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Biomedical subjects

A E Meinders

Publications and source records attributed to A E Meinders.

At least 37 records · Page 2Linked to original sources

Effects of recombinant human leptin treatment as an adjunct of moderate energy restriction on body weight, resting energy expenditure and energy intake in obese humans.

We explored the effects of recombinant human leptin (rL) as an adjunct of mild energy restriction (2092 kJ/day less than needed) in the treatment of obese humans as part of a larger multicentre trial. In a double blind, randomised, placebo (P)-controlled design, the effects of 10 mg of rL once daily vs twice daily (rL OD/BID, by s.c. injection) upon body weight, resting energy expenditure (REE) and energy intake were compared. The study groups comprised 9 (P), 15 (rL OD) and 6 (rL BID) healthy subjects (body mass index 27.5-35 kg/m2). We observed in both groups treated with rL a decline of body weight. [2.8+/-1.1 kg (P), 5.2+/-0.9 kg (rL OD), 7.9+/-1.4 kg (rL BID), p < 0.035]. No significant effects of rL treatment upon energy intake or REE were observed. However, rL tended to reduce the decline of energy expenditure associated with energy restriction, whereas the tendency of energy intake to increase back to baseline levels in placebo-treated subjects was largely prevented in subjects treated with rL. Thus, rL appears to enhance the loss of body weight in obese humans in a dose-dependent fashion if prescribed as an adjunct of energy restriction. This effect might be mediated by rL ability to counteract the behavioural and metabolic adaptations that accompany weight loss attempts.

Adaptation, Physiological↗

Adipose tissue as an endocrine organ: impact on insulin resistance.

It is well known that obesity is associated with insulin resistance and an increased risk for type 2 diabetes mellitus. Formerly it was postulated that increased lipolysis and consequently free fatty acid (FFA) production, from with triglycerides overloaded fat cells, would disrupt glucose homeostasis via Randle's hypothesis. Lipodystrophy, however, also leads to insulin resistance. Recently it has become clear that adipose tissue functions as an endocrine organ and secretes numerous proteins in response to a variety of stimuli. These secreted proteins exert a pleiotropic effect. The proteins that are involved in glucose and fat metabolism and hence can influence insulin resistance are discussed in this paper. They include leptin, resistin, adiponectin, acylation-stimulating protein, tumour necrosis factor-alpha and interleukin-6. The stimuli for production and the site and mechanism of action in relation to insulin resistance will be discussed. None of these proteins are, however, without controversy with regard to their mechanism of action. Furthermore, some of these proteins may influence each other via common signalling pathways. A theory is presented to link the interrelationship between these adipocyte secretory products and their effect on insulin resistance.

Adipose Tissue↗

Insulin resistance but not hypertriglyceridemia per se is associated with endothelial dysfunction in chronic hypertriglyceridemia.

OBJECTIVES: To infer the relative impact of elevated triglyceride levels and insulin resistance on endothelial dysfunction in patients with chronic hypertriglyceridemia (HTG). METHODS: Endothelial function was studied in 11 HTG patients and 16 normolipidemic controls. Cumulative-dose infusions of 5-hydroxytryptamine (5HT) and sodium nitroprusside were infused locally into the brachial artery to study endothelium-dependent and endothelium-independent vasodilation, respectively. Data of the HTG patients were dichotomized around the median of insulin resistance, calculated as HOMA-index, forming HTG groups with mild (HTG-MIR) and severe insulin resistance (HTG-SIR). RESULTS: HTG patients had higher triglyceride levels and smaller LDL particle size than controls (both P< or =0.001), whereas these parameters did not differ between both HTG groups. Insulin resistance was higher in both HTG groups than in controls (11.1 (7.0-14.5) and 4.9 (4.0-6.7) vs. 2.4 (4.9-5.2), respectively, both P<0.001). Similarly, free fatty acid levels, another indicator of insulin resistance, were highest in the HTG-SIR group, followed by those in the HTG-MIR and control group (0.7 (0.6-0.8), 0.5 (0.4-0.6) and 0.4 (0.3-0.4) mmol/l, respectively, all P<0.05). Endothelial-dependent vasodilation was similar in HTG-MIR and controls. In contrast, the response to 5HT was attenuated in the HTG-SIR group compared to controls (low and high dose by, respectively, -60 and -44%, both P<0.01), and tended to be lower than in the HTG-MIR group (-43%, P=0.068 and -41%, P=0.100, respectively). Endothelium-independent vasodilation did not differ between the three groups. CONCLUSION: These findings indicate that chronic hypertriglyceridemia per se is not associated with endothelial dysfunction. In contrast, the presence of insulin resistance, characterized by hyperinsulinemia and FFA elevation, contributes to the induction of endothelial dysfunction in chronic HTG.

Adult↗

Dynamics of the pituitary-adrenal ensemble in hypocretin-deficient narcoleptic humans: blunted basal adrenocorticotropin release and evidence for normal time-keeping by the master pacemaker.

Narcolepsy is a sleep disorder caused by disruption of hypocretin (orexin) neurotransmission. It has been suggested that anomalous timing by the biological clock contributes to the symptomatology. Hypocretins stimulate the pituitary-adrenal (PA) axis in rodents. We explored whether hypocretin deficiency disrupts circadian timing and blunts PA hormone release. We deconvolved 24-h plasma profiles of ACTH and cortisol, and determined their circadian rhythm by cosinor analysis in seven hypocretin-deficient narcoleptic males and seven matched controls. Basal and total ACTH production were blunted in narcoleptics [310 +/- 86 vs. 760 +/-160 ng/liter.24 h (P = 0.02) and 920 +/- 147 vs. 1460 +/- 220 ng/liter.24 h (P = 0.04), respectively], whereas pulsatile release did not differ between groups. In contrast, basal, pulsatile and total cortisol secretion were similar in both groups. The cross-approximate entropy of the joint ACTH/cortisol time series was higher in narcoleptics (1.26 +/- 0.07 vs. 1.07 +/- 0.04; P = 0.04), reflecting reduced secretory process regularity. The acrophases of both ACTH and cortisol occurred at similar clock times (approximately 0830 h) in patients and controls, which supports the idea that the master pacemaker is intact in narcolepsy. The reduced (basal) ACTH secretion and the diminished secretory process regularity of the ACTH/cortisol ensemble conjointly suggest that hypocretin deficiency induces changes in the interplay between PA hormones.

Adrenal Glands↗

Reduction of plasma leptin levels and loss of its circadian rhythmicity in hypocretin (orexin)-deficient narcoleptic humans.

Recent observations have implicated hypocretin deficiency in the pathogenesis of narcolepsy. Hypocretin neurotransmission also affects energy balance, and narcoleptic patients tend to become obese. Because hypocretins appear to have important neuroendocrine effects, we hypothesized that the neuroendocrine systems that regulate energy balance might be distinctly set in narcolepsy. As leptin is a pivotal part of these systems, we explored the 24-h plasma leptin (20-min sampling interval) concentration profile in six narcoleptic males and six normal controls, matched for age, sex, body mass index, waist/hip ratio, and fat mass. We thus demonstrated a reduction of the mean 24-h leptin concentration in narcoleptics to 52% of that in controls (5.9 microg/liter in narcolepsy vs. 11.4 microg/liter in controls; P < 0.05). Further, a nocturnal acrophase (clock time of the highest concentration), which is typical of normal leptin secretion, was observed in controls (mean, 2335 h; 95% confidence interval, 2105-0205 h), but not in narcoleptic patients. The mechanisms that potentially disturb the circadian rhythm of leptin levels in hypocretin-deficient narcoleptic humans include anomalies of the sleep-wake cycle and/or disruption of the circadian distribution of autonomic activity. As leptin deficiency clearly leads to morbid obesity in experimental animals and humans, we infer that the observed reduction of plasma leptin levels may predispose narcoleptic humans to weight gain.

Adult↗

Selection for the internal medicine residency programme in the Leiden region.

BACKGROUND: The selection and the professional training for a resident in internal medicine requires a great investment of time, training effort and money. Drop-outs are therefore considered a failure of the selection procedure. To evaluate our selection model and outcome of the training programme, we determined the drop-out rate at the Leiden University Medical Centre with its affiliated hospitals. METHODS: Data were collected from all files that have been kept from 1988 onwards of all internists trained and registered in Leiden. These files contained the application forms, the assessments of the trainers and references and the specifications of the programme. Also the first employment as board-certified internist is registered. RESULTS: The drop-out percentage of the training programme was 8.5%. The drop-outs did not differ in study characteristics from those who successfully completed the programme. The reports from the training team members showed that the drop-outs were as suitable and motivated as the other candidates. During the training programme 8.5% of the residents moved to another university to complete their training as an internist. All board-certified internists who graduated at the Leiden University Medical Centre found a job. CONCLUSIONS: The efficacy of the selection procedure for trainee internists is more than 90%. There are no studies in the literature for a comparison of data.

Adult↗

[Role of statins in prevention of stroke and dementia].

There is accumulating evidence that statins reduce stroke risk, even though total cholesterol is not a risk factor for stroke. The explanation for this discrepancy is subject to discussion. It should be realised that the beneficial effects of statins on stroke risk have only been demonstrated in a select population, i.e. middle-aged men with ischaemic heart disease. Several clinical trials are underway to examine the effects of statins on stroke risk in more characteristic groups of patients who are at increased risk of developing stroke. The results of these studies should be awaited before statins are recommended for the prevention of stroke. Recently it has been reported that statins lower the risk of developing dementia. These conclusions were drawn from two cross-sectional studies. Because of the nature of the studies, only an association between the use of statins and a lower risk of developing dementia was shown, and not a causal relationship. Experimentally-controlled studies have to be designed to investigate the effect of statins on dementia.

Anticholesteremic Agents↗

[The thiazolidinedione derivates: a new class of oral blood glucose lowering agents].

The thiazolidine-dione derivatives are a new class of oral blood-glucose lowering drugs in type 2 diabetes. They increase the sensitivity of target tissues to insulin, thereby reducing insulin resistance. They act by activation of a specific nuclear receptor--the peroxisome proliferator-activated receptor gamma (PPAR-gamma)--which increases transcription of certain genes involved in adipocyte differentiation and lipid and glucose metabolism. They increase glucose disposal, reduce hepatic glucose output and reduce both plasma glucose and circulating insulin. By reducing insulin requirements the hypersecretion of the beta cell can be diminished, thereby sparing beta cell function. Thiazolidine-dione derivatives reduce plasma glycosylated haemoglobin (HbA1c) by about 1 to 2%. Combination therapy with sulphonylurea derivatives or metformin seems to be more effective, i.e. lower dosages of either agent or both are sufficient to achieve the same reduction in plasma glucose and HbA1c as monotherapy. The thiazolidine-dione derivatives are generally well tolerated and the new drugs such as rosiglitazone and pioglitazone do not seem to be associated with idiosyncratic hepatotoxicity.

Administration, Oral↗

Atrial natriuretic peptide infusion and nitric oxide inhalation in patients with acute respiratory distress syndrome.

AIM: To study the effects of infusion of atrial natriuretic peptide (ANP) versus the inhalation of nitric oxide (NO) in patients with an early acute respiratory distress syndrome (ARDS). METHODS: Ten patients with severe ARDS were studied in a crossover study design, within 72 hours after starting mechanical ventilation. We studied the effects of ANP infusion (10 ng/kg/min for 1 hour) and of inhalation of NO (20 ppm for 1 hour) on hemodynamic and respiratory patient parameters, as well as the effects on plasma levels of ANP, guanosine 3',5'-cyclic monophosphate, nitrate and endothelin-1. RESULTS: Despite an approximate 50% increase in mixed venous ANP plasma concentration (from 86 +/- 21 to 123 +/- 33 ng/l, P < 0.05) during ANP infusion, there were no changes in mean pulmonary artery pressure, pulmonary vascular resistance index, extravascular lung water index, or in pulmonary gas exchange. NO inhalation, in contrast, lowered mean pulmonary artery pressure (from 26 +/- 1.9 to 23.9 +/- 1.7 mmHg, P < 0.01), pulmonary vascular resistance index (from 314 +/- 37 to 273 +/- 32 dynes/cm5/m2, P < 0.05) and central venous pressure (from 8.2 +/- 1.2 to 7.3 +/- 1.1 mmHg, P < 0.02). Furthermore, NO inhalation improved pulmonary gas exchange, reflected by a decrease in alveolar-arterial oxygen gradient (from 41.9 +/- 3.9 to 40.4 +/- 3.6 kPa, P < 0.05), a small increase in oxygenation (PaO2/FiO2 from 17.7 +/- 1.4 to 19.7 +/- 1.1 kPa, P = 0.07) and a small decrease in venous admixture (Qs/Qt from 35.7 +/- 2.0 to 32.8 +/- 2.7%, P = 0.11). CONCLUSION: This study shows that, in contrast to NO inhalation, infusion of ANP neither improves oxygenation nor attenuates pulmonary hypertension or pulmonary edema in patients with severe ARDS.

Administration, Inhalation↗

[From gene to disease; leptin and obesity].

Homozygous mutations of the ob gene, encoding leptin, are associated with severe obesity, hyperphagia and insulin resistance in humans. Leptin conveys a signal from adipose tissue to hypothalamic nuclei that integrate whole body fuel metabolism, informing those nuclei about the magnitude of fuel reserves. In the absence of leptin, the brain perceives energy availability as insufficient and therefore activates powerful mechanisms to restore fuel depots. If leptin synthesis or signal transduction is perturbed in the presence of food, a severely obese phenotype ensues.

DNA Mutational Analysis↗

Impaired endothelium-dependent vasodilation in type 2 diabetes mellitus and the lack of effect of simvastatin.

OBJECTIVE: Although type 2 diabetes is recognized as an independent risk factor for cardiovascular disease and cardiovascular disease is associated with endothelial dysfunction, the influence of type 2 diabetes per se on the endothelial function is controversial. HMG-CoA-reductase inhibitors have been shown to have short-term beneficial effects on endothelial dysfunction among patients with dyslipidemia or cardiovascular disease. The effect of HMG-CoA reductase inhibitors on the endothelial function in diabetes is largely unknown. METHODS: Seventeen patients with type 2 diabetes, free of cardiovascular disease and no other cardiovascular risk factors, except for dyslipidemia, were studied together with ten healthy volunteers. The effect of 5-hydroxytryptamine, as an endothelium-dependent vasodilator, and sodium nitroprusside, as an endothelium-independent vasodilator, on the forearm blood flow was measured using venous occlusion plethysmography. RESULTS: 5-Hydroxytryptamine and sodium nitroprusside, infused in the brachial artery, caused a dose-dependent vasodilation. The vasodilator response to 5-hydroxytryptamine was significantly lower among the diabetic patients, 42 and 56%, than among the controls, 73 and 103%, at a dose of 0.3 and 0.9 ng/kg/min, respectively (P<0.05 and P<0.001). Vasodilator responses to sodium nitroprusside were comparable among the diabetic patients and controls. A 6-week treatment with simvastatin 40 mg once daily did not change the vasodilator responses to 5-hydroxytryptamine or sodium nitroprusside among the patients with diabetes. CONCLUSIONS: The results of this study indicate that the endothelial function is impaired in type 2 diabetes and is not restored after a 6-week treatment period with simvastatin 40 mg.

Case-Control Studies↗

Lithium-induced nephrogenic diabetes insipidus.

Two patients with severe lithium-induced nephrogenic diabetes insipidus are described. Although it is known lithium can cause diabetes insipidus, one should be especially alert in psychiatric patients, as the main defence mechanisms thirst and drinking behaviour may not function adequately in these patients. The major form of therapy in both patients consisted of drinking, a thiazide diuretic, as well as a protein and sodium restricted diet.

Aged↗

Sixty-eight-year-old patient with hypokalemia.

A 68-year-old patient with severe hypokalemia and metabolic alkalosis is described. Six years before admission he had been treated for a small cell bronchial carcinoma. We discuss the diagnostic approach of hypokalemia and the way in which we reached the diagnosis. The patient suffered from metastatic small cell carcinoma with a very high plasma adrenocorticotropic hormone concentration, possibly due to production of corticotropin-releasing hormone by the malignancy.

Aged↗

Hyponatremia due to hypothyroidism: a pure renal mechanism.

Hyponatremia is a common disorder. When hyponatremia is the result of hypothyroidism it can be successfully treated with thyroid hormone substitution. We followed cumulative sodium- and fluid balances of a patient with hyponatremia, resulting from hypothyroidism. We concluded that hyponatremia in hypothyroidism is due to a pure renal mechanism, and cannot be ascribed to inappropriate secretion of antidiuretic hormone.

Aged↗

Hypernatremia in a non insulin dependent (type 2) diabetic patient with central diabetes insipidus.

We describe a patient with central diabetes insipidus who presented with hyperosmolar, non-ketotic hyperglycaemia. The role in this case of reduced thirst sensation with decreased water intake and abnormal AVP production illustrates the importance of these protective mechanisms in normal physiology regarding maintenance of normal plasma osmolality. Despite the complex pathophysiology in this patient, fluid resuscitation aimed at normalisation of the water deficit resulted in full recovery.

Brain Neoplasms↗

Hyponatremia in intracranial disorders.

Hyponatremia is a common electrolyte disturbance following intracranial disorders. Hyponatremia is of clinical significance as a rapidly decreasing serum sodium concentration as well as rapid correction of chronic hyponatremia may lead to neurological symptoms. Especially two syndromes leading to hyponatremia in intracranial disorders need to be distinguished, as they resemble each other in many, but not all ways. These are the syndrome of inappropriate ADH secretion (SIADH) and the cerebral salt wasting syndrome (CSW). The syndrome of inappropriate ADH secretion is characterized by water retention, caused by inappropriate release of ADH, leading to dilutional hyponatremia. The cerebral salt wasting syndrome on the other hand, represents primary natriuresis, leading to hypovolemia and sodium deficit. SIADH should be treated by fluid restriction, whereas the treatment of CSW consists of sodium and water administration. However, in the literature there is abundant evidence that hyponatremia in intracranial diseases is mostly caused by CSW. Therefore, treatment with fluid and salt supplementation seems indicated in patients with intracranial disorders who develop hyponatremia and natriuresis.

Brain Diseases↗

Lactic acidosis: pathophysiology, diagnosis and treatment.

Lactic acidosis is common in severely ill patients. We describe four patients with a lactic acidosis combined with other acid-base disturbances. In daily practice it is important to consider these combined disturbances since there is no specific treatment in lactic acidosis. Treating the underlying causes of the acid-base disturbances is the only warranted intervention. However, lactic acidosis is still associated with high mortality.

Acidosis, Lactic↗