During long-term fasting in birds and mammals, protein utilization initially decreases (phase I), is thereafter maintained at a low value (phase II), and then further increases (phase III). To delineate hormonal and biochemical changes responsible for these modifications, the effect of food deprivation for 50 days was studied in 6 male king penguins captured at the beginning of their natural breeding fast. During phase II, both rate of mass loss and plasma uric acid concentration remained at low levels, whereas plasma beta-hydroxybutyrate concentration increased. In phase III there was by contrast a 2.5-fold increase in the rate of mass loss, an eightfold increase in plasma uric acid, and an 80% drop in plasma beta-hydroxybutyrate. Plasma corticosterone was low and steady in phase II and increased three times in phase III. During the overall fast, there were no significant variations in plasma insulin, but there was a fourfold increase in plasma glucagon and a decrease in plasma thyroxine and triiodothyronine. These findings suggest that protein sparing (phase II) requires low levels of corticosterone, insulin, and thyroid hormones, whereas the further increase in protein utilization (phase III) is due to an increase in plasma corticosterone. The high plasma glucagon concentration in phase III is presumably responsible for a transient increase in plasma glucose observed at this stage; such increase in glucagon could enhance gluconeogenesis from amino acids.

The stress that might result in animals from the routine handling that most experimental studies involve, e.g., weighing, injecting, and blood sampling, is usually assumed to be minimal when the animals look quiet. However, the intensity of this stress remains largely ignored. We have developed a system that allows blood samples to be taken from freely behaving geese without entering the animal room. In these entirely undisturbed geese, the humoral indexes of stress, i.e., blood levels of catecholamines, corticosterone, and lactate, were as low or even lower than the lowest values previously reported for birds. Remarkably, the mean basal values for epinephrine and norepinephrine were 90-fold and 5-fold, respectively, below the lowest values in the literature. Stress-induced variations in pH that would have concealed detection of nutrition-induced changes in pH were eliminated. In contrast, even though the birds looked quiet during a short 5-min routine handling procedure, to which they had been accustomed for weeks, there was a dramatic increase in the level of humoral indexes of stress. These increased severalfold within only 2 min, and the return to initial values could take up to 1 h. Acid-base balance was also disrupted. Thus, in studies on animals, the absence of stress cannot be deduced from only behavioral observations. Only a system for taking blood without human interference may enable stress-free investigations.

The decline of 3 plasma pancreatic hormones, glucagon (G), insulin (I) and somatostatin (S) was studied in fasting ducks after total pancreatectomy. The results show that the decrease of plasma glucose is highly correlated with the disappearance of G, while no important variation of the G/I ratio occurs during the period of observations (80 minutes) the animal being kept fasted. No participation of pancreatic S in glucose metabolism could be detected, the origin of peripheral S in the fasting state seeming due to the intestine for about 50%.

Human pancreatic GH-releasing factor (hpGRF) increased the concentrations of plasma GH when infused i.v. into immature ducks. A dose-dependent increase in plasma GH was observed within 10 min of the start of infusion and was maintained during the 30-min infusion period. Simultaneous infusion of somatostatin S-14 prevented the increase in plasma GH induced by hpGRF, but when the infusion had finished there was a rebound increase in plasma GH. Infusion of the highest dose of hpGRF (800 ng/kg per min) in adult ducks had no significant effect on plasma GH. Plasma somatostatin concentrations were reduced during the infusion of hpGRF in young but not in adult ducks. This observation suggests that the stimulatory effect of hpGRF on GH secretion may be partly due to its inhibitory effect on somatostatin secretion. Infusion of hpGRF in ducklings also increased the concentrations of glucagon and decreased levels of insulin in the plasma. Peripheral plasma glucagon and insulin levels in adult ducks were unaffected by hpGRF infusion. These results indicate that in ducklings, hpGRF increases plasma GH and glucagon concentrations and lowers plasma somatostatin and insulin levels. In the adult, these hormonal responses to hpGRF are not maintained. The highly stimulatory effect of hpGRF on GH secretion in ducklings may explain why plasma GH concentrations are high in these birds.

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