Acute plasma volume expansion: effect on metabolism during submaximal exercise.
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To examine the effect of acute plasma volume expansion (PVE) on substrate selection during exercise, seven untrained men cycled for 40 min at 72 +/- 2% peak oxygen uptake (VO(2 peak)) on two occasions. On one occasion, subjects had their plasma volume expanded by 12 +/- 2% via an intravenous infusion of the plasma substitute Haemaccel, whereas on the other occasion no such infusion took place. Muscle samples were obtained before and immediately after exercise. In addition, heart rate and pulmonary gas and venous blood samples were obtained throughout exercise. No differences in oxygen uptake or heart rate during exercise were observed between trials, whereas respiratory exchange ratio, blood glucose, and lactate were unaffected by PVE. Muscle glycogen and lactate concentrations were not different either before or after exercise. In addition, there was no difference in total carbohydrate oxidation between trials (control: 108 +/- 2 g; PVE group: 105 +/- 2 g). Plasma catecholamine levels were not affected by PVE. These data indicate that substrate metabolism during submaximal exercise in untrained men is unaltered by acute hypervolemia. (+info)
Interactions between endothelin-1 and the renin-angiotensin-aldosterone system.
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The renin-angiotensin-aldosterone (RAA) system and the endothelin (ET) system entail the most potent vasopressor mechanisms identified to date. Although they were studied in depth in relation to arterial hypertension and cardiovascular diseases, limited information on their interrelationships in causing hypertension and related target organ damage exists. The identification of consensus sequences for jun in the regulatory region of the preproendothelin-1 (ppET-1) gene raised the possibility of its transcriptional regulation by angiotensin II (Ang II). This was confirmed by the finding that stimulation with Ang II of cultured vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) induced expression of the ppET-1 gene and synthesis of ET-1. Endogenously produced ET-1 was found to contribute to the hypertrophic response of cardiomyocytes to Ang II and thereby to cardiac hypertrophy. Furthermore, ET-1 exerts multifaceted effects on the RAA system, such as dose-dependent inhibition of renin synthesis, and stimulation of aldosterone secretion. The finding of abundant specific ET-1 receptors in the adrenocortical zona glomerulosa (ZG) suggested a direct secretagogue effect of ET-1. In rats, ETB receptors mediate such an effect, whilst in humans, both ETA and ETB receptor subtypes intervene in regulating the transcription of the aldosterone synthase gene. In addition, ET-1 stimulates DNA synthesis and proliferation of ZG cells via ETA receptors and, therefore, might play a role in cell turnover of the normal adrenal cortex and in the onset of adrenal tumours. Studies on the in vivo interactions between ETs and the RAA system have given conflicting results, insofar as some suggested a participation of ET-1 in the pressor and cellular effects of exogenously administered Ang II, whereas others did not in the transgenic TGR(Ren 2m)27 rats and in the two-kidney, one clip. (+info)
Effects of a three-day head-down tilt on renal and hormonal responses to acute volume expansion.
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To clarify whether exposure to 6 degrees head-down tilt (HDT) leads to alterations in body fluid volumes and responses to a saline load similar to those observed during space flight we investigated eight healthy subjects during a 4-day, 6 degrees HDT and during a time-control ambulatory period with cross-over. Compared with the ambulatory period, HDT was associated with greater urinary excretion of water and sodium (UV, U(Na)V) from 0 to 12 h (cumulated UV 1,781 +/- 154 vs. 1,383 +/- 170 ml, P < 0.05; cumulated U(Na)V 156 +/- 14 vs. 117 +/- 9 mmol, P < 0.05), and with higher plasma atrial natriuretic factor (ANF) at 4 h. Hemoglobin and hematocrit increased over the first 24 h, and blood and plasma volumes were decreased after 48 h of HDT (P < 0.05). Plasma renin activity (PRA) and aldosterone did not differ between the two groups. With prolongation of HDT, UV and U(Na)V returned close to baseline values. On the fourth HDT day, a 30-min infusion of 20 ml/kg isotonic saline was performed, while a large oral water load maintained a high urine output. The ambulatory period experiment was done with the subjects in the acute supine posture. Sodium excreted within 4 h of loading was 123 +/- 8 mmol during HDT vs. 168 +/- 16 mmol during the ambulatory period (P < 0.05). The increase in plasma ANF and decrease in PRA were greater during HDT than during the ambulatory period (ANF 30 +/- 5 vs. 13 +/- 4 pg/ml, P < 0.05; PRA -1.4 +/- 0.4 vs. -0.5 +/- 0.2 ng. ml(-1). h(-1), P < 0.05). Our data suggest that after a 3-day HDT period, thoracic volume receptor loading returns to the level seen in the upright position, leading to blunted responses to volume expansion, compared with acute supine control. (+info)
Plasma-volume contraction and exercise-induced hypoxaemia modulate erythropoietin production in healthy humans.
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This study examined exercise-induced hypoxaemia (EIH) and plasma volume contraction as modulators of serum erythropoietin (Epo) production. Five athletes cycled for 3 min at supra-maximal power outputs, at each of two different elevations (1,000 m and 2,100 m). Five subjects were exposed to normobaric hypoxia (F(I)O(2)=0.159), seven subjects underwent plasmapheresis to reduce plasma volume and eight subjects were time controls for Epo levels. Oxyhaemoglobin saturation was significantly reduced during exercise and during normobaric hypoxia. The time period of haemoglobin oxygen saturation <91% was 24+/-29 s (mean+/-S.D., n=5) for exercise at 1000 m, 136+/-77 s (mean+/-S.D., n=5) for exercise at 2100 m and 178+/-255 s (mean+/-S.D., n=5) with resting hypoxic exposure. However, significantly increased serum Epo levels were observed only following exercise (24+/-3%; mean+/-S.D., n=5 at 1,000 m and 36+/-5%; mean+/-S.D., n=5 at 2,100 m). Volume contraction also resulted in increased serum Epo (35+/-6%; mean+/-S.D., n=7) in spite of a significant rise in haematocrit of 2.2%. Despite similar degrees of arterial desaturation, only the hypoxaemia induced by exercise was associated with an increase in serum Epo. This finding indicates that other factors, in addition to hypoxaemia, are important in modulating the production of Epo in response to exercise. Volume depletion in the absence of exercise resulted in increases in Epo levels that were comparable with those observed in response to exercise. The paradoxical responses of the increased haematocrit and the increase in Epo in subjects undergoing plasmapheresis suggests that plasma volume may also modulate the production of Epo. (+info)
Clinical efficacy of peritoneovenous shunting for the treatment of severe ovarian hyperstimulation syndrome.
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We investigated prospectively the clinical efficacy of a newly developed continuous autotransfusion system of ascites (CATSA) without protein supplement in patients with severe ovarian hyperstimulation syndrome (OHSS). Peritoneovenous shunting was used to recirculate ascites. The CATSA was performed for 5 h at a rate of 100-200 ml/h once a day. Eighteen patients were treated with the CATSA (CATSA group) and 36 were treated with an intravenous 37.5 g/day of albumin supplement (albumin group). Hospital stay was significantly shorter in the CATSA group than in the albumin group (10.0 +/- 5.7 versus 13.9 +/- 6.2 days, P < 0.01). Haematocrit value reached <40% significantly earlier in the CATSA group (on hospital days 3.9 +/- 3.2 versus 5.9 +/- 2.5, P < 0.01). Using a single procedure, haemoconcentration, urinary output and pulse pressure were markedly improved in the CATSA group compared with the albumin group. Discomfort due to massive ascites diminished promptly and did not recur in nine of 18 CATSA group patients, whereas it persisted in all 36 patients in the albumin group. The serum concentration of protein was maintained in the CATSA group, whereas it did not increase in the albumin group despite daily supplementation with 37. 5 g of albumin. Apparent adverse effects of each procedure were not observed in either group. The mean values of several parameters in the serum pertinent to the coagulation-fibrinolysis system did not change significantly in either group after the procedure. It was concluded that the CATSA procedure expanded circulating plasma volume without exogenous albumin and appeared to lead to a prompt recovery from severe conditions of OHSS. (+info)
Intense exercise stimulates albumin synthesis in the upright posture.
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We tested the hypothesis that an elevation in albumin synthetic rate contributes to increased plasma albumin content during exercise-induced hypervolemia. Albumin synthetic rate was measured in seven healthy subjects at 1-5 and 21-22 h after 72 min of intense (85% peak oxygen consumption rate) intermittent exercise and after 5 h recovery in either upright (Up) or supine (Sup) postures. Deuterated phenylalanine (d(5)-Phe) was administrated by a primed-constant infusion method, and fractional synthetic rate (FSR) and absolute synthetic rate (ASR) of albumin were calculated from the enrichment of d(5)-Phe in plasma albumin, determined by gas chromatography-mass spectrometry. FSR of albumin in Up increased significantly (P < 0.05) from 4.9 +/- 0.9%/day at control to 7.3 +/- 0.9%/day at 22 h of recovery. ASR of albumin increased from 87.9 +/- 17.0 to 141.1 +/- 16.6 mg albumin. kg body wt(-1). day(-1). In contrast, FSR and ASR of albumin were unchanged in Sup (3.9 +/- 0.4 to 4.0 +/- 1.4%/day and 74.2 +/- 8.9 to 85.3 +/- 23.9 mg albumin. kg body wt(-1). day(-1) at control and 22 h of recovery, respectively). Increased albumin synthesis after upright intense exercise contributes to the expansion of greater albumin content and its maintenance. We conclude that stimuli related to posture are critical in modulating the drive for albumin synthesis after intense exercise. (+info)
Effect of acute postexercise ethanol intoxication on the neuroendocrine response to resistance exercise.
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This investigation was conducted to determine the effect of postexercise ethanol intoxication (21.97 +/- 1.09 mmol/l blood) on the response of selected aspects of the neuroendocrine system to a resistance exercise (Ex) session. Nine resistance-trained men (25.0 +/- 1.4 yr, 179.4 +/- 3.4 cm, 79.7 +/- 3.3 kg) were used to compare three 3-day treatments: control, Ex, and ethanol after exercise (ExEt). Blood was collected serially from an antecubital vein before exercise, immediately after exercise, and for pooled analysis at 20-40 (2 samples), 60-120 (4 samples), and 140-300 (9 samples) min after exercise on day 1 and in the morning (2 samples each) on days 2 and 3. Ethanol did not increase circulating epinephrine, norepinephrine, or cortisol concentration (Cort) above Ex elevations. At 60-120 min, only ExEt Cort was greater than control Cort. Concentrations of testosterone, luteinizing hormone, and corticotropin were not affected by either treatment. It is concluded that, although this blood ethanol concentration is insufficient to acutely increase Cort above that caused by Ex alone, it appears that ethanol may have a prolonged effect beyond the Ex response. This blood ethanol concentration does not further stimulate the sympathoadrenal system during the postexercise response. (+info)
The pressor response to water drinking in humans : a sympathetic reflex?
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BACKGROUND: Water drinking increases blood pressure profoundly in patients with autonomic failure and substantially in older control subjects. The mechanism that mediates this response is not known. METHODS AND RESULTS: We studied the effect of drinking tap water on seated blood pressure in 47 patients with severe autonomic failure (28 multiple system atrophy [MSA], 19 pure autonomic failure patients [PAF]). Eleven older controls and 8 young controls served as control group. We also studied the mechanisms that could increase blood pressure with water drinking. Systolic blood pressure increased profoundly with water drinking, reaching a maximum of 33+/-5 mm Hg in MSA and 37+/-7 in PAF mm Hg after 30 to 35 minutes. The pressor response was greater in patients with more retained sympathetic function and was almost completely abolished by trimethaphan infusion. Systolic blood pressure increased by 11+/-2.4 mm Hg in elderly but not in young controls. Plasma norepinephrine increased in both groups. Plasma renin activity, vasopressin, and blood volume did not change in any group. CONCLUSIONS: Water drinking significantly and rapidly raises sympathetic activity. Indeed, it raises plasma norepinephrine as much as such classic sympathetic stimuli as caffeine and nicotine. This effect profoundly increases blood pressure in autonomic failure patients, and this effect can be exploited to improve symptoms due to orthostatic hypotension. Water drinking also acutely raises blood pressure in older normal subjects. The pressor effect of oral water is an important yet unrecognized confounding factor in clinical studies of pressor agents and antihypertensive medications. (+info)