Biomedical subjects

M Follenius

Publications and source records attributed to M Follenius.

At least 55 records · Page 3Linked to original sources

PubMed1990

Growth hormone and prolactin response to rehydration during exercise: effect of water and carbohydrate solutions.

The effect of progressive rehydration with either water or a carbohydrate solution on the plasma growth hormone (GH) and prolactin (PRL) response to exercise was examined together with plasma somatostatin. Five subjects underwent four 3-h experimental sessions at 36 degrees C in which 25-min exercise periods alternated with 5-min rest periods. The sessions were conducted without fluid replacement (DH) or under rehydration with either water or isosmotic carbohydrate solutions AISO (acid) or NISO (neutral). The fluid was given every 10 min after the 1st h of exercise. Plasma GH increased significantly (p less than 0.01) under DH after 2 and 3 h of exercise; this increase was prevented by rehydration with water, AISO and NISO. Plasma glucose was significantly higher following AISO and NISO rehydration compared with DH. This possibly influenced the GH response, but there was no difference between plasma glucose levels under DH and water rehydration at any time. The solutions tended to attenuate the increase in heart rate, rectal temperature and plasma cortisol, suggesting that the lack of GH response under rehydration conditions is a result of decreasing physiological stress levels. The GH response could not be explained by plasma somatostatin, which tended to decline in all sessions. Plasma PRL did not increase in any of the sessions, confirming that exercise without rehydration is a more potent stimulator of GH than of PRL. It is concluded that progressive rehydration with water is sufficient to prevent the exercise-induced increase in plasma GH.

Adult↗

PubMed1990

Physiological effects of dehydration and rehydration with water and acidic or neutral carbohydrate electrolyte solutions.

Five healthy young men exercised on an ergocycle for six 25-min periods separated by 5-min rest intervals in a warm dry environment (36 degrees C). After 1 h of exercise without fluid intake, the subjects continued to be dehydrated or were rehydrated either with water (W) or with isosmotic electrolyte carbohydrate solutions, either acidic (AISO) or close to neutrality (NISO). The average amount of the fluid ingested progressively every 10 min (120 ml) at 20 degrees C was calculated so as to compensate for 80% of the whole body water loss due to exercise in the heat. Dehydration associated with hyperosmotic hypovolaemia elicited large increases in heart rate (HR), and in rectal temperature (Tre), while no decrease was found in either whole body or local sweat rates. Rehydration with water significantly reduced the observed disturbances, except for plasma osmolality and Na+ concentration which were significantly lower than normal. With both AISO and NISO there was no plasma volume reduction and osmolality increase. Although a plasma volume expansion was induced by NISO ingestion, the cardiac cost was not improved, as reflected by the absence of a decrease in HR. With NISO, sweating was not enhanced and Tre tended to remain higher. It is concluded that efficient rehydration requires the avoidance of plasma volume expansion at the expense of interstitial and intracellular rehydration. During rehydration by oral ingestion of fluid, the pH of the drink may be an important factor; its effect remains unclear, however.

Administration, Oral↗

PubMed1990

Nocturnal oscillations of plasma aldosterone in relation to sleep stages.

This study examined the relationship between aldosterone secretion and sleep stages in conjunction with two aldosterone regulating hormone systems, the renin-angiotensin system (RAS) and adrenocorticotropin (ACTH), and also K+. Nocturnal plasma patterns of aldosterone, plasma renin activity (PRA), ACTH and K+ were established in blood collected at 10-min intervals in two groups of 6 subjects. Both groups underwent two 9 hour overnight-studies, consisting of one control night and one experimental night. The first group was maintained on a low Na diet and the other was given a beta-blocker, atenolol. Polygraphic recordings of sleep were scored according to established criteria. For the control night, REM sleep usually began at peak level or in the descending phase of aldosterone oscillations. As previously described, PRA reflected REM-NREM sleep alteration, levels increased in NREM and decreased during REM sleep. ACTH fluctuations did not oscillate with sleep stages, but levels were very seldom in the ascending phase at REM sleep onset. Plasma K+ remained almost constant throughout the night. The relative importance of the ACTH and the RAS on nocturnal aldosterone secretion and the relationship between aldosterone oscillations and sleep stages remained unclear. Modulating renin levels by either consuming a low Na diet or administration of a beta-blocker enabled this relationship to be clarified. The RAS dominated aldosterone secretion when stimulated by a low sodium diet. Aldosterone oscillations then reflected PRA oscillations with a delay of about 20 min and the relationship of aldosterone to sleep stages was dependent on the relationship of PRA with sleep stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1990

Modulation of episodic renin release during sleep in humans.

We previously described a strong concordance between nocturnal oscillations in plasma renin activity and sleep cycles. To examine whether modifying renal renin content or release influences the response to central stimuli linked to sleep stage alternation, plasma renin activity was measured every 10 minutes from 11:00 PM to 8:00 AM in three groups of six subjects. The first group received one 40 mg dose of the diuretic furosemide; the second group underwent the night experiment after 3 days on a low sodium diet; the third group received one 100 mg dose of the beta-blocker atenolol. Each subject underwent a control night when a placebo was given. The nocturnal curves were analyzed with a pulse detection program. For the control nights, 74 of the 83 sleep cycles were associated with significant plasma renin activity oscillations; non-rapid eye movement sleep occurred in the ascending portions and rapid eye movement sleep in the declining portions of the oscillations. These oscillations persisted in the three groups of subjects during the experimental nights and the relation with the sleep stages was not disturbed. Acute stimulation by furosemide amplified the oscillations and led to a general upward trend of the nocturnal profiles. Similarly, a low sodium diet, which led to a slow increase in renal renin content, provoked large oscillations with high initial levels. However, in both cases the mean relative amplitude of the oscillations, expressed as a percentage of the nocturnal means, was similar to that of the control nights and approximated 60%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

The influence of the initial state of hydration on endocrine responses to exercise in the heat.

This study examines the effect of the initial state of hydration on hormone responses to prolonged exercise in the heat. Five subjects at two initial hydration levels (hypohydrated and hyperhydrated) were exposed to a 36 degrees C environment for 3 h of intermittent exercise. During exercise, the subjects were either fluid-deprived, or rehydrated with water or an isotonic electrolyte sucrose solution (ISO). Both the stress hormones, adrenocorticotropic hormone and cortisol, and the main fluid regulatory hormones, aldosterone, renin activity (PRA) and arginine vasopressin (AVP), were measured in blood samples taken every hour. Prior hyperhydration significantly reduced initial AVP, aldosterone and PRA levels. However, except for AVP, which responded to exercise significantly less in previously hyperhydrated subjects (p less than 0.05), the initial hydration state did not influence the subsequent vascular and hormonal responses when the subjects were fluid-deprived while exercising. Concurrent rehydration, either with water or with ISO, reduced or even abolished the hormonal responses. There were no significant differences according to the initial hydration state, except for PRA responses, which were significantly lower (p less than 0.01) in previously hyperhydrated subjects who also received water during exercise. These results indicate that prior hydration levels influence only slightly the hormonal responses to prolonged exercise in the heat. Progressive rehydration during exercise, especially when extra electrolytes are given, is more efficient in maintaining plasma volume and osmolarity and in reducing the hormonal responses.

Adrenocorticotropic Hormone↗

PubMed1989

Amplification of nocturnal oscillations in PRA and aldosterone during continuous heat exposure.

To assess the effect of continuous heat exposure on the nocturnal patterns of renin, aldosterone, adrenocorticotropic hormone (ACTH), and cortisol, six young men were exposed to thermoneutral environment for 5 days, followed by a 5-day acclimation period in a hot dry environment (35 degrees C). Blood was collected at 10-min intervals during the second night at thermoneutrality (N0) and during the first (N1) and the last (N5) nights of heat exposure. Polygraphic recordings of sleep were scored according to established criteria. Continuous heat exposure led to progressive decreases in the 24-h urinary volume and in Na excretion, whereas urinary osmolality increased. After 5 days of uninterrupted heat, significant increases were found in plasma volume (P less than 0.05), osmolality (P less than 0.01), plasma Na (P less than 0.01), and protein levels (P less than 0.05). Sweat gland output increased during the first 3 days and then declined without any concomitant increases in body temperature. Compared with N0, there were no differences in plasma renin activity (PRA) and aldosterone (PA) profiles during N1 at 35 degrees C. However, during N5 the mean PRA and PA levels were significantly (P less than 0.05) enhanced, and their nocturnal oscillations were amplified (P less than 0.05). This amplification occurred mainly in the second part of the night when regular rapid-eye-movement and non-rapid-eye-movement sleep cycles were observed, leading to a general upward trend in the nocturnal profiles. The relationship between the nocturnal PRA oscillations and the sleep cycles was not modified. ACTH and cortisol patterns were not affected by continuous heat exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1989

Effect of rehydration on atrial natriuretic peptide release during exercise in the heat.

In an attempt to investigate their relationships with plasma volume (PV), heart rate (HR), and other hormonal systems, plasma atrial natriuretic peptide (ANP) levels were determined in response to exercise in the heat, associated with dehydration and rehydration with various fluids. Five normal subjects underwent four 3-h experiments, in a 36 degree C environment, in which 25-min exercise periods on a cycle ergometer at 90 W alternate with 5-min rest periods. Blood samples were collected hourly and ANP, arginine vasopressin (AVP), adrenocorticotropin (ACTH), and cortisol were analyzed in four experimental sessions: without fluid supplement (DH) and with progressive rehydration either with water (W), acid isotonic solution (AISO), or neutral isotonic solution (NISO). Exercise in the heat, accompanied by a decrease in PV and an increase in osmolality, elicited an increase of 28 +/- 1.6 pg/ml in plasma ANP, with concomitant increases in AVP (5.1 +/- 1.4 pg/ml), ACTH (49.6 +/- 12.3 pg/ml), and cortisol (8.4 +/- 2.0 micrograms/100 ml). Progressive rehydration maintained PV and blunted ANP, AVP, ACTH, and cortisol responses. These results demonstrate the importance of rehydration, during exercise in a warm environment, in preventing hormonal increases. They suggest that under our conditions, the PV changes and the inferred atrial pressure changes may not be the primary factors controlling ANP release, as under other physiological conditions. The exercise-related activation of pituitary and adrenals and the stimulation of HR counteract the influence of PV changes due to vascular fluid shifts.

Adrenocorticotropic Hormone↗

PubMed1988

Increase in atrial natriuretic peptide in response to physical exercise.

Circulating atrial natriuretic peptide (ANP) level was determined during physical exercise to investigate the correlation between changes in ANP level and heart rate increases. Six subjects exercised at a work level of 75% VO2max for 30 min, two also performed two successive exercises at 75% VO2max while two more exercised for longer at 55% VO2max. Plasma ANP levels and heart rate increased in all the exercising subjects. At the end of the exercise, the ANP level fell immediately, suggesting an immediate reduction in ANP secretion by the heart. Pre-exercise values were reached after 30 min. Successive exercises gave the same heart rate related ANP patterns without previous secretory episodes having any effect. These results lead to the conclusion that ANP intervenes in the cardiovascular adjustments to exercise.

Adult↗

PubMed1988

Nocturnal fluctuations of plasma atrial natriuretic peptide in normotensive and hypertensive men.

Plasma levels of immunoreactive atrial natriuretic peptides (ANP) were measured at 10-min intervals during night-sleep in 4 normotensive and in 4 moderate, essential hypertensive subjects. The mean ANP levels ranged from 24.3 to 27.9 pg.ml-1 for the normal subjects. These mean levels were not significantly different in the hypertensive subjects (range: 26.3 to 37.2 pg.ml-1). Fluctuations, often of small amplitude, were observed around this mean, without any defined periodicity. Changes in plasma ANP were not associated with changes in heart rate. Analysis of the ANP profiles and the concomitant sleep stage patterns did not reveal any temporal relationship between ANP fluctuations and specific sleep stages or waking periods. The ANP profiles did not differ between the groups, which indicates no abnormality in ANP secretion in moderate essential hypertension.

Adult↗

PubMed1988

Nocturnal oscillations in plasma renin activity and REM-NREM sleep cycles in humans: a common regulatory mechanism?

To establish the strength of the relationship between the nocturnal oscillations in plasma renin activity (PRA) and the sleep stage patterns, 42 PRA profiles from blood collected at 10-min intervals and the concomitant polygraphic sleep recordings were analyzed. In all cases, PRA curves exactly reflected the pattern of sleep stage distribution. When sleep cycles were complete, PRA levels oscillated at a regular 100-min period, with a strong spectral density. Declining PRA levels always coincided with REM sleep phases and increasing levels with NREM sleep phases. More precisely, peak levels corresponded to the transition from deep sleep stages toward lighter ones. The start of the rises in PRA generally marked the transition from REM sleep to stage 2. For incomplete sleep cycles, PRA curves reflected all disturbances and irregularities in the sleep structure. Spontaneous and provoked awakenings blunted the rise in PRA normally associated with NREM sleep, which indicates that disturbing sleep modifies the renin release from the kidneys. These results suggest that a common mechanism within the central nervous system controls both PRA oscillations and the REM-NREM sleep alternation.

Adult↗

PubMed1988

Absence of the dawn phenomenon in normal subjects.

The existence of the dawn phenomenon, defined as an increase in plasma glucose levels and/or insulin requirements in the early morning hours, is well established in diabetic patients but remains controversial in normal subjects. To verify whether this phenomenon occurs in normal subjects, the nocturnal profiles in plasma glucose, insulin, and C-peptide levels; insulin to glucose ratio; and prehepatic insulin production were studied at short intervals (4 and 10 min) in 10 normal men. The first part of the night was characterized by a decrease in all values and the presence of 1 or 2 postprandial fluctuations, followed by a steady state until 0800 h. The individual profiles were frequently superimposable, with rapid 8- to 14-min oscillations. These results do not indicate the existence of a dawn phenomenon in normal subjects.

Adult↗

PubMed1988

REM sleep in humans begins during decreased secretory activity of the anterior pituitary.

The purpose of this study was to define the temporal relationship between anterior pituitary hormone profiles and rapid-eye-movement (REM) sleep occurrence. Plasma levels of prolactin (PRL), adrenocorticotropic hormone (ACTH), luteotropin (LH), thyroid-stimulating hormone (TSH) and growth hormone (GH) were measured in 10 min blood samples. Analysis of the nocturnal profiles for these hormones and the concomitant patterns of sleep stage distribution indicate that the onset of REM sleep very seldom occurred during the increasing phase of secretory episodes. In 93-98% of cases, depending on the hormone studied, it occurred either during the declining phase, at peak level, or at nadir, each of these phases reflecting a decrease in glandular activity. This relationship differed from the very close association previously found between the sleep stage alternation and plasma renin activity. These findings seem to fit in with the concept of reduced sympathetic activity and disruption of the vegetative functions during REM sleep.

Adrenocorticotropic Hormone↗

PubMed1987

Night-day differences in the ultradian rhythmicity of plasma renin activity.

During night-sleep, plasma renin activity displays periodic oscillations which are closely related to the alternation of REM-NREM sleep. To see whether this nocturnal rhythm persisted during the day-time, plasma renin activity was measured every 10 min for 24 hours in 4 human volunteers and in 4 others over a 10-h day-time period. To avoid the influence of repeated food intake which stimulates renin release, the subjects were on continuous enteral nutrition. Spectral analyses of the data revealed clear differences between the nocturnal and the diurnal PRA patterns. In subjects on enteral nutrition, sustained 100-min oscillations with strong spectral densities persisted during the night. They were closely related to REM-NREM cycles. During the day-time, however, the fluctuations were damped and less regular, and power spectra were split into 2 or 3 peaks without any predominant period. These results demonstrate that regular 100-min PRA oscillations could only be detected during night-sleep. The clear night-day differences suggest that the underlying oscillatory mechanisms may be weaker during day-time or may be counteracted by other physiological processes.

Activity Cycles↗

PubMed1987

Postprandial oscillations of plasma glucose, insulin and C-peptide in man.

Postprandial plasma glucose, insulin and C-peptide profiles were studied in eight normal subjects, in the afternoon or in the evening. Two to five synchronous oscillations, with a mean period of 51 to 112 min were detected. The oscillations were highest after meals and were then damped, reverting to fasting levels after up to 340 min. Additional short-term oscillations, with periods of 20-30 min and 9-14 min, were observed. Cross-correlation studies of glucose and insulin and of insulin and C-peptide revealed a high correlation in the frequency bands considered. The synchronous oscillations of insulin and C-peptide suggest cyclic variations in pancreatic secretion rather than cyclic changes in insulin degradation.

Adult↗

PubMed1987

Ultradian plasma corticotropin and cortisol rhythms: time-series analyses.

24-h plasma patterns of ACTH and cortisol were established in 6 subjects who had standard meals and in 4 subjects under continuous enteral nutrition. Temporal relationships between both hormones were analyzed. The individual assay data were subjected to time-series analyses to identify the periods of the oscillations in the plasma levels. The spontaneously occurring cortisol peaks were preceded by increases in ACTH levels, but z-score transformations clearly revealed that ACTH and cortisol were not quantitatively linked throughout the day. Individual subjects' power spectra gave evidence of a predominant periodicity in the oscillations of both hormones. These periodicities varied between individuals. They were 55-140 min for ACTH and 95-180 min for cortisol, indicating that, on occasion, a single cortisol peak may be initiated by two ACTH peaks. Cross spectral analysis of the individual data gave coherence spectra with a large peak which accounted for a substantial concordance of their period length, and cross variance spectra showed a consistent phase relationship between both hormones. These time series analyses applied to the data further support the concept that ACTH is the stimulating factor of cortisol release under basic conditions.

Activity Cycles↗

PubMed1987

Ultradian oscillations of plasma glucose, insulin, and C-peptide in man during continuous enteral nutrition.

The profiles of plasma glucose, insulin, and C-peptide were studied in normal men receiving continuous enteral nutrition. Large oscillations occurred with periods of 53-113 min. Their mean amplitudes, expressed as a percentage of the 24-h mean, were as high as 20% for glucose, 54% for insulin, and 56% for C-peptide. The oscillations of plasma insulin levels throughout the 24 h were concomitant with those of C-peptide. Rapid 8- to 14-min plasma insulin and glucose oscillations were smaller in magnitude and could only be detected in some segments of the longer period oscillations. These results indicate that in addition to the previously described 8- to 14-min oscillations, plasma glucose, insulin, and C-peptide oscillate at a mean 80-min periodicity in man during continuous enteral nutrition. These oscillations may reflect a pancreatic oscillatory mechanism and/or cyclic variations in gastrointestinal motility or peripheral glucose uptake.

Activity Cycles↗

PubMed1986

Vascular fluid shifts and endocrine responses to exercise in the heat. Effect of rehydration.

This study examines the relationships between vascular changes and endocrine responses to prolonged exercise in the heat, associated with dehydration and rehydration by fluids of different osmolarity. Five subjects were exposed, in a 34 degrees C environment for 4 h of intermittent exercise on a cycle ergometer at 85 +/- 12 Watts (SD). Fluid regulatory hormones and cortisol were analysed in 3 experimental sessions: one without any fluid supplement (NO FLUID), and two with progressive rehydration, either by spring water (WATER) or isotonic solution (ISO), given after 70 min of exercise. Results were expressed in terms of differences between the mean values observed at the end of the exercise and the first hour values taken as references. Dehydration (NO FLUID) elicited a 4.0 +/- 0.8% (SE) decrease in plasma volume (PV) and an increase in osmolarity (8.4 +/- 3.1 mosmol X l-1). Concomitantly, plasma aldosterone (PA), renin activity (PRA), arginin vasopressin (AVP) and cortisol (PC) levels increased greatly in response to exercise in the heat (PA: 37.2 +/- 10.8 ng. 100 ml-1; PRA: 13.4 +/- 2.5 ng X ml-1 X h-1; AVP: 3.8 +/- 1.3 pg X ml-1; PC: 12.2 +/- 2.7 micrograms X 100 ml-1). Rehydration with water led to decreased osmolarity (-8.2 +/- 2.1 mosmol X l-1) with no significant changes in PV. With ISO, PV increased by 6.0 +/- 1.3% and the decrease in osmolarity was-5.8 +/- 1.8 mosmol X l-1. With both modes of rehydration, the increases in PRA, AVP and cortisol were blunted; only ISO prevented the rise in PA.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1986

Plasma free cortisol during secretory episodes.

Plasma free cortisol fractions were determined in normal men during spontaneous cortisol secretory episodes and ACTH- or exercise-provoked cortisol peaks in the physiological range. The percentage of free cortisol was measured using ultrafiltration by centrifugation at 37 C, and total cortisol concentrations were measured by RIA. The percent free cortisol varied with the time of day, as did total cortisol. It increased parallel to total cortisol increases, whether they were spontaneous, as occurring in the early morning or postprandially, or provoked by external stimulation. A highly significant positive correlation between relative increases in free and total cortisol was found throughout the experiment. As reported previously, total cortisol increases, according to their origin, did or did not reduce the effects of subsequent stimuli. The present results indicate that the variations in the percent free cortisol are not responsible for the differences in the cortisol responses to these stimuli.

Adrenocorticotropic Hormone↗