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Biomedical subjects

L Stevens

Publications and source records attributed to L Stevens.

At least 37 records · Page 2Linked to original sources
PubMed1990

Contractile properties of rat soleus muscle after 15 days of hindlimb suspension.

The properties of the contractile elements interacting to develop force in atrophied rat soleus muscle were studied by using single skinned fibers, which permitted direct access to the contractile apparatus. Muscle atrophy was induced by 15 days of hindlimb suspension. Suspension resulted in a decrease of maximal tension relative to an important decline in fiber diameter. Ca affinity of the contractile proteins was not changed insofar as the tension-pCa relationship was not shifted along the pCa axis. However, after hindlimb suspension 1) the value of the Hill coefficient from the tension-pCa curve was found to be higher, 2) a higher Ca threshold for activation was reported, and 3) a significant increase in contraction kinetics was described. All these results suggested that after suspension the mechanical properties of the slow-twitch soleus appeared to resemble more closely those of a fast-twitch muscle. Our results were in complete agreement with published histochemical data.

Animals↗
PubMed1989

Purification and characterisation of NAD-glutamate dehydrogenase from Aspergillus nidulans.

NAD-Glutamate dehydrogenase has been purified from mycelia of A. nidulans. The enzyme comprises subunits of 110 kDa. It is located in the cytosol. It is completely denatured by 1.0 M guanidine hydrochloride, and is not renatured by subsequent dilution. Isophthalate is a strong competitive inhibitor and the enzyme is also inhibited by thiol reagents. The properties of the enzyme were compared to those from other fungi in terms of size, sensitivity to inhibitors, intracellular distribution and mode of regulation, and were found to resemble most closely those of Neurospora crassa.

Aspergillus nidulans↗
PubMed1989

Compared properties of the contractile system of skinned slow and fast rat muscle fibres.

Chemically skinned fibres from soleus and plantaris rat muscles were used to compare the contractile properties of slow and fast muscles. The maximal isometric tension appeared larger in plantaris than in soleus fibres. The apparent Ca2+ threshold for activation was lower in slow than in fast fibres while Ca2+ concentrations required to obtain either the maximal tension or half maximal tension (pCa50) were lower in fast than in slow fibres. This apparent difference in Ca2+ sensitivity will be discussed. As could be expected from other studies, a faster force development in plantaris than in soleus fibres occurred. However, one interesting new result showed that in soleus, the kinetics of the tension development estimated by the tmax parameters were slightly dependent on the Ca2+ concentration whereas the t50 parameter changed significantly with the Ca2+ concentration. In plantaris, both tmax and t50 parameters were found to depend strongly on the Ca2+ concentration. Finally, the plantaris muscle showed a greater caffeine sensitivity than the soleus muscle. All the results suggested that the Ca-regulatory mechanism in the slow fibres was essentially different from that in the fast fibres.

Animals↗
PubMed1989

Cardiac assistance with electrically stimulated skeletal muscle.

This study examined the ability of a skeletal muscle-powered assist ventricle (SMV) to augment cardiac output in ten dogs with pharmacologically induced heart failure under acute conditions. An SMV was surgically constructed in each dog by wrapping the untrained rectus abdominis muscle around a compressible pouch that was inserted into a left ventricular apex-to-aortic vascular conduit. The multiple motor nerves to the rectus muscle were then stimulated during ventricular diastole at a rate which equalled a ratio of 1:2, 1:3, or 1:4 with the natural ventricular beat. There was an increased cardiac output during SMV assistance compared with preassistance values in all ten dogs at each stimulation ratio with a mean increase of 46 +/- 4 per cent with a ratio of 1:2, 25 +/- 4 per cent with a ratio of 1:3, and 31 +/- 7 per cent with a ratio of 1:4 (p less than 0.01 for all values). The diastolic blood pressure and mean blood pressure were both increased (p less than 0.01 and p less than 0.05, respectively) during SMV stimulation at ratios of 1:2 and 1:3, but not 1:4. We have shown that untrained rectus abdominis muscle, when used as the power supply for a SMV in an apico-aortic conduit, can temporarily augment cardiac output in dogs with pharmacologically induced heart failure.

Abdominal Muscles↗
PubMed1989

Environmental factors affecting reproductive incompatibility in flour beetles, genus Tribolium.

This paper reports the effect of high temperatures on the reproductive compatibility of geographic strains of flour beetles, Tribolium confusum. Some geographic strains are reproductively incompatible with other strains owing to a maternally inherited microorganism: Males infected with the microorganism are reproductively incompatible with uninfected females. All other crosses are fertile. Previous reports indicated that infected strains can be cured of the microorganisms by culturing the beetles on medium containing tetracycline and that cured males become reproductively compatible. This study reports that raising larvae at high temperatures (37 degrees C) promotes curing. The proportion of individuals cured is a function of sex and the period of exposure to high temperature.

Animals↗
PubMed1989

A skeletal muscle ventricle made from rectus abdominis muscle in the dog.

This study examined the ability of a skeletal muscle-powered assist ventricle to augment cardiac output in 10 dogs with experimentally induced heart failure. Heart failure was induced with the use of the beta-blocking agents atenolol and propranolol. A "skeletal muscle ventricle" was then surgically constructed by wrapping the rectus abdominis muscle, with an intact neurovascular supply, around a double open-ended compressible pouch. The skeletal muscle ventricle was then interposed in a left ventricular apicoaortic conduit. The motor nerves to the skeletal muscle ventricle were stimulated by a custom designed pulse generator and caused tetanic contraction of the ventricle during diastole of every fourth natural heart beat. Stimulation was continued for 60 min. Cardiac output, systolic and diastolic blood pressures, mean blood pressure, left ventricular end diastolic pressure, and central venous pressure were then monitored prior to, during, and several times after skeletal muscle ventricle stimulation to evaluate assist ventricle function. There was an increased cardiac output in all 10 dogs at all recording times during skeletal muscle ventricle assistance compared to the cardiac output prior to stimulation of the assist ventricle. The mean increase in cardiac output after 30 min of assist ventricle stimulation was 31.0 +/- 14% (P less than 0.01), and at 60 min was 8.0 +/- 1% (P less than 0.05). The mean diastolic blood pressure after 1 and 30 min of skeletal muscle ventricle assistance (50.0 +/- 2.9 and 48.6 +/- 2.2 mm Hg, respectively) was increased (P less than 0.05) vs the preassistance value (44.9 +/- 2.8 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Effects of alcohol abuse and familial alcoholism on physical health in men and women.

Detoxified alcoholic men (n = 76) and women (n = 72) and nonalcoholic control men (n = 50) and women (n = 51) were given a structured interview that assessed five categories of physical health: medical history, alcohol-related disorders, trauma history, drug use history, and, for females, female-related disorders. Approximately half the subjects in each group were family history positive for alcoholism. Significant differences between alcoholics and controls were found for all five categories; family history effects were significant for four of the five categories, and sex differences were present in two categories. The results indicate that (a) alcoholics suffer pervasive physical health difficulties, (b) a family history of alcoholism is predictive of health problems in both alcoholics and controls, (c) the effects of alcohol abuse and family history of alcoholism on health appear to be independent and additive, and (d) women may be more "illness prone" than men and exhibit an increased vulnerability to the adverse effects of alcoholism.

Adult↗
PubMed1989

Strength properties of three zinc phosphate cements mixed to two different consistencies.

When hand-mixing is used, clinicians mix zinc phosphate cement to consistencies which allow proper seating of restorations. Slump tests have indicated that the same two preferred consistencies (one for cementing a single unit restoration, the other for cementing a multiple unit restoration) could be obtained at different slab temperatures for three cements by mixing to certain powder-liquid ratios which were different for each cement. Each cement could be repeatedly mixed to the preferred consistency by using the appropriate powder-liquid ratio. The compressive and tensile strengths of the cements varied, although mixed to the same consistency. Selection of a cement for clinical use should be based on its strength properties when mixed to a preferred consistency.

Dental Stress Analysis↗
PubMed1989

Monitoring ovarian function and pregnancy in the giant panda (Ailuropoda melanoleuca) by evaluating urinary bioactive FSH and steroid metabolites.

Urinary excretion of oestrone conjugates, pregnanediol-3 alpha-glucuronide (PdG) and 20 alpha-hydroxypregn-4-en-3-one were measured from 8 weeks before oestrus to 2 weeks post partum and bioactive FSH was monitored during the periovulatory interval in a female giant panda. A biphasic urinary bioactive FSH excretory profile appeared to indicate a broad (approximately 10 day) follicular phase followed by a sharp preovulatory bioactive FSH surge coincident with an acute increase in urinary oestrone conjugates and behavioural oestrus. Weekly concentrations of urinary oestrone conjugates and PdG increased (P less than 0.001) by Week 9 of gestation with 20 alpha-hydroxypregn-4-en-3-one levels increasing 10-30-fold (P less than 0.001) between Weeks 11 and 14. These observations indicate that the monoestrous giant panda does not appear to require a prolonged period of endogenous FSH release or multiple FSH peaks for ovarian priming and follicle selection to proceed normally. Furthermore, the delayed rise in urinary steroid excretion during the second half of gestation in the giant panda supports the concept of delayed implantation while the estimation of steroid conjugates in urine offers a non-invasive approach for monitoring pregnancy status in this endangered species.

20-alpha-Dihydroprogesterone↗
PubMed1988

The effects of repeated withdrawals from alcohol on the memory of male and female alcoholics.

The measure of number of withdrawals, as a separate drinking variable of relevance to cognitive functioning in alcoholics, is a relatively uninvestigated measure. An ethanol withdrawal hypothesis has been suggested that would predict poorer cognitive performance with increased number of withdrawals from alcohol. In this study, the effects of withdrawals (defined as a 24 hr period of abstinence following the consumption of alcohol) on tests of learning and memory were examined. Using 76 male and 67 female alcoholics, results indicate that greater number of withdrawals is related to poorer memory test performance. Results provide support for the ethanol hypothesis of poorer cognitive performance with increasing number of withdrawals, and suggest that females may exhibit accelerated responses to the effects of alcohol misuse.

Adult↗