Hydration during exercise

Summary Five young unacclimatised subjects were exposed for 4 h at 34 C (10 C dew-point temperature and 0.6 m · s^–1 air velocity), while exercising on a bicycle ergometer: 25 min work — 5 min rest cycles for 2 hours followed by 20 min work — 10 min rest cycles for two further hours. 5 experimental sessions were carried out: one without rehydration (NO FLUID) resulting in 3.1% mean loss of body weight ( M_b), and four sessions with 20 C fluid ingestion of spring water (WATER), hypotonic (HYPO), isotonic (ISO) and hypertonic (HYPER) solutions to study the effects of fluid osmolarity on rehydration. Mean final rehydration (±SE) after fluid intake was 82.2% (±1.2). Heart rate was higher in NO FLUID while no difference among conditions was found in either M_b or hourly sweat rates. Sweating sensitivity was lowest in the dehydration condition, and highest in the WATER one. Modifications in plasma volume and osmolarity demonstrated that NO FLUID induced hyperosmotic hypovolemia, ISO rehydration rapidly led to plasma isoosmotic hypervolemia, while WATER led to slightly hypoosmotic normovolemia.It is concluded that adequate rehydration through ingestion of isotonic electrolyte-sucrose solution, although in quantities much smaller than evaporative heat loss, rapidly restored and expanded plasma volume. While osmolarity influenced sweating sensitivity, the plasma volume changes ( PV) within the range –6% PV+4% had little effect on temperature adjustments in our conditions.     

Overcompensation of food intake following brief periods of food restriction

Four adult female Sprague-Dawley rats, maintained on an ad lib feeding schedule were deprived for either 0, 0.5, 1, 2, 4, 6, or 8 hours during the dark phase of the day-night cycle. It was found that the latency to initiate the first meal following the deprivation was independent of the previous deprivation interval. The animals were found to overcompensate for the periods without food by eating a large initial meal that increased proportionately in size with the duration of food restriction. Furthermore, the animals continued to overeat throughout the day. This deprivation-induced overeating by the animals resulted in an overcompensation in total food consumption that was 21–56% greater than on control days. The role of food intake as a regulator of body weight is discussed.     

Comparison of gastric, duodenal and jejunal contributions to the inhibition of food intake in the rat

Rats equipped with tubes leading to their stomach, duodenum or jejunum were infused with a liquid diet for 9 hr (4 ml/hr) and were allowed to eat during the last 8 hr of infusion. All rats ate significantly less on diet infusion days than on saline or no infusion days. A second study showed that a taste aversion could not be conditioned to flavored water associated with diet infusion. Apparently, intrajejunal injection of nutrients produces satiety and not discomfort. Infusion of the diet for 5 consecutive days into the stomach, duodenum or jejunum consistently and significantly lowered food intake by reducing meal size, not meal frequency. Results suggest that the small intestine below the infusion site contributes to normal satiety.     

Rhythmic patterns of food and water intake in the dog: preliminary study (author's transl)]

The spontaneous rhythmic patterns of food and water intake in the dog during periods of 24 hr have been studied under three experimental conditions: natural light, continuous light and artificial light with day and night sequences. Under natural light there is a rhythmic pattern in the frequency of food intake and the amount of food consumed. During the night, periods of food consumption are numerous and the amount of food ingested is significant. During the day both the number of periods of food intake and the amount of food consumed is less. Similar results were obtained under continuous light. Under artificial light, with day and night sequences, there is a tendency to equalize the amount of food consumed through the 24 hr. This produced a displacement of frequency curves. In these three situations there seems to be an important relationship between the amount of food consumed and the time intervals following periods of food intake. Generally, similar results were obtained for water intake.     

The Relationship Between Cardiac Activity and Sensory Acuity

The relationship between cardiac activity and sensory acuity suggested by Lacey and Lacey was tested by recording heart rates of Ss attempting to detect a threshold-level visual stimulus. Heart rate decelerations during a warning tone preceding the threshold stimulus were found in be greater on hit trials than on miss trials, supporting the suggested relationship.     

Water intake, pleasure and water temperature in humans

The influence of water temperature on intake and affective ratings was explored in human subjects. Dehydration whether by profuse sweating (body weight loss: 289 +/- 11 g, N = 20) or mountain climbing (body weight loss: 1660 +/- 58 g, N = 20) resulted in the same intake. Maximal intake was observed for water at 15 degrees C with respectively 199.0 +/- 17.0 ml and 222.7 +/- 17.4 ml. Colder and warmer water was ingested to a lesser extent. When 20 subjects were allowed to mix water to their preferred temperature, they chose 14.9 +/- 1 degree C and drunk 211.0 +/- 19.5 ml. Votes on a pleasure/displeasure scale increased from 50 degrees C to 0 degree C. Cold water was therefore both more pleasureable and less drunk. Dehydration resulted in a negative alliesthesia for warm water. Positive alliesthesia for cold water was probably the result of hyperthermia rather than dehydration.     

Estradiol and insulin: independent effects on eating and body weight in rats.

The effects of ovariectomy and estradiol replacement were determined in streptozotocin-diabetic female rats maintained on daily injections of protamine zinc insulin. Similar changes in food intake and body weight in these animals and in nondiabetic control animals indicate that the effects of estradiol on these measures are probably not dependent on changes in pancreatic insulin secretion. Acute and chronic insulin challenges in ovariectomized rats maintained on estradiol benzoate, nafoxidine or oil were also examined. The effects of insulin were not attenuated by prior estrogen conditioning, and there was no evidence of insulin resistance. These experiments suggest that the effects of estradiol on body weight and food intake in female rats are not dependent upon altered insulin levels nor attenuation of the effects of insulin. Estradiol may exert its influence on eating and body weight via separate and possibly more direct pathways. The data also are consistent with the suggestion that ovariectomy-induced and hypothalamic obesities are separate phenomena.     

Hypotension and thirst in rats after isoproterenol treatment

Drinking induced in rats by systemic isoproterenol treatment is markedly attenuated after bilateral nephrectomy. The present experiments demonstrate that the hypotension produced by iso-proterenol treatment was more profound, and lasted much longer, in nephrectomized rats than in intact animals. When arterial blood pressure was partially elevated by central administration of angiotensin II or carbachol (Experiment 1) or by intraarterial infusion of epinephrine (Experiment 2), drinking behavior was restored in the nephrectomized animals and their water intakes approximated the amounts consumed by intact rats given isoproterenol. In general, an inverted U-shaped curve was found to define the relation between blood pressure and water intake in rats after isoproterenol treatment. Drinking was most probable when mean arterial blood pressures were in the range of 70–85 mm Hg, whereas rats were unlikely to drink when blood pressures were much below or above this range. These findings indicate that isoproterenol-induced thirst is not dependent on a renal dipsogen, and suggest instead that the hypersecretion of renin that occurs in intact rats is simply permissive of drinking behavior by modulating the hypotensive effects of the drug treatment.     

Benzbromarone disposition and uricosuric action; evidence for hydroxilation instead of debromination to benzarone

Summary Benzbromarone is one of the main uricosuric drugs currently used. We determined plasma concentrations of benzbromarone, bromobenzarone, and benzarone and 24 hour uric acid excretion in ten healthy individuals following fasting application of two different non-micronised benzbromarone brands. In addition we explored the influence of adjusting urinary pH to near neutral values and of concomitant food intake. Benzbromarone was more rapidly absorbed from the test preparation than from the reference preparation; the extent of systemic availability did not differ significantly. Urinary pH adjustment had no clearcut effect, whereas food intake retarded drug absorption (even though not significant because of the variability of the data). Binding of benzbromarone to plasma proteins exceeded 99%. Bromobenzarone and benzarone were not detectable and are unlikely to be major metabolites of benzbromarone. Instead we found two other compounds suggestive of metabolites, one of them being monohydroxilated benzbromarone. The plasma concentrations of the parent compound in one subject exceeded those of the rest of the group, possibly indicating genetic differences in drug metabolism. The uricosuric effect was not related to benzbromarone plasma concentrations.Abbreviations AUC area under the (plasma concentration time) curve - GC-MS gas chromatography-mass spectrometry - HPLC high performance liquid chromatography - t1/2 plasma elimination half life Dedicated to Professor Dr. N. Zöllner on the occasion of his 65th anniversary     

Effect of aerobic capacity on sweat rate and fluid intake during outdoor exercise in the heat

We measured the aerobic capacity, sweat rate and fluid intake of trained athletes during outdoor exercise and examined the relationship between aerobic capacity and thermoregulatory responses at high ambient temperatures. The maximal aerobic capacity ( ) of the subjects, nine male baseball players of college age, was determined by maximal exercise tests on a cycle ergometer. The subjects practised baseball regularly without drinking fluids from 1330 to 1530 hours. After 30 min rest, they played a baseball game with free access to a sports drink at 15°C from 1600 to 1830 hours. At a mean ambient temperature of 36.7 (SEM 0.2)°C, the mean percentage of body mass loss (m _b) and increase of oral temperature (T _o) from 1330 to 1530 hours was 3.47 (SEM 0.12)% and 0.81 (SEM 0.14)°C, respectively. The sweat loss from 1330 to 1830 hours was 56.53 (SEM 1.56)ml · kg^–1 of body mass (M _b) while the mean fluid consumption was 44.78 (SEM 2.39)ml · kg^–1 ofm _b, with recovery of 76.08 (SEM 2.81)% of sweat loss. The was significantly inversely correlated withm _b, fluid intake and rehydration amount, but showed no correlation withT _o. These results would suggest that at a given exercise intensity in subjects with a higher aerobic capacity body temperature is maintained with a lower sweating rate than that in subjects with a lower aerobic capacity.