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Biomedical subjects

M Silver

Publications and source records attributed to M Silver.

At least 217 records · Page 12Linked to original sources
PubMed1976

Adrenal and pancreatic endocrine responses to hypoxia in the conscious calf.

1. Pancreatic and adrenal responses to intense hypoxia have been examined in conscious unrestrained calves 3-5 weeks after birth. 2. The outputs of both cortisol and corticosterone from the right adrenal gland rose steadily in response to hypoxia and this cortical secretory response was accompanied by a pronounced increase in blood flow through the gland. The changes in both steroid output and adrenal blood flow corresponded with those which occur in response to supramaximal doses of corticotrophin in calves of the same age. 3. Neither adrenaline nor noradrenaline were released in significant amounts from the adrenal medulla until the arterial PO2 had fallen below 15 mmHg. Such severe hypoxia caused secretion of catecholamines at rates comparable with those recorded during maximal stimulation of the sympathetic innervation to the gland in anaesthetized calves. The response to intense hypoxia in these conscious calves differed from that which occurs under anaesthesia in that the amount of adrenaline released was invariably greater than that of noradrenaline. 4. Severe hypoxia produced a rapid but transient increase in plasma glucagon concentration, followed by a pronounced rise in plasma glucose concentration in animals with abundant liver glycogen. No change in plasma insulin concentration was observed during hypoxia although it rose subsequently in response to hyperglycaemia. 5. Bilateral section of the splanchnic nerves virtually abolished the release of catecholamines in response to hypoxia but the adrenal cortical and pancreatic responses did not appear to be affected.

Adrenal Glands↗
PubMed1976

Microbiological oxidation of synthetic chalcocite and covellite by Thiobacillus ferrooxidans.

The microbiological oxidation of synthetic chalcocite and covellite has been investigated using an adapted strain of Thiobacillus ferrooxidans. Biodegradation of chalcocite was found to be 90 to 100% and that of covellite 45 to 60%. Optimum conditions for the oxidation of chalcocite were: pH, 1.7 to 2.3; temperature, 35 C; and ferric iron concentration in the range of 0.004 to 0.01 M. For covellite, the optimum conditions were: pH 2.3; temperature, 35 C; and ferric iron concentration in the range of 0.004 to 0.02 M. The energies of activation were determined to be 16.3 kcal (ca. 6.8 X 10(4) J) per mol and 11.7 kcal (ca. 4.8 X 10(4) J) per mol for chalcocite and covellite, respectively.

Biodegradation, Environmental↗
PubMed1976

Base competition of DNA isolated from Thiobacillus ferrooxidans grown on different substrates.

The present study indicates some anomalies with respect to the DNA base composition of Thiobacillus ferrooxidans when it is cultured on different substrates. The % GC of the DNA of this bacterium has been calculated by three different methods (melting temperature, CsCl density gradient centrifugation and ultra-violet absorbancy ratios) using Escherichia coli and Rhodospirillum rubrum as references. The main values for T. ferrooxidans grown on ferrous iron, chalcopyrite and lead sulfide concentrates were calculated to be 56.0, 60.1 and 54.4% GC respectively. Although these large differences are not completely understood, an attempt has been made to explain this phenomenon.

Centrifugation, Density Gradient↗
PubMed1975

Outbreak of food-borne type-A hepatitis in Greater Glasgow.

In a fourteen-day period between December, 1974, and January, 1975, 12 out of 118 members of a Glasgow golf club, who had attended their annual dinner/dance at a popular hotel in Glasgow six weeks previously, developed acute icteric hepatitis. Epidemiological investigations suggest that the infection was due to contamination of the cream used in fruit salad and sherry trifle prepared by a pastry-cook at a time when he was incubating type-A hepatitis.

Adult↗
PubMed1975

Endocrine responses to insulin hypoglycaemia in the young calf.

1. Variations in the output of glucocorticoids and catecholamines from the right adrenal gland, in response to insulin hypoglycaemia, have been investigated in calves 2-5 weeks after birth. These have been correlated with changes in the concentration of glucocorticoids and glucagon in arterial plasma. 2. Moderate hypoglycaemia for a limited period (0-1 u. insulin/kg), elicited a prompt increase in steroid output from the adrenal gland followed by a significant rise in plasma glucagon concentration. By comparison, changes in both catecholamine output and peripheral plasma glucocorticoid concentrations were found to be trivial in this group of animals. 3. Administration of a larger dose of insulin (0-5 u./kg) produced a more substantial fall in plasma glucose concentration followed by spontaneous recovery within 2-3 hr. This stimulus elicited the release of greater amounts of both cortisol and corticosterone, followed by a significant increase both in the output of adrenaline and in plasma glucagon concentration. Increase in steroid output was accompanied by an increase in adrenal blood flow and was associated with elevated concentrations of both steroids in arterial plasma. 4. The adrenal cortical response and associated changes in plasma steroid concentration were found to be transient even in response to persistent and intense hypoglycaemia (4 u. insulin/kg). The increase in plasma glucagon concentration in this group of animals was not significantly greater than that produced by smaller doses of insulin. However, substantial amounts of adrenaline (78 plus or minus 14 ng. kg-minus 1 min-minus 1; maximum; n equals 9) together with a little noradrenaline (10 plus or minus 3 ng.kg-minus 1 min-minus 1; maximum; n equals 9) were released from the right adrenal gland under these conditions. 5. Changes in adrenal blood flow could be related to adrenal glucocorticoid output in calves given 0-1 or 0-5 u. insulin/kg. In animals given the largest dose of insulin adrenal blood flow was found to increase coincidentally with rising steroid output but this hyperaemia then persisted after steroid output had subsided to values within the normal range. 6. Calves given the largest dose of insulin (4-0 u./kg) invariably collapsed and convulsed after 2-3 hr, but these symptoms could not be related to any particular endocrine response. No clinical signs of hypoglycaemia were observed in the other animals. 7. The results are discussed in relation to previous studies of adrenal function in this and other species.

Adrenal Glands↗
PubMed1975

Cardiovascular and endocrine responses to feeding in the young calf.

A number of cardiovascular and endocrine responses which occur during and after feeding in the unweaned calf are described. 2. There was a substantial increase in both heart rate and mean aortic blood pressure during feeding in these animals. This occurred within the first few seconds and persisted throughout the period of ingestion. 3. The concentrations of glucose, insulin and gastrin in arterial plasma rose abruptly during, or immediately after, feeding and elevated values persisted for at least 2 hr. A transient increase in glucagon concentration was also observed. In contrast, feeding appeared to produce no immediate rise in enteroglucagon concentration. 4. The adrenal output of glucocorticoids rose transiently in response to feeding but that of catecholamines was unaffected. 5. Cardiovascular responses to feeding were also examined in other species. In unweaned kids the changes were essentially similar to those observed in the calf but were less pronounced. In lambs a persistent hypertension occurred which was associated with a brief initial tachycardia. In adult dogs ingestion of solid food also caused tachycardia but although the aortic blood pressure rose for a short period at the beginning of feeding, hypotension developed thereafter. 6. The possibility that both the cardiovascular and endocrine responses, which occur during or immediately after feeding, are mediated by the autonomic nervous system is discussed.

Age Factors↗
PubMed1975

The soluble adenosine triphosphatase of Thiobacillus ferrooxidans.

Adenosine triphosphatase (ATPase) from Thiobacillus ferrooxidans was purified 55-fold. Polyacrylamide gel electrophoresis of the most purified fraction showed only one major band; histochemical analysis showed that the ATPase activity was associated with this band. The pH optimum is 9-10. The enzyme hydrolyzed ATP stoichiometrically to ADP and inorganic phosphate, the Km for this substrate being 7.75 times 10-3 M. GTP and ITP are alternate substrates, the Km values for these being 6.71 times 10-3 M and 3.12 times 10-3 M, respectively. ADP is slightly hydrolyzed. Magnesium, manganese, and calcium can serve as cofactors; Km values for these are 2.0 times 10-3 M, 9.4 times 10-4 M, and 8.0 times 10-4 M, respectively. The enzyme activity was not activated by either sodium or potassium, but a combination of the two ions were inhibitory. Azide and p-hydroxymercuribenzoate strongly inhibited the enzyme activity, whereas cyanide, dinitrophenol, and N,N'-dicyclohexylcarbodiimide (DCCD) were without effect. The enzyme was cold labile at 0 degrees-C, but was more stable at 18-24 degrees-C.

Adenosine Diphosphate↗
PubMed1975

Thiobacillus acidophilus sp. nov.; isolation and some physiological characteristics.

After a brief exposition to glucose, Thiobacillus acidophilus was isolated from a culture of iron-grown T. ferrooxidans. Physicochemical analysis of its DNA showed a G+C content of 62.9-63.2%. The new isolate grows best at 25-30 degrees C and at pH 3.0. Growth is possible between pH 1.5 and 6.0. Thiobacillus acidophilus is apparently strictly aerobic. Ammonium salts are the only suitable source of nitrogen. The bacterium is a facultative autotroph. In addition to elemental sulfur, it obtains energy from organic compounds such as D-glucose, D-galactose, D-fructose, D-mannitol, D-xylose, D-ribose, D-arabinose, L-arabinose, sucrose, sodium citrate, malic acid,dl-aspartic acid, and dl-glutamic acid. Thiobacillus acidophilus possesses the key enzymes of the tricarboxylic acid (TCA) cycle including NAD-and NADP-linked isocitric dehydrogenase and alpha-ketoglutarate dehydrogenase, and the key enzymes of the hexose monophosphate pathway (glucose-6-phosphate and 6-phosphogluconate dehydrogenase, and fructose 1,6-diphosphate aldolase). NADH oxidase has been found in particulate fraction of extracts. Rhodanese and thiosulfate oxidase have also been detected.

Aerobiosis↗
PubMed1975

The use of intravascular catheters for long-term studies on the mare and fetus.

Methods developed for the insertion of catheters into the umbilical artery and vein and the uterine vein of the pregnancy mare are described. The technique requires careful anaesthesia and the maintenance of normal blood gas tensions, pH and arterial blood pressure. Fetal survival was variable: three mares delivered live foals and six fetuses survived more than 15 days with a maximal period of 41 days. The erythrocytes sedimentation rate (ESR) of the fetal foal was always very low at operation but subsequently increased slightly; a sudden large rise in ESR usually indicated imminent fetal death. The relatively sudden death in utero of catheterized fetuses maintained for 10 days or more remains unexplained. Nevertheless, the stability and relatively long duration of some of these preparations are sufficient to investigate various aspects of placental exchange and the endocrine climate of the fetus.

Anesthesia↗
PubMed1975

Plasma progestagens and oestrogens in fetus and mother in late pregnancy.

Normal Thoroughbred and catheterized Pony mares and their fetuses were used. Fetal oestrogen and progestagen concentrations in late gestation were much higher than maternal values. A major feature of the umbilical steroid concentrations was a large venous-arterial difference in progestagens and total oestrogens throughout late gestation which may indicate a metabolic cycle in the fetus between progesterone and other steroid metabolites. Metabolites of 20alpha-dihydroprogesterone were present in high concentrations in maternal and fetal plasma. In Thoroughbreds, and to a lesser extent in Pony mares, plasma progestagens rose towards parturition while total plasma oestrogen fell. The only oestrogen which showed a rise in concentration near term was oestradiol-17beta. In one Pony mare and fetus, fetal plasma progestagen fell 24 to 36 hr before parturition when maternal peripheral progestagen concentrations remained high.

Animals↗
PubMed1975

Studies on fetal, neonatal and maternal cortisol metabolism in the mare.

Fetal plasma cortisol concentrations (mean +/- S.E.M.) in ten animals with indwelling umbilical catheters ranged from 13-9 +/- 1-5 ng/ml (227 to 244 days) to 18-1 +/- 2-2 ng/ml (290 to 310 days). Maternal values did not change over this period (15-9 +/- 1-7 ng/ml). Fetal cortisol production rates in two fetuses were 3-6 and 3-8 mg/kg/day at 291 days; there was little placental transfer of cortisol. In three fetuses (319 to 321 days) plasma cortisol values 1 to 10 days before birth were higher (30 to 50 ng/ml) than in any other group, and at birth the values were comparable with those found in intact Thoroughbred foals at birth. After birth plasma cortisol concentrations fell rapidly in most foals, but very high values were found in two foals with postnatal convulsions. Plasma cortisol levles remained low in two Thoroughbred foals born prematurely: similar values were found in one catheterized foal both before and after parturition.

Animals↗
PubMed1975

Morphologic observations on heart valve prostheses made of fascia lata.

A cooperative, international study permitted morphologic observations on 58 fascia lata heart valve prosthese. Thirty-nine had been in position less than a year, the remainder for periods up to 50 months. The fascial cusps, no matter whether free or stent mounted, underwent changes that included death of the original fascia and vacuolar, degenerative changes if a valve had been in situ more than 3 years. Formation of a pseudointima on a cusp's surface caused it to shrink. The rate of progression and severity of the changes varied from prosthesis to prosthesis. Severe cusp shrinkage caused valve incompetence. That seemed particularly likely in mitral and tricuspid prostheses and explains why their use has been abandoned. Clinically, fascia lata aortic valves function satisfactorily for several years. However, their long-term value is still uncertain. Morphologically, the specter of late calcification and other degenerative changes haunt their use until more, from long-term survivors, are available for study.

Aortic Valve↗