premenopausal controls. T3 stimulation of early postmenopausal and premenopausal women significantly increased the markers of bone resorption: sICTP (56% vs. 44%), uOHP (45% in both groups), and UPYR (83% vs. 17%) without any significant differences between groups. Of the formative markers, only sBGP increased significantly after stimulation (34% vs. 41%), but both sBGP and sBAP displayed significant increases from days 15 to 57. Thus, stimulation with thyroid hormone results in an immediate stimulation of ongoing bone formation and bone resorption, but also initiation of new remodeling which, after 8 weeks, reached the formative phase. PTH decreased (p < 0.01) in both groups but serum calcium and serum phosphate were unaltered. In conclusion, menopause is not characterized by altered levels of thyroid hormones or altered skeletal responsiveness to thyroid hormones.

GLP-1 does not not acutely affect insulin sensitivity in healthy man

Previous studies have suggested that glucagon-like peptide-1 (GLP-1) (7-36 amide) may have the direct effect of increasing insulin sensitivity in healthy man. To evaluate this hypothesis we infused GLP-1 in seven lean healthy men during a hyper insulinaemic (0.8 mU.kg-1.min-1), euglycaemic (5 mmol/l) clamp. Somatostatin (450 micrograms/h was infused to suppress endogenous insulin secretion, and growth hormone (3 ng.kg-1.min-1) and glucagon (0.8 ng.kg-1.min-1) were infused to maintain basal levels. GLP-1 (50 pmol.kg-1.h-1) or 154 mmol/l NaCl (placebo) was infused after 3 h of equilibration, i.e. from 180-360 min. GLP-1 infusion resulted in GLP-1 levels of approximately 40 pmol/l. Plasma glucose, insulin, growth hormone, and glucagon levels were similar throughout the clamps. The rate of glucose infusion required to maintain euglycaemia was similar with or without GLP-1 infusion (7.69 +/- 1.17 vs 7.76 +/- 0.95 mg kg-1.min-1 at 150-180 min and 8.56 +/- 1.13 vs 8.55 +/- 0.68 mg.kg-1.min-1 at 330-360 min) and there was no difference in isotopically determined hepatic glucose production rates (-0.30 +/- 0.23 vs -0.16 +/- 0.22 mg.kg-1.min-1 at 330-360 min). Furthermore, arteriovenous glucose differences across the forearm were similar with or without GLP-1 infusion (1.43 +/- 0.23 vs 1.8 +/- 0.29 mmol/l), (ANOVA; p > 0.60, in all instances). In conclusion, GLP-1 (7-36 amide) administered for 3 h, leading to circulating levels within the physiological range, does not affect insulin sensitivity in healthy man.

Effects of growth hormone on serum lipids and lipoproteins: possible significance of increased peripheral conversion of thyroxine to triiodothyronine

The role of growth hormone (GH) and thyroid hormone in the regulation of lipid and lipoprotein metabolism is not fully established. Furthermore, the possible linkage between the well-known GH-induced increase in peripheral thyroxine (T4) to triiodothyronine (T3) generation and the effects of GH on lipid and lipoprotein metabolism has not been elucidated. In this double-blind placebo-controlled study, we compared the effects of GH and T3 administration alone and in combination on lipid and lipoprotein metabolism in a group of healthy young adults. The dose of T3 was selected to mimic the T2 increase seen during exogenous GH exposure. Eight normal male subjects (aged 21 to 27 years; body mass index, 21.11 to 27.17 kg/m2) were randomly studied during four 10-day treatment periods with (1) daily subcutaneous placebo injections and placebo injections and placebo tablets, (2) daily subcutaneous GH injections (0.1 IU/kg.d) and placebo tablets, (3) daily T3 administration (40 micrograms on even dates or 20 micrograms on uneven dates) plus placebo injections, and (4) daily GH injections plus T3 administration. GH administration increased free T3 (FT3) to the same level as during T3 administration. GH caused decreased levels of total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol and increased levels of triglycerides (TG) and lipoprotein(a) (Lp(a)), but no changes in high-density lipoprotein (HDL) cholesterol and apolipoprotein B (apo B). T3 administration caused no alteration in these parameters, except for decreased levels of TC comparable to those seen after GH administration. Combined GH and T3 administration caused changes identical to those seen after GH administration, in addition to decreased apo B levels and a further decrease of TC levels. We conclude that GH and iodothyronines in the physiologic range exert distinct but disparate effects on lipids and lipoproteins, and do not support the hypothesis that the effects observed during GH administration are exclusively secondary to changes in peripheral T3 levels.

Insulin resistance in relatives of NIDDM patients: the role of physical fitness and muscle metabolism

First degree relatives of patients with non-insulin-dependent diabetes mellitus (NIDDM) are often reported to be insulin resistant. To examine the possible role of reduced physical fitness in this condition 21 first degree relatives of NIDDM patients and 22 control subjects without any history of diabetes were examined employing a 150-min hyperinsulinaemic (0.6 mU insulin. kg-1.min-1) euglycaemic clamp combined with the isotope dilution technique (3-(3)H-glucose, Hot GINF), the forearm technique and indirect calorimetry. During hyperinsulinaemia glucose disposal (Rd) and forearm glucose extraction were significantly diminished in the relatives (p < 0.01 and p < 0.05), but glucose oxidation and the suppressive effect on hepatic glucose production were normal. Arteriovenous differences across the forearm of the gluconeogenic precursors lactate, alanine and glycerol as well as the increments in forearm blood flow during hyperinsulinaemia were similar in the two groups. Maximal oxygen uptake (VO2 max) was lower in the relatives than in the control subjects (36.8 +/- 1.9 vs 42.1 +/- 2.0 ml.kg-1.min-1; p = 0.03). There was a highly significant correlation between Rd and VO2 max in both relatives and control subjects (r = 0.68 and 0.66, respectively; both p < 0.001). Comparison of the linear regression analyses of insulin-stimulated Rd on VO2 max in the two groups showed no significant differences between the slopes (0.10 +/- 0.03 vs 0.09 +/- 0.02) or the intercepts. In stepwise multiple linear regression analyses with insulin-stimulated Rd as the dependent variable VO2 max significantly determined the level of Rd (p < 0.01), whereas forearm blood flow and anthropometric data did not. In conclusion, the insulin resistance in healthy first degree relatives of patients with NIDDM is associated with a diminished physical work capacity. Whether, this finding is ascribable to environmental or genetic factors (e.g. differences in muscle fibre types, capillary density etc) remains to be determined.

Glucose turnover, fuel oxidation and forearm substrate exchange in patients with thyrotoxicosis before and after medical treatment

OBJECTIVE

Accelerated metabolism is a hallmark of thyrotoxicosis, but the underlying biochemical mechanisms are incompletely understood and the majority of studies have investigated normal subjects rendered only modestly hyperthyroid for a brief period of time. We have therefore studied a group of thyrotoxic patients using several different techniques.

DESIGN

Twelve patients with newly diagnosed diffuse (10 patients) or nodular (2 patients) toxic goitre (10 women, 2 men; age 42.8 +/- 3.2 years; BMI 21.6 +/- 0.7 kg/m2) before ('pretreatment') and after ('treated') 11.2 +/- 1.0 weeks treatment with methimazole and compared these patients to a control group ('control') of 11 subjects (9 women, 2 men; age 40.5 +/- 3.9 years; BMI 22.5 +/- 1.0 kg/m2). All were studied for 3 hours in the basal state, using indirect calorimetry, isotope dilution for the measurement of glucose turnover and the forearm technique for assessment of muscle metabolism.

RESULTS

Prior to treatment patients with thyrotoxicosis were characterized by increased (P < 0.05) levels of T3 (3.75 +/- 0.23 nmol/l (pretreatment), 1.89 +/- 0.08 (treated) and 1.75 +/- 0.11 (control)), resting energy expenditure (130.5 +/- 3.5 (pretreatment), 107.7 +/- 2.7 (treated) and 106.3 +/- 3.1 (control), % of predicted), protein oxidation (0.67 +/- 0.03 (pretreatment), 0.54 +/- 0.06 (treated) and 0.46 +/- 0.05 (control), mg/kg/min), lipid oxidation (1.34 +/- 0.08 (pretreatment), 1.00 +/- 0.06 (treated) and 1.02 +/- 0.04 (control), mg/kg/min), endogenous glucose production (2.51 +/- 0.13 (pretreatment), 1.86 +/- 0.12 (treated) and 1.85 +/- 0.12 (control), mg/kg/min), non-oxidative glucose turnover (1.28 +/- 0.16 (pretreatment), 0.75 +/- 0.18 (treated) and 0.71 +/- 0.11 (control), mg/kg/min) and a 50% increase in total forearm blood flow. Glucose oxidation (1.23 +/- 0.09 (pretreatment), 1.13 +/- 0.10 (treated) and 1.21 +/- 0.11 (control) mg/kg/min), exchange of substrates in the muscles of the forearm and circulating levels of insulin, C-peptide, growth hormone or glucagon were not influenced by hyperthyroidism. Propranolol (20 mg thrice daily) given to 7 of the patients for 2 days did not affect circulating levels of thyroid hormones, energy expenditure or glucose turnover rates.

CONCLUSIONS

These results suggest that all major fuel sources contribute to the hypermetabolism of thyrotoxicosis and that augmented non-oxidative glucose metabolism may further aggravate the condition. All abnormalities diminish with medical treatment of the disease.

Calorigenic effects of growth hormone: the role of thyroid hormones

GH administration increases energy expenditure, independent of changes in lean body mass, in healthy, obese, and GH-deficient subjects. This may be causally linked to the well known GH-induced increase in peripheral T4 to T3 generation, but experimental data are sparse. In this study we have addressed whether 1) the calorigenic effects of GH administration could be reproduced by oral supplementation of T3 in a dose selected to mimic the GH-induced increase in peripheral T3 levels; and 2) combined GH and T3 administration have a synergistic effect on resting energy expenditure (REE). Eight normal male subjects (aged 21-27 yr; body mass index, 21.11-27.17 kg/m2) were randomly studied during four 10-day treatment periods with 1) daily sc placebo injections and placebo tablets, 2) daily sc GH injections (0.1 IU/kg x day) and placebo tablets, 3) daily T3 administration (40 microg on even dates, 20 microg on uneven dates) plus placebo injections, and 4) daily GH injections plus T3 administration. GH administration increased both free T3 (FT3) levels [mean +/- SE, 6.2 +/- 0.3 (control) vs. 7.3 +/- 0.5 (GH) pmol/L; P < 0.05] and REE [mean +/- SE, 1959 +/- 67 (control) vs. 2164 +/- 55 (GH) Cal/24 h; P < 0.01]. T3 administration yielded comparable levels of FT3 (7.7 +/- 0.5 pmol/L; T3 vs. GH, P = 0.37), but did not increase REE (2015 +/- 48 Cal/24 h; T3 vs. control, P = 0.23). Combined GH and T3 administration increased REE to a level higher than that seen with T3 alone (2279 +/- 68 Cal/24 h; T3 vs. GH plus T3, P < 0.01). Significant increments in serum levels of insulin-like growth factor I and insulin were recorded with GH administration, but not with T3 alone. Resting heart rate increased to a similar degree after GH administration and T3 supplementation, respectively. Tympanic temperature remained unaltered in all four studies. The results suggest that the calorigenic effect of GH is not mediated solely through increased conversion of T4 to T3.

Effects of long-term growth hormone (GH) and triiodothyronine (T3) administration on functional hepatic nitrogen clearance in normal man

BACKGROUND/AIMS

A decline in urea excretion is seen following long-term growth hormone administration, reflecting overall protein anabolism. Conversely, hyperthyroidism is characterized by increased urea synthesis and negative nitrogen metabolism. These seemingly opposite effects are presumed to reflect different actions on peripheral protein metabolism. The extent to which these hormonal systems have different direct effects on hepatic urea genesis has not been fully characterized.

METHODS

We measured urea nitrogen synthesis rates and blood alanine levels concomitantly before, during, and after a 4-h constant intravenous infusion of alanine (2 mmol.kg bw-1.h-1). Urea nitrogen synthesis rate was estimated hourly as urinary excretion corrected for gut hydrolysis and accumulation in body water. The slope of the linear relationship between urea nitrogen synthesis rate and alanine concentration represents the liver function as to conversion of amino-N, and is denoted the functional hepatic nitrogen clearance. Eight normal male subjects (age 21-27 years; body mass index 22.4-27.0 kg/m2) were randomly studied four times: 1) after 10 days of subcutaneous saline injections, 2) after 10 days of subcutaneous growth hormone injections (0.1 IU/kg per day), 3) after 10 days of triiodothyronine administration (40 micrograms on even dates, 20 micrograms on uneven dates) and 4) after 10 days given 2)+3). All injections were given at 20 00 h.

RESULTS

Growth hormone decreased functional hepatic nitrogen clearance (l/h) by 30% (from 33.8 +/- 3.2 l/h (control) to 23.8 +/- 1.5 l/h (10 days growth hormone) (mean +/- SE) (ANOVA; p < 0.01)). Triiodothyronine did not change functional hepatic nitrogen clearance (36.7 +/- 3.2 l/h), but triiodothyronine given together with growth hormone abolished the effect of growth hormone functional hepatic nitrogen clearance (38.8 +/- 4.8 l/h).

CONCLUSIONS

The results show that long-term growth hormone administration acts on liver by decreasing functional hepatic nitrogen clearance, thereby retaining amino-N in the body. Triiodothyronine has no effect on functional hepatic nitrogen clearance, but given together with growth hormone, it abolishes the effect of growth hormone on functional hepatic nitrogen clearance. A possible mechanism is the known effect of thyroid hormones in reducing the bioavailability of insulin-like growth factor-I. Thus, the effects of growth hormone and triiodothyronine on amino-N homeostasis are interdependent and to some extent exerted via interplay in their regulation of liver function as to amino-N conversion.

Acute effects of the human amylin analog AC137 on basal and insulin-stimulated euglycemic and hypoglycemic fuel metabolism in patients with insulin-dependent diabetes mellitus

Amylin has been reported to decrease glycogen storage in rodent skeletal muscles and produce insulin resistance in intact rats. To test the acute effect of a human amylin analog (AC137) on glucose metabolism in man, seven IDDM patients were infused in a randomized, double blind, cross-over study with AC137 (100 micrograms/h, n = 1; 50 micrograms/h, n = 6) or placebo for 330 min during a two-step euglycemic clamp (insulin infusion rates, 0.2 and 0.6 mU/kg.min; basal and hyperinsulinemic period, respectively) followed by a hyperinsulinemic hypoglycemic clamp (insulin infusion rate, 1.5 mU/kg.min; hypoglycemic period). During euglycemia, no differences were found in glucose disposal (step 1, 2.43 +/- 0.20 vs. 2.03 +/- 0.26; step 2, 4.28 +/- 0.54 vs. 4.11 +/- 0.45 mg/kg.min; AC137 vs. placebo, mean +/- SEM), arteriovenous substrate balances across the forearm, or hepatic glucose production. During hypoglycemia, glucose fluxes were also similar. However, lactate release from the forearm was more pronounced (P < 0.05) with the analog than with placebo (area under the curve, -11.2 +/- 4.6 vs. -1.4 +/- 2.2 mmol/min.L). Despite similar plasma glucose nadirs (2.7 +/- 0.0 vs. 2.6 +/- 0.1 mmol/L; AC137 vs. placebo), circulating cortisol and GH rose to significantly higher levels during hypoglycemia with the amylin analog (P < 0.05). In conclusion, acute administration of the amylin analog AC137 did not influence insulin-stimulated glucose metabolism during euglycemic conditions. During imposed hypoglycemia, lactate release from skeletal muscle was, however, enhanced, and the rise in cortisol and GH was augmented.