Search

1. When marsupial brush-tailed possums were maintained on a normal fruit and vegetable diet with access to water ad libitum, I.V. infusion of synthetic angiotensin II at rates of 0.035-3.5 mug/kg. min caused short-latency drinking in up to seven of eleven animals tested. These rates also had significant pressor effects.2. There was a positive correlation between the rate of angiotensin infusion and the percentage of tested animals which responded by drinking, as well as the amount of water drunk by such animals. The amount drunk during a second infusion 1 hr later was reduced. There was a negative correlation between the rate of infusion and the latency to drinking.3. Of six animals given access to both water and 1.8% sodium chloride solutions, five drank some saline during maintenance and control periods and all responded with short-latency drinking of water to infusion of angiotensin II at 0.35 mug/kg. min.4. Withdrawal of 10% of blood volume, known to stimulate renin production in the possum, caused an increase in water intake in only one of six possums.5. Infusion of isoprenaline I.V. at 20 mug/kg. min, which caused a profound fall in B.P., had no effect on drinking by all six possums.6. It is concluded that these marsupials share with eutherian mammals responsiveness to a dipsogenic action of angiotensin II, which appears to be inhibited by preceding ingestion of water and potentiated by preceding ingestion of hypertonic saline. The physiological significance of this effect is uncertain.

Brush-tailed opossums were prepared surgically with indwelling heatic and jugular venous catheters for blood sampling without disturbance in the conscious state. Hepatic extraction of Rose Bengal was 21 +3 (s.d.) % and hepatic clearance, used as a measure of hepatic blood flow, was 42.5 +7 ml/kg/min. Hepatic relaease of new glucose, calculated from the thorias vena caval-hepatic venous difference in glucose specific activity at equilibrium during i.v. infusion of [14C]glucose and hepatic blood flow, was 3.5 + o.0 mg/kg/mim. This was not changed by i.v. infusions of 10% ethanolic aline or cortisol in ethanolic saline, at 1mg/kg/h for 90 min, although the cortisol infusion caused the peripheral blood glucose concentration to rise form 56.5 + 7.3 to 83.2 + 10.3 mg/100ml. The rate of metabolic clearance of glucose fell from 6.1 +1.1 to 4.2 +0.9 ml/kg/min during i.v. cortisol infusion. Daily i.m. injection of 1 mg cortisol accetate/kg for 5 days caused an increase in hepatic new glucose release to 8.0 + 1.6 mg/kg/min. The findings support the propostion that, in the marsupial, the short-term effect of cortisol on plasma glucose concentration is due to inhibition of peripheral glucose utilization, whereas the long-term effect is due to increased hepatic glucose production.

Using the techniques of equilibrium dialysis at 36 degrees C and gel filtration at 4 degrees C, a high-affinity, transcortin-like, corticosteroid binding system has been demonstrated in the blood plasma of the marsupial Trichosurus vulpecula. The affinity constant for non-albumin binding was 4-018 +/- 1-032 X 10(7) (S.C.) 1/mol for males and 4-046 +/- 0.981 X 10(7) for females. The concentration of non-albumin binding sites was 1-82 +/- 0.76 X 10(-7) mol/1 in males and 1-86 +/- 0-57 X 10(-7) mol/1 for females. Oestrogen administration, sufficient to cause marked hypertrophy of the genital tract in the femlaes, had no effect on the affinity constant or the concentration of the non-albumin binding sites in either males or females. The general condition of the animals deteriorated during oestrogen administration and there were significant falls in the concentrations of albumin and cortisol in the blood plasma. In one animal which died during oestrogen treatment, the adrenal glands were significantly hypertrophied.