Jolanta Chwalbińska-Moneta

Threshold increases in plasma growth hormone in relation to plasma catecholamine and blood lactate concentrations during progressive exercise in endurance-trained athletes

Plasma human growth hormone ([HGH]), adrenaline ([A]), noradrenaline ([NA]) and blood lactate ([La−]b) concentrations were measured during progressive, multistage exercise on a cycle ergometer in 12 endurance-trained athletes [aged 32.0 (SEM 2.0) years]. Exercise intensities (3 min each) were increased by 50 W until the subjects felt exhausted. Venous blood samples were taken after each intensity. The [HGH] and catecholamine concentrations increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to the lactate threshold ([La−]-T). Close correlations (P < 0.001) were found between [La−]b and plasma [HGH] (r = 0.64), [A] (r = 0.71) and [NA] (r = 0.81). The mean threshold exercise intensities for [HGH], [A] and [NA], detected by log-log transformation, [154 (SEM 19) W, 162 (SEM 15) W and 160 (SEM 17) W, respectively] were not significantly different from the [La−]-T [161 (SEM 12) W]. The results indicated that the threshold rise in plasma [HGH] followed the patterns of plasma catecholamine and blood lactate accumulation during progressive exercise in the endurancetrained athletes.

Greater serum GH response to arm than to leg exercise performed at equivalent oxygen uptake.

SummaryThe aim of this study was to provide information concerning the mechanism of exercise-induced stimulation of growth hormone (GH) release in human subjects. For this reason serum GH as well as some hemodynamic variables and blood concentrations of noradrenaline (NA), insulin (IRI), lactate (LA), glucose (BG), and free fatty acids (FFA) were determined in seven healthy male subjects exercising on a bicycle ergometer with arms or legs and running on a treadmill at equivalent oxygen consumption levels. Significantly greater increases in serum GH concentration accompanied arm exercises than those observed during the leg exercises. This was accompanied by greater increases in heart rate, blood pressure, and plasma NA and blood lactate concentrations. Serum IRI decreased during both leg exercises and did not change during the arm exercise. There were no differences in BG and plasma FFA concentrations between the three types of exercise.The role of humoral and neural signals responsible for the greater GH response to arm exercise is discussed. The findings are consistent with the hypothesis that neural afferent signals sent by muscle “metabolic receptors” participate in the activation of GH release during physical exercise. It seems likely that the stimulation of these chemoreceptors is more pronounced when smaller muscle groups are engaged at a given work load. However, a contribution of efferent impulses derived from the brain motor centres to the control system of GH secretion during exercise is also possible.

ADH and thermal sweating.

SummarySweating responses to heat exposure were compared in healthy subjects pretreated with pitressin or alcohol and in the control group. Between the three groups, there were no consistent differences in the rate of sweating expressed both as a total body weight loss during 2-h heat exposure and in mg of sewat per skin area covered by a paper disc. Likewise, there were no differences in the sweat osmolality or electrolyte concentration. There was also no evidence of inverse correlation between plasma ADH level and rate of sweat secretion or its concentration when pooled data of all subjects were analyzed. It was concluded that ADH did not substantially affect thermal sweating in men.

Renal function changes during preoptic-anterior hypothalamic heating in the rabbit

SummaryThermoregulatory reactions evoked by selective preoptic-anterior hypothalamic (PO/AH) heating in conscious rabbits were associated with significant changes in renal function. Urine flow rate decreased from a control value of 0.92±(S.E.) 0.08 to 0.47±0.07 ml/min after 10–20 min of heating, urine osmolality increased from 273±34 to 417±46 Osm/kg H2O, and free water clearance per 100 ml GFR decreased from 1.11±0.46 to −0.50±0.23 ml/min. These changes were followed by a gradual recovery despite continued heating. Clearances of exogenous creatinine and p-aminohippurate fell transiently during the first 10 min of heating and then returned to normal.Plasma antidiuretic activity (ADA) measured by rat bioassay increased regularly and markedly during PO/AH heating but was poorly correlated with changes in urine concentration. Moreover, a similar increase in plasma ADA observed with selective heating of a different brain area (supraoptic nucleus) never produced urine concentration or other renal changes. This suggests that a large and variable fraction of ADA appearing in rabbit blood in response to thermal stimuli was not identical with antidiuretic hormone. Therefore, the causal relationship of ADH release and antidiuresis associated with thermoregulatory reactions could not be clearly demonstrated. The physiological role of renal water conservation would be to compensate for extrarenal water loss related to thermal sweating or panting.

Plasma noradrenaline response to sustained handgrip in patients with essential hypertension

SummaryThe responses of plasma noradrenaline, arterial blood pressure, and heart rate to sustained handgrip at 30% maximal voluntary contraction were studied in untreated patients with essential hypertension and in healthy subjects of comparable age.There were no significant differences between these two groups in the intensity and duration of handgrip. Increases in heart rate and blood pressure induced by the effort were similar in hypertensive patients and normotensive control subjects, whereas the absolute levels of blood pressure were considerably higher in the patients.In the first 1–2 min of exercise the increases in plasma noradrenaline concentration were similar in both groups. Subsequently, plasma noradrenaline concentration tended to plateau in hypertensive patients while in control subjects it continued to increase. The elevation of plasma noradrenaline in the last minute of effort was, therefore, significantly smaller in hypertensive patients than in the control group.

PLASMA CATECHOLAMINES DURING SUSTAINED ISOMETRIC EXERCISE IN HEALTHY SUBJECTS AND PATIENTS WITH ESSENTIAL HYPERTENSION AND DIABETES MELLITUS

Publisher Summary Evidence indicates a powerful sympathetic activation in response to the stress of static effort. Sustained isometric muscular contractions produce a marked increase in arterial blood pressure and heart rate. A study with pharmacological adrenergic and cholinergic blocking agents suggested that the cardiovascular response to static effect is elicited by an increase in sympathetic tone and by a release of heart from vagal inhibition. The present study was undertaken to obtain information concerning the adrenergic response to isometric exercise-stress in healthy subjects and in patients with essential hypertension and diabetes mellitus. Activation of the adrenergic system is not related to the muscle pain or fatigue since the increase in plasma noradrenaline (NA) occurred as early as in 30 sec of handgrip, when there was no fatigue or pain. Plasma NA concentration stabilized in the final period of exercise in healthy subjects and decreased in myasthenic patients, when the perceived exertion and muscle pain attained its maximal intensity. The pattern of the changes in plasma NA in healthy subjects and in patients with myasthenia does not support the hypothesis that the increase in sympathetic activity is a result of a direct action, of impulses from motor cortex on the circulatory sympathetic centers, because the efferent impulses to muscles have been shown to increase when the maximal force decreases as a result of fatigue.