Influence of immersion on respiratory requirements during 30-min cycling exercise.

Immersion is considered to facilitate exercise-based rehabilitation. However, the drag effect of moving limbs in water, likely to increase the respiratory requirements at exercise, is not mentioned in many reports. The energetic and ventilatory requirements of 30 min steady state cycling exercise performed by healthy male subjects in air and during immersion up to the xiphoid in 33 degrees C water were compared. In the first experimental series nine subjects exercised at the same 60% maximal oxygen consumption (V'O2,max) in air and water. In the two ambient conditions, ventilatory variables had similar values, but the ergometric setting had to be reduced during water immersion so that the workload rated only 69+/-20 W (mean+/-SD) in water versus 121+/-32 W (p<0.001) in air. In the second experimental series, the same ergometric work load (122 W) was achieved by nine subjects with an average V'O2 of 2,210+/-300 mL x min(-1) in air versus 2,868+/-268 mL x min(-1) in water (p<0.001). Resting water immersion caused a marked trend for decreasing vital capacity (p=0.06), but no modification of other ventilatory variables. During exercise at similar V'O2, the average values of minute ventilation (V'E), tidal volume (VT), respiratory frequency (fR), tidal inspiratory time (VT/tI) were not different between water and air. However, at similar ergometric workload, V'E, VT, fR, VT/tI and plasma lactate levels were significantly higher in water than in air. Such consequences of the drag effect of water upon limb movements have not been reported in previous studies relying on shorter exercise bouts. Thus, maintaining steady exercise levels in water either led to a decrease in the workload or required a 25% higher oxygen consumption than in air. These findings may be relevant to the prescription of water immersion rehabilitation programmes.

Characterization of human platelet receptors for atrial natriuretic peptide: evidence for clearance receptors.

Characterization of human platelet receptors for atrial natriuretic peptide (ANP) has been performed using two different methods. First, intracellular cGMP levels were measured after platelet stimulation with humanANP (hANP) and CNP, in order to detect the presence of ANP-A or ANP-B receptors. The intracellular cGMP content was not modified either after hANP or CNP platelet stimulation and thus indicated the lack of biological active receptors on these cells. Second, displacements of 125I-hANP were similar when induced by hANP or C4-23ANP (specific ligand of clearance receptor). Consequently, these results confirmed that human platelet membranes bore only clearance receptors for atrial natriuretic peptide.

Atrial natriuretic factor receptors on human platelets.

Specific binding sites for ANF have been identified on human platelets. To determine maximal binding (Bmax) and dissociation constant (Kd), we adapted the only original method by developing a specific sequence of platelet preparation. From venous blood collected on citrated anticoagulant, platelets were prepared by successive centrifugations at 20 degrees C (blood centrifugated at 1500 rpm for 10 min., supernatant centrifugated at 3000 rpm for 1 min., supernatant centrifugated at 2800 rpm for 10 min, the inner platelet-rich layer resuspended in citrated solution) and aliquoted (200 microliters at 5.10(5) platelets/microliters). Competition experiments [incubation of platelets with fixed concentration (20-25 pM) of labeledhuman ANF (125Ih ANF) and increasing concentrations (10(-12) to 10(-6) pM) of unlabeled hANF] led to the drawing of a mean displacement curve (n = 8), usable as reference, and to verification of the specificity of binding assay (cross-reactivity with ratANF, no cross-reactivity with arginine-vasopressine). From saturation experiments [incubation of platelets with increasing concentrations (3.5 to 63.7 pM) of labeled hANF and with (10(-8) M) or without unlabeled hANF], we determined (n = 11): Bmax (m +/- SEM) = 4.5 +/- 0.7 pM or 5.4 +/- 0.8 sites per cell and Kd (m +/- SEM) = 10.84 +/- 1.70 pM.

Hemodynamic responses to 30-min cycling exercise at 70% VO2 max both in ambiant air and during chest-immersion.

The aim of this study was to examine the influence of water immersion to the chest on cardio-vascular adaptation to exercise. Upright or sitting immersion causes an increase in central blood volume, but it remains controversial whether central blood volume remains elevated during dynamic exercise in water and facilitates cardiac adaptation, depending particularly on the intensity of exercise which can be matched for O2 consumption (metabolic range) or for mechanical intensity (work load). We have compared hemodynamic variables measured during two cycling exercises at the same mechanical intensity, performed both in ambiant air and during immersion up to the chest.

Carbohydrate metabolism and urinary excretion of calcium and oxalate after ingestion of polyol sweeteners.

Polyols are widely used instead of glucose and sucrose in sweets and dietary products because they are barely cariogenic, and their energy value is lower. In addition, it has been shown that calciuria and oxaluria increase after an oral glucose (Glu) load. We, therefore, investigated the effects of a single polyol ingestion on carbohydrate, calcium, phosphate, and oxalate metabolism in 10 healthy subjects. On 5 experimental days, subjects ingested 20 g Glu, Lycasin (Lyc), Maltisorb (Mal), sorbitol (Sor), or xylitol (Xyl). Glu, Lyc, and Mal intake caused an increase in glycemia [respectively, +34% (P < 0.001), +15% (P < 0.001), and +15% (P < 0.001)], insulinemia [respectively, +358% (P < 0.001), +88% (P < 0.05), and +94% (P < 0.01)], and C-peptide level [respectively, +170% (P < 0.001), +15% (P < 0.01), and +15% (P < 0.001)]. Conversely, no change occurred in glycemia, insulinemia, or C-peptide levels after ingestion of Sor or Xyl. Urinary calcium increased after Glu (+64%; P < 0.01) and Xyl (+74%; P < 0.01) intake, and urinary phosphate increased after Xyl (+27%; P < 0.05), but decreased after a Glu load (-68%; P < 0.01). Only Xyl increased urinary excretion of oxalate (+53%; P < 0.05). Our results suggest that ingestion of polyols causes a much lesser pancreatic stimulation than Glu intake. Also, Lyc, Mal, and Sor sweeteners have no effect on urinary excretion of calcium and oxalate, whereas calciuria and oxaluria increase after Xyl ingestion.

Influence of hypertonic monosaccharide infusions on the release of plasma arginine vasopressin in normal humans.

Six healthy men were investigated to determine the osmotic efficiency of hypertonic monosaccharide solutes on the release of plasma arginine vasopressin (AVP). Twenty percent hypertonic glucose infused at 0.187 mmol/kg body weight/min. over 15 min. increases plasma osmolality but not AVP. In contrast, 20% hypertonic fructose administered identically obtains an increase in both. An initial 71% rise in AVP concentration (p less than 0.01) occurred 10 min. post-infusion accompanied by a peak in plasma osmolality and we did not expect AVP to rise by 336% (p less than 0.01) 45 minutes after infusion as plasma osmolality was returning to baseline values. The first increase in plasma AVP reflects an osmotic efficiency probably resulting from the fact that fructose does not cross the membrane of osmoreceptor cells. The mechanism of the second and unexpected increase is discussed, especially the influence of plasma insulin released as a result of fructose infusion.

Arginine vasopressin response to insulin-induced hypoglycemia in insulin-dependent diabetics with asymptomatic hypoglycemia.

Insulin-induced hypoglycemia causes an increase in plasma vasopressin (AVP) in healthy subjects but the response in diabetics is not established. We investigated the effect of insulin-induced hypoglycemia on ten insulin-dependent diabetics with asymptomatic hypoglycemia, and compared the results with those for seven healthy subjects. The lack of adrenergic symptoms of hypoglycemia in insulin dependent diabetics being attributed to a diminished beta-adrenergic sensitivity, the effect of isoprenaline infusion was investigated as control. Insulin-induced hypoglycemia resulted in both populations in significant increase (P less than 0.01) in AVP in addition to significant increases in heart rate, plasma epinephrine (E), norepenephrine (NE) and cortisol (COR). Effective osmolality and mean arterial blood pressure did not vary. Diabetics showed smaller increase in AVP (P less than 0.01) and heart rate (P less than 0.05) than controls. Maximal E, NE and COR values did not differ between the two populations. Isoprenaline infusion resulted in increase in heart rate and plasma renin activity, but AVP and COR did not vary in the two populations. In conclusion, insulin-induced hypoglycemia released AVP in diabetics with asymptomatic hypoglycemia, but the response was weaker than in healthy subjects. A causal hypothalamic alteration of beta-adrenergic or glycopenia sensitivity is discussed.

The role of posture on the changes in plasma atrial natriuretic factor and arginine vasopressin levels during immersion.

In seven healthy male volunteers we investigated changes in plasma atrial natriuretic factor [( ANF]), arginine vasopressin [( AVP]) and plasma volume (PV) during supine immersion. Twenty minutes head-out water immersion in a supine position in a thermo-neutral water bath attenuated the increase in PV induced by 20 min in a supine position in air, but increased the mean plasma [ANF] from 32.0 pg.ml-1, SEM 5.1 to 53.3 pg.ml-1, SEM 3.6 and decreased the mean plasma [AVP] from 1.4 pg.ml-1, SEM 0.1 to 0.9 pg.ml-1, SEM 0.04. Simultaneously, diuresis and natriuresis increased markedly. During a 20-min control period in the supine posture without immersion, PV, plasma [ANF] and [AVP] remained unaffected while diuresis and natriuresis did not increase to the same extent. These data suggest that an increase in the central blood volume induced by a weak external hydrostatic pressure during supine immersion triggered the changes in plasma [ANF] and [AVP] and that the increase was probably due to a shift of blood volume from peripheral to central vessels. The changes in plasma [ANF] contributed to the changes in natriuresis.

Urinary calcium and oxalate excretion during oral fructose or glucose load in man.

We studied urinary calcium and oxalate excretion in response to oral fructose load and to oral glucose load each on two different randomized mornings in twelve healthy subjects. Oral fructose load provoked an increase in calciuria and a decrease in oxaluria while oral glucose load induced an increase in both calciuria and oxaluria. These results suggested that in healthy subject, the decrease in oxaluria observed during fructose load reduced the product urinary [calcium] x [oxalate] which was the main factor in the genesis of urinary calcium oxalate stones while glucose load increased the risks of urolithiasis by means of the rise in both calciuria and oxaluria.

Plasma levels of beta-endorphin, prolactin and gonadotropins in male athletes after an international nordic ski race.

Plasma beta-endorphin, prolactin (PRL), FSH and LH were measured in 17 volunteer male subjects at rest and under the stress caused by a long-distance nordic ski race. The race induced increased levels of beta-endorphin and PRL in all skiers. The changes in PRL with exercise were significantly related to the changes in beta-endorphin (r = 0.69, p less than 0.001). Furthermore, the highly trained skiers training over 150 km.week-1 of nordic ski showed consistently higher post-exercise beta-endorphin and PRL levels than the moderately trained skiers who trained for 20 km.week-1. In addition the race induced slight falls in FSH and LH; however plasma gonadotropin levels did not show any correlation with plasma beta-endorphin concentrations and did not differ between the two groups of skiers. These results suggest that endogenous opioid peptides may modulate PRL secretion in heavy exercise, since they are of minor importance in the release of FSH and LH in such a situation. The observations also suggest that the degree of previous training and the exercise intensity do seem to be responsible for the hormonal changes.

[Radioimmunological assay of plasma arginine-vasopressin in man. Comparison of 2 methods of extraction]. / Dosage radioimmunologique de l'arginine-vasopressine plasmatique chez l'homme. Comparaison de deux méthodes d'extraction.

Two methods of extraction, prior to radio-immunoassay (RIA) of human plasma arginine vasopressin (AVP) were tested: ethanol extraction (ETH), chromatography with ODS-Silica (ODS-Sil). Recovery of 125I AVP was higher when using ODS-Sil than when using ETH. Recovery of standard AVP and plasma enriched with standard AVP was found to be more efficient and reproducible for ODS-Sil. However, the RIA used, performed after chromatography with ODS-Sil, is not enough sensitive to detect low concentrations but is able to detect high concentrations and physiological variations of plasma AVP.

Relative effects of the supine posture and of immersion on the renin aldosterone system at rest and during exercise.

The relative influences of the supine posture and of immersion on the renin-aldosterone system (RAS) were studied at rest and during moderate exercise in five healthy men. When supine, resting or immersion to the neck for 20 min in a thermoneutral environment both induced a decrease in plasma renin activity (PRA) when compared with the levels measured after 15 min sitting at rest (resting: -44%, p less than 0.05. Immersion: -45%, p less than 0.05). There was no significant difference in PRA decrease between the two situations. Aldosterone (ALDO) values were lower after supine rest or immersion than those observed after sitting at rest, but the difference was not significant. Two types of exercise at a constant relative work load (40-50% maximal oxygen uptake), namely cycling on an ergocycle in the supine position and free-style swimming, induced increases in PRA and ALDO when compared with the levels measured after 15 min rest when sitting (respectively, PRA = +35%, p less than 0.05, and +45%, p less than 0.05, ALDO = +32%, p less than 0.01 and +35%, p less than 0.05). Increases in PRA and ALDO did not differ between the two exercises. Thus inhibitory effects on RAS of change in external pressure are negligible during water immersion to the neck in the supine position and during swimming at moderate intensity.

Assessment of plasma opioid peptides, beta-endorphin and met-enkephalin, at the end of an international nordic ski race.

Plasma met-enkephalin, beta-endorphin, cortisol and lactic acid concentrations were measured in seventeen volunteer male subjects at rest and after a long-distance nordic ski race. Immediately after the race, mean plasma met-enkephalin did not show any significant change, but significant rises in beta-endorphin, cortisol and lactic acid were noted in all skiers. The change in beta-endorphin with exercise was significantly related to the change in cortisol (r = 0.68; p less than 0.001) and to the change in plasma lactic acid (r = 0.60; p less than 0.001). Furthermore, the experienced skiers training over 150 km X week-1 of nordic ski had significantly faster skiing times in this event and showed greater beta-endorphin, cortisol and lactic acid levels than the recreational skiers who trained for 20 km X week-1. Our results imply that the changes in plasma beta-endorphin depend on the intensity of exercise. However the significance of higher levels of skiing training or previous nordic ski experience in the release of beta-endorphin is expected and cannot be excluded.

Blood pressure and plasma renin activity after magnesium supplementation in the spontaneously hypertensive rat: a study during developing and established hypertension.

The effects of a dietary magnesium supplementation have been studied both on systolic blood pressure and plasma renin activity in the spontaneously hypertensive rat (SHR). This study has been conducted in young (developing hypertension) and mature (established hypertension) male SHR fed during 6 weeks with a normal magnesium diet or with a high magnesium diet. After 6 weeks of diets, the systolic blood pressure was lower in young and mature SHR fed with an increased dietary amount of magnesium than in the young and mature SHR fed with a normal amount of dietary magnesium. Plasma renin activity was similar after the two different diets in young SHR while it was greater in mature SHR receiving a high magnesium diet than in mature SHR receiving a normal diet. Hence, dietary supplementation with magnesium inhibits the development of hypertension in young SHR, and reduces arterial blood pressure in mature SHR. The hypotensive effect observed during magnesium supplementation is not related to an inhibition of the renin release.

Plasma renin and aldosterone changes during twenty minutes' moderate exercise. Influence of posture.

The influence of posture on plasma renin and aldosterone changes during exercise performed at a constant relative work load (40%-50% maximal oxygen uptake) was studied in eight healthy men. Each subject carried out two 20-min exercises on an ergocycle at an interval of 8 days; the first exercise was performed in the normal sitting position (upright exercise), the second in a comfortable supine position (supine exercise). In both cases, heart rate and blood pressure were measured as well as plasma renin activity (PRA), aldosterone (ALDO) and osmolality, before and immediately after exercise, and 15 min following the end of exercise. An increase in heart rate, blood pressure, PRA, ALDO and osmolality was noted at the end of each exercise. This increase was greater in the supine exercise than when upright for PRA and ALDO; plasma osmolality and blood pressure showed identical increases for both types of exercise; increase in heart rate was greater when supine than when upright. PRA and ALDO were still elevated 15 min after the upright activity, but had regained their base values in that time after the supine exercise. Our results show that moderate, relatively brief periods of exercise stimulate the production of renin and aldosterone, but the response is less when supine than in the normal upright position.

[Variations in circulating levels of prolactin and growth hormone during physical exercise in man: influence of the intensity of the workout]. / Variations de la prolactine et de l'hormone de croissance circulantes au cours d'un exercice physique chez l'Homme: influence de la puissance du travail fourni.

In trained subjects, circulating PRL and GH increase significantly after a 20 minutes exercise on ergometer bicycle performed either at submaximal or maximal intensity. The magnitude of PRL response appeared to be similar for both kinds of exercise, but the increase in GH level is higher after maximal exercise than after submaximal one.

Expression of plasma renin activity in terms of urinary sodium excretion and posture in normal subjects on free sodium intake.

Supine and upright plasma renin activities (PRA) were measured in 151 normal subjects on free sodium intake. Supine and upright plasma renin activities were then related to the 24-hour urinary sodium or the 2-hour urinary sodium excretion, measured in the morning after overnight fasting. Urinary sodium excretion was expressed as the urinary rate per hour or as the urinary Na/creatinine ratio. Correlations were found between both supine and upright PRA and 2 h urinary sodium excretion expressed as the Na/creatinine ratio. Supine and upright PRA values are expressed in terms of these correlations with confidence intervals.