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Biomedical subjects

B Martin

Publications and source records attributed to B Martin.

At least 397 records · Page 22Linked to original sources
PubMed1982

The assessment and significance of habituation to a repeated stimulus by the human fetus.

Habituation is the progressive decrease in response by an organism when it is stimulated repeatedly. This process is a basic form of learning and a normal pattern may be one indication of intact central nervous system function. This study assessed habituation of a behavioral response by the human fetus to repeated vibrotactile stimuli. Of the 40 normal fetuses studied 37 habituated after 10 to 50 stimuli. The gestational age at which the fetus first responded to the stimulus ranged from 22 to 30 weeks. Female fetuses responded 2 weeks earlier than males. The possible value of this assessment in obstetrical practice is presented.

Central Nervous System↗
PubMed1982

Uracil-DNA glycosylase. Purification and properties of uracil-DNA glycosylase from Micrococcus luteus.

A uracil-DNA-glycosylase from Micrococcus luteus has been purified more than 3,000-fold. The enzyme preparation appears homogeneous, according to the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It is devoid of nonspecific endonucleases, specific endonucleases for apurinic and apyrimidinic sites, 3-methyladenine or 7-methylguanine-DNA-glycosylases. It behaves as a monomer protein of 19,400 daltons. It has an isoelectric point of 7.0 +/- 0.1. It has an optimal activity between pH 5.0 and 7.0. It has no cofactor requirement and is not inhibited by EDTA. Uracil-DNA-glycosylase is highly specific for DNA containing dUMP residues, releasing uracil as product of the reaction. It is 2-fold more active on single-stranded DNA than on double-stranded DNA. If it releases uracil dimers from ultraviolet-irradiated PBS1 DNA, it is at the threshold of the detection. The apparent Km is 7 X 10(-8) M, and uracil acts as a noncompetitive inhibitor with a Ki of 3.2 X 10(-4) M. Cis-syn cyclogbutadiuracil also is a potent inhibitor, while some analogs, produced by x-irradiation of uracil and thymine, are weak inhibitors. Spermine, between 10 and 400 microM, increases the enzymatic activity by 50% and is not inhibitory at other concentrations. Spermidine activates the enzyme at concentrations of 40 to 120 microM, but becomes inhibitory at 200 and 400 microM. A new finding is that drugs which intercalate in DNA, such as ethidium bromide and ellipticine, cause a 2- to 2.5-fold activation of this enzyme activity. The concentrations giving maximal activation depend on the drug. The enzyme does not behave as a processive enzyme during uracil excision.

DNA↗
PubMed1982

Monitoring pre-service reproductive status in dairy cows.

Combinations of oestrus detection, ovarian palpation and milk progesterone assays were used to monitor pre-service reproductive status of cows in two dairy herds over two successive years. Non-cyclical cows were identified as having no luteal tissue in their ovaries on two occasions 10 days apart. Absence of luteal tissue was determined by the presence of basal mild progesterone initially followed either by a repeat of this result or by failure to palpate a corpus luteum per rectum. In the period 32 to 56 days post partum the number of non-cyclical cows on farm A years 1 and 2 was eight out of 31 (25 . 5 per cent), and 10 out of 62 (16 . 1 per cent) and on farm B years 1 and 2 was 10 out of 68 (14 . 7 per cent) and 11 out of 85 (12 . 9 per cent) respectively. The farm A herd was high yielding, (average lactation 6380 litres), whereas the farm B herd was of average yield (4717 litres). In both herds 60 day milk yield was not related to cyclical status of pre-service cows. There was however a trend toward a greater proportion of young cows being non-cyclical. With the exception of a prolonged calving to conception interval for farm A in year 1, whether a pre-service cow was cyclical or not had no effect on when the cow was first served or on when the animal conceived. The routine incorporation of pre-service monitoring to herd fertility control programmers may however be of value in recognising the incidence of non-cyclical cows and giving an early indication of oestrus detection efficiency.

Animals↗
PubMed1982

Human exposure to styrene. IV. Industrial hygiene investigations and biological monitoring in the polyester industry.

An industrial hygiene study of 10 glassfiber reinforced polyester plants (including 90 workers) was undertaken to investigate the styrene exposure in this industry and to estimate biological limit values (BLV's) for the urinary metabolites of styrene: mandelic (MA) and phenylglyoxylic acids (PGA). Time weighted average (TWA) styrene exposures were found ranging from 2 to 200 ppm. The urinary elimination of metabolites correlated well with exposure and the BLV's corresponding to an 8-h exposure at 100 ppm were consistent with earlier laboratory findings (end-of-shift sample: MA 1640, PGA 510, MA + PGA 2150; next-morning sample: MA 330, PGA 330, MA + PGA 660 mg/g creat.). Total metabolites (MA + PGA) in the next-morning sample or mandelic acid in the end-of-shift sample are recommended for routine monitoring of exposure to styrene. The study revealed the need for further research on how to reduce styrene exposure in this industry.

Air↗
PubMed1982

Self-selected exercise intensity is unchanged by sleep loss.

Sleep loss alters the perceptual response to exercise: subjects describe constant external work loads as more severe after sleep deprivation. However, since subjects cannot be "blind" to their sleep status and have knowledge of previous exertional ratings, it remains unknown if this increase in perceived exertion merely represents expectations of increased difficulty of exercise after sleep loss. As one approach to this problem, we asked 24 subjects to produce equivalent "very hard" efforts, once after normal sleep, and once after 30 h without sleep. This was done by allowing the subject, while walking at constant speed, to adjust treadmill grade, without knowledge of the actual elevation. We found that exercise at equal perceived exertion was associated with the choice of a nearly equal absolute work load after sleep deprivation as after normal sleep (17.1 vs. 17.5% grade; p = n.s.). In addition, after 10 min of exercise at the self-selected intensity, subjects displayed identical ventilation, oxygen uptake, and CO2 production. However, heart rate was significantly lower during exercise after sleep loss (170 +/- 3 vs. 178 +/- 3 b X min-1; p less than 0.001). These results suggest that previously measured increases in perceived exertion during constant-load exercise after sleep loss may be spurious.

Adult↗
PubMed1982

Specific recipient-donor unresponsiveness mediated by a suppressor cell system in human kidney allograft tolerance.

The immunological responsiveness of a panel of 26 consecutive cadaver kidney allograft patients with good graft tolerance was studied against cells from the specific donor. Among these 26 patients, 11 underwent acute cellular rejection and were studied during the rejection episode. An additional eight transplant patients, who lost their graft as a result of cellular rejection, were nephrectomized and studied 6 months after their return to hemodialysis as the control group of patients "at equivalent risk." A low responsiveness against the specific donor was observed in cases of good graft tolerance, but was absent during rejection and in the control group. By using mixing experiments, cells from tolerant patients were able to actively and selectively suppress the response of their autologous pretransplant cells stimulated by the specific donor cells. These suppressor cells were effective only when added during the first 48 hr of the culture and could respond at a suppressor to responder cell ratio from 1:1 to 1:4. Finally, our observations indicate that allogeneic unresponsiveness between donor-recipient pairs may be associated with the presence of suppressor cells affecting the generation of helper T cells only in the specific situation, i.e., donor-recipient, and only in cases of good graft tolerance.

Adult↗
PubMed1982

Insensitivity of Water-Oxidation and Photosystem II Activity in Tomato to Chilling Temperatures.

Chilling tomato plants (Lycopersicon esculentum Mill. cv. Rutgers and cv. Floramerica) in the dark resulted in a sizable inhibition in the rate of light- and CO(2)-saturated photosynthesis. However, at low light intensity, the inhibition disappeared and the absolute quantum yield of CO(2) reduction was diminished only slightly. The quantum yield of photosystem II (PSII) electron flow was 18% lower when measured in chloroplasts isolated from chilled leaves than in chloroplasts isolated from unchilled leaves. Even though the maximum rate of PSII turnover in these chloroplasts was 12% lower subsequent to chilling, it was in all cases two or more times that required to support the light- and CO(2)-saturated rate of photosynthesis measured in the attached leaf. The concentration of active PSII centers in chloroplasts isolated from leaves either before or after chilling was determined by measurement of the products of water oxidation from a series of saturating flashes short enough to turnover the electron transport carriers only a single time. There was no significant change in the concentration of active PSII centers due to dark chilling.It was concluded that PSII activity and water oxidation capacity are not significantly impaired in tomato by chilling in the dark and therefore are not primary aspects of the inhibition of CO(2) reduction observed in attached leaves.

Journal Article↗
PubMed1982

Fetal habituation in high-risk pregnancies.

Habituation is a basic form of learning and probably requires an intact central nervous system. Habituation in the behavioural response to vibration in 40 normal human fetuses was compared with that in a group of high-risk pregnancies with an increased risk of fetal neurological damage. Highly significant differences in habituation patterns between the high-risk groups and normal control subjects were found. This test may offer a method of assessing the integrity of the fetal central nervous system.

Anencephaly↗
PubMed1982

Exercise performance after ventilatory work.

Although increased ventilation is one of the most readily observed physiological responses to exercise, it is uncertain how severely this hyperpnea stresses the ventilatory muscles. As one approach to this question, we compared short-term maximal running performance in nine subjects with and without prior ventilatory work designed to reduce ventilatory muscle endurance. This work consisted of 150 min of sustained maximum ventilation performed isocapnically while the subjects were seated. Both the level of sustained expired minute ventilation and the O2 uptake associated with it slowly declined with time during this 150-min period. On the average, subjects were able to maintain two-thirds of their 12-s maximum voluntary ventilation (MVV) during this long-term breathing test. The test had no effect on subsequently measured vital capacity, forced expiratory volume in 1 s, or the MVV. However, in short-term maximal running, at constant speed upgrades increased 1% each minute until volitional exhaustion, performance after prior breathing work was reduced as compared with control (6.5 vs. 7.6 min; P less than 0.01). Subjects ceased work at significantly lower ventilation (117 vs. 124 1.min-1 BTPS; P less than 0.05) and heart rate (179 vs. 187 beats.min-1; P less than 0.01) and reached significantly lower peak O2 uptake (3.07 vs. 3.24 1.min-1 STPD; P less than 0.05) during maximal running after ventilatory work. We conclude that reduced ventilatory muscle endurance alone is sufficient to decrease short-term maximal running performance.

Adult↗