Catecholamines, ATP and dopamine-beta-hydroxylase in the adrenal medulla of the hedgehog in the prehibernating state and during hibernation

Sympathoadrenal activity and hypoglycemia in the hibernating garden dormouse

The hibernating garden dormouse is spontaneously hypophagic during the prehibernating period at which time we found a low peripheral sympathetic activity (S.A.). The aim of this work was to investigate the link between dietary intake and S.A. The S.A. was evaluated by measurement of catecholamines in both plasma and adrenal glands by HPLC. Food intake, body weight, energy expenditure and plasma glucose were measured during the reentry phase of the hibernating period. The following results were obtained: the energy intake in pretorpid animals (55 to 83 kJ/24 h/100 g body weight) was less than energy expenditure which was between 145 and 97 kJ/24 h/100 g. The energy deficit induces marked hypoglycemia immediately before the onset of hypothermia (117 mg/dl vs. 76 mg/dl) and leads to a drastic drop in the peripheral sympathetic system. This, in turn, reduced energy production, causing the hypothermia.

Acute cold exposure increases the glucagon sensitivity of thermogenic metabolism in the rat

Administration of glucagon to rats at 25 degrees C had no effect upon their VO2, while administration of noradrenaline or noradrenaline plus glucagon raised the VO2. At 5 degrees C, noradrenaline had no effect upon the cold-enhanced VO2, while glucagon caused a rise of 13.7%, implying increased glucagon sensitivity at 5 degrees C. The glucagon-induced enhancement of VO2 was abolished by concurrent administration of noradrenaline.

Heterogeneity in the adrenomedullary storage of catecholamines, ATP, calcium and releasable dopamine beta-hydroxylase activity

Bovine adrenomedullary granules were separated into two subfractions by isopycnic density centrifugation. A small subfraction (approximately 10% of the total population) was sedimented into 2.2 M sucrose while the main population (80% of the total) was recovered at the interphase between 1.6 and 2.2 M sucrose. The concentrations of catecholamine (CA) and calcium showed marked seasonal variations for both subfractions, with lowest levels in the spring and highest levels in the winter. Throughout the year the concentrations of CA and calcium were 2-3 times higher in the minor subpopulation which also accounted for an abundance of noradrenaline (NA); on average 68% NA of total CA, 6.6 mumol CA and 225 nmol calcium/mg protein. The two subpopulations stored CA in similar ratios to ATP and calcium; i.e. 30 mol CA: 4 mol ATP: 1 mol Ca2+, indicating storage of CA largely independent of an equivalent amount of ATP, at least during winter when CA storage was 3.3 and 9.9 mumol/mg protein in the major and minor subpopulation respectively. The two subpopulations differed significantly in ratio of releasable dopamine beta-hydroxylase (DBH) activity per mole CA due to insignificant differences in specific activity of releasable DBH (0.4 unit/mg protein). The results show: (1) that the adrenomedullary granules are heterogeneous with respect to releasable activity of DBH per mole CA and subject to considerable seasonal variations; (2) a large portion of the NA-storing granules has a high concentration of releasable constituents; (3) both adrenaline (A)- and NA-storage are closely associated with that of calcium and occur in excess of that balanced by equivalent amounts of ATP.