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PubMed1989

Transduction heats in retinal rods: tests of the role of cGMP by pyroelectric calorimetry.

The sensory dark current of vertebrate retinal rods is believed to be controlled by light activation of a chain of coupled biochemical cycles that finally regulate the cationic conductance of the plasma membrane by hydrolytically reducing the level of cGMP in rod outer segment cytoplasm. The scheme has been tested by measuring heat production by live frog retinas when stimulated with sequences of light flashes of progressively increasing energy. Using pyroelectric poly(vinylidene 1,1-difluoride) detectors that simultaneously measure transretinal voltage and retinal temperature change, four heat effects assignable to known biochemical cycles in rods have been found. As the dark current shuts down after a flash causing 180-1800 rhodopsin photoisomerizations per rod, a heat burst, q1, raises the retinal temperature 1-2 microK. q1 is closely regulated in size and slightly precedes dark current shutdown. Isobutylmethylxanthine slows and enlarges q1, delaying the dark-current response. Increasing cytoplasmic Ca2+ stops the dark current without affecting q1. Although rod heat production is consistent with splitting of 1-3 microM of free cytoplasmic cGMP during transduction, the kinetics of the two processes do not match the predictions of current cGMP control models.

Animals↗
PubMed1976

The utilization of diets containing acetate salts by growing lambs as measured by comparative slaughter and respiration calorimetry, together with rumen fermentation.

1. In a comparative slaughter experiment, growing lambs were given concentrate diets in which 14 or 19% metabolizable energy (ME) provided by barley was replaced by sodium, calcium and potassium salts of acetic acid. As the proportion of ME as acetate was increased, energy retention decreased. ME intake was 9271, 9430, and 9217 +/- 67 kJ/d and energy retention was 2698, 2422 and 2280 +/- 71 kJ/d for the diets containong 0, 14 or 19% ME as acetate respectively. There were no differences in protein deposition. The efficiency of utilization of acetate for energy retention (kf) was calculated by difference to be 3 and 10 +/- 13% respectively for the diets containing 14 and 19% ME as acetate.

Acetates↗
PubMed1984

Whole-body calorimetry studies in adult men. 2. The interaction of exercise and over-feeding on the thermic effect of a meal.

Studies have claimed that an enhancement of the thermic effect of a meal (TEM) is an important adaptive mechanism to account for energy wastage during over-feeding. Eight healthy normal-weight young men were studied during 1 week on a weight-maintenance diet and again during 1 week when they were over-fed by 50% with fat. During each experimental week, the subject occupied a whole-body indirect calorimeter at 26 degrees for two separate periods of 36 h. The periods differed in the amount of exercise they contained. The thermic responses to the identical meals were measured during rest on one occasion and during exercise on a bicycle ergometer on the other. On the maintenance diet the absolute TEM (kJ/min) was 1.51 (SD 0.42) at rest and 1.31 (SD 0.75) during exercise (no significant difference). The equivalent values (kJ/min) on the over-feeding diet were 2.2 (SD 0.48) and 1.97 (SD 0.64) (no significant difference). The absence of a significant interaction between TEM and exercise was also demonstrated by the fact that the effect of over-feeding on total 24 h energy expenditure was unaffected by the subject's level of physical activity while in the calorimeter. In conclusion, the present study has provided no evidence to support the hypothesis that TEM is enhanced during exercise.

Adult↗
PubMed2004

The use of uniaxial accelerometry for the assessment of physical-activity-related energy expenditure: a validation study against whole-body indirect calorimetry.

Assessing the total energy expenditure (TEE) and the levels of physical activity in free-living conditions with non-invasive techniques remains a challenge. The purpose of the present study was to investigate the accuracy of a new uniaxial accelerometer for assessing TEE and physical-activity-related energy expenditure (PAEE) over a 24 h period in a respiratory chamber, and to establish activity levels based on the accelerometry ranges corresponding to the operationally defined metabolic equivalent (MET) categories. In study 1, measurement of the 24 h energy expenditure of seventy-nine Japanese subjects (40 (SD 12) years old) was performed in a large respiratory chamber. During the measurements, the subjects wore a uniaxial accelerometer (Lifecorder; Suzuken Co. Ltd, Nagoya, Japan) on their belt. Two moderate walking exercises of 30 min each were performed on a horizontal treadmill. In study 2, ten male subjects walked at six different speeds and ran at three different speeds on a treadmill for 4 min, with the same accelerometer. O2 consumption was measured during the last minute of each stage and was expressed in MET. The measured TEE was 8447 (SD 1337) kJ/d. The accelerometer significantly underestimated TEE and PAEE (91.9 (SD 5.4) and 92.7 (SD 17.8) % chamber value respectively); however, there was a significant correlation between the two values (r 0.928 and 0.564 respectively; P<0.001). There was a strong correlation between the activity levels and the measured MET while walking (r(2) 0.93; P<0.001). Although TEE and PAEE were systematically underestimated during the 24 h period, the accelerometer assessed energy expenditure well during both the exercise period and the non-structured activities. Individual calibration factors may help to improve the accuracy of TEE estimation, but the average calibration factor for the group is probably sufficient for epidemiological research. This method is also important for assessing the diurnal profile of physical activity.

Acceleration↗