Dexamethasone in resting and exercising men. I. Effects on bioenergetics, minerals, and related hormones.

A placebo and a low and a high dose of dexamethasone (Dex) were administered for 4.5 days, at 3-wk intervals, to 24 healthy men, following a double-blind, random-order, crossover procedure. After the last dose the subjects performed a maximal cycling exercise, during which respiratory exchanges, electrocardiogram, and blood pressures were monitored. Blood was sampled just before and after each exercise bout. Dex showed no significant effect on fitness, sleep, exhaustion during exercise, maximal O(2) consumption, ventilatory threshold, maximal blood lactate, or rest and exercise blood pressures. On the contrary, both doses of Dex significantly decreased heart rate at rest and during maximal exercise. Blood glucose at rest was higher after both doses of Dex than after placebo; the opposite was found during exercise. Blood levels of ACTH, beta-endorphin, cortisol, and cortisol-binding globulin were lowered by Dex at rest and after exercise. Dex stimulated the increase in atrial natriuretic factor during exercise and lowered rest and postexercise aldosterone. Finally, no difference between "fit or trained" and "less fit or untrained" subjects could be found with respect to Dex effects.     

Regional heat flows of resting and exercising men immersed in cool water

Trunk (HT), limb (HL), and whole-body (HDIR = HT + HL + Hforehead) skin-to-water heat flows were measured by heat flow transducers on nine men immersed head out in water at critical temperature (TCW = 30 +/- 2 degrees C) and below [overall water temperature (TW) range = 22-32 degrees C] after up to 3 h at rest and exercise. Body heat flow was also determined indirectly (HM) from metabolic rate corrected for changes in heat stores. At rest at TCW [O2 uptake (VO2) = 0.33 +/- 0.07 l/min, n = 7], HT = 52.3 +/- 14.2 (SD) W, HL = 56.4 +/- 14.6 W, HDIR = 120 +/- 27 W, and HM = 111 +/- 29 W (significantly different from HDIR). TW markedly affected HDIR but only slightly affected HM (n = 22 experiments at TW different from TCW plus 7 experiments at TCW). During light exercise (3 MET) at TCW (VO2 = 1.06 +/- 0.26 l/min, n = 9), HT = 122 +/- 43 W, HL = 130 +/- 27 W, HDIR = 285 +/- 69 W, and HM = 260 +/- 60 W. During severe exercise (7 MET) at TCW (VO2 = 2.27 +/- 0.50 l/min, n = 4), HT = 226 +/- 100 W, HL = 262 +/- 61 W, HDIR = 517 +/- 148 W, and HM = 496 +/- 98 W. Lowering TW at 7-MET exercise (n = 9, plus 4 at TCW) had no effect on HDIR and HM. In conclusion, resting HL and HT are equal. At TW less than TCW at rest, HDIR greater than HM, showing that unexpectedly the shell was still cooling. During exercise, HL increases more than HT but less than expected from the heat production of the working limbs. Therefore some heat produced by the limbs is probably transported by blood to the trunk. During heavy exercise, HDIR is constant at all considered TW; apparently it is regulated by some thermally dependent mechanism, such as a progressive cutaneous vasodilation occurring as TW increases.     

Effects of syphilis infection on adrenocortical function in men.

It is becoming apparent that severe stress leads to a reduction in 19C-steroid production in the adrenals of humans. Based on the finding in a prior study of high levels of cortisol (F) and subnormal levels of dehydroepiandrosterone sulfate (DS) in umbilical cord serum of newborns having congenital syphilis, we sought to investigate adrenal function in adult men having syphilis and sera from 30 normal men who were pair-matched with the syphilitic men for age and time of blood sampling were compared with respect to their concentrations of DS and F and the DS to F ratio. Serum levels of F (nmol/liter) were significantly higher in syphilitic men (322 +/- 25) than in control men (226 +/- 16), P = 0.0018. Serum DS levels (mumol/liter) were significantly reduced in syphilitic men (5.80 +/- 0.80) compared with normal men (9.84 +/- 0.94), P = 0.0018. Also, the DS to F ratio in syphilitic men was less than 50% than that of the control men, P = 0.0001). Men having advanced (secondary) syphilis had the greatest alteration in adrenocortical function. We hypothesize that the apparent divergence in adrenal production of DS compared with that of F probably is due to factors other than altered pituitary production of adrenocorticotropic hormone, because patterns of adrenal DS and F production similar to those in syphilitic men have been observed by others to occur in conditions of excessive as well as subnormal pituitary adrenocorticotropic hormone secretion.     

Serum and saliva adrenocortical hormones in obese diabetic men during submaximal exercise

The aim of this study was to evaluate serum and saliva adrenocortical hormones and their relationships at rest and during submaximal exercise and recovery in 9 obese diabetic middle-aged men (BMI: 35.2 ± 1.6 kg/m (2)). Blood and saliva samples were taken at rest, every 10 min of a 30-min cycling exercise at 70% of maximal heart rate, and after 10 min of recovery in order to analyze cortisol, dehydroepiandrosterone sulfate (DHEA-S) and dehydroepiandrosterone (DHEA). Serum and saliva cortisol increased significantly during recovery (p<0.05), but no significant difference was observed between the rest, exercise, and recovery DHEA-S and DHEA concentrations. A strong correlation was found at rest between both serum and saliva cortisol (r=0.72, p<0.001) and DHEA-S and DHEA (r=0.93, p<0.001). Serum DHEA-S and saliva DHEA remained strongly correlated during and after the submaximal exercise (r=0.81, p<0.001), whereas a weaker but still significant relationship was observed between serum and saliva cortisol during and after the exercise (r=0.52, p<0.001). In conclusion, these results suggest that saliva adrenocortical hormones, and especially saliva DHEA, may offer a practical surrogate for serum concentrations during both rest and exercise in obese diabetic men.     

Oxygen-conserving effects of apnea in exercising men.

We sought to determine whether apnea-induced cardiovascular responses resulted in a biologically significant temporary O(2) conservation during exercise. Nine healthy men performing steady-state leg exercise carried out repeated apnea (A) and rebreathing (R) maneuvers starting with residual volume +3.5 liters of air. Heart rate (HR), mean arterial pressure (MAP), and arterial O(2) saturation (Sa(O(2)); pulse oximetry) were recorded continuously. Responses (DeltaHR, DeltaMAP) were determined as differences between HR and MAP at baseline before the maneuver and the average of values recorded between 25 and 30 s into each maneuver. The rate of O(2) desaturation (DeltaSa(O(2))/Deltat) was determined during the same time interval. During apnea, DeltaSaO(2)/Deltat had a significant negative correlation to the amplitudes of DeltaHR and DeltaMAP (r(2) = 0.88, P < 0.001); i.e., individuals with the most prominent cardiovascular responses had the slowest DeltaSa(O(2))/Deltat. DeltaHR and DeltaMAP were much larger during A (-44 +/- 8 beats/min, +49 +/- 4 mmHg, respectively) than during R maneuver (+3 +/- 3 beats/min, +30 +/- 5 mmHg, respectively). DeltaSa(O(2))/Deltat during A and R maneuvers was -1.1 +/- 0.1 and -2.2 +/- 0.2% units/s, respectively, and nadir Sa(O(2)) values were 58 +/- 4 and 42 +/- 3% units, respectively. We conclude that bradycardia and hypertension during apnea are associated with a significant temporary O(2) conservation and that respiratory arrest, rather than the associated hypoxia, is essential for these responses.     

Effect of lactate on FFA and glycerol turnover in resting and exercising dogs.

The rates of appearance of FFA (RaFFA) and that of glycerol (RaGLY) were measured simultaneously with [1-14 C]palmitate and [2-3H]-glycerol, in dogs with indwelling arterial and venous catheters. Lipolysis was stimulated by exercise (treadmill run on 10% slope) or by the infusion of norepinephrine (0.5 mug/kg-min). Na-L(+)-lactate (L), Na-pyruvate (Py), or Na-nicotinate (N) were infused. All three components decreased RaFFA. RaGLY was increased by L, unaltered by Py, and decreased by N. There was an inverse correlation (P less than 0.001) between the logarithms of RaFFA and plasma lactate. A linear correlation was obtained between RaGLY and plasma lactate when this latter was increased by the infusion of L. It is suggested that a) lactate in physiological concentrations inhibits the release of FFA stimulated by exercise and b) the increase of the NADH/NAD ratio leads to the formation of alpha-glycerophosphate which in turn yields glycerol. Therefore changes in plasma glycerol do not reflect lipolysis when blood lactate increases. c) The effect of lactate on RaFFA can be explained by an enhanced reesterification, although a direct inhibition on lipase could not be excluded.     

Interrelationship of FFA and glycerol turnovers in resting and exercising dogs.

Dogs with indwelling arterial and venous catheters ran on a treadmill on a 10% or on a 15% slope at 100 m/min. Glycerol turnover ([2-3H]-glycerol) and FFA turnover ([1-14C]palmitate) were measured simultaneously. Both turnovers were greatly increased by exercise. Similar increases were produced in resting dogs by norepinephrine infusions (0.5 mug/kg-min). At rest, as well as during exercise, there was a straight-line correlation between the ratio of disappearance of each substrate and their respective plasma concentrations. Over a wide range there was a straight-line correlation between the rate of production of FFA (RaFFA) and that of glycerol (RaGLY) at rest as well as during exercise. At any given RaFFA, RaGLY was higher in the running than in the resting dog. At rest the ratio of RaFFA/RaGLY was found to give the theoretical value of 3.0 only when RaFFA was 10-15 mumol/kg-min, below this the ratio was lower and above this it was higher. During exercise the ratio was lower than at rest and at heavier load lower than at lighter work. The results suggest that in vivo a combination of partial and complete lipolysis as well as reesterification occurs. The glucose equivalent of the glycerol turnover (if 100% converted) represents (under the given experimental conditions) 14-18% of the hepatic glucose output on the 15% slope and 20-25% of it on the 10% slope.     

Effect of furosemide on pulmonary blood flow distribution in resting and exercising horses.

We determined the spatial distribution of pulmonary blood flow (PBF) with 15-micron fluorescent-labeled microspheres during rest and exercise in five Thoroughbred horses before and 4 h after furosemide administration (0.5 mg/kg iv). The primary finding of this study was that PBF redistribution occurred from rest to exercise, both with and without furosemide. However, there was less blood flow to the dorsal portion of the lung during exercise postfurosemide compared with prefurosemide. Furosemide did alter the resting perfusion distribution by increasing the flow to the ventral regions of the lung; however, that increase in flow was abated with exercise. Other findings included 1) unchanged gas exchange and cardiac output during rest and exercise after vs. before furosemide, 2) a decrease in pulmonary arterial pressure after furosemide, 3) an increase in the slope of the relationship of PBF vs. vertical height up the lung during exercise, both with and without furosemide, and 4) a decrease in blood flow to the dorsal region of the lung at rest after furosemide. Pulmonary perfusion variability within the lung may be a function of the anatomy of the pulmonary vessels that results in a predominantly fixed spatial pattern of flow distribution.     

Effect of warm rearing on temperature regulation in resting and exercising rats

1. 1.|Hypothalamic and rectal temperatures were recorded in 8 warm-reared (wr) and in 12 warm-acclimated control rats during resting in the heat and during 30 min running under thermoneutral conditions.

2. 2.|Brain and body temperatures of wr rats were significantly higher (P < 0.001) than control rats, both in normothermia as well as in hyperthermia; at rest, and also during exercise.

3. 3.|Warm-reared rats were more tolerant to heat.

4. 4.|During normothermia a weak selective brain cooling was present in control but absent in wr rats. During hyperthermia, however, the cooling intensified in control and occurred in wr rats.

5. 5.|The main strategy of adaptation to heat in wr rats is an upward resetting of the temperature set-point and increased passivity.

Effects of strength training on muscle power and serum hormones in middle-aged and older men.

Effects of 16-wk strength training on maximal strength and power performance of the arm and leg muscles and serum concentrations [testosterone (T), free testosterone (FT), and cortisol] were examined in 11 middle-aged (M46; 46 +/- 2 yr) and 11 older men (M64; 64 +/- 2 yr). During the 16-wk training, the relative increases in maximal strength and muscle power output of the arm and leg muscles were significant in both groups (P < 0.05-0.001), with no significant differences between the two groups. The absolute increases were higher (P < 0.01-0.05) in M46 than in M64 mainly during the last 8 wk of training. No significant changes were observed for serum T and FT concentrations. Analysis of covariance showed that, during the 16-wk training period, serum FT concentrations tended to decrease in M64 and increase in M46 (P < 0.05). However, significant correlations between the mean level of individual serum T and FT concentrations and the individual changes in maximal strength were observed in a combined group during the 16-wk training (r = 0.49 and 0.5, respectively; P < 0.05). These data indicate that a prolonged total strength-training program would lead to large gains in maximal strength and power load characteristics of the upper and lower extremity muscles, but the pattern of maximal and power development seemed to differ between the upper and lower extremities in both groups, possibly limited in magnitude because of neuromuscular and/or age-related endocrine impairments.