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Biomedical subjects

M Silver

Publications and source records attributed to M Silver.

At least 253 records · Page 14Linked to original sources
PubMed1972

Comparison of the hyperglycaemic and glycogenolytic responses to catecholamines with those to stimulation of the hepatic sympathetic innervation in the dog.

1. The effects of stimulation of the splanchnic innervation to the adrenal medullae, in dogs with cut hepatic nerves, were compared with those obtained previously in response to splanchnic and hepatic nerve stimulation in adrenalectomized dogs.2. Maximal stimulation of both adrenal medullae via the splanchnic innervation (20 c/s for 9 min), in dogs with cut hepatic nerves, produced closely similar hyperglycaemic and glycogenolytic responses to those obtained previously in adrenalectomized dogs with intact hepatic nerves.3. The rise in plasma glucose concentration in response to maximal stimulation of the adrenal medullae in dogs with intact hepatic nerves was found to be comparable to that which occurs in response to maximal stimulation of the hepatic sympathetic innervation alone. In contrast, the rise in haematocrit during maximal stimulation of the entire splanchnic innervation was substantially greater than that observed after removal of both adrenal glands.4. The output of adrenaline and noradrenaline from the left adrenal gland was determined during maximal stimulation of the left splanchnic nerve (20 c/s for 9 min). These results were then used to compute doses of the two amines which would reproduce the output of catecholamines from both glands under such conditions. The extent of the rise in mean plasma glucose concentration in response to these infusions was similar to that produced by maximal stimulation of both adrenal glands, but the duration of hyperglycaemia and depletion of liver glycogen were significantly less.5. Stimulation of the splanchnic innervation was found to produce an initial ;surge' in the release of catecholamines from the adrenal medullae, followed by a rapid decline in output when stimulation was continued for longer than 30 sec. Evidence was obtained which showed that this pattern of release is well suited to produce rapid mobilization of liver glycogen.6. Comparable changes in plasma glucose concentration occurred in response to stimulation of either the adrenal medullae or the sympathetic innervation to the liver at low frequency (2.0 c/s for 5 min). Stimulation of both pathways simultaneously, at the same frequency, produced smaller responses.7. Intramesenteric infusions of noradrenaline at 1.0 mug.kg(-1) min(-1) for 5 min produced comparable changes in plasma glucose concentration to those observed during stimulation of either pathway alone at low frequency. The mean plasma noradrenaline concentration of portal blood was raised by between 92 and 105 ng/ml. during these infusions.8. It is concluded that stimulation of either the splanchnic innervation to the liver, or of both adrenal medullae, at high frequency (20 c/s for 9 min) represents a supramaximal stimulus for hepatic glycogenolysis. Comparison of the responses to stimulation at low frequency (2.0 c/s for 5 min) suggests that the hepatic glycogenolytic mechanism is equally sensitive to stimulation via either route in this species.

Adrenal Glands↗
PubMed1971

Catecholamine secretion by the adrenal medulla of the foetal and new-born foal.

1. The content and output of adrenaline and noradrenaline from the equine adrenal medulla has been investigated under different conditions in foetuses, foals and adult mares.2. In the foetus only small amounts of both amines were secreted in response to stimulation of the peripheral ends of the splanchnic nerves to the gland; during anoxia the adrenal discharge was far greater and was independent of any nervous mechanism.3. Whereas in the ruminant a direct adrenal response to low P(O2) is confined to the noradrenaline cells during foetal life only, the adrenal medulla of the foetal foal secreted both adrenaline and noradrenaline during asphyxia, and the direct response persisted for some days after birth. Noradrenaline was the amine predominantly released during asphyxia in the foetus.4. Catecholamine output from the equine adrenal medulla changed with age, in that there was a gradual increase in both the absolute and relative amount of adrenaline released, irrespective of the stimulus applied, although at any given stage of development a higher proportion of adrenaline was secreted in response to stimulation of the splanchnic nerves than during anoxia.5. The relative proportions of the two amines in the effluent blood bore little resemblance to those found in the glands, removed after prolonged asphyxia, in either foetuses or foals. Preliminary observations have indicated that more noradrenaline is present in the glands when the foetus remains relatively undisturbed within the uterus.6. The possible significance of the larger adrenal response to asphyxia in the foetal foal in comparison with other species is discussed in relation to the development of the innervation and the growth of the adrenal cortex.

Adrenal Glands↗
PubMed1970

Daily changes in foetal and maternal blood of conscious pregnant ewes, with catheters in umbilical and uterine vessels.

1. Blood gas tensions, pH, packed cell volume (PCV) and the levels of glucose, fructose and lactic acid have been followed in foetal and maternal blood for periods of 3-30 days in conscious ewes between 80 days gestation and term ( approximately 147 days).2. Blood samples were withdrawn through indwelling catheters placed in one or both umbilical vessels, a uterine vein and a maternal artery.3. The success of the operation appeared to depend on the maintenance of maternal blood gas and pH levels within normal limits as well as on the final position of the tip of the catheter. The difficulties and limitations of the technique are discussed.4. Foetal blood gas tensions, pH, PCV, lactic acid and glucose levels did not change markedly during the last 50-60 days of gestation. The fructose concentration fell during this period, the greatest change was between 100 and 120 days gestation.5. Small fluctuations in P(O2), P(CO2) and pH in umbilical venous blood were associated with similar changes in the uterine vein, so that the gradients across the placenta appeared to remain constant.6. Daily changes in maternal plasma glucose levels were reflected in similar changes in foetal plasma fructose and by much smaller alterations in the foetal glucose levels. The glucose concentration in the foetal plasma was less than 25% of that in maternal plasma.7. The existence of a general relationship between maternal plasma glucose and foetal plasma fructose was masked by the independent fall in fructose levels with age. However, at any given stage of gestation, there was a significant correlation between foetal fructose and maternal glucose.8. Few changes in the umbilical blood were associated with impending abortion or birth. Blood gas tensions remained constant, but a sharp fall in fructose levels often occurred 48 hr before any changes in pH, PCV and lactate concentration.9. Present and other findings on conscious animals are compared with previous observations on acute, anaesthetized preparations.

Animals↗
PubMed1970

PO2, PCO2 and pH levels in the umbilical and uterine blood of the mare and ewe.

1. Foetal and maternal blood gas tensions and pH levels have been investigated in the mare and the ewe during late pregnancy under a number of experimental conditions.2. Observations were made on anaesthetized animals with the foetus in utero. Simultaneous blood samples were withdrawn from a maternal artery and uterine vein, and from the two umbilical vessels, through catheters inserted at the beginning of each experiment.3. At normal maternal arterial P(O2) (80-110 mm Hg) the umbilical venous P(O2) of the foal was very high (49 mm Hg) and the P(O2) in the umbilical artery (33 mm Hg) was similar to that in the umbilical vein of the lamb (34 mm Hg).4. The P(O2) difference between the umbilical and uterine venous blood was 17 mm Hg in the ewe but only 4 mm Hg in the mare. The corresponding P(CO2) gradients were about one quarter of those for oxygen in both species.5. When the maternal arterial P(O2) was raised above 100 mm Hg both uterine venous and umbilical P(O2) increased in the mare, and the gradient between the uterine vein and umbilical vein was reversed, whereas little change occurred in the corresponding vessels of the ewe.6. Alterations in maternal arterial P(CO2) were associated with concomitant changes in the blood in the other three vessels but in both species the P(CO2) difference between uterine and umbilical venous blood appeared to remain constant.7. Foetal blood pH levels followed those of the mother if the changes in the maternal blood were of respiratory origin. The effects of prolonged changes in maternal pH on foetal levels were investigated in the ewe. Foetal pH remained unchanged during maternal alkalaemia (pH 7.7) induced by Na(2)CO(3) infusions, but increased during a similar rise in maternal pH induced by hyperventilation.8. The present observations have been compared with findings on the conscious animal and possible explanations for the differences between the two species are discussed.

Animals↗
PubMed1970

The glycogenolytic response to stimulation of the splanchnic nerves in adrenalectomized calves.

1. The effects of stimulation of the peripheral ends of one or both splanchnic nerves have been investigated in adrenalectomized calves at different ages.2. During the first 24 hr after birth unilateral splanchnic nerve stimulation led to a prompt rise in the plasma glucose concentration and this response was more than doubled when both nerves were stimulated simultaneously. Under these latter conditions hyperglycaemia was found to be associated with a measurable loss of glycogen from the liver.3. Both the glycogenolytic and hyperglycaemic effects of splanchnic stimulation became more pronounced with age; at 5 weeks of age liver glycogen was depleted by approximately 2/3 and plasma glucose raised by about 200 mg/100 ml. after stimulation of the right splanchnic nerve for 9 min.4. Splanchnic stimulation also caused a rise in mean arterial blood pressure and haematocrit during the period of stimulation at all ages studied; the rise in haematocrit was greatest in the oldest animals.5. The hyperglycaemic response to splanchnic stimulation persisted after pancreatectomy and was also demonstrated in calves in which the whole of the portal effluent blood flow was collected during splanchnic stimulation. The plasma from blood collected in this way had no apparent hyperglycaemic effect when infused into a branch of the mesenteric vein in recipient calves.6. In adrenalectomized calves in which the liver had been partially denervated before stimulation both the hyperglycaemic and the glycogenolytic responses were substantially reduced, although the rise in haematocrit was unaffected, during stimulation of both splanchnic nerves.7. It is concluded that glycogenolysis occurs in the liver as a result of stimulation via the hepatic innervation in the new-born calf and that this response increases with age during the first few weeks after birth.

Adrenal Glands↗