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Biomedical subjects

A Burger

Publications and source records attributed to A Burger.

At least 91 records · Page 5Linked to original sources
PubMed1987

Visual acuity, corrective lenses, and accidents in helicopter pilots.

The visual acuity of 38 helicopter pilots experiencing serious air accidents was compared to that of a control group of 72 pilots, matched for age, aircraft, and hours of flight. Decrease in visual acuity was divided into two groups: 1) minor decreases in vision up to 20/25 (not requiring corrective lenses); and 2) visual acuity of 20/30 or less with correction to 20/20. Minor decreases in visual acuity were found in 23.7% (9/38) of those in the accident group compared to 25.0% (18/72) in the control group. There were more pilots in the control group who needed corrective lenses (12.5% (18/72) versus 2.8% (1/38), p less than 0.07). We conclude that helicopter pilots with corrective lenses or minor uncorrected decreases in visual acuity are not at increased risk for serious air accidents.

Accidents, Aviation↗
PubMed1986

[Hyperthyroidism induced by amiodarone].

The incidence of amiodarone-induced thyrotoxicosis remains unclear, partly due to the difficulties encountered in making a firm diagnosis based on thyroid hormone levels. Amiodarone is known to inhibit thyroxine (T4) metabolism, thus bringing plasma T4 concentrations up to levels that may simulate T4 toxicosis. On the other hand, the iodine overload due to the drug itself may create true hyperthyroidism. The purpose of this paper is to suggest practical means of detecting thyrotoxicosis in patients on amiodarone and to discuss the treatment of this side-effect.

Amiodarone↗
PubMed1986

Adrenocortical responsiveness after discontinuous corticosteroid therapy.

Plasma cortisol levels and the response of the adrenal gland to 0.25 mg ACTH administration were measured in 12 patients receiving 15 mg or more of a short-acting steroid (fluocortolone or prednisone) on three out of four days, in 10 patients on daily steroid treatment (15 mg prednisone or more per day), and in 9 normal subjects. The basal plasma cortisol level of the first group was between that of patients on daily prednisone treatment and that of normal subjects. The adrenal function in patients on the three out of four day treatment schedule appeared to be slightly diminished, yet still within the accepted limits for adrenals capable of responding adequately to stress. The adrenal function proved insufficient in all patients on daily steroids. The three out of four day steroid regimen thus offers a solution with many advantages over continuous steroid treatment for patients refractory to the alternate-day schedule.

Adolescent↗
PubMed1985

Does the carrier of chromaffin granules transport the protonated or the uncharged species of catecholamines?

By osmotic lysis in the presence of urea ghosts (60-100 nmol catecholamine/mg prot.) were prepared from chromaffin granules (4-6 mumol catecholamine/mg prot.) of the bovine medulla. In the presence of 1-300 mumol/l 3H-catecholamine and ATP-Mg2+, ghosts show a net uptake of catecholamine. The net uptake is sensitive to reserpine or agents (uncouplers and ammonium) which diminish the electrochemical potential difference for protons at the granule membrane (delta p). The same uptake was found by 3H-counting or by fluorimetric measurements. At various pH-values (pH 6.2-8.2) the Km and Vmax of the ATP-stimulated rate of uptake of 3H-catecholamine into ghosts was determined (at 30 degrees C) to identify the species of catecholamine (protonated, uncharged, or anionic) which is the substrate for the granule carrier. The pH difference (delta pH = pHout - pHin) and the electrical potential difference (delta psi) were determined to calculate delta p under conditions of 3H-catecholamine uptake. When the pHout was increased (pH 6.2, 7.4, 8.2), the apparent Km of uptake decreased (50, 5, 1-2 mumol/l), showing a linear relation between pH and logarithm of Km. The Km was calculated for the uncharged catecholamine (with pK1 = 8.8 and pK2 = 10.0); it was nearly pH-independent and amounted to about 0.2 mumol/l. The Vmax declined only in the extreme pH-range. Between pH 6.6 and 7.8 Vmax and delta p showed a slight increase from 16 to 20 nmoles/(mg prot. X min) and from 110 to 140 mV, resp. In the same pH-range the pHin inside ghosts increased from pH 5.2 to 5.7, whereas delta psi was constant (30 mV). At constant pHout (= 7.3) ammonium (0-30 mmol/l) caused an increase of pHin from 5.5 to 6.6. The increase of pHin was accompanied by an increase of Km from 5 to 20 mumol/l 3H-catecholamine and by a decrease of both Vmax and delta p from 20 to 5 nmoles/(mg prot. X min) and from 123 to 85 mV, respectively. From the dependence of the Km of uptake on pHout is concluded that the uncharged species of catecholamine is transported, whereas the dependence of Km on pHin suggests that the translocation of the catecholamine-carrier complex across the granule membrane is not the rate-limiting step of catecholamine uptake.

Adenosine Triphosphate↗
PubMed1984

Thyroid hormones and thermogenesis: the metabolic cost of food and exercise.

To mimic plasma T3 levels observed in a previous overfeeding study, six lean healthy men received replacement amounts of L-thyroxine (200 micrograms/d) to block endogenous thyroid hormone production while consuming their habitual diet. After 4 weeks equilibration on T4, L-triiodothyronine (T3) was given (45 micrograms/d) in addition to T4, to produce mild T3-thyrotoxicosis, for another 2 weeks. At the end of this period T3 was discontinued but the subjects continued to receive T4 for another 2 weeks. Resting metabolic rate, exercise efficiency, and the thermic effect of food were measured using a ventilated hood, open circuit indirect calorimeter at the end of each phase of the experiment. There was a significant increase in the resting metabolic rate of 6% (P less than 0.01) while the subjects were mildly T3-thyrotoxic. The increase in energy expenditure however, during exercise on a bicycle ergometer or following a 500 kcal liquid-formula meal remained unaltered in the same situation. Thus, mild T3-toxicosis does not alter the efficiency of exercise or the thermic effect of food. These results suggest that the increased plasma T3 levels, observed in overfeeding, could explain corresponding increases in resting metabolic rate but not changes in the efficiency of exercise or the utilization of food.

Adult↗
PubMed1984

The role of thyroid hormones in the control of energy expenditure.

Thyroid hormones have a direct effect on the basal or resting metabolic rate in man and a permissive effect on the adaptive thermogenesis of small animals, while altering the energy expended in exercise to the extent that patients with thyroid disorders exercise to a greater or lesser degree. The physiological concepts of energy expenditure need to be seen in the context of a new method for measuring 'thyroid thermogenesis'. Thyroid hormones seem, in evolutionary terms, to have developed a thermogenic role during the transition from poikilothermy to homeothermy; they are responsible for the increased heat production required for homeotherms to maintain body temperature above that of the environment. The potential mechanisms responsible for thyroid hormone-controlled energy expenditure are complex. Uncoupled oxidative phosphorylation is probably not responsible for thyroid hormone-controlled thermogenesis except in the special case of brown adipose tissue thermogenesis, where thyroid hormones act permissively. The concept that increased ATP generation must be coupled to ATP utilization needs to be linked with the idea that thyroid hormone-controlled thermogenesis must be through inefficient pathways of metabolism. Several of these potentially important pathways of intermediary metabolism in thyroid hormone-controlled thermogenesis can now be defined and measured, but their role in the regulation of nutritionally induced alterations in thyroid status and thermogenesis remains to be explored.

Body Temperature Regulation↗
PubMed1984

Further characteristics of the ATP-stimulated uptake of calcium into chromaffin granules.

The ATP-stimulated uptake of 45Ca2+ [and [3H](-)-noradrenaline ([3H]NA)] into chromaffin granules and that into mitochondria are driven by a protonic gradient delta mu H+, composed of the components delta pH (concentration gradient of protons) and delta psi (electrical potential difference). The granular ATPase pumps protons into the matrix (delta pH inside acid, delta psi positive), but the mitochondrial ATPase ejects protons from the matrix (delta pH alkaline, delta psi negative inside). To show different driving forces of uptake, the rate of the ATP-stimulated uptake of 45Ca2+ (and [3H]NA) into chromaffin granules was compared with the rate of the ATP-stimulated uptake of 45Ca2+ into mitochondria (adrenomedullary or rat liver). In the presence of nitrate, the rate of the ATP-stimulated uptake of 45Ca2+ into chromaffin granules is higher than in the presence of acetate, because the lyotropic anion nitrate stimulates the granular ATPase and increases delta pH (acid inside). Compared with nitrate, the rate of the ATP-stimulated uptake of 45Ca2+ into mitochondria is higher in the presence of the proton-carrying anion acetate, which, after permeation, provides protons for ejection by the ATPase. In the absence of ATP, a valinomycin-mediated potassium influx (delta psi inside positive) stimulates the granular uptake of [3H]NA, which has an electrogenic component, but not the granular uptake of 45Ca2+, which is electroneutral. The electrogenic uptake of 45Ca2+ into mitochondria is stimulated by a valinomycin-mediated potassium efflux (delta psi negative inside). The ATP-stimulated uptake of 45Ca2+ into chromaffin granules is sensitive to ruthenium red, suggesting a carrier-mediated mechanism of uptake, and it is sensitive to atractyloside, indicating the simultaneous uptake of ATP. After collapse of delta pH by ammonia, the ATP-stimulated uptake of 45Ca2+ into chromaffin granules is abolished, but not that into mitochondria. In the presence of ammonia, the rate of the ATP-stimulated uptake of [3H]NA is very low, and an ATP-independent uptake of 45Ca2+ into chromaffin granules is observed which is similar to the ATP-independent Ca2+/Na+ exchange at the granular membrane.

Acetates↗
PubMed1982

Familial elevations of total and free thyroxine in healthy, euthyroid subjects without detectable binding protein abnormalities.

Elevations of serum thyroxine without thyrotoxicosis or binding protein abnormalities have been documented in 8 of 13 family members, representing 4 generations. This syndrome appears to represent an elevated threshold for the amount of free thyroxine substrate required to maintain adequate T3 production form the peripheral monodeiodination of T4. It reiterates the need for a prudent re-evaluation of all clinically euthyroid patients with elevated serum thyroxine concentrations before concluding that they are indeed thyrotoxic.

Adult↗