Quarterly journal of experimental physiology (Cambridge, England)最新文献

In five dogs gastric emptying of low, medium and high viscosity meals was measured via a duodenal cannula. The rate of emptying depended on the viscosity of the test meals: the time for half emptying was 4.5 +/- 2.2 min with the low viscosity liquid meal (1 centipoise), 28.9 +/- 9.5 min with the test meal of medium viscosity (10(5) centipoise), and 43 +/- 11.8 min with the test meal of high viscosity (10(6) centipoise). The emptying curves of the medium and high viscosity meals were sigmoid, whereas the curve representing the emptying of the low viscosity liquid meal followed an exponential pattern. Results indicate that the viscosity of the meal is an important factor for the rate of gastric emptying.

Normal conscious dogs were given a meal of meat or doses of individual amino acids by stomach tube. The concentration of amino nitrogen in systemic arterial plasma and the rate of urea production both increased; the magnitude and time course of these increases varied with the individual amino acid administered. There was a relationship between the plasma amino nitrogen concentration and urea production following L-serine, L-alanine, L-proline. dicarboxylic acids and L-cystine similar to that obtained after meat ingestion. It is suggested that these amino acids were transaminated as rapidly as they were absorbed to produce an increase in a general pool of amino acids. Following L-threonine, L-valine, D-serine and immediately after glycine, a small increase in urea production was accompanied by a larger increase in plasma amino nitrogen concentration. It is suggested that these amino acids 'escaped' transamination in the gut wall and liver and that the increase in plasma amino nitrogen was due to a high concentration of the individual amino acid administered.

The effect of a chronic mild elevation of plasma triiodothyronine levels upon the contractile properties and fibre distribution of skeletal muscle was studied. The isometric twitch characteristics and passive tension-length relationship were studied in the soleus and extensor digitorum longus muscles of anaesthetized rats injected for increasing periods with triiodothyronine. This treatment results in a progressive speeding in the rates of isometric contraction and relaxation of the soleus and in a concomitant decrease in the elasticity of the muscle. There was also a conversion of slow to fast fibre types in the soleus, demonstrated histochemically. It is concluded, in view of differences in the magnitudes and time courses of the various changes, that triiodothyronine increases the rates of contraction and relaxation of existing slow fibres and contraction in the soleus muscle as a whole before any change occurs which is attributable to slow-fast fibre interconversion. The possible mechanisms of the early thyroid hormone effects on muscle are discussed.

Furazolidone (0.4% w/w in the feed, 10 days) reduced the feed intake and growth in 9 week old chickens, and increased the amount of 5-hydroxytryptamine (5-HT) in the brain. The drug also increased the stimulation of transketolase activity by thiamine pyrophosphate (TPP) in lysed blood cells (TPP effect), and the concentrations of pyruvate and lactate in the blood. Experiments with pair-fed birds showed that the reduction in feed intake in furazolidone-treated chickens could account for the reduced growth. The drug also produced anorexia in ducklings and turkey poults. In chickens, the anorectic action of furazolidone was unaffected by methergoline (1 mg/kg, twice daily, I.M), and in ducklings furazolidone did not consistently produce anorexia, although it always inhibited monoamine oxidase (MAO) activity in the brain. These observations suggest that the anorectic action of the drug was not tryptaminergic in nature. The increase in the TPP effect found in preparations from furazolidone-treated chickens was absent in preparations from pair-fed birds on unmedicated feed. Thus the TPP effect could be used as an indicator of the effect of the drug on the thiamine status of chickens. However, the increase in the concentrations of pyruvate and lactate in blood was found both in furazolidone-treated birds and pair-fed birds on unmedicated feed, showing that they were attributable to the reduction in feed intake. The TPP effect in furazolidone-treated chickens, 14-49 +/- 2.33% (n = 10), was sufficient to suggest a mild deficiency of thiamin pyrophosphate. Thiamin, given at a dosage above the requirement of the vitamin for chickens, did not reduce the anorexia or the TPP effect of furazolidone-treated birds, although it stimulated the feed intake and growth of birds on unmedicated feed. It is proposed that furazolidone antagonized the utilization of thiamin, perhaps by inhibiting its phosphorylation. Following the withdrawal of furazolidone, the TPP effect returned to the control value and the rate of growth of the birds increased and matched that the controls. Thus the effect of the drug was reversible. Addition of furazolidone to the feed at a concentration of 0.01% w/w for 28 days did not produce anorexia in chickens or affect the amount of 5-HT in the brain. Thus at this level, it is unlikely that the drug would produce adverse effects in poultry.

Urine osmolality was measured daily from day of cannulation (80-110 d) until term in six chronically cannulated ovine fetuses. Fetal urine was hypertonic to plasma following surgery, and 24-36 h before parturition. On fifty-five occasions plasma antidiuretic hormone (ADH) concentration was measured concurrently with urine osmolality. When fetal urine osmolality was 154 +/- 45 mosmol/kg water, plasma ADH was 5.6 +/- 2.1 pg/ml (mean +/- S.D.; n = 33) in fetuses less than 120 d gestation. In ten samples from fetuses from 121 d to term urine osmolality was 118 +/- 35 mosmol/kg water when the concurrent plasma ADH concentration was 5.5 +/- 2.1 pg/ml. Urine osmolality greater than 300 mosmol/Kg water was associated with endogenous plasma ADH concentrations of 6.2-9.2 pg/ml in fetuses 86 d until term. However, when exogenous synthetic arginine vasopressin (AVP) was infused into non-stressed fetuses with initial urine osmolalities less than 200 mosmol/Kg water, the minimum plasma ADH concentration that had to be established in order to induce the production of a hypertonic urine was 22.1 pg/ml at gestational ages 95-105 d, 11-1 pg/ml at 110-120 d and 7 pg/ml at 121-130 d. The fetal kidney thus becomes more responsive to infused AVP over the last half of gestation. Under conditions of in utero stress, however, hypertonic urine can be produced at lower endogenous plasma ADH concentrations than required to be established by infusion in non-stressed fetuses, suggesting that urinary concentrating mechanisms independent of ADH are established in these fetuses.

Normal conscious dogs were given 100 mmol glycine, L-serine, L-alanine, L-threonine, L-proline, L-glutamic acid (50 mmol), L-aspartic acid and L-valine by stomach tube. All these amino acids increased glomerular filtration rate (G.F.R.). There was no increase in G.F.R. following L-cystine or D-serine. The intravenous infusion of L-proline, but not glycine, caused increase in G.F.R. The results suggest that the increase in G.F.R. was not due to a high plasma concentration of the individual amino acids but was related to the metabolism of amino acids with production of urea. It is postulated that after meat and during the metabolism of amino acids a factor is released which reaches and acts on the kidney to cause the increase in G.F.R.