PubMed Health⌕ Search

Biomedical subjects

R W Hubbard

Publications and source records attributed to R W Hubbard.

At least 55 records · Page 3Linked to original sources
PubMed1988

Responses of plasma human atrial natriuretic factor to high intensity submaximal exercise in the heat.

No data exists regarding responses of human atrial natriuretic factor (ANF) to exercise in the heat. The purpose of this study was to examine the responses of plasma ANF to high intensity submaximal (71% +/- 0.9 VO2max) exercise in the heat over an eight day acclimation period. Fourteen healthy males volunteered to participate in the study. Subjects performed intermittent exercises on a treadmill (0% grade) during 50 min of each 100 min trial in an environmental chamber maintained at 41.2 +/- 0.5 degrees C, 39.0 +/- 1.7% relative humidity. Blood was obtained from an antecubital vein after standing 20 min in the heat prior to exercise, and immediately after exercise. Measures were compared on days 1, 4 and 8. ANF did not change pre- to post-exercise nor did it change over the eight day heat acclimation period despite other heat acclimation adaptations. Conversely, plasma aldosterone (ALDO), renin activity (PRA) and cortisol (COR) all increased (p less than 0.05) pre- to post-exercise on each day but again no changes were observed over the eight day period. These data support that ANF may not increase when ALDO and PRA increases are observed.

Acclimatization↗
PubMed1988

Testing a mechanism of control in human cholesterol metabolism: relation of arginine and glycine to insulin and glucagon.

Eight men were given 2 casein meals, one with and one without a supplement of arginine and glycine, to measure the effect on plasma amino acids, insulin and glucagon. Supplementation resulted in increased levels of plasma glucagon, glycine and arginine, a tendency to decreased insulin and significantly lower insulin/glucagon ratio, tryptophan and tyrosine. The data suggest that insulin and glucagon, which control cholesterol metabolism, respond to dietary and postprandial plasma amino acid levels of arginine and glycine.

Amino Acids↗
PubMed1988

Carbamates, atropine, and diazepam: effects on performance in the running rat.

We have reported that when rats (500 g, male) are exercised to exhaustion on a treadmill, pretreatment with the centrally acting carbamate physostigmine reduced endurance (run time, RT) and increased the rate of rise of core temperature (Tc+). Both RT and Tc+ were restored to control levels by pretreatment with either or a combination of atropine (A), and diazepam (D). Our objective in the present work was to determine whether A+D could also restore the performance and thermoregulatory decrements induced by the peripherally acting carbamate pyridostigmine (PY). After drug administration, rats were run (11 m/min, 6 degrees elevation, Ta = 26 degrees C) to exhaustion. PY treatment resulted in a reduced RT and an increased heat gain that neither A nor D alone (A+PY and D+PY) could restore to control levels. On the other hand, a combination of both A and D restored these variables to control levels. In conclusion, A+D can restore the performance and thermoregulatory decrements resulting from the administration of either a centrally or a peripherally acting carbamate.

Animals↗
PubMed1988

Separate effects of dietary protein and fat on serum cholesterol levels: another view of amino acid content of proteins.

Casein or soy protein with vegetable or animal fat were used to determine the dietary protein or fat effects and their possible interaction on serum cholesterol levels. Young, male New Zealand white rabbits with a mean weight of 2.1 kg were divided into groups of six and fed one of four different diets containing 20% of the calories as protein, 30% as fat (according to dietary guidelines for the United States) and 50% as carbohydrate. The diets contained casein or soy (lysine/arginine ratio = 2.2 or 0.9, respectively) as the protein sources with fat from either almond oil or butter. There was no significant difference in weight gain among the diet groups. Total serum cholesterol level was highest among animals fed the diet containing butter with casein (177 +/- 25 mg/dl) or soy protein (189 +/- 50 mg/dl), it was intermediate in animals fed the vegetable oil with casein (121 +/- 14 mg/dl), and lowest in the soy protein with vegetable oil group (58 +/- 12 mg/dl). There was a significant difference in serum cholesterol levels due to the protein effect when vegetable oil was used (p less than 0.05) but not with butter. There was also a significant fat effect on serum cholesterol when the diet contained soy protein (p less than 0.005) but not when the protein was casein. No significant interaction was observed between the dietary fat and protein sources on serum cholesterol levels, which suggests that dietary protein and fat independently affect the levels of serum cholesterol. Thus, dietary protein has a significant effect on serum cholesterol levels and may be a factor in the low levels of serum cholesterol observed among vegetarians and in humans of Third World countries where the diets is primarily of vegetable origin.

Animals↗
PubMed1988

Heat intolerance, heat exhaustion monitored: a case report.

A 32-year-old male (Mr. A.), monitored during an 8-d heat acclimation (HA) investigation, unexpectedly exhibited heat intolerance and heat exhaustion. Thirteen other males completed HA without indications of either heat intolerance or heat exhaustion. Because Mr. A. responded normally to HA on days 1-4, the intervention of an unknown host factor on days 5-8 was suggested. Mr. A.'s heat exhaustion episode (day 8) was apparently forewarned by loss of body weight and increased delta HR, delta Tsk (days 5-8) and delta Tre (days 7-8) during daily 90-min trials. His symptoms indicated classical salt depletion heat exhaustion, but the calculated salt deficit (less than 0.1 g NaCl.kg-1 body weight) was mild. Post-heat exhaustion serum enzyme levels were either normal (ALT, AST) or acutely elevated (CPK). Blood beta-endorphin and cortisol levels were six times and two times greater than control values, respectively. This case report is unique because clinical/physiological measurements and blood analyses were performed before, during, and after heat intolerance and heat exhaustion.

Acclimatization↗
PubMed1988

Intramuscular and intravenous atropine: comparison of effects in the heat-stressed rat.

In our rat model of human heat injury we have administered atropine intravenously (iv); for clinical use in man, administration is by either the intramuscular (im) or iv route. In order to determine potential differences due to route of administration, we compared the dose-response effects of im and iv administration in rats. Adult male rats (500 g) were heat-stressed (41.5 degrees C) while unrestrained which enabled them to thermoregulate by saliva spreading activity. We quantitated the effects of im or iv atropine (10-4000 micrograms.kg-1) on the following variables: heating rate (rate of rise of core temperature), % weight loss (saliva production), and fecal loss (intestinal motility). Further, we examined the effects of atropine on pupil dilation in restrained rats at 26 degrees C. Heating rate was identical for both routes of atropine administration at 200 micrograms.kg-1 (equivalent to the standard 2-mg dosage in man), but the range of doses over which there was a dose-response effect on heating rate with iv administration (10-1000 micrograms.kg-1) was markedly truncated with the im route (10-50 micrograms.kg-1). Both im and iv atropine had similar effects on weight loss rate and mydriasis. The iv route is preferred because that route produced the most consistent results and the most sensitive physiological response (heating rate) is affected over a wider dose range.

Animals↗
PubMed1987

Evaluation of a temperate environment test to predict heat tolerance.

A temperate environment heat tolerance test (HTT) was formerly reported (Shvartz et al. 1977b) to distinguish heat acclimatized humans from former heat stroke patients. The purpose of this investigation was to evaluate the ability of HTT to measure acute individual changes in the HR and Tre responses of normal subjects, induced by classical heat acclimation procedures, thereby assessing the utility and sensitivity of HTT as a heat tolerance screening procedure. On day 1, 14 healthy males performed HTT (23.2 +/- 0.5 degrees C db, 14.9 +/- 0.5 degrees C wb) by bench stepping (30 cm high, 27 steps x min-1) for 15 min at 67 +/- 3% VO2max. On days 2-9, all subjects underwent heat acclimation (41.2 +/- 0.3 degrees C db, 28.4 +/- 0.3 degrees C wb) via treadmill exercise. Heat acclimation trials (identical on days 2 and 9) resulted in significant decreases in HR (170 +/- 3 vs 144 +/- 5 beats x min-1), Tre (39.21 +/- 0.09 vs 38.56 +/- 0.17 degrees C), and ratings of perceived exertion; plasma volume expanded 5.2 +/- 1.7%. On day 10, subjects repeated HTT; day 1 vs day 10 HR were statistically similar (143 +/- 6 vs 137 +/- 6 beats x min-1, p greater than 0.05) but Tre decreased significantly (37.7 +/- 0.1 vs 37.5 +/- 0.1 degrees C, p less than 0.05). Group mean HTT composite score (day 1 vs day 10) was unchanged (63 +/- 5 vs 72 +/- 6, p greater than 0.05), and individual composite scores indicated that HTT did not accurately measure HR and Tre trends at 41.2 +/- degrees C in 6 out of 14 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1987

Novel approaches to the pathophysiology of heatstroke: the energy depletion model.

De-emphasis of the role of anhydrosis as the primary cause of heatstroke has resulted in increased usage and acceptance of animal models for heatstroke research. When the total amount of work achieved by the running rat prior to exhaustion was plotted against the rate of heat storage, a heretofore unrecognized relationship emerged. These new data suggest that physical exhaustion and heat exhaustion represent opposite ends of a continuum related to the rate of heat storage. Changes in thermoregulatory and/or physical performance can be estimated by a two-dimensional shift in the work-output/thermal storage ratio. Potassium depletion reduces thermoregulatory/physical performance; a combination of atropine plus diazepam appears to improve it. The role of the cholinergic nervous system in eliciting alterations in thermoregulatory and physical ability is reviewed; endurance training, shivering, acclimatization, set-point theory, the anticholinergic syndrome, lithium intoxication, and choline deficiency are discussed.

Adaptation, Physiological↗
PubMed1987

Urinary and hematologic indexes of hypohydration.

As part of a large-scale field feeding system test we were able to collect and study hundreds of aliquots of overnight urine samples obtained immediately prior to a fasting blood sample on days 1, 20, and 44 of the field test. The large number of experimental samples (greater than 650) and concomitant collection of blood and urine aliquots along with data on body weights gave us the opportunity to assess and quantitate the sensitivity of commonly used criteria of hypohydration. Urine aliquots for all test days were initially categorized by specific gravity (SG) greater than or equal to 1.03 (n = 124) or less than 1.03 (n = 540). Creatinine levels were elevated (P less than 0.001) in the concentrated urine samples, but a decreased trend in sodium-to-potassium ratios in these samples failed to achieve statistical significance (P greater than 0.05). However, when individuals with high SG urine were subclassified by a criterion of weight loss greater than 3% from original body weight, then creatinine concentrations were elevated (P = 0.05), whereas sodium-to-potassium ratios were decreased (P = 0.05) when subjects also with high SG but weight loss less than 3% were compared. Because of the moderate altitude (2,000 m) of the field site and the time of sojourn (44 days), there occurred a slight, but significant (P less than 0.001), erythropoietic response. Hematocrit and serum osmolality were not significantly different when examined by the criteria of high or low SG urine and weight loss greater than or less than 3% original body weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Urea Nitrogen↗
PubMed1987

Carbamate-induced performance and thermoregulatory decrements restored with diazepam and atropine.

When rats (500 g, male) are exercised on a treadmill, pretreatment with the carbamate physostigmine reduces endurance capacity (run time, RT) and increases the rate of rise of core temperature (heating rate, HR). Because physostigmine is a potential nerve agent pretreatment drug, our objective was to determine whether pharmacological intervention could reverse these decrements in performance and thermoregulation. The following drugs were administered separately via tail vein: vehicle-control (C), atropine (200 micrograms.kg-1, A), diazepam (500 micrograms.kg-1, D), and physostigmine (200 micrograms.kg-1, PH). After drug administration, rats were run (11 m.min-1, 6 degrees elevation, Ta = 26 degrees C) to exhaustion. PH administration resulted in reduced RT (41 min PH vs. 53 min C, p less than 0.05) with greater HR (0.090 degrees C.min-1 PH vs. 0.057 degrees C.min-1 C, p less than 0.01) than control rats. However, when A and D were also given to PH treated rats, the RT and HR were restored to control levels. Further, A and D without PH improved RT and HR (82 min, 0.047 degrees C.min-1) over control levels. Serial administration of an anticholinergic, an anticonvulsant, and an anticholinesterase resulted in no significant change in performance from control levels.

Animals↗
PubMed1987

Heat acclimatization during summer running in the northeastern United States.

Five highly trained distance runners (DR) were observed during controlled 90-min thermoregulation trials in spring (T1) and late summer (T2) to document the nature of heat acclimatization in the northeastern United States. These trials simulated environmental (30.3 +/- 0.1 degrees C dry bulb, 34.9 +/- 0.5% relative humidity, 4.47 m X s-1 wind speed) and exercise (treadmill running at 80, 120, 160, and 200 m X min-1) stresses encountered by DR during summer training in the northeastern United States. Between T1 and T2, DR trained outdoors for 14.5 +/- 0.4 wk, but consequently exhibited few physiological adaptations classically associated with heat acclimatization. Statistical comparison of T1 and T2 indicated no significant differences in mean heart rate, rectal temperature, sweat Na+ and K+, plasma Na+ and K+, or change in plasma volume during exercise. Mean weighted skin temperature was unchanged except at 50 min of exercise, and sweat rate was also unchanged except during the initial 30 min segment: 73 +/- 6 vs 93 +/- 8 ml X m-2 X h-1. Significant decreases (P less than 0.05) in submaximal VO2 were observed: T1 vs T2 values were 13.97 +/- 0.27 vs 10.19 +/- 1.19, 31.38 +/- 1.15 vs 27.91 +/- 1.45, and 44.97 +/- 0.85 vs 41.24 +/- 0.97 ml X kg-1 X min-1, at treadmill speeds of 80, 120, and 200 m X min-1, respectively. We conclude that DR did not require 14.5 wk of summer training to maintain safe rectal temperatures (less than or equal to 38.4 degrees C) during T1, which simulated the hottest days of summer in the northeastern United States.

Acclimatization↗