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Biomedical subjects

A R Michell

Publications and source records attributed to A R Michell.

At least 73 records · Page 4Linked to original sources
PubMed1985

Sodium in health and disease: a comparative review with emphasis on herbivores.

This review aims to illustrate the relationships between a number of basic and clinical aspects of sodium metabolism with special emphasis on herbivores, particularly ruminants. These animals provide a challenge to some traditional views based essentially on humans, dogs and laboratory rats reared on liberal sodium intakes. Detailed attention is focussed on two central issues; the magnitude of sodium requirement and the relative importance of the kidney and the gut in regulating body sodium. Both provide strong reasons to question accepted beliefs.

Animal Nutritional Physiological Phenomena↗
PubMed1985

Effect of oestrogen and progesterone on sodium, potassium and water balance in sheep.

The effects of oestrogen and progesterone, injected alone or during successive periods, were studied in mature ovariectomised ewes on sodium intakes ranging from 1 to 4 mmol kg-1 d-1. Progesterone had no effect on fluid and electrolyte balance. Oestrogen (17 beta oestradiol) inhibited drinking but had little effect on water excretion whereas it reduced both food intake and urinary potassium concentration. Since the resulting changes in potassium intake and excretion were very similar, oestrogen had little net effect on potassium balance; neither change lasted beyond the treatment period. Oestrogen had a biphasic effect on urinary and faecal sodium excretion, an initial enhancement of salt loss being followed by sodium retention. Faecal sodium retention and the biphasic effect on renal sodium excretion were independent of changes in food intake. These observations are discussed in relation to the pattern of change of electrolyte balance during the reproductive cycle and the influence of changes in food intake and factors affecting sodium preference. The fact that a variety of responses is involved in a coordinated change of sodium balance is emphasised and its possible importance is considered.

Animals↗
PubMed1983

Biochemical and haematological effects of phenylbutazone in horses.

Five matched pairs of horses were used to investigate the effects of phenylbutazone on a range of physiological, biochemical and haematological variables. The drug was given by mouth daily for 15 consecutive days at the manufacturer's recommended dose rates to one group of horses (Group A); the second group (Group B) received equivalent doses of a placebo. For some of the measured parameters, significant changes were recorded in both groups, indicating background instability. Significant decreases in serum total protein, albumin, plasma pH, viscosity and magnesium, and an increase in albumin: globulin ratio occurred in Group A, but not in Group B. These changes were, therefore, attributed to phenylbutazone or its metabolites. Toxicologically, the change in pH is probably unimportant but the decrease in protein concentration may have resulted from a protein losing enteropathy and/or from decreased synthesis in the liver. In one animal which received phenylbutazone, clinical signs of toxicity (lethargy, inappetence, oedema) were observed and evidence of hepatotoxicity and haematological changes were also noted in this horse. It is concluded that recommended dose rates of phenylbutazone should never be exceeded and that the period for which the highest dose (4.4 mg/kg body weight twice daily for four days) is administered should be reduced. In clinical cases, where phenylbutazone toxicity is suspected, measurement of serum or plasma protein concentration might provide an indication of the need to reduce dose levels or stop therapy.

Animals↗
PubMed1983

Fluid therapy for alimentary disease: origins and objectives.

Fluid therapy took nearly a century to gain acceptance in human medicine, despite excellent early work demonstrating its rationale and its effectiveness. Progress in veterinary fluid therapy lagged behind, partly because of skepticism and partly because of real practical difficulties. From the earliest to the most recent developments, human cholera has provided the impetus for much of the progress in fluid therapy. The challenge of treating such a severe diarrhoea in primitive surroundings with severe limits on cost and supervision has led to the emergence of oral fluid therapy as the prime technique. It is not simply an alternative to parenteral treatment but, in most cases, a superior approach relating more directly to the underlying problem--electrolyte malabsorption. Similar principles can be applied to other forms of diarrhoea and in various species. The example is clear for those concerned with veterinary fluid therapy. Repair of extracellular fluid volume is the key objective in all forms of fluid therapy; oral hydration offers not only a practicable way of achieving this in farm animals but one with the potential for outstanding clinical and economic success.

Animals↗
PubMed1982

The optimum pH of renal adenosine triphosphatase in rats: influence of vanadate, noradrenaline and potassium.

In the presence of vanadate, the optimum pH of renal (Na+, K+)-ATPase in rats is reduced and lies in the range of intracellular pH. This explains the difference in optimum pH observed with ATP extracted from equine muscle. Removal of vanadate from such ATP (with noradrenaline) raises the optimum to the accepted range obtained with synthetic ATP. Changes in the sensitivity of the enzyme to potassium concentration contribute to the alterations in optimum pH. The optimum pH of Mg-ATPase is unaffected by vanadate. Since vanadate may be an intracellular regulator of (Na+, K+)-ATPase changes of optimum pH in relation to intracellular pH could well contribute to the regulation of sodium pump activity.

Adenosine Triphosphatases↗
PubMed1981

Fluid and electrolyte excretion in sheep: comparison of the effect of reduced food and water intake with oestrus.

Food and water intake were restricted by 29% for 48 h in ovariectomized ewes, to see whether such changes could cause a pattern of water and electrolyte excretion similar to that observed during the oestrous cycle. The closest resemblance appeared in the effect on water balance and there was also a rise in sodium excretion, as at oestrus. Restriction of intake failed to duplicate the marked sodium retention or, more particularly, the persistent potassium retention which follow natural oestrus. Restriction of food alone produced changes less similar to those seen at oestrus, mainly because this treatment caused a large increase in urine output. The similarity between the effects of restriction and 'fasting natriuresis' is discussed, with particular reference to the mildness of the stimulus in these experiments. Indications that the gut may be as important as the kidney in the regulation of salt and water balance are discussed in relation to other herbivores and to man.

Animals↗
PubMed1980

Sodium appetite and the oestrous cycle in sheep: effect of oestrogen, progesterone and changes in food intake.

Previous studies of voluntary sodium intake and electrolyte excretion in sheep suggested that the pattern of intake associated with the oestrous cycle was not a response to alterations in sodium balance. The pattern thus seemed likely to be dictated by changes in either hormonal levels or food intake. These possibilities were examined in experiments with ovariectomized sheep. Physiological doses of oestrogen or progesterone had no effect on sodium preference, whether given in isolation or succession. Depression of food intake by 25% (as at oestrus) did affect preference slightly (though significantly) but in the opposite direction to the change at oestrus. It is concluded that none of these 3 factors is responsible for the varying sodium preference during the oestrous cycle and that direct hypothalamic control of this pattern is an interesting possibility.

Animals↗
PubMed1979

The pathophysiological basis of fluid therapy in small animals.

The principles underlying fluid therapy and their application to some medical problems in small animals are presented. The renal mechanisms which normally regulate the volume, electrolyte concentration and pH of extracellular fluid are reviewed. The major clinical disturbances are considered together with the specific means of correcting them by fluid therapy.

Acid-Base Equilibrium↗
PubMed1979

Water and electrolyte excretion during the oestrous cycle in sheep.

Electrolyte excretion was observed during 24 oestrous cycles in housed sheep, together with mixed salivary Na/K ratio during 10 additional cycles. 1. The sharp fall in food and fluid intake at oestrus accompanied a peak of sodium excretion which changed to peak retention 3 days later, both in faeces and urine. 2. Potassium excretion declined with food intake at oestrus but subsequently failed to recover to pre-oestrous levels dispite full recovery of dietary intake. 3. Curiously, water intake also recovered completely whereas urinary and faecal water retention continued; faecal loss actually exceeded renal excretion on these liberal water intakes. 4. Changes in salivary, urinary and faecal Na/K indicated an aldosterone peak neither during the luteal phase nor at oestrus but three days later. The data raise questions concerning the regulation of water and electrolyte balance within the normal cycle. They also provide a baseline for the investigation of renal effects of gonadal steroids. Possible roles for aldosterone, ADH and progesterone in maintaining fluid and electrolyte balance are discussed, emphasising problems confronting species which have evolved with heavy obligatory potassium excretion but undependable supplies of sodium and water.

Animals↗