Vascular and metabolic responses of the liver to insulin

The role of the liver in non-shivering thermogenesis in the rat

1. The temperatures of the liver and afferent aortic and portal blood were measured in 20 degrees C acclimated rats at different environmental temperatures (T(a)) between 20 and 37 degrees C. The heated-thermocouple technique was used to measure the metabolic heat production of the liver, its blood flow, and to correct the temperature difference between it and the reference junction for blood flow.2. The temperature of the liver was higher than that of the afferent blood. On raising T(a) from 20 to 30 degrees C the liver temperature fell and the temperature difference between the liver and the aortic blood was reduced despite the decrease in the thermal gradient between the liver and the exterior and a small reduction in hepatic blood flow. A further rise in T(a) to 37 degrees C led to an increase in the liver and blood temperatures. The same pattern was seen when the temperature differences were corrected for blood flow.3. Metabolic heat production in the liver decreased when T(a) was raised from 20 to 30 degrees C.4. In a 20 degrees C environment inhibition of non-shivering thermogenesis with propranolol HCl (10 mg/kg body wt. I.V.) led to a fall in the temperature of the liver and its metabolic heat production towards levels found in untreated rats at T(a) = 30 degrees C. Consequently, in treated rats the change in metabolic heat production on raising T(a) to 30 degrees C was less than in untreated ones.5. These results are interpreted as evidence for the participation of the liver in thermoregulatory non-shivering thermogenesis.

Nutritional aspects of amino acid metabolism. 3. The effects of diabetes on blood and liver amino acid concentrations in the rat

1. Measurements of the concentrations of amino acids in the plasma of blood from the portal vein and hepatic vein in the livers of rats made diabetic with streptozotocin or alloxan and starved for 1 d were compared with similar measurements from normal rats starved for 1 d.

2. The concentrations of many of the amino acids in the blood plasma were lower in the streptozotocin diabetic rats than in the normal animal while the liver concentrations tended to be increased. This suggests that there is enhanced concentration of these amino acids by the liver in diabetics, as is also found in starvation, which is probably due to factors other than the direct absence of insulin.

3. The direction of flow of the groups of amino acids into and out of the liver was unchanged in the diabetic compared with the normal rat except that the output of tryptophan was abolished, and that of the branched-chain group was abolished in alloxan diabetes though apparently enhanced in streptozotocin diabetes. The rates of movement of amino acids in both directions appeared to be increased in the streptozotocin diabetic animals.

4. The changed amino acid pattern in the alloxan diabetic rats was to some extent similar to that of the streptozotocin diabetic rats but the changes were more difficult to interpret, perhaps because of side-effects of alloxan on tissues including liver.

Myocardial and haemodynamic effects of the beta-adrenoceptor blocking drug alprenolol (H56/28) in anaesthetized cats

1. The effects of the beta-adrenoceptor blocking drug alprenolol (H56/28) on myocardial and general haemodynamics were studied in anaesthetized cats.2. Alprenolol (0.5 mg/kg and 1.0 mg/kg) reduced femoral systolic and diastolic pressures, heart rate and left ventricular systolic pressure. The rate of rise of the left ventricular pressure pulse (dp/dt) was reduced despite a significant elevation of left ventricular end-diastolic pressure. This is evidence for decreased myocardial contractility. On some occasions there was a transient initial increase in +ve dp/dt max. possibly indicative of moderate beta-adrenoceptor stimulant activity.3. Myocardial and liver blood flows were measured using a heated thermocouple technique. Alprenolol slightly decreased both myocardial and liver blood flows (mean of 17% and 15% respectively with a dose of 1.0 mg/kg). Myocardial and liver vascular resistances were only very slightly increased.4. Alprenolol had no direct effect on calculated myocardial and liver metabolic heat production.5. In doses up to 1.0 mg/kg alprenolol had no effect on airway resistance but occasionally decreased (in vivo) intestinal muscle movement.6. Since alprenolol (although reducing calculated myocardial oxygen consumption and the myocardial and metabolic heat stimulant effects of catecholamines) has no significant effect on myocardial vascular resistance, it is suggested that it would be a useful adjunct in the therapy of angina pectoris.