Changes in glucagon level associated with anxiety or stress

Liver ultrastructure during acute stress

An ultrastructural, morphologic and histochemical study was made on the livers of rats exposed to eight different acute stressors: fasting, cortisol injecions, reserpine injections, restraint, spinal cord transection, immersion in hot water, exposure to cold and forced muscular exercise in a revolving drum. After 48 hours of exposure to stress, electron microscopy of the liver revealed rough endoplasmic reticulum fragmentation and dilatation, glycogen depletion, and mitochondrial enlargment. The most striking change, however, was an increase in the number and size of autophagic vacuoles which were limited by single or multiple membranes. A cytochemical study revealed that in the former case, the vacuolar membranes did not show a glucose-6-phosphatase positive reaction, whereas they did in the latter case. The vacuoles contained acid phosphatase positive material as well as organelles in various stages of degradation. Following exposure to most of the stressors, a marked increase of plasma corticosterone was noted, with a lowered rectal temperature and the appearance of the typical stress triad (adrenal hypertrophy, thymicolymphatic involution and gastrointestinal ulcers). The severity of the morphologic changes appeared to parallel the degree of hypothermia caused by the stressor. The results suggest that autophagy in the liver may be an adaptive response to stressors at the subcellular level.

The mechanism by which glucagon induces the release of amino acids from muscle and its relevance to fasting

A raised level of glucagon was attained rapidly, and maintained steadily, for an hour or more in the circulation of fed, or of fasted, rabbits. During this time the concentrations of 18 amino acids, of glucose and of insulin, were measured in samples of arterial blood and of blood leaving the skeletal muscles, taken simultaneously. The glucagon raised the level of glucose in the arterial blood, while, at the same time, decreasing the levels of most of the amino acids. The rate of release of amino acids from the skeletal muscles increased during this time. When the store of hepatic glycogen had been depleted by a previous injection of glucagon, or by fasting, glucagon still caused a rise in blood glucose, but the rise was less, and was less well sustained, than that seen when the glycogen stores of the liver were normal. The second injection of glucagon, or fasting, caused the glycogen depleted liver to convert certain amino acids, obtained from the blood, into glucose, lowering the blood levels of these amino acids. The muscles now released amino acids. There was no detectable difference in the release of amino acids from muscle whether glucagon was given systemically or into the artery supplying the muscles. However, a systemic injection of L-alanine, together with glucagon, abolished the fall in the level of amino acids in the blood, and suppressed their release from muscle. During fasting a steady fall in the blood levels of five amino acids occurred, probably due to their use by the liver for glucose synthesis; the temporary rise in the levels of other amino acids, which are not readily used for glucose synthesis, seems to be due to their concomitant release, from the breakdown of muscle protein. We conclude that the elevated level of glucagon, which is found in fasting, ensures that an acceptable level of the blood glucose is maintained by means of two mechanisms; first by releasing glucose from liver glycogen, and then, when fasting is prolonged, by causing the liver to synthesize glucose from certain of the amino acids in the blood, thus decreasing their concentration in the blood. This fall in the levels of these amino acids in the blood is, we believe, the stimulus which leads first to the release of amino acids from the muscles, and then to the breakdown of muscle protein to replace these released amino acids, and thus to maintain a continuous supply of these amino acids for glucose synthesis.

Stimulatory and inhibitory effects of cyclic AMP on pancreatic glucagon release from monolayer cultures and the controlling role of calcium

When glucagon release from monolayer cultures of newborn rat pancreas was measured over four hours in media containing 2.5 mM Ca++, a significant cyclic AMP-related inhibition of release was observed. This was noted whether intracellular cyclic AMP levels were raised by the addition of exogenous cyclic AMP or dibutyryl cyclic AMP, by phosphodiesterase inhibition with theophylline, or by the stimulation of adenylate cyclase with cholera toxin. The inhibition was concentration dependent for cyclic AMP and could not be reproduced by the addition of AMP, ADP or ATP. Adenosine also inhibited glucagon release while ATP was stimulatory. From time course studies it appeared that the inhibitory effects of cyclic AMP and cholera toxin were progressive after two hours of incubation. With cholera toxin an early stimulation of glucagon release was observed. The effects of cyclic AMP and cholera toxin on arginine-stimulated glucagon release were to stimulate further the glucagon release during the first hour of the incubation. Thus, the effects of raising intracellular cyclic AMP levels were biphasic in that both an early stimulation and a late inhibition of glucagon release were observed. In examining the nature of these responses a remarkable controlling role for Ca++ was uncovered: at Ca concentrations of 0.3 mM and lower no effect of cyclic AMP on glucagon release was found. With 1 mM Ca++ in the medium cyclic AMP stimulated glucagon release early (30 min) and thereafter had no further effect. In the presence of 2.5 mM Ca++ cyclic AMP did not stimulate early but did cause the delayed inhibition of release. It is concluded that the effect of cyclic AMP on glucagon release can be either stimulatory or inhibitory depending upon the Ca++ concentration of the medium and the duration of exposure to raised cyclic AMP levels.

Anti-inflammatory action of glucagon in rats

1 Subcutaneous administration of glucagon (1 and 0.5 mg/kg) 30 min before the injection of carrageenin or dextran into the rat's paw reduced oedema and the local exudation of Evans blue previously given intravenously. 2 The effect persisted after removal of the adrenal medulla but not after adrenalectomy. 3 When glucagon (1 mg/kg, s.c.) was given daily after a local reaction to Freund's adjuvant injected into the paw had developed, a decrease in the reaction was observed up to 12 days. Blood sugar levels remained within the normal range. 4 Glucagon may exert an anti-inflammatory effect through the release of adrenal corticosteroids and thus help modulate inflammatory reactions.

The metabolic consequences of adrenergic blockade: a reveiw

The effects in man of adrenergic blocking agents on plasma insulin, glucagon, growth hormone, and lipid metabolism are reviewed. Whereas basal insulin may be slightly inhibited by beta- and enhanced by alpha-adrenergic blockade, more marked suppression may be achieved under circumstances of high exogenous or endogenous catecholamine stimulation. The relative effects of beta1 or combined beta 1 and beta2 blockers in man are unknown. Glucagon release is probably provoked by beta- and inhibited by alpha-stimulation in man. Muscle glycogenolysis is inhibited by propranolol, and under situations of hepatic glycogen depletion, clinical hypopglycemia may occur. This may also account for the failure of significant hyperglycemia to be observed in short-term experiments on fasting subjects in whom insulin release may be suppressed and glucagon release enhanced. Growth-hormone release is enhanced by beta-adrenergic blockade. Free fatty acid formation in vivo is inhibited by intravenous beta blockade, but the effects of oral administration on triglyceride production and lipoprotein profiles remain uncertain. The inter-relationships between the effects of adrenergic blockade at different sites of hormone and substrate release are unclear but may have important consequences in alteration in carbohydrate tolerance and lipid metabolism. The relative effects of beta-blocking drugs with differing specificity must be determined.

Spontaneous and amino acid-stimulated glucagon secretion in the immediate postnatal period. Relation to glucose and insulin

The extent and significance of spontaneous glucagon secretion in the immediate postnatal period were investigated in groups of normal infants studied cross-sectionally and longitudinally. Arginine-and alanine-stimulated glucagon secretion was also studied. Plasma glucagon concentrations were correlated with prevailing glucose and insulin concentrations. The characteristic fall in blood glucose, reaching a nadir within hours of birth, was associated with a significant increase in glucagon concentration. Despite persistence of relative glucopenia, glucagon did not change appreciably between 2 and 24 h of life. A further significant elevation in glucagon concentration occurred from day 1 to day 3 of life associated with a return of glucose to euglycemic levels. In contrast to the sluggishness of pancreatic glucagon release, glucagon-like immunoreactivity rose markedly to mean levels of approximately 2,000 pg/ml after introduction of formula feeding. No significant changes in insulin levels were observed in these studies. Arginine infusion via an umbilical vein catheter into six infants within 6 h of birth elicited a brisk, almost threefold increment in glucagon concentration (from 339+/-85 to 940+/-254 pg/ml) in blood obtained from, or close to, the portal circulation. Bolus injection of alanine (1 mmol/kg) into a peripheral vein to six infants resulted in significant increments in glucagon (mean maximal, 128 pg/ml) as well as glucose and insulin. The observations suggest that spontaneous glucagon secretion may be an important factor in neonatal glucose homeostasis. Secretion seems more brisk in response to amino acid stimulation than to a falling glucose concentration.

The role of the sympathetic innervation in the control of plasma glucagon concentration in the calf

1. The extent to which the splanchnic sympathetic innervation is implicated in the control of plasma glucagon concentration has been investigated in the young calf.2. Stimulation of the peripheral ends of both splanchnic nerves (0.5-10.0 c/s for 10 min) caused an abrupt increase in plasma glucagon concentration in adrenalectomized calves 3-5 weeks after birth. This effect was found to be statistically significant (P < 0.01) at each of these frequencies. In calves tested during the first 24 hr after birth comparatively small responses were obtained.3. The hyperglycaemia produced by splanchnic nerve stimulation in older calves caused an abrupt rise in plasma insulin concentration when stimulation was discontinued but insulin release was completely inhibited throughout the period of stimulation at all frequencies tested.4. It is concluded that tonic changes in sympathetic efferent activity are likely to modify plasma glucagon concentration in the normal conscious calf.