Fasting in king penguin. I. Hormonal and metabolic changes during breeding

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.

Stress in birds due to routine handling and a technique to avoid it

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.

Pancreatic hormones disappearance after total pancreatectomy in the duck: correlation between plasma glucagon and glucose

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%.

Glucagon and somatostatin secretion from the perfused splenic bulb of duck pancreas

Glucagon, somatostatin and insulin secretions were evaluated in a new type of perfusion preparation: the naturally A and D cell rich splenic bulb of duck pancreas. Stable basal levels were observed with 11 mM glucose, corresponding to normoglycaemia, and all secretions were stimulated by 1 mM 3-isobutyl-1-methyl-xanthine and by 10 mM arginine, demonstrating the technique's validity. In the absence of aminoacids in the perfusion medium, A cell blindness to glucose was corrected by physiological levels of insulin (2 ng/ml); insulinodependency of A cells, and unresponsiveness of D cells to glucose, probably not ruled by insulin, were observed. However, in the presence of aminoacids, glucagon was inhibited and somatostatin secretion stimulated by glucose (33 mM), independently of insulin (2 ng/ml). Aminoacids greatly influenced pancreatic hormone release.

Progressive loss of sensitivity of the A cell to insulin in geese made diabetic by subtotal pancreatectomy

The effects of insulin deficiency on pancreatic A cell responsiveness to glucose was studied in subtotally depancreatized geese. In geese operated for 3 to 5 days and receiving insulin therapy (I.M.: 0.5-1.0 U/kg/24 h), A cell response to glucose (I.V. injection: 0.5 g/kg) was abolished, but could be restored to normal range by insulin (I.V. injection: 0.025-0.2 U/kg) together with glucose. After 5 weeks of therapy, A cell sensitivity declined: the physiological amount of insulin (0.025 U/kg) was insufficient to suppress glucagon during the glucose load, whereas the large dose (0.2 U/kg) partially restored A cell response. In addition, daily insulin treatment prevented a severe increase of fasting plasma glucose and glucagon. Geese receiving no insulin therapy showed "total blindness" to glucose, even when given insulin at the time of the test. These data suggest a progressive loss of sensitivity of the A cell to insulin. Endocrine and/or panacrine insulin deficiency may play a role on the dysfuncion of the glucose-glucagon feedback mechanism.

Glucose, insulin and glucagon in the diabetic goose

The relationships between plasma glucose, insulin and glucagon were studied in geese made diabetic by subtotal pancreatectomy. As early as the first hours after the operation, the plasma glucose increases and a permanent diabetes develops. This diabetic state is characterized by two features: a very low plasma insulin level, which does not vary during the survival of the diabetic animals and a concentration of plasma glucagon (of pancreatic origin) which transiently diminishes then rises far above the normal level, and is correlated with the basal concentration of plasma glucose. The impaired glucose tolerance observed in diabetic animals is related to the suppression of the glucose-insulin and glucose-glucagon feedback mechanisms.

Plasma growth hormone, somatostatin, insulin and glucagon inter-relationships during infusion of human pancreatic growth hormone-releasing factor in young and adult ducks (Anas platyrhynchos)

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.

Thyrotrophin-releasing hormone-induced growth hormone secretion in ducks: independence of peripheral plasma somatostatin, insulin, and glucagon

In young, but not old, ducks the iv infusion of thyrotrophin-releasing hormone (TRH) markedly increased peripheral plasma growth hormone (GH) concentrations, which remained elevated throughout the 30-min period of infusion. This GH response to TRH was suppressed by the simultaneous infusion of somatostatin, which increased the level of circulating somatostatin-like immunoreactivity (SLI) to supraphysiological levels. Basal concentrations of plasma SLI in both young and old birds were suppressed by TRH infusion. Concentrations of glucagon-like immunoreactivity (GLI) were increased by the infusion of TRH in young birds but not in adults, whereas plasma immunoreactive insulin (IRI) was decreased in young birds and increased in adults following TRH infusion. These results indicate that TRH-induced GH secretion in ducks is unrelated to changes in peripheral plasma SLI, GLI, or IRI induced by TRH infusion.

Effect of insulin on the response of gut glucagon-like immunoreactivity (GLI) to oral glucose and food ingestion in the goose

Gut GLI levels were measured in the plasma of normal, totally and subtotally depancreatized geese, using an antiserum specific for avian pancreatic glucagon and another one which crossreacts with intestinal extracts. Gut GLI was determined by difference between "total" GLI and immunoreactive pancreatic glucagon (IRG). Glucose given orally or a meal rich in carbohydrates elicited an elevation in plasma gut GLI. The increment of gut GLI was greater when the pancreas was removed. The over-stimulation of gut GLI was corrected by the administration of insulin. This is the first study which reports a correlation between insulin and gut GLI secretion in birds.

Effects of cysteamine administration on plasma concentration of metabolites, pancreatic glucagon and insulin in the chicken

1. The effects of subcutaneous injection of cysteamine (2-mercaptoethylamine, 300 mg/kg) were investigated in 5-6 week-old chickens. 2. In the short term (1 hr), cysteamine increased plasma levels of glucose, free fatty acids and insulin, and decreased that of alpha-amino non protein nitrogen. 3. In a longer term (17-24 hr), cysteamine increased the plasma level of glucose, did not modify those of alpha-amino non protein nitrogen, insulin and glucagon and decreased that of free fatty acids. 4. The disposal of an oral glucose load was impaired and the glucose-induced inhibition of pancreatic glucagon and stimulation of insulin release were blunted 17 hr after cysteamine administration. 5. Therefore, cysteamine exerts multiple effects on chicken pancreatic islet cells.

Early insulin response after food intake in geese

Plasma glucose and insulin levels were measured in chronically catheterized, freely moving, undisturbed geese, which were offered a free standard meal after an overnight fast. The insulin level markedly rose within the first minute after the start of food ingestion, whereas plasma glucose did not increase. This early insulin response was not correlated with the size of the meal. In contrast, both postabsorptive insulin response and plasma glucose changes were dependent on meal size. When a small amount of food (2-6 g) was eaten, insulin returned to basal level within 30 min, whereas plasma glucose remained unchanged. Larger meals (15-20 g) maintained plasma insulin at a higher level and induced a sustained rise of plasma glucose. These results indicate that there is a cephalic phase of insulin secretion at the beginning of the meal in birds as previously described in mammals.

Growth hormone and somatostatin in the plasma of transiently diabetic ducks: basal variation and response to glucose

In the duck, subtotal pancreatectomy induces a transient diabetes, with decreased insulin and glucagon basal levels as well as responses to glucose. At the same time, a transient increase in basal peripheral somatostatin occurs, followed by an increase in growth hormone in the postdiabetic state. Intravenous glucose induces a slight decrease in somatostatin secretion in normal, but not in diabetic animals, and no significant variation in growth hormone secretion at any state. An obvious role of growth hormone or somatostatin in the development of this transient diabetes in the duck could not be detected in this study.

Protein sparing on very low calorie diets: ground squirrels succeed where obese people fail

During seasonal cycles in ground squirrels, as in many other species, there are periods of spontaneous loss of appetite, very low calorie intake and a 30% loss in body mass. Measurements of nitrogen balance during early and later stages of the mass loss phase of the cycle (-1.2 +/- 6.7 and +13.1 +/- 8.8 mg/24 h, respectively) showed a total sparing of protein, indicating a selective use of fat. However, when no food at all was available, nitrogen balance was negative (-45 +/- 5 mg/24 h). Provided that they have access to some food, ground squirrels are therefore able to compensate for any protein utilization, while at the same time selectively losing large amounts of fat. It appears that a factor related to spontaneous reduction in food intake enables these animals to achieve the total sparing of protein that eludes dieting humans on comparably low caloric intakes.

Glucagon-insulin balance in genetically lean or fat chickens

Circulating levels of insulin, glucagon, glucose and non-esterified fatty acids (NEFA) were compared in genetically lean (LL) or fat (FL) lines of chickens between 5 and 6 weeks of age. FL birds exhibited lower levels of plasma glucose and higher levels of NEFA when fasted or fed; however no genotypic differences were found for insulin or glucagon. Oral glucose tolerance test induced higher insulin concentrations in FL chickens with faster glucose tolerance whereas glucagon was similar between genotypes. Refeeding led to lower plasma glucose and insulin in FL chickens but similar levels of glucagon in both lines. Exogenous insulin (0.25 or 0.50 U/kg) had less hypoglycemic effects but induced higher levels of glucagon in fasted LL chickens at 0.50 U. The insulin to glucagon ratio cannot explain differences in fattening between genotypes. Lipolysis is slightly higher in FL chickens. A difference between the 2 genotypes for their glucose-insulin balance is probably the main mechanism involved.