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J Clench

Publications and source records attributed to J Clench.

11 recordsLinked to original sources
PubMed1982

Effect of chronic altitude hypoxia on hematologic and glycolytic parameters.

The physiological effect of chronic exposure to altitude hypoxia on the glycolytic intermediates, adenosine triphosphate and 2,3-diphosphoglyceric acid, and the hematologic parameters, hemoglobin, hematocrit, and mean cell hemoglobin concentration, has been examined in an indigenous population, the Aymara, of the Departamento de Arica, Chile. This population normally resides at three altitudes: the coast (0-500 m), the sierra (2,500-3,500 m), and the altiplano (above 4,200 m). After isolation of altitude from other environmental factors (age, sex, body build, ethnicity, smoking, and residential permanence), an increase in 2,3-diphosphoglycerate and a decrease in adenosine triphosphate was observed. Both hemoglobin and hematocrit increased as expected, but mean cell hemoglobin concentration declined. It is proposed that a decline in the activity of a single enzyme, pyruvate kinase, can account for these observed changes and suggests a pivotal role for pyruvate kinase in the physiological adaptation to altitude hypoxia.

2,3-Diphosphoglycerate↗
PubMed1981

Circadian changes in the bioavailability and effects of indomethacin in healthy subjects.

Nine subjects, 19 to 29 years old (2 females) synchronized with activity from 07.00 to 00.00 received a single daily oral dose (100 mg) of indomethacin at fixed hours: 07.00, 11.00, 15.00, 19.00 and 23.00, in random order and at weekly intervals. 1) Chronopharmacokinetics: Venous blood (sampled at: 0, 0.33, 0.67, 1.0, 1.5, 2.0, 4.0, 6.0, 8.0 and 10.0 h post ingestion) was used for plasma drug determination. Circadian changes in peak height, time to peak, area under the concentration-time curve and the disappearance rate were used to characterize indomethacin chronopharmacokinetics. A circadian rhythm of both peak height and time to peak was validated. An evening ingestion led to smallest peak height and longest time to peak. 2) Circadian changes in a set of effects: Eleven physiologic variables were investigated (post absorption) at delta t = 2 h. Circadian rhythms were detected: i) on control day and ii) with evening ingestion for ten of the eleven variables indicating that the subjects' temporal structure did not become altered by an evening ingestion, whereas it did become so by morning ones. Transient changes (n minutes post absorption) measured as T240 min post absorption/Tcontrol day, same clock hour ratio were also circadian rhythmic for most variables. Again, evening ingestion appeared least disturbing.

Adult↗
PubMed1981

2,3-Diphosphoglycerate and night vision.

Recovery of night vision at altitude has been examined in relationship to changes of 2,3,diphosphoglycerate (DPG). It appears that, if DPG influences night adaptation, its effect is small. Inter-individual variability is large, both in terms of DPG and performance on the MESOP, the device used to measure dark adaptation.

2,3-Diphosphoglycerate↗
PubMed1975

[Circadian rhythms in the urinary excretion of salicylate (chronopharmacokinetics) in healthy adults].

Six healthy adults volunteered to ingest a 1 g solution/24 h of sodium salicylate in a study consisting of 4 standardized tests. The difference between tests was the timing of drug absorption: 07(00), 11(00), 19(00) and 23(00) respectively. The 4 separate tests were performed at least 1 week apart. Subjects; synchronization : diurnal routine activity with light-on at 07(00) and light-off at 23(00) Urine was collected at four-hour intervals, for 48 hours following drug ingestion. By the mean cosinor summary of least squares fits of a 24-hour cosine curve, or by other testing, a within-day difference is established for several chronopharmacokinetic parameters characterizing urinary salicylate excretion. By criteria including the height of the peak excretion, the span necessary to reach the peak, etc., it is shown that, as compared to drug administration at other times, salicylate is excreted faster into the urine, reaches higher values sooner and falls off faster when the drug is ingested between 19(00) and 23(00).

Adult↗
PubMed1975

[Circadian variations of the effects of ethanol and of blood ethanol values in the healthy adult man. Chronopharmacological study].

Six healthy young men (22 to 26 years) who had fasted for 12 hours volunteered for this study (subject synchronization: diurnal activity from 07(00) to midnight and nocturnal rest). A set dose of ethanol (0.67 g/kg body weight) was ingested at the fixed (and random) hours of 07(00), 11(00), 19(00) and 23(00), with a week between tests. A set of physiological variables: psychological tests (selft-rating of mood, of physical vigor and of ebriety, tempo, random number addition test); physical variables (heart rate, systolic and diastolic blood pressure, peak expiratory flow, oral temperature and grip strength); blood variables (plasma ethanol, cortisol, lactic acid, pyruvic acid, glucose and erythrocyte K+) and urinary variables (volume, epinephrine, nor-epinephrine and 5-HIAA) were documented at least at 4 hourly intervals and set times. The cosinor method was used for chronobiological statistical analyses. The parameters characterizing the ethanol pharmacokinetics (chronopharmacokinetics) demonstrated a circadian rhythm (p less than 0.05): e. g. the peak height of ethanolemia is greater when ethanol is ingested at 07(00) than at other times. Also a circadian rhythm in biosystems susceptibility can be demonstrated (p less than 0.05) (chronesthesy) with a peak time not necessarily corresponding either to that of ethanolemia or to that of other variables. The overall circadian changes in ethanol effects (chronergy) can be viewed as a combination of both ethanol chronesthesy and chronokinetics.

Adult↗
PubMedDate not supplied

Genetic components of variations of red cell glycolytic intermediates at two altitudes among the South American Aymara.

Red cell haemoglobin (Hb), haematocrit (Ht), 2,3-diphosphoglycerate (DPG), and adenosine triphosphate (ATP) levels were measured in 876 individuals from six villages at two altitude levels (altiplano and coast) of the Departmento de Arica of Northern Chile. Of these, data on 761 individuals are subjected to analysis to search for the evidence of genetic adaptation to a hypoxic environment at a high altitude. Total phenotypic variance for each of the variables is higher at the altiplano as compared to their counterparts at the coastal level. Data on 1127 pairs of relatives of six degrees of relationships are used to determine the genetic component of variation in each of these four traits. To a certain extent the larger familial correlations as well as higher variances at altiplano are explained by the apparent assortative mating (which may again be due to their restricted population size) at the higher elevation. Yet, at least in three variables (Hb, Ht, and DPG) no reduction in the additive genetic component of variation is noticed at the higher altitude. ATP seems to have the highest degree of genetic component of variance, particularly at the coastal level. Some implications of these results are discussed in the light of their roles in the glycolytic pathway.

2,3-Diphosphoglycerate↗
PubMedDate not supplied

Circadian heart rate rhythmicity: comparison between an Eskimo and other population groups.

This brief communication reports the results of 24-ambulatory cardiac monitoring of a Bering Strait Eskimo population and compares the findings with 3 other populations. Similar heart rate rhythmicity and almost identical acrophases are found in the Eskimo, Aymara Indian and French populations. However, the Alaskan Eskimo and Aymara Indian 24-h means vary by approximately 15 beats/min, with the American population between these two. The mesor displays most radical differences.

Adolescent↗