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Biomedical subjects

G Mitchell

Publications and source records attributed to G Mitchell.

At least 199 records · Page 11Linked to original sources
PubMed1980

Effects of temperature, adenosine triphosphate and magnesium concentrations on the contraction of actomyosin isolated from halothane-sensitive and -insensitive German Landrace pigs.

The effects of temperature, adenosine triphosphate and magnesium on the calcium sensitivity of actomyosin were investigated on actomyosin obtained from six halothane-sensitive and five halothane-resistant German Landrace pigs. No difference in the contractile properties was found in actomyosin from the two types of pig. However, in both types calcium sensitivity of the actomyosin was lost at temperatures slightly greater than those occurring physiologically. Both ATP and Mg2+ protect against the loss of calcium sensitivity. These results suggest that the basic lesion in halothane-induced malignant hyperthermia does not lie in the contractile proteins. It is likely, however, that the decreases in intracellular ATP and Mg2+ concentrations which occur in pigs during malignant hyperthermia, contribute to the development of the syndrome.

Actomyosin↗
PubMed1980

Substance P increases hypothalamic blood flow via an indirect adrenergic-cholinergic interaction.

1 Hypothalamic blood flow (HBF) was measured in conscious rabbits by the 133xenon washout technique. 2 Substance P in a dose of 50 or 500 ng increases HBF while 5 ng is without effect. 3 Cholinoceptor blockade, with either atropine or mecamylamine abolishes the vasodilator effect of substance P. 4 Chemical sympathectomy of the hypothalamus with 6-hydroxydopamine, or adrenoceptor blockade with either propranolol or phenoxybenzamine abolishes the effect of substance P on HBF. 5 Destruction of the intracerebral noradrenergic pathway (INP), or blockade of its vasodilator action, with barbiturate or bicarbonate, likewise prevent the vasodilator action of substance P. 6 These results suggest that substance P may cause an increase in HBF via the release of endogenous acetylcholine, which in turn stimulates the INP.

Acetylcholine↗
PubMed1980

Plasmodium falciparum strains from Papua New Guinea: culture characteristics and drug sensitivity.

Seven strains of Plasmodium falciparum from Papua New Guinea have been established in continuous in vitro culture. Samples with a high initial parasitaemia were more likely to form continuous lines, possibly due to the time required for transport of infected blood samples from Papua New Guinea to laboratories in Australia. Most but not all established lines were resistant to chloroquine and all were resistant to pyrimethamine, possibly reflecting the parasite strain characteristics in that region.

Adolescent↗
PubMed1980

A halothane-induced biochemical defect in muscle of normal and malignant hyperthermia-susceptible Landrace pigs.

Muscle adenosine triphosphate (ATP), glucose-6-phosphate, phosphocreatine, and pH were measured in nine malignant hyperthermia (MH)-susceptible and 14 MH-resistant Landrace pigs. Muscle biopsies were taken before (under barbiturate anesthesia) and after exposure to halothane. When compared to levels during barbiturate anesthesia, exposure to halothane had no immediate effect on muscle ATP levels in either MH-susceptible or -resistant pigs. However, once malignant hyperthermia developed in susceptibe pigs ATP levels decreased significantly. In both susceptible and resistant pigs halothane increased muscle glucose-6-phosphate and decreased muscle phosphocreatine and pH significantly below control levels observed during barbiturate anesthesia. In susceptible pigs these changes were significantly more marked than were the changes produced in resistant pigs. These data indicate that the effect of halothane on muscle metabolism is similar in both MH-resistant and -susceptible pigs. The results suggest that the effect of halothane is to inhibit aerobic metabolism by preventing mitochondrial dehydrogenation of pyruvate. Inhibition is complete in susceptible pigs but only retarded in resistant pigs. In susceptible pigs the consequent lactacidosis, hyperthermia, and reduction in ATP synthesis contribute to the development and maintenance of rigidity.

Adenosine Triphosphate↗
PubMed1980

A systematic study of the effect of vitamin C supplementation on the humoral immune response in ascorbate-dependent mammals. I. The antibody response to sheep red blood cells (a T-dependent antigen) in guinea pigs.

We have investigated the humoral immune response to Sheep Red Blood Cells (S.R.B.C.--a T-dependent cellular antigen) in two groups of random-bred guinea pigs. A control group of animals was maintained on "minimal" ascorbate intake, while the test group animals received supplementary vitamin C in their drinking water. Serum haemolytic antibody levels were monitored at various intervals subsequent to immunization with S.R.B.C. The primary antibody response of the ascorbate-supplemented animals differed statistically significantly from that of the controls in two respects. The peak antibody titre was both higher and occurred earlier in the test animals. No significant difference in the antibody response to a secondary injection of antigen was manifest. Our observations suggest that vitamin C stimulates the elaboration of Ig M-type antibodies in particular.

Animals↗
PubMed1979

Evidence for an indirect cholinergic regulation of blood flow in the hypothalamus of conscious rabbits.

1 The effects of methacholine, atropine and adrenoceptor blockade on hypothalamic blood flow (HBF) were measured in conscious rabbits. 2 A dose of 1 microgram methacholine increased HBF while smaller and larger doses had no significant effect. 3 The vasodilatation induced by methacholine was blocked by atropine and by chemical sympathectomy of the hypothalamus with 6-hydroxydopamine. 4 The vasodilatation was reversed by propranolol but was not affected by phenoxybenzamine. 5 These results suggest that the vasodilator action of muscarinic receptor agonists on hypothalamic resistance vessels depends upon the integrity of a noradrenergic system, and is mediated via beta-adrenoceptors.

Animals↗
PubMed1978

Strain differences in the immune response of mice to homologous sperm-specific lactate dehydrogenase (LDH-C4).

The sperm-specific isozyme of murine lactate dehydrogenase (LDH-C4) was injected into female mice of various strains. Two regulatory phenotypes characterize the resultant immunity to LDH-C4: one is manifested by high, intermediate or low levels of response, the other by the immediate or delayed maturation of peak titer. The response of several strains can be classified as high (SWR, SJL, BABL/c, C3H/He) and intermediate to low (A, CBA, DBA/2, DBA/1, C57BL/6) according to the level of antibody production and cell mediated immunity. BALB/c, SJL and SWR strains are immediate responders while DBA/2 and C3H/He mice are clearly delayed responders. Maturation and magnitude of response do not appear to be related. Both the antibody and cell mediated responses are T-dependent, but are not obviously associated with Ig allotype or H-2 regulation.

Animals↗
PubMed1978

X-ray fluorescence analysis of lead in teeth of urban children in situ: correlation between the tooth lead level and the concentration of blood lead and free erythroporphyrins.

The tooth lead level of 30 lead-exposed children was measured in situ using an X-ray fluorescence technique. The tooth lead concentration divided by the child's age correlated with the free erythroporphyrin (FEP) (r = 0.51) and the blood lead levels (r = 0.31). The mean tooth lead concentrations of 10 Class IV children (FEP greater than or equal to 190 micrograms/100 ml; blood lead 30-80 micrograms/ml) was 14.5 +/- 5.5 ppm/year. Reexamination of the histories of children who had been classified as Class II or III, but who had tooth lead concentrations within 1 SD of the Class IV level, indicated that many of these children could also be considered to be Class IV children. When the x-ray fluorescence technique was used to screen an urban population of 300 children, the tooth lead values indicated that 72% of the children had been exposed to low levels of environmental lead. Six percent of the children were found to have tooth lead concentrations in excess of 9 ppm/year and within 1 SD of the mean value exhibited by Class IV children. These children were considered to have a high body lead burden. The percentage of children having an elevated tooth lead level is similar to the number previously reported using exfoliated deciduous teeth.

Child↗
PubMed1978

Vasodilator mechanism of the intracerebral (non-sympathetic) adrenergic pathway.

Stimulation of the intracerebral noradrenergic pathway causes a vasodilatation in the hypothalamus. We have investigated whether this vasodilatation is caused by a direct vascular innervation or whether it is secondary to an activation of hypothalamic neurons. Non-specific neuronal activation using glutamate increased the mean hypothalamic blood flow. Depression of neuronal activity using barbiturate reduced hypothalamic blood flow and blocked the glutamate and the intracerebral noradrenergic pathway-induced vasodilatation. These results suggest that stimulation of the intracerebral noradrenergic pathway increases hypothalamic neuronal activity which indirectly causes a vasodilatation.

Animals↗
PubMed1977

Measurement of lead content of children's teeth in situ by x-ray fluorescence.

The central nervous system of young children is particularly sensitive to neurological damage due to excessive lead exposure. The lead stored in a tooth is permanent and related to the quantity of ingested lead. The lead is assayed by measuring the characterisitc radiation from lead in a tooth in situ irradiated with gamma rays from a cobalt-57 source. The sensitivity of the method is adequate to measure lead levels commonly associated with environmental background. The X-ray exposure to the tooth necessary for this determination is approximately one tenth of that required for a routine dental examination.

Child↗
PubMed1977

Sucrose-negative variants of Candida tropicalis.

Four cultures of a Candida sp. that lacked alpha-glucosidase activity were isolated from clinical specimens. Physiological, morphological, and serological characterizations of the yeasts and deoxyribonucleic acid reassociation studies supported their classification as a variant of C. tropicalis.

Antigens, Fungal↗
PubMed1976

Antenatal diagnosis of neural tube defects.

One hundred women with pregnancies at risk for the recurrence of neural tube defects have entered our monitoring programme of echography and alphafetoprotein estimation (AFP) on amniotic fluid and maternal serum during the second trimester. The results of these pregnancies, the application of the programme, sources of error, and the reliability of alphafetoprotein levels are discussed. Conclusions regarding the value of the tests and routine antenatal screening are made.

Adult↗