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Biomedical subjects

M Houston

Publications and source records attributed to M Houston.

At least 37 records · Page 2Linked to original sources
PubMed1985

Solubilization of an adenosine uptake site in brain.

Procedures are described for the solubilization of adenosine uptake sites in guinea pig and rat brain tissue. Using [3H]nitrobenzylthioinosine [( 3H]NBI) the solubilized site is characterized both kinetically and pharmacologically. The binding is dependent on protein concentration and is saturable, reversible, specific, and high affinity in nature. The KD and Bmax of guinea pig extracts are 0.13 +/- 0.02 nM and 133 +/- 18 fmol/mg protein, respectively, with linear Scatchard plots obtained routinely. Similar kinetic parameters are observed in rat brain. Adenosine uptake inhibitors are the most potent inhibitors of [3H]NBI binding with the following order of potency, dilazep greater than hexobendine greater than dipyridamole. Adenosine receptor ligands are much less potent inhibitors of binding, and caffeine is without effect. The solubilized adenosine uptake site is, therefore, shown to have virtually identical properties to the native membrane site. The binding of the adenosine A1 receptor agonist [3H]cyclohexyladenosine [( 3H]CHA) to the solubilized brain extract was also studied and compared with that of [3H]NBI. In contrast to the [3H]NBI binding site [3H]CHA binds to two apparent populations of adenosine receptor, a high-affinity site with a KD of 0.32 +/- 0.06 nM and a Bmax of 105 +/- 30 fmol/mg protein and a lower-affinity site with a KD of 5.50 +/- 0.52 nM and Bmax of 300 +/- 55 fmol/mg protein. The pharmacology of the [3H]CHA binding site is consistent with that of the adenosine receptor and quite distinct from that of the uptake [( 3H]NBI binding) site. Therefore, we show that the adenosine uptake site can be solubilized and that it retains both its binding and pharmacologic properties in the solubilized state.

Adenosine↗
PubMed1983

Morphology of the brachial biceps muscle and elbow flexion in man.

This study was undertaken to determine whether skeletal muscle fibre characteristics could be demonstrated to be of significance for muscle function in voluntary contraction in man. 4 male and 4 female adult subjects were studied. During elbow flexion force and velocity was measured at the hand with the forearm in a 100 degree position. A motor-driven heavy flywheel guaranteed a constant velocity or movement at the time of measurement. Force was registered by a straingauge dynamometer, and velocity by two sets of photocells. Cross-sectional area of the brachial biceps muscle was determined by computerized tomography scanning. Muscle fibre composition and fibre cross-sectional areas were assessed histochemically on needle biopsy samples obtained superficially from the brachial biceps muscle, the more superficial of the two large elbow flexor muscles. At contraction velocities from 2 to 7 radians per second (rad/s) a close relationship existed between the relative force output and the relative area of fast-twitch fibers (p less than 0.01). Maximal voluntary isometric contraction force averaged 189 N (120 to 309 N), and showed a close relationship with total cross-sectional area of the brachial biceps muscle. The specific tension (maximal isometric tension) of the muscle averaged 33 N/cm2 with no demonstrable difference between subjects of widely different fibre compositions, suggesting that maximal tetanic tension is similar in fast- and slow-twitch fibres in man.

Adenosine Triphosphatases↗
PubMed1982

Catechol O-methyltransferase. 10. 5-Substituted 3-hydroxy-4-methoxybenzoic acids (isovanillic acids) and 5-substituted 3-hydroxy-4-methoxybenzaldehydes (isovanillins) as potential inhibitors.

A series of 5-substituted 3-hydroxy-4-methoxybenzoic acids (isovanillic acids) and -benzaldehydes (isovanillins) have been synthesized and evaluated as inhibitors of rat liver catechol O-methyltransferase. The compounds exhibited either noncompetitive or competitive patterns of inhibition when 3,4-dihydroxybenzoic acid was the variable substrate. The benzaldehydes were significantly more potent inhibitors than the corresponding benzoic acids, and electron-withdrawing substituents in the 5 position greatly enhanced their inhibitory activity.

Animals↗
PubMed1981

The clinical spectrum of autonomic dysfunction.

Classic cases of idiopathic autonomic dysfunction are easily recognized, but certain presentations may not immediately suggest the diagnosis. Among 297 cases in the experience of our institutions, eight have been selected as illustrative of the difficulties which may be encountered. The disorder may present as angina pectoris, Parkinsonism, night blindness, nasal stuffiness, malignant hypertension, postprandial fainting, intracerebral hemorrhage and respiratory arrest. About half of the patients with idiopathic orthostatic hypotension manifest supine hypertension. These subjects are extremely sensitive to pressor and depressor agents; those who have angina pectoris complicating their disease are characteristically worsened by nitroglycerin.

Aged↗
PubMed1981

Acute immune intravascular hemolysis due to hydrochlorothiazide.

Acute near-fatal intravascular hemolysis and renal failure developed in a patient after he had ingested 15 to 20 tablets of both methyldopa (Aldomet) nd hydrochlorothiazide (HydroDiuril). Serologic test results were inconsistent with those associated with methyldopa-induced hemolytic anemia and suggested that hemolysis was caused by hydrochlorothiazide antibodies reacting by an immune complex mechanism.

Acute Kidney Injury↗
PubMed1980

The relationship between suckling-induced prolactin response and lactogenesis.

The PRL response to suckling was studied during the first week of the puerperium. Mean basal levels of PRL showed no significant changing during the first week of the puerperium, but there were progressive rises in both the maximum suckling-induced response and the total area under the response curve, which reached peak values on the fourth day after delivery. Despite large variations between individuals in basal PRL levels (range, 0.3-7.0 U/liter), peak suckling-induced response (range, 0.1-9.9 U/liter), and total response (range, 0.6-63.0 arbitrary units), there was much less variability within individuals between consecutive feeds. Using an electronic balance, 20 patients on days 5 and 6 were classified either as good feeders (greater than 60 g milk/feed) or poor feeders (less than or equal to 60 g milk/feed) on the basis of 2 consecutive test weights. The mean PRL response to suckling in 11 good feeders was no different from that in 9 poor feeders, and there was no significant correlation between milk yield and PRL response. Six patients whose infants were in the special care nursery had lactation initiated and maintained by breast pump for an average of 5.6 days. Although the PRL response to the breast pump was very small, these patients also had satisfactory milk yields (mean, 86 g). Although the presence of PRL is essential for lactation, the data in this paper suggest that there is no close temporal correlation between PRL concentrations and milk yield.

Body Weight↗
PubMed1979

Alterations in ventilation and gas exchange during exercise-induced carbohydrate depletion.

The relationship between ventilation (VE), oxygen consumption (VO2), and carbon dioxide production (VCO2) during work were studied in four trained males during exercise-induced carbohydrate depletion. Repeated bouts of heavy treadmill exercise (6 min at 95% VO2 max) were performed once per hour for 24 h in order to promote a shift in energy substrate from carbohydrate to fat. Measurements of VO2 and VCO2 recorded during each minute indicated that VO2 was unaffected by the number of runs, whereas VCO2 showed a progressive reduction which amounted to 24% during the final run. A corresponding decline of 19% was observed in the respiratory exchange ratio. No significant change in VE occurred between any of the runs. It is concluded that during heavy, repeated, muscular exercise, reductions in VO2, strongly suggestive of an increased fat oxidation, are not accompanied by a corresponding change in ventilation.

Adult↗
PubMed1976

Time-motion and physiological assessments of ice hockey performance.

Ice hockey performance was studied during 10 contests to assess time-motion characteristics and associated physiological changes that occur for each position. Depending on the position played, the actual playing time per game for forwards and defensemen ranged between 20.7 and 28.0 min. The number of shifts ranged from 14 to 21 with an average playing time of 85.4 s/shift. Further analysis of each shift indicated that there was an average of 2.3 play stoppages which averaged 27.1 s, producing a continuous playing time of 39.7 s. Telemetered recordings of heart rate during each shift revealed sustained rates of between 170 and 174 beats/min over the three periods of the game. For both the forwards and defensemen, values for blood lactates were highest during the first and second periods (x = 78.0 and 66.1 mg/100 ml), then declined considerably during the third period (x = 44.5 mg/100 ml). Blood glucose showed a similar tendency (x = 139.3, 133.7, 114.1 mg/100 ml), while hematocrit and total protein showed little tendency to change.

Adult↗