Systemic interleukin-1 α and interleukin-2 secretion in response to acute stress and to corticotropin-releasing hormone in humans*

Abstract Acute stress results in activation of the hypothalamic-pituitary-adrenal (HPA) axis. ACTH and cortisol secretion is stimulated by corticotropin-releasing hormone (CRH). It has also been shown that activation of the HPA axis during stress is accompanied by changes in the immune response. However, little is known about the influence of acute stress on the release of cytokines such as inteleukin-1 (IL-1) or interleukin-2 (IL-2). In this study, we determined serum IL-1 α and IL-2 levels in 19 patients undergoing the acute stress of angioplasty for coronary artery disease. A second protocol was devised to determine serum IL-1 α and IL-2 concentrations as well as lymphocyte subpopulations in 10 normal volunteers receiving 1 μ kg^-1 human CRH intravenously. Finally, IL-1 α concentrations were measured in CRH-incubated mononuclear cell (MNC) and monocyte cultures. In response to the stress of angioplasty, ACTH and cortisol as well as IL-1 α and IL-2 concentrations were clearly above baseline levels (IL-1 α, mean ± SEM, baseline: 1·39 ± 0·34 ng ml^-1, after angioplasty: 2·64 ± 0·73 ng ml^-1, P < 0·05; IL-2, baseline: 1·2 ± 0·13 ng ml^-1, after angioplasty: 2·8 ± 1·14 ng ml, P < 0·05). A similar pattern was obtained in normal subjects in response to CRH (IL-1 α, baseline: 0·8 ± 0·2 ng ml^-1, after angioplasty: 3·7 ± 1·4 ng ml^-1, P < 0·05; IL-2, baseline: 1·9 ± 0·4 ng ml^-1, after angioplasty: 5·4 ± 2·2 ng ml^-1, P < 0·02). The percentage of IL-2 receptor-positive lymphocytes rose from 3·9 ± 1·2% to 6·2 ± 1·6% (P < 0·05), the relative number of CD-3 lymphocytes rose from 74·5 ± 1·6% to 78·3 ± 2·0% (P < 0·05). No significant changes were observed in the number of CD-4, CD-8, natural killer and B cells. In vitro, IL-1 α concentrations in cultures containing CRH were not significantly different from control cultures. Our data demonstrate significant activation of the HPA axis and secretion of IL-1 α and IL-2 in response to both angioplasty and CRH. Furthermore, CRH administration resulted in activation of the cellular immune system (indicated by an increase in IL-2 receptor positive lymphocytes). Our in vitro data suggest that CRH may not directly act on blood mononuclear cells to induce IL-1 α release or, alternatively, sources other than blood mononuclear cells may account for the elevated IL-1 α levels observed in vivo. We conclude that CRH may play a major role in neuroendocrine-immune interactions during acute stress.     

Lack of effect of desmopressin on ACTH and cortisol responses to ovine corticotropin-releasing hormone in anorexia nervosa

Abstract. Both arginine vasopressin (AVP) and corticotropin-releasing hormone (CRH) are involved in the release of ACTH in man. Desmopressin (DDAVP), a synthetic analogue of AVP, has been shown to have a CRH-like action (able to promote ACTH and cortisol release) in animals but not in normal man. Nevertheless, DDAVP is able to release ACTH and cortisol in ACTH-dependent Cushing's disease. We studied eight anorexia nervosa (AN) patients [as AN is a condition in which chronic activation of the hypothalamic-pituitary-adrenal (HPA) axis is commonly reported] in a refeeding phase of the disease, to evaluate whether, after weight gain, ACTH and cortisol response to ovine corticotropin-releasing hormone (oCRH) [1 μg kg^-1 body weight (BW) i.v.] is restored. We also wanted to ascertain the effect on the HPA axis of 10 μg i.v. DDAVP alone and as pretreatment to oCRH (1 μg kg^-1 BW i.v.)-induced secretion of ACTH and cortisol. We studied six normal women as control subjects. No significant differences in ACTH and cortisol responses to oCRH were found between AN patients and control subjects. DDAVP was not able to stimulate ACTH or cortisol release in AN patients or in control subjects, but in the latter it was able to significantly enhance (P < 0.05) ACTH [area under curve (AUC): 590.0± 104.4 pmol L^-1 120 min^-1 and cortisol (AUC: 28899.0 ± 6935.2nmol L^-1 120 min^-1) responses to oCRH (ACTH AUC: 325.7 ± 101.7 pmol L^-1 120 min^-1, cortisol AUC: 14197.4 ± 2930.0 nmol L^-1 120 min^-1). The present data show that DDAVP does not stimulate ACTH and cortisol in AN patients or, as previously reported, in normal subjects. However, DDAVP is able to enhance ACTH and cortisol release after oCRH administration in normal subjects but not in AN patients. This finding could be due to a down-regulation of hypophyseal DDAVP V3 receptors in AN as a direct consequence of the hypercortisolaemic status usually present.     

Acute hormonal responses following different velocities of eccentric exercise

The aim of this study was to compare the acute hormonal responses following two different eccentric exercise velocities. Seventeen healthy, untrained, young women were randomly placed into two groups to perform five sets of six maximal isokinetic eccentric actions at slow (30° s^?1) and fast (210° s^?1) velocities with 60‐s rest between sets. Growth hormone, cortisol, free and total testosterone were assessed by blood samples collected at baseline, immediately postexercise, 5, 15 and 30 min following eccentric exercise. Changes in hormonal responses over time were compared between groups, using a mixed model followed by a Tukey's post hoc test. The main findings of the present study were that the slow group showed higher growth hormone values immediately (5·08 ± 2·85 ng ml^?1, P = 0·011), 5 (5·54 ± 3·01 ng ml^?1, P = 0·004) and 15 min (4·30 ± 2·87 ng ml^?1, P = 0·021) posteccentric exercise compared with the fast group (1·39 ± 2·41 ng ml^?1, 1·34 ± 1·97 ng ml^?1 and 1·24 ± 1·87 ng ml^?1, respectively), and other hormonal responses were not different between groups (P>0·05). In conclusion, slow eccentric exercise velocity enhances more the growth hormone(GH) response than fast eccentric exercise velocity without cortisol and testosterone increases.     

Vasoactive neuroendocrine responses associated with tolerance to lower body negative pressure in humans

The purpose of this investigation was to test the hypothesis that peripheral vasoconstriction and orthostatic tolerance are associated with increased circulating plasma concentrations of noradrenaline, vasopressin and renin–angiotensin. Sixteen men were categorized as having high (HT, n=9) or low (LT, n=7) tolerance to lower body negative pressure (LBNP) based on whether the endpoint of their pre‐syncopal‐limited LBNP (peak LBNP) exposure exceeded ?60 mmHg. The two groups were matched for age, height, weight, leg volume, blood volume and maximal oxygen uptake, as well as baseline blood volume and plasma concentrations of vasoactive hormones. Peak LBNP induced similar reductions in mean arterial pressure in both groups. The reduction in legarterial pulse volume (measured by impedance rheography), an index of peripheral vascular constriction, from baseline to peak LBNP was greater (P<0·05) in the HT group (?0·041 ± 0·005 ml 100 ml^?1) compared to the reduction in the LT group (?0·025 ± 0·003 ml 100 ml^?1). Greater peak LBNP in the HT group was associated with higher (P<0·05) average elevations in plasma concentrations of vasopressin (pVP, Δ=+7·2 ± 2·0 pg ml^?1) and plasma renin–angiotensin (PRA, Δ=+2·9 ± 1·3 ng Ang II ml^?1 h^?1) compared to average elevations of pVP (+2·2 ± 1·0 pg ml^?1) and PRA (+0·1 ± 0·1 ng Ang II ml^?1 h^?1) in the LT group. Plasma noradrenaline concentrations were increased (P<0·05) from baseline to peak LBNP in both HT and LT groups, with no statistically distinguishable difference between groups. These data suggest that the renin–angiotensin and vasopressin systems may contribute to sustaining arterial pressure and orthostatic tolerance by their vasoconstrictive actions.     

Blood glucose concentration dependent ACTH and cortisol responses to prolonged exercise

Summary. The purpose of this study is to investigate responses of serum ACTH and cortisol concentration to low intensity prolonged exercise. In experiment 1, 10 subjects fasted for 12 h and performed bicycle exercise at 49·3%V?O₂max (±4·3%) until exhaustion or up to 3 h. During the early part of the exercise, serum ACTH and cortisol concentrations did not increase from the pre-exercise values (ACTH: 44±5 μg/1, cortisol: 139±52 μg/1). Whilst the time to serum ACTH concentration increasing varied among the subjects (60·180 min), the increases of this hormone occurred for all subjects (175±85 ng/1, P<0·05) when blood glucose concentration decreased to a critical level of 3·3 mmol/1. At the end of the exercise, blood glucose concentration decreased to 2·60±0·21 mmol/1, and serum ACTH and cortisol concentrations increased to 313±159 μg/1 and 371±151 μg/1, respectively. In experiment 2, four subjects performed the same intensity exercise until exhaustion, and were then given 600 ml of 20 g glucose solution, and immediately afterwards, they were asked to repeat the same exercise. The subjects continued the exercise for between 30 to 90 min until again reaching exhaustion. During the second exercise, blood glucose concentration increased to the pre-exercise value (2·72±0·58 to 4·00±0·22 mmol/1, P<0·05) and simultaneously, serum ACTH concentration decreased considerably (354±22 to 119±54 ng/1, P<0·05). The results of the present study suggest that serum ACTH and cortisol concentration during low intensity prolonged exercise may be dependent on blood glucose concentration.     

Increased serum angiotensin converting enzyme activity in type T insulin—dependent diabetes mellitus: its relation to metabolic control and diabetic complications

Abstract. Serum angiotensin-converting enzyme (ACE) was measured in 150 insulin-dependent diabetes mellitus (IDDM) patients and 72 healthy subjects by radioassay, using [³H]-hippuryl-glycyl-glycine as a substrate. Mean (SD) serum ACE activity in diabetic patients was 120 ± 33 nmol ml^?1 min^?1 (range 46–215) and was significantly increased by 56% compared to control values (77 ± 23 nmol ml^?1 min^?1, range 46–125, P < 0·001). ACE activity > 125 nmol ml^?1 min^?1 was observed in 60 of 150 IDDM patients. 96 IDDM patients were normoalbuminuric (< 22 mg 24 h^?1) and 49 patients were micro- or macroalbuminuric (range 22–6010 mg 24 h^?1). Micro- and macroalbuminuric IDDM patients were found to have significantly greater ACE activity values than normoalbuminuric patients (128 ± 36 vs. 115 ± 30 nmol ml^?1 min^?1, P = 0·025). Metabolically well-controlled IDDM patients (glycosylated haemoglobin ≤ 8%) had lower ACE activity values than the patients with glycosylated haemoglobin greater than 8% (109 ± 20 vs. 127 ± 32 nmol ml^?1 min^?1, P < 0·02). A significant correlation between degree of metabolic control and ACE activity was found (r = 0.435, P < 0·001) so that an increase in one glycosylated quartile unit is accompanied by an increase in ACE activity of 10·5 nmol ml^?1 min^?1. Thus ACE activity in the serum of IDDM patients was increased by 56% in 40% of the patients. It was increased in IDDM patients without complications and in patients with retinopathy or nephropathy. In diabetic patients with nephropathy, ACE activity was greater than in diabetic patients without nephropathy. ACE activity was positively correlated with metabolic control. The role of increased ACE activity in the development of diabetic nephropathy remains to be established.     

Altered skeletal muscle glucose transport and blood lipid levels in habitual cigarette smokers

We determined whether habitual cigarette smoking alters insulin-stimulated glucose transport and GLUT4 protein expression in skeletal muscle. Vastus lateralis muscle was obtained from 10 habitual cigarette smokers and 10 control subjects using an open muscle biopsy procedure. Basal 3-O-methylglucose transport was twofold higher (P > 0·01) in muscle from habitual smokers (0·05 ± 0·08 vs. 1·04 ± 0·19 μmol ml^?1 h^?1; controls vs. smokers respectively). Insulin (600 pmol l^?1) increased glucose transport 2·6-fold (P > 0·05) in muscle from control subjects, whereas no significant increase was noted in habitual smokers. Skeletal muscle GLUT4 protein expression was similar between the groups. FFA levels were elevated in the smokers (264 ± 49 vs. 748 ± 138 μmol l^?1 for control subjects vs. smokers; P < 0·05), and serum triglyceride levels were increased in the smokers (0·9 ± 0·2 vs. 2·3 ± 0·6 mmol l^?1 for control subjects vs. smokers; P < 0·05). Skeletal muscle carnitine palmitil (acyl) transferase activity was similar between the groups, indicating that FFA transport into the mitochondria was unaltered by cigarette smoking. In conclusion, cigarette smoking appears to have a profound effect on glucose transport in skeletal muscle. Basal glucose transport is markedly elevated, whereas insulin-stimulated glucose transport is impaired. These changes cannot be explained by altered protein expression of GLUT4, but may be related to increased serum FFA and triglyceride levels. These findings highlight the importance of identifying habitual cigarette smokers in studies aimed at assessing factors that lead to alterations in lipid and glucose homeostasis in people with non-insulin-dependent diabetes mellitus (NIDDM).     

The impact of short duration,high intensity exercise on cardiac troponin release

The aim of this study was to assess the appearance of cardiac troponins (cTnI and/or cTnT) after a short bout (30 s) of ‘all‐out’ intense exercise and to determine the stability of any exercise‐related cTnI release in response to repeated bouts of high intensity exercise separated by 7 days recovery. Eighteen apparently healthy, physically active, male university students completed two all‐out 30 s cycle sprint, separated by 7 days. cTnI, blood lactate and catecholamine concentrations were measured before, immediately after and 24 h after each bout. Cycle performance, heart rate and blood pressure responses to exercise were also recorded. Cycle performance was modestly elevated in the second trial [6·5% increase in peak power output (PPO)]; there was no difference in the cardiovascular, lactate or catecholamine response to the two cycle trials. cTnI was not significantly elevated from baseline through recovery (Trial 1: 0·06 ± 0·04 ng ml^?1, 0·05 ± 0·04 ng ml^?1, 0·03 ± 0·02 ng ml^?1; Trial 2: 0·02 ± 0·04 ng ml^?1, 0·04 ± 0·03 ng ml^?1, 0·05 ± 0·06 ng ml^?1) in either trial. Very small within subject changes were not significantly correlated between the two trials (r = 0·06; P>0·05). Subsequently, short duration, high intensity exercise does not elicit a clinically relevant response in cTnI and any small alterations likely reflect the underlying biological variability of cTnI measurement within the participants.     

Restoration of peak vascular conductance after simulated microgravity by maximal exercise

We sought to determine if (i) peak vascular conductance of the calf was reduced following prolonged exposure to simulated microgravity, and (ii) if maximal cycle ergometry performed at the end of microgravity exposure stimulated a restoration of peak calf vascular conductance. To do this, peak vascular conductance of the calf was recorded following ischaemic plantar flexion exercise to fatigue in seven men after 16 days of head-down tilt (HDT) under two conditions: (i) after one bout of maximal supine cycle ergometry completed 24 h prior to performance of ischaemic plantar flexion exercise, and (ii) in a control (no cycle ergometry) condition. Following HDT, peak vascular conductance was reduced in the control condition (0·38 ± 0·02 to 0·24 ± 0·02 ml 100 ml^?1 min^?1 mmHg^?1; P = 0·04), but was restored when subjects performed cycle ergometry (0·33 ± 0·05 to 0·28 ± 0·04 ml 100 ml^?1 min^?1 mmHg^?1; P = 0·46). After HDT, time to fatigue during ischaemic plantar flexion exercise was not different from pre-HDT 24 h after performance of exhaustive cycle ergometry (120 ± 24 vs. 122 ± 19 s), but was decreased in the control condition (116 ± 11 vs. 95 ± 8 s; P = 0·07). These data suggest that a single bout of maximal exercise can provide a stimulus to restore peak vascular conductance and maintain time to fatigue during performance of ischaemic plantar flexion exercise.     

Angiotensin II attenuates reflex decrease in heart rate and sympathetic activity in man

Summary. Circulatory variables and hormone concentrations in arterial plasma were measured in six normal subjects during angiotensin II (ANG II) step-up infusion of 0·25 and 1·00 ng kg^-1× min. During the 1·00 ng kg^-1× min infusion ANG II plasma concentrations increased from 11 ± 2 to 48 ± 6 pg ml^-1; i.e., similar to those obtained during acute hypotensive hypovolemia in man. Mean arterial pressure increased (P<0·05) from a resting value of 89±3 to 97±5 mmHg. Heart rate and catecholamine concentrations did not change. Plasma aldosterone increased (P<0·05) from 36 ± 4 to 77 ± 10 pg ml^-1 during the infusion. Plasma concentrations of vasopressin, adrenalin and pancreatic polypeptide did not change during the investigation. During the 0·25 and 1·00 ng kg^-1× min infusion subcutaneous blood flow decreased (P= 0·06) to 67 ±20 and 66 ±26%, respectively, of control. It is concluded that: (1) ANG II in physiological doses in man may augment the sympathetic activity on the circulatory system since compensatory decreases in heart rate or in plasma catecholamines were not observed during the increased arterial pressure; (2) ANG II does not induce a general decrease in vagal tone as plasma pancreatic polypeptide concentrations were unchanged; (3) the obtained plasma concentrations of ANG II do not stimulate the release of vasopressin to plasma; and (4) the threshold for reducing the subcutaneous blood flow is reached within relatively small increments in plasma ANG II.     

Reduction of the acute bioavailability of metformin by the α-glucosidase inhibitor acarbose in normal man

In a double-blind cross-over study, we investigated a possible influence of the α-glucosidase inhibitor acarbose on the bioavailability of the biguanide compound metformin. Each of the six healthy young male volunteers was randomly allocated during two consecutive 7 day periods to either acarbose (days 1–3: 3 times 50mg day^?1; days 4–7: 3 times 100 mg day^?1) or placebo. At day 7 and 14 of the study, the overnight-fasted subjects ingested 1000mg metformin with the first bite of a standardized breakfast (500kcal; 60 g carbohydrates) and together with either placebo or 100 mg acarbose. Acarbose significantly (P < 0·05) reduced the meal-induced increase in blood glucose and plasma insulin levels. Acarbose induced a significant (P < 0·05) reduction in early (90, 120, 180min) serum levels, peak concentrations (Cmax: 1·22 ± 0·14 vs. 1·87 ± 0·60 mgl^?1) and area under the curve of metformin (AUC 0–540min: 423±55 vs. 652±55 mg minl^?1), but did not diminish its 24 h urinary excretion. In conclusion, acarbose significantly reduces the acute bioavailability of metformin in normal subjects.     

Postprandial impairment of resistance vessel function in insulin treated patients with diabetes mellitus type‐2

Reduced postischaemic reactive hyperaemia, is considered a marker of impaired resistance vessel function. Acute postprandial hyperlipidaemia has been shown to induce vascular dysfunction. In the present study, the impact of postprandial hyperglycaemia on resistance vessel reactivity was investigated in insulin treated type‐2 diabetic patients. The study was performed in 16 insulin treated type‐2 diabetics (eight male/eight female, age 47 ± 3 years, HbA1c 7·2 ± 0·2) and 16 controls. Reactive hyperaemia was measured in the forearm by venous occlusion plethysmography after 5 min of ischaemia in the fasting state and 90 min after a test meal. In diabetics, blood glucose increased from 8·7 ± 1·1 to 15·3 ± 1·0 mmol l^?1 (P<0·001) postprandially. This resulted in (i) a significant increase of resting blood flow (3·4 ± 0·3 to 4·8 ± 0·4 ml min^?1 100 ml^?1, P<0·01) and (ii) in a reduced peak reactive hyperaemia (52·3 ± 7·4 to 36·8 ± 4·3 ml min^?1 100 ml^?1, P<0·005). In controls, a similar effect of the meal on resting flow was observed but reactive hyperaemia was unaltered. In the absence of a test meal, basal flow as well as peak reactive hyperaemia remained unchanged in diabetic as well as in non‐diabetic subjects. Our data provide evidence that in the postprandial state resistance vessel reactivity becomes reduced in insulin treated type‐2 diabetic patients.     

The effect of different exercise‐testing protocols on atrial natriuretic peptide

The aim of this study was to examine and to compare alterations in the secretion of atrial natriuretic peptide (ANP) during different exercise‐testing protocols in moderately trained men. Fifteen healthy male physical education students were studied (mean age 22·3 ± 2·5 years, training experience 12·3 ± 2·5 years, height 1·80 ± 0·06 m, weight 77·4 ± 8·2 kg). Participants performed an initial graded maximal exercise testing on a treadmill for the determination of VO_2max (duration 7·45–9·3 min and VO_2max 55·05 ± 3·13 ml kg^?1 min^?1) and were examined with active recovery (AR), passive recovery (PR) and continuous running (CR) in random order. Blood samples for plasma ANP concentration were taken at rest (baseline measurement), immediately after the end of exercise as well as after 30 min in passive recovery time (PRT). The plasma ANP concentration was determined by radioimmunoassay (RIA). The results showed that ANP plasma values increased significantly from the rest period to maximal values. In the short‐term graded maximal exercise testing the ANP plasma values increased by 56·2% (44·8 ± 10·4 pg ml^?1 versus 102·3 ± 31·3 pg ml^?1, P<0.001) and in the CR testing the ANP levels increased by 29·2% (44·8 ± 10·4 pg ml^?1 versus 63·3 ± 19·8 pg ml^?1, P<0.001) compared to the baseline measurement. Moreover, the values of ANP decreased significantly (range 46·4–51·2%, P<0.001) in PRT after the end of the four different exercise modes. However, no significant difference was evident when ANP values at rest and after AR and PR were compared. It is concluded that the exercise testing protocol may affect the plasma ANP concentrations. Particularly, short‐term maximal exercise significantly increases ANP values, while the intermittent exercise form of active and passive recovery decreases ANP concentrations.     

Autonomic nervous function at rest in aerobically trained and untrained oldermen

Therelationship between aerobictraining, vagal influence on the heart and ageing was examined by assessing aerobic fitness andresting heart rate variability in trained and untrained older men. Subjects were 11 trained cyclistsand runners (mean age=6±61·6 years) and 11 untrained, age-matchedmen (mean age=66±1·2 years). Heart rate variability testing involvedsubjects lying supine for 25 min during which subjects’ breathing was paced andmonitored (7·5 breaths min^?1). Heart rate variability was assessedthrough time series analysis (HRV_ts) of the interbeat interval. Results indicated thattrained older men (3·55±0·21 l min^?1) hadsignificantly (P<0·05) greater VO _2maxthan that of control subjects (2·35±0·15 l min^?1).Also, trained older men (52±1·8 beats min^?1) hadsignificantly (P<0·05) lower supine resting heart rate than that of controlsubjects (65±4·2 beats min^?1). HRV_ts at highfrequencies was greater for trained men (5·98±0·22) than for untrainedmen (5·23±0·32). These data suggest that regular aerobic exercise inolder men is associated with greater levels of HRV_ts at rest.     

Reduced cardiac sympathetic autonomic tone after long-term nasal continuous positive airway pressure in obstructive sleep apnoea syndrome

The increased sympathetic activation that occurs in obstructive sleep apnoea (OSA) may play an important role in associated morbidity. We investigated the effect of long-term (3 month) nasal continuous positive airway pressure (CPAP) on the autonomic nervous system assessed by heart rate variability (HRV). Fourteen patients (12 men), mean age 61·4 ± 8·1 years, with OSA underwent continuous synchronized electrocardiographic and polysomnographic monitoring. The apnoea/hypopnoea index (AHI) decreased from 50·6 ± 13·7 to 2·2 ± 2·5 events h^?1 after CPAP. HRV analysis showed significant decreases in low frequency (LF; from 7·12 ± 1·06 to 6·22 ± 1·18 ln ms² Hz^?1; P<0·001), high frequency (HF; from 5·91 ± 0·87 to 5·62 ± 0·92 ln ms² Hz^?1; P<0·05) and LF/HF (from 1·21 ± 0·12 to 1·11 ± 0·15 ln ms² Hz^?1; P<0·001) when the patients were asleep. The decrease in LF/HF was prolonged into the daytime (from 1·33 ± 0·22 to 1·24 ± 0·21 ln ms² Hz^?1; P<0·001). Treatment of OSA by CPAP significantly reduced the parameters of cardiac sympathetic tone, a favourable effect.     

Interactions of stress hormones on lipid and carbohydrate metabolism in man with partial insulin deficiency

Abstract. The metabolic responses to 4-h infusions of adrenaline (3 μg kg^-1 h^-1) and cortisol (10 mg m^-2 h^-1 for 2 h followed by 5 mg m^-2 h^-1 for 2 h), separately and in combination, have been studied in six healthy subjects with concurrent somatostatin infusion (250 μg h^-1). A combined infusion of adrenaline, cortisol, glucagon (180 ng kg^-1 h^-1) and somatostatin has also been studied. Somatostatin plus adrenaline and somatostatin plus cortisol resulted in hyperglycaemia (at 240 min, somatostatin plus adrenaline 11·4 ± 0·4 mmol l^-1, P < 0·001; somatostatin plus cortisol 6·7 ± 0·3 mmol l^-1, P < 0·05; somatostatin alone 4·9 ± 0·4 mmol l^-1). No synergistic effect on blood glucose was seen with adrenaline and cortisol together. When glucagon was added, blood glucose rose more rapidly than without glucagon (9·3 ± 0·4 mmol l^-1v. 7·2 ± 0·5 mmol l^-1 at 45 min, P < 0·001), but plateau values were similar. Plasma NEFA levels were raised by somatostatin plus adrenaline (0·55 ± 0·04–1·82 ± 0·11 mmol l^-1 at 60 min). Somatostatin plus cortisol had no more effect on plasma NEFA than somatostatin alone. During the combined infusion of somatostatin plus adrenaline plus cortisol, a synergistic effect on plasma NEFA was observed (2·30 ± 0·11 mmol l^-1 at 60 min, P < 0·01 v. somatostatin plus adrenaline). This occurred despite a small escape of insulin secretion. The lipolytic actions of adrenaline are potentiated by elevated circulating cortisol levels in insulin-deficient man. Glucagon does not modify this response, but accelerates the development of hyperglycaemia.     

Effects of di-isopropylfluorophosphate and isopropanol on the measurement of plasma renin activity

Since the protease inhibitor, di-isopropylfluorophosphate (DFP), inhibits the cryoactivation of inactive renin, its addition to stored plasma should prevent unintended renin activation and thereby minimize this source of inaccuracy in the assay of plasma renin activity. However, we have found that 6 mmol/1 DFP in stored frozen plasma actually reduced plasma renin activity from 4.89 ± 0.13 (S.D.) to 2.48 ± 0.17 ng · ml^?1 · h^?1 (p < 0.001). This effect did not occur if DFP was added immediately before assay, suggesting that the decreased renin activity reflected an action of DFP on components of the renin system during storage rather than any interference with the assay method itself. The organic solvent isopropanol, which is required to dilute the DFP, appeared responsible for this phenomenon, for when the isopropanol alone, in concentrations of 20 and 40 μl/ml, was added to stored frozen plasma it decreased plasma renin activity from 3.6 ± 0.3 to 2.2 ± 0.1 and 0.6 ± 0.1 ng · ml^?1 · h^?1, respectively (p < 0.001 in each case). Correspondingly, plasma renin substrate concentrations were decreased to 71% and 6% of control, indicating that the renin activity reductions produced by isopropanol were due to its denaturation of substrate. Moreover, addition of exogenous sheep renin substrate (1400 ng/ml) immediately before assay restored plasma renin activity to control. Thus, although DFP effectively prevents inadvertent renin activation in stored frozen plasma, it would seem important that subsequent assays for plasma renin activity be performed in the presence of added exogenous substrate.     

Effects of intense exercise training on endothelium-dependent exercise-induced vasodilatation

To determine whether intense exercise training affects exercise-induced vasodilatation, six subjects underwent 4 weeks of handgrip training at 70% of maximal voluntary contraction. Exercise forearm vascular conductance (FVC) responses to an endothelium-dependent vasodilator (acetylcholine, ACH; 15, 30, 60 μg min^?1) and an endothelium-independent vasodilator (sodium nitroprusside, SNP; 1·6, 3·2, 6·4 μg min^?1) and FVC after 10 min of forearm ischaemia were determined before and after training. Training elicited significant (P<0·001) increases in grip strength (43·4 ± 2·3 vs. 64·1 ± 3·5 kg, before vs. after, mean ± SEM), forearm circumference (26·7 ± 0·4 vs. 27·9 ± 0·4 cm) and maximal FVC (0·4630 ± 0·0387 vs. 0.6258 ± 0·0389 units, P<0·05). Resting FVC did not change significantly with training (0·0723 ± 0·0162 vs. 0.0985 ± 0·0171 units, P>0·4), but exercise FVC increased (0·1330 ± 0·0190 vs. 0.2534 ± 0·0387 units, P<0·05). Before and after the training, ACH increased exercise FVC above the control (no drug) exercise FVC, whereas SNP did not. Training increased (P<0·05) the exercise FVC responses to ACH (0·3344 ± 0·1208 vs. 0.4303 ± 0·0858 units, before vs. after training, 60 μg min^?1) and SNP (0·2066 ± 0·0849 vs. 0.3172 ± 0·0628 units, 6·4 μg min^?1). However, these increases were due to the increase in control (no drug) exercise FVC, as the drug-associated increase in exercise FVC above control did not differ between trials (P>0·6). These results suggest that exercise FVC is increased by both exercise training and stimulating the release of endothelium-dependent vasodilators. However, training does not affect the vascular response to these vasodilators.     

The effect of a very low-calorie diet-induced weight loss on the severity of obstructive sleep apnoea and autonomic nervous function in obese patients with obstructive sleep apnoea syndrome

The aim of this study was to examine the effect of a very low-calorie diet (VLCD)-induced weight loss on the severity of obstructive sleep apnoea (OSA), blood pressure and cardiac autonomic regulation in obese patients with obstructive sleep apnoea syndrome (OSAS). A total of 15 overweight patients (14 men and one woman, body weight 114 ± 20 kg, age 52 ± 9 years, range 39–67 years) with OSAS were studied prospectively. They were advised to follow a 2·51–3·35 MJ (600–800 kcal) diet daily for a 3-month period. In the beginning of the study, the patients underwent nocturnal sleep studies, autonomic function tests and 24-h electrocardiograph (ECG) recording. In addition, 15 age-matched, normal-weight subjects were studied. They underwent the Valsalva test, the deep-breathing test and assessment of heart rate variability at rest. The sleep studies and autonomic function tests were repeated after the weight loss period. There was a significant reduction in weight (114 ± 20 kg to 105 ± 21 kg, P<0·001), the weight loss being 9·2 ± 4·0 kg (range 2·3–19·5 kg). This was associated with a significant improvement in the oxygen desaturation index (ODI4) during sleep (31 ± 20–19 ±18, P<0·001). Before the weight loss the OSAS patients had significantly higher blood pressure (150 ± 18 vs. 134 ± 20, P<0·05, for systolic blood pressure, 98 ± 10 vs. 85 ± 13, P<0·05, for diastolic blood pressure) and heart rate (67 ± 10 beats min^?1 vs. 60 ± 13, P<0·05) at rest than the control group. They had also lower baroreflex sensitivity (4·7 ± 2·8 ms mmHg^?1 vs. 10·8 ± 7·1 ms mmHg^?1, P<0·01). During the weight reduction, the blood pressure declined significantly, and the baroreflex sensitivity increased by 49%. In conclusion, our experience shows that weight loss with VLCD is an effective treatment for OSAS. Weight loss improved significantly sleep apnoea and had favourable effects on blood pressure and baroreflex sensitivity that may have prognostic implications.     

Determinants of post-ischaemic reactive hyperaemia in patients with diabetes mellitus type II

Dysfunction of resistance arteries is thought to be an early reversible stage in the development of atherosclerosis. Dynamics of post-ischaemic reactive hyperaemia are believed to constitute a useful tool for monitoring resistance vessel function. Patient characteristics influencing reactive hyperaemia, however, need to be defined more precisely. Since reactive hyperaemia is a dynamic process, yielding submaximal peak values after 5 min of ischaemia, this period was chosen to investigate the determinants of reactive hyperaemia in 100 type II diabetic patients as well as in 61 control subjects. Reactive hyperaemia was measured by venous-occlusion plethysmography; clinical and laboratory data were acquired by routine methods. Statistical comparison was performed with SYSTAT 5·0 for Apple Macintosh. Overall, no significant differences between diabetic patients and controls were observed by group comparison. In control subjects, only gender showed an influence on peak reactive hyperaemia (females 40·5 ± 15·3; males 51·8 ± 17·7 ml min^–1 100 ml^–1, P<0·01). In diabetic patients, in addition to gender, actual blood glucose (r=0·377, P<0·05) and meal intake (non-fasting 42·8 ± 19·2; fasting 51·2 ± 19·5 ml min^–1 100 ml^–1, P<0·05) were found to influence reactive hyperaemia. Further investigation revealed a loss of the correlation between peak reactive hyperaemia and actual blood glucose observed in the fasting state (P<0·001) in non-fasting diabetic patients, indicating an influence of meal intake on resistance vessel reactivity. Our results suggest that, in diabetic subjects, in addition to gender actual blood glucose and the postprandial situation impacts on peak reactive hyperaemia.