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Biomedical subjects

D G Armstrong

Publications and source records attributed to D G Armstrong.

At least 145 records · Page 8Linked to original sources
PubMed1985

Insulin action and glucose metabolism in sheep fed on dried-grass or ground, maize-based diets.

The effect of an exogenous supply of glucose, provided by the digestion of maize starch in the small intestine, on endogenous glucose metabolism and insulin action was studied in sheep using the euglycaemic insulin clamp procedure. Insulin was infused intravenously at rates of 0.2, 0.5, 1.0 and 6.0 mU/min per kg live weight for four consecutive periods in each of four sheep fed on dried-grass and maize-based diets. Glucose was also infused intravenously at a variable rate, sufficient to maintain the plasma glucose concentration at basal levels. Whole-body rates of glucose metabolism were determined using a continuous infusion of [6-3H]glucose. From the resulting insulin dose-response curves, it was observed that, when the sheep were fed on the dried-grass diet, the responsiveness of glucose metabolism to insulin was less than that reported for non-ruminants. When fed the maize-based diet, the glucose metabolic clearance rates (MCR) observed during insulin infusions were significantly greater (P less than 0.05) than those observed for the dried-grass diet. However, after correcting for the non-insulin-mediated glucose disposal, differences between diets were not significant. The sensitivity of glucose utilization to insulin was not affected by diet. The plasma insulin concentrations causing half-maximal insulin-mediated glucose MCR were 103 (SE 21) and 85 (SE 11) mU/l for the dried-grass and maize-based diets respectively. The sensitivity of endogenous glucose production to insulin was also unaffected by diet. The plasma insulin concentrations resulting in the suppression of endogenous glucose production to half the basal level were 80 (SE 26) and 89 (SE 29) mU/l for the dried-grass and maize-based diets respectively. It is concluded that the observed increase in glucose utilization on the maize-based diet was due partly to a slight change in responsiveness to insulin and also partly to a change in the rate of non-insulin-mediated glucose disposal.

Animal Feed↗
PubMed1985

The digestion by cattle of silage-containing diets fed at two dry matter intakes. 2. Digestion of total amino acids and of D-alanine and D-glutamic acid.

In a 4 X 4 Latin square experiment four cows were given, twice daily, diets consisting of (g/kg dry matter (DM)) 500 barley, 400 grass silage and 100 soya-bean meal. The diets were given at either 1.15 (L) or 2.3 (H) times maintenance energy requirements and the soya-bean meal was either untreated (U) or formaldehyde (HCHO)-treated (T). The passage of digesta to the duodenum was estimated using chromic oxide as a flow marker; 35S was used to estimate the amount of microbial protein entering the small intestine. A microbial fraction was prepared by differential centrifugation from duodenal digesta. Samples of bacteria and of protozoa from rumen digesta were also prepared. The total amino acid contents of feedingstuffs, duodenal digesta, duodenal microbial material, rumen bacteria and rumen protozoa were determined by ion-exchange chromatography. The D-alanine and D-glutamic acid contents of the samples were determined by gas-liquid chromatography. The quantity of each amino acid entering the small intestine was significantly (P less than 0.001) increased by increasing DM intake and tended to be increased by formaldehyde-treatment of the soya-bean meal. There were net losses of all amino acids across the forestomachs except for lysine, methione, D-alanine and D-glutamic acid for which there were net gains. There were significant (P less than 0.05) differences in amino acid composition between rumen bacteria and duodenal microbial material; differences in amino acid composition between rumen bacteria and rumen protozoa were also observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1985

Changes in aromatase activity in small ovarian follicles of the domestic fowl (Gallus domesticus) during growth and atresia.

The tritium release assay for measuring aromatase activity was adapted to measure oestrogen production in intact small ovarian follicles of the domestic fowl. The activity was measured in three types of follicle classified as normal, atretic or grossly atretic. Normal follicles were distinguished from atretic by the presence of small haemorrhages on the surface of the atretic follicles. Grossly atretic follicles were identified by their deformed shape. The aromatase activity in normal and atretic follicles was related to follicular weight, the activity in atretic follicles being less than that in normal follicles. The aromatase activity in grossly atretic follicles was independent of follicular weight. The enzyme activity in this group of follicles was significantly less than that in either normal or atretic follicles. The significance of these results is discussed in relation to the induction of atresia within the small ovarian follicles of the domestic fowl.

Animals↗
PubMed1985

Changes in 3 beta-hydroxy- delta 5-steroid dehydrogenase activity in granulosa tissue during the ovulatory cycle of the laying hen (Gallus domesticus).

The object of this study was to examine changes in the activity of granulosa 3 beta-hydroxy-delta 5-steroid dehydrogenase during the ovulatory cycle of the domestic fowl. The enzyme activity in granulosa tissue from the largest follicle increased significantly during the period 8-14 h before an expected ovulation. The increase in activity occurs before the preovulatory surge of LH and near the time of lights off. During the 4-8 h period before an ovulation, i.e. the time of maximal plasma LH concentrations, 3 beta-hydroxy-delta 5-steroid dehydrogenase activity decreased in granulosa tissue from the largest follicle. This observation is explained by proposing that the enzyme is inhibited by the large amounts of progesterone found in the tissue at this time. The results indicate that important biochemical changes are taking place within granulosa tissue of the largest ovarian follicle before the preovulatory LH surge.

3-Hydroxysteroid Dehydrogenases↗
PubMed1984

Changes in metabolism and cell size of the anaerobic bacterium Selenomonas ruminantium 0078A at the onset of growth in continuous culture.

Initial metabolism of Selenomonas ruminantium 0078A in continuous culture was characterized by a high lactate and low volatile fatty acid production; this was associated with poor growth as determined by bacterial dry weight production, yet individual cells were considerably larger than those of the inoculum. Biomass production increased, cell size decreased and the fermentation pattern reverted to the characteristic low lactate and high volatile fatty acid production after approximately 90 h growth.

Animals↗
PubMed1984

Changes in metabolism of the rumen bacterium Streptococcus bovis H13/1 resulting from alteration in dilution rate and glucose supply per unit time.

Streptococcus bovis H13/1 was grown in a glucose-limited chemostat. A concomitant increase in dilution rate and glucose supply per unit time caused both an increase in lactate production per mole of glucose fermented and a linear increase in growth yield over the dilution rate range 0.052 to 0.141/h. When the dilution rate was increased with no change in glucose supply per unit time there was a reduction in lactate production and an increase in that of acetate and ethanol coinciding with a non-linear increase in growth yield. YMaxglu = 38.6 and a maintenance coefficient, ms = 0.290 mmol/l glucose/g cells/h were calculated. The results also suggested an interaction between the formate and CO2 pools.

Acetates↗
PubMed1984

Ovarian aromatase activity in the domestic fowl (Gallus domesticus).

Fowl ovarian aromatase activity was measured by an assay based on the stereospecific elimination of tritium from [1,2-3H]testosterone. The production of tritiated water was shown to provide a valid estimate of aromatase activity under the conditions used. The small yellow follicles and ovarian stroma contained 50% of the total ovarian aromatase activity. The activity in the thecal tissue from the rapidly growing follicles reached a maximum level in the fourth largest follicles (17% of the total ovarian activity) and thereafter declined to low levels in the largest follicle and first post-ovulatory follicle. No activity was detected in the granulosa tissue from the rapidly growing follicles. It is proposed that the basal levels of plasma oestrogen in hens are maintained by production in the small yellow follicles and/or ovarian stroma. The variation in plasma oestrogen during the ovulatory cycle probably arises from secretion by the rapidly growing follicles.

Animals↗
PubMed1982

Properties of 5-ene-3 beta-hydroxysteroid dehydrogenase in granulosa tissue from the domestic fowl (Gallus domesticus).

Microsomal 5-ene-3 beta-hydroxysteroid dehydrogenase activity from fowl preovulatory granulosa tissue was solubilised by treatment with 2.0 M KCl. The efficiency of the solubilisation procedure was assessed by measuring the amount of activity remaining in the supernatant after centrifugation at 105,000 g for 8 h. The microsomal activity was resolved into two components: a fraction solubilised by the salt treatment and a fraction remaining membrane bound. The results indicate that the enzyme exists in two different environments within the membrane. The time course for the thermal inactivation of the microsomal enzyme supported this conclusion. The properties of the solubilised enzyme were compared with the untreated microsomal preparation, with respect to steroidal inhibition. Progesterone, 4-androstene-3,17-dione and oestradiol-17 beta all inhibited the enzyme and no difference was observed between the two preparations. The results are discussed in relation to the involvement of 5-ene-3 beta-hydroxysteroid dehydrogenase in the control of progesterone production in fowl granulosa tissue.

3-Hydroxysteroid Dehydrogenases↗
PubMed1982

3 beta-hydroxy-delta 5-steroid dehydrogenase activity in the rapidly growing ovarian follicles of the domestic fowl (Gallus domesticus).

The total and specific activity of 3 beta-hydroxy-delta 5-steroid dehydrogenase, isocitrate dehydrogenase (NADP+) and glucose-6-phosphate dehydrogenase were measured in ovarian follicles from the domestic fowl. The enzymes were assayed in the five largest yolk-filled follicles which were sampled twice during the ovulatory cycle, at 1 h and 16 h before an expected ovulation. The total and specific activity of granulosa enzymes increased throughout the hierarchy and reached a maximum in the largest follicle. The relative increase in 3 beta-hydroxy-delta 5-steroid dehydrogenase activity was greater than that of the other two enzymes examined. The total thecal 3 beta-hydroxy-delta 5-steroid dehydrogenase activity reached a maximum in the third and fourth largest follicles. Thereafter its activity decreased up to the time of ovulation. The activity of 3 beta-hydroxy-delta 5-steroid dehydrogenase and glucose-6-phosphate dehydrogenase in follicles collected 1 h before and ovulation were significantly less than the activity in corresponding follicles collected 16 h before an ovulation.

3-Hydroxysteroid Dehydrogenases↗
PubMed1979

Subcellular distribution of delta 5-3 beta-hydroxy steroid dehydrogenase in the granulosa cells of the domestic fowl (Gallus domesticus).

1. The distribution of 3 beta-hydroxy steroid dehydrogenase was examined in the subcellular fractions of granulosa cells collected from the ovary of the domestic fowl. 2. 3 beta-hydroxy steroid dehydrogenase activity was observed in the mitochondrial (4000g for 20min) and microsomal (105 000g for 120min) fractions. 3. Approximately three times more 3 beta-hydroxy steroid dehydrogenase activity was associated with the cytochrome oxidase activity (a mitochondrial marker enzyme) in anteovulatory-follicle granulosa cells than with that of the postovulatory follicle. 4. Comparison of the latent properties of mitochondrial 3 beta-hydroxy steroid dehydrogenase with those of cytochrome oxidase and isocitrate dehydrogenase indicated that 3 beta-hydroxy steroid dehydrogenase is located extramitochondrially. 5. This apparent distribution of 3 beta-hydroxy steroid dehydrogenase is explained on the basis that the mitochondrial activity is either an artefact caused by a redistribution in the subcellular location of the enzyme, occurring during homogenization, or by the existence of a functionally heterogeneous endoplasmic reticulum that yields particles of widely differing sedimentation properties.

3-Hydroxysteroid Dehydrogenases↗