No description available.

Call number: LD2668 .T4 1984 H365 / Master of Science

No description available.

No description available.

The purpose of this investigation was to quantify the acute pressor response to caffeine at rest and during exercise, and to compare responses for different reportings of caffeine consumption and sensitivity. Eight young men with high use (HU) consumption patterns (<600 mg/day) and eight with low use (LU) patterns (<90 mg/day) participated. Caffeine (C) (4.5 mg/kg fat free mass) and placebo (P) were administered, double-blind and counterbalanced. Systolic (SBP), diastolic blood pressure (DBP) and heart rate (HR) were monitored during baseline, 40 minutes of absorption and graded treadmill walking. Oxygen consumption (V02) and rating of perceived exertion (RPE) were monitored during exercise. No significant differences were found for the responses to C between HU and LU nor between sensitive and not sensitive groups. Following a 12 hour abstinence, caffeine significantly increase SBP and DBP at absorption compared to P (11/9 mm Hg). The increase was additive with exercise for SBP but not DBP. Caffeine significantly increased VO2 compared to P. No significant differences were found for HR nor RPE between C and P trials. The present data indicate chronic caffeine consumption does not build tolerance to the acute pressor response to caffeine ingestion, the resting pressor response is additive with the pressor response to exercise for SBP, and individual perceptions of caffeine sensitivity are not accurate predictors of pressor responses. / School of Physical Education

The influence of vitamin C on the pharmacokinetics of caffeine was investigated in ten elderly males, age 66 to 86 years. Caffeine (4 mg kg⁻¹) was administered intravenously on three different occasions over a seven-week period: before vitamin C restriction, after approximately four weeks of vitamin C restriction (15 mg dietary intake per day), and after two weeks of vitamin C supplementation (500 mg orally, twice daily). Blood and urine samples were collected over a 48-hour period following each caffeine administration. The plasma half-life (t₁/₂), rate constant of elimination (K), apparent volume of distribution (V), total body clearance (TBC), renal clearance (RC), and metabolic clearance (MC) of caffeine were determined. Simultaneous plasma (PVC), whole blood (WBVC), and leukocyte (WBCVC) vitamin C concentrations were obtained. All of the mean vitamin C values determined at the first kinetic trial (KT-1) were within the normal ranges for the respective biologic fluid or tissue. All of the mean vitamin C values changed significantly during the study; decreasing to below the normal ranges by the second kinetic trial (KT-2) following dietary vitamin C restriction, and increasing to the normal ranges by the third kinetic trial (KT-3) following vitamin C supplementation. All of the decreases and increases in the individual and average vitamin C concentrations paralleled the observed decreases and increases in the daily vitamin C intake. None of the caffeine pharmacokinetic parameters evaluated changed significantly during the study. The mean rate constant of elimination was approximately 0.15 hr⁻¹, the average plasma half-life was approximately 4.5 hours, and the mean apparent volume of distribution was approximately 500 ml kg⁻¹ for all three kinetic trials. The average total body, renal, and metabolic clearances were approximately 76.9, 1.3, and 76.0 (ml hr⁻¹)kg⁻¹, respectively, for all three kinetic trials. With the exception of V and TBC, the various pharmacokinetic characteristics investigated were in general agreement with data reported for younger subjects. The average apparent volume of distribution determined at any of the kinetic trials was about 16% lower than the value reported for young, healthy subjects. Similarly, the mean total body clearance observed was about 21% lower than that observed in young, healthy subjects. Since the average elimination rate constant observed in these elderly subjects is similar to the values observed in younger subjects and since TBC is equal to the product of V times K, the reduced TBC observed in this study appears to be due to the reduction in V, rather than to a decrease in the intrinsic metabolic capacity of the liver with aging. No relationship between vitamin C intake and/or body levels and the pharmacokinetics of caffeine was observed. These results indicate that the elimination of caffeine in the elderly is not affected significantly by the concentrations of vitamin C achieved during the study.

While considerable information exists regarding the independent effects of caffeine and psychological stress on cardiovascular activity, there is relatively little information on their combined effects. Since caffeine may enhance cardiovascular responsivity to psychological stress, research on hemodynamic responses to caffeine-stress combinations may help elucidate mechanisms of hypertension development. In a series of studies, regular consumers of caffeine were exposed to laboratory and naturalistic stressors with and without prior caffeine intake. Among the findings were (1) caffeine and stress produced additive increases in blood pressure, (2) caffeine appears to potentiate beta-adrenergic responsivity to active coping, but not passive coping, stressors, (3) caffeine enhanced emotional responses to stress, and (4) cardiovascular responses to caffeine and stress in a naturalistic setting were similar to those observed in the laboratory. These results indicate that caffeine may enhance cardiovascular and psychological responses to stress, and that these responses may contribute to risk for essential hypertension.

The intent of this thesis was to study the effects of caffeine ingestion on substrate utilization and muscle metabolism during exercise, as reflected by endurance time to exhaustion. For this purpose, seven trained cyclists performed work bouts at 80% of maximal oxygen consumption to exhaustion after ingestion of caffeine (CAF trial) end under control (CON trial) conditions.Although the work time to exhaustion was not significantly different between the CAF trial, 91.8 (S.E. ± 7.7) min and the CON trial, 85.2 (S.E. ± 10.5) min, five of he subjected did show an average 18% increase in performance following ingestion of 330 mg caffeine. Since there was no elevation of FFA prior to exercise, it was expected that no muscle glycogen sparing would occur during the first 30', 41.7 (S.E. ± 6.1) mM/kg in the CAF trial and 42.1 (S .E. + 6.6) mM/kg in the CON trial. Serum glycerol concentration was significantly (P< .05) during the CAF trial at 10' and 30'. R values were significantly lower during the CAF trial, .87 (S.E. ± .01) than the CON trial, .91 (S.E. ± .01) at exhaustion. Significantly lower (p<.05) perceived exertion ratings were also observed during the CAF trial. These data suggest a positive effect on endurance exercise performance following caffeine ingestion.

The effect of caffeine consumption on blood pressure has been widely studied. Robertson et al. (J Clin Invest 67: 1111-1117, 1981) cited findings of tolerance to humoral and hemodynamic effects from caffeine within four days when caffeine is consumed with each meal. These findings of tolerance have not been verified. The purpose of this study was to determine the effect of caffeine intake pattern on the development of tolerance to hemodynamic effects of caffeine. Fourteen volunteers were randomly assigned to two groups of seven. One group received 250 mg of caffeine in the morning only (MO), the other group received 250 mg of caffeine in the morning, afternoon, and evening (All Day-AD). Subjects underwent a seven day trial during which blood pressure (BP) and heart rate (HR) were assessed; morning beverage (250 mg of caffeine) was ingested and BP and HR assessments were obtained every 10 minutes for 50 minutes at rest, and after 10 minutes of cycling at 100 Watts. Afternoon and evening beverages were consumed which contained 250 mg caffeine each or placebo. No significant change in SBP, DBP, or HR from rest to 40 minutes post-caffeine absorption or between caffeine dosing pattern across trial days was found. A main effect was found for SBP post caffeine consumption (MO=5.4 vs. AD= 1.3). Mean values for DBP were stable across days 3-7 (M0=3.14-4.7 mmHg) but decreased from (3.86-.14 mmHg) from days 3 to 7 (AD). SBP revealed a significant interaction during exercise and across trial days. SBP and HR for the morning only group was higher than the all day caffeine consumption group across days. However DBP was lower across days for the morning only vs. the all day intake pattern. Therefore, caffeine dosing pattern does not appear to have an effect on tolerance to the hemodynamic effects of caffeine at rest or during exercise. / School of Physical Education

The purpose of the present study was to elucidate if caffeine ingestion reduced perception of effort at submaximal intensities during a maximal exercise test. A secondary purpose of this study was to examine the role of a single nucleotide polymorphism (SNP) at intron 1 of cytochrome P-450 gene in modulating caffeine’s influence on ratings of perceived exertion (RPE) at the same submaximal exercise intensities. Twelve healthy men (age: 24±1 yr., BMI: 23.9±1.2 kg.m2) volunteered to participate in the present study. Subjects consumed 6 mg.kg-1 of USP grade caffeine in 200ml of non-caloric, coloured and flavoured water, or a placebo-matched drink in a single-blind, randomised and crossover style design. Subjects remained seated for 1 hour after consuming the assigned drink, and subsequently completed an incremental maximal exercise test on a bicycle ergometer, which started at 0 Watts for 1 minute and increased by 25 Watts per minute until volitional exhaustion. RPE was reported every third minute during the test. DNA was obtained from whole blood samples and genotypes were determined using previously described methods. Similar to previous studies looking at this SNP, subjects were categorised into groups of AA homozygotes and C allele carriers for statistical analyses between genotypes. Two-way repeated measures ANOVA’s were performed (Treatment × Genotype) for RPE responses at submaximal workloads up to 300 Watts. Significant results were followed up using the bonferroni post-hoc method. There were no significant differences between individuals homozygous for the A variant and C allele carriers for age, height, weight, body mass index (BMI), and VO2max. A significant Time × Treatment interaction was observed (F=5.804, p<0.05) for the rate of increase in RPE between trials. A significant Treatment × Genotype interaction was also found (F=5.714, p<0.05), by which C allele carriers exhibited greater reductions in RPE during the caffeine trial compared to AA homozygotes. The findings of the present study indicate that perception of effort is reduced in individuals who metabolise caffeine at a slower rate (i.e. in C allele carriers). It is postulated that AA homozygotes do not experience reductions in RPE due to a greater cardiovascular workload and enhanced CNS excitability following caffeine ingestion / School of Physical Education, Sport, and Exercise Science