Effects of fasting, pancreatectomy, and hypophysectomy in the yellow eel, Anguilla rostrata

Protein and lipid metabolism adjustments in silver catfish (Rhamdia quelen) during different periods of fasting and refeeding

The fish may experience periods of food deprivation or starvation which produce metabolic changes. In this study, adult Rhamdia quelen males were subjected to fasting periods of 1, 7, 14, and 21 days and of refeeding 2, 4, 6, and 12 days. The results demonstrated that liver protein was depleted after 1 day of fasting, but recovered after 6 days of refeeding. After 14 days of fasting, mobilization in the lipids of the muscular tissue took place, and these reserves began to re-establish themselves after 4 days of refeeding. Plasmatic triglycerides increased after 1 day of fasting, and decreased following 2 days of refeeding. The glycerol in the plasma oscillated constantly during the different periods of fasting and refeeding. Changes in the metabolism of both protein and lipids during these periods can be considered as survival strategies used by R. quelen. The difference in the metabolic profile of the tissues, the influence of the period of fasting, and the type of reserves mobilized were all in evidence.

Lipolytic response of adipose tissue and metabolic adaptations to long periods of fasting in red tilapia (Oreochromis sp., Teleostei: Cichlidae)

Adaptive changes of carbohydrate and lipid metabolism induced by 7, 15, 30, 60, 90, 150 and 200 days of fasting were investigated in red tilapia (Oreochromis sp.). Plasma glucose, lactate and free fatty acids (FFA) levels, liver and muscle glycogen and total lipid contents and rates of FFA release from mesenteric adipose tissue (MAT) were measured. Plasma glucose levels showed significant differences only after 90 days of fasting, when glycemia was 34% lower (50±5mg.dL-1) than fed fish values (74±1mg.dL-1), remaining relatively constant until 200 days of fasting. The content of liver glycogen ("15%) in fed tilapia fell 40% in 7 days of food deprivation. In 60, 90 and 150 days of fasting, plasma FFA levels increased 49%, 64% and 90%, respectively, compared to fed fish values. In agreement with the increase in plasma FFA, fasting induced a clear increase in lipolytic activity of MAT incubated in vitro. Addition of isobutylmethylxanthine (cAMP-phosphodiesterase inhibitor) and isoproterenol (non selective beta adrenergic agonist) to the incubation medium induced a reduction of lipolysis in fasted fish, differently to what was observed in mammal adipose tissue. This study allowed a physiological assessment of red tilapia response to starvation.

Plasma catecholamines do not respond to insulin-induced hypoglycemia in a teleost, Anguilla rostrata

The importance of epinephrine as a counterregulatory hormone in hypoglycemia is still debated. In the American eel (Anguilla rostrata), a species particularly sensitive to the hyperglycemic effect of exogenous epinephrine, insulin-induced hypoglycemia does not provoke an increase of plasma catecholamines; nor does a 35-fold rise of endogenous epinephrine within 5 min cause a statistically significant hyperglycemia. Together with findings in several other species of greatly varying phylogenetic position, these observations suggest that in vertebrates plasma epinephrine does not have significant, if any, glucoregulatory functions.

Histological changes in insulin-immunoreactive pancreatic β-cells, and suppression of insulin secretion and somatotrope activity in brook trout (Salvelinus fontinalis) maintained on reduced food intake or exposed to acidic environment

Immature brook trout (Salvelinus fontinalis) were randomly divided into a pH control, a pH and food control and an acid-stressed group. Fish in the first two groups were held at neutral pH and those in the last group were maintained at pH 4.2 for up to two months. The food supply to the pH and food control group was restricted to simulate the reduction in food intake demonstrated for acid-stressed trout. Plasma insulin levels were significantly decreased from 5-20 ng/ml to 1-2 ng/ml and plasma cortisol levels were significantly increased from 5-10 ng/ml to as high as 70 ng/ml in the acid-stressed brook trout. Concomitantly, a significant decrease of 21-39% in the proportion (volume density) of insulin immunoreactive β-cells was observed within the principal pancreatic islets. Somatic growth was stunted and ultrastructural morphometry revealed the suppression of somatotrope secretory activity in the acid-stressed fish. Restriction of food supply induced a smaller but still significant decrease in circulating levels of insulin which was however not accompanied by a reduction in insulin immunoreactive β-cells. The rise in plasma cortisol levels was not significant, and the plasma levels of glucose and protein were unaffected. Nevertheless, somatotrope secretory activity was suppressed and somatic growth was stunted. This study demonstrates for the first time the complexity of the endocrine response to acid stress and that some of the response to acid stress can be attributed to the lowering of food intake.

Maturation of the endocrine pancreas in the sea bass, Dicentrarchus labrax L. (Teleostei): an immunocytochemical and ultrastructural study. I. Glucagon-producing cells

The structure of the endocrine pancreas in the sea bass (Dicentrarchus labrax L.) was studied with special reference to glucagon-immunoreactive cells. As described in most of the teleosts, the sea bass was found to have a diffuse pancreas. In the adult, endocrine cells were clustered in a principal islet and numerous accessory islets where the glucagon A cells were localized peripherally. Under electron microscopy, the A cells displayed a clear hyaloplasm with granules having typical spherical or polyhedral cores, as in other vertebrates. The maturation of the endocrine pancreas was monitored under rearing conditions. The endocrine pancreas appeared during the prelarval stage, 3 days after hatching, and consisted of a single cluster of morphologically similar cells, containing very small cytoplasmic granules. During the larval stage, cytodifferentiation resulted in modifications of cell shape and increased granule size. Typical granules appeared in 8-mm-long larvae. Cells immunoreactive with mammalian glucagon antibodies appeared only at the beginning of the juvenile stage (3 months/20 mm). Electron microscope observations revealed that the storage of hormone in numerous cytoplasmic granules began at this stage.

The sources of plasma catecholamines in the American eel, Anguilla rostrata

The origin of the catecholamines (CAs) in the systemic blood of the American eel, Anguilla rostrata, was studied by three approaches: (1) determination of the CA content of tissues suspected to release large quantities of dopamine, norepinephrine, and/or epinephrine into the circulation; (2) measurement of local CA titers in selected regions of the cardiovascular system; and (3) removal of tissues with high CA concentrations, followed by determination of its impact on stimulated CA release. Large quantities of all three CAs were found in the walls of the posterior cardinal veins, from their caudal origin within the opisthonephric kidney to their termination in the ductus Cuvieri. Near the ductus Cuvieri, the CA concentration was 1-3 orders of magnitude above that in other tissues. In this region, which contains the presumed adrenal medulla equivalent, occur the highest plasma levels of the CAs. Strong CA release also in the opisthonephric kidney region raises the question if these CAs affect locally the kidney functions, and/or via the hepatic portal vein (which originates in this region), the liver. Other organs (especially brain and heart) contain CA concentrations high enough to potentially affect the CA level in the systemic blood, if instantly released. However, neither partial removal of the brain nor hypophysectomy, "adrenomedullectomy," Stanniectomy, or urophysectomy had an appreciable impact on stimulated CA release. Together with previous data, these findings show that in the eel (a) the region of the presumed adrenal medulla equivalent is the most important source of all three CAs in systemic plasma; (b) that strong CA-stimulated CA release also occurs outside this region; and (c) that the pituitary, forebrain, and midbrain are not necessary for the CA-stimulated CA release.

Serum cortisol, glucose and lipids in plaice (Pleuronectes platessa L.) exposed to starvation and aquarium stress

Plaice were maintained in the aquarium (11-12 degrees C) during May for 15 days without feeding. Within 48 hr, there was a decline in serum total lipids (P less than 0.001), phospholipids (P less than 0.01), triglycerides (P less than 0.001), cortisol (P less than 0.01) and glucose (P less than 0.001), but an increase in nonesterified fatty acids (NEFA; P less than 0.01). There was a significant inverse correlation between NEFA and glucose over 15 days (P less than 0.001) and between NEFA and cortisol over the first 5 days (P less than 0.01). Cortisol and glucose showed a significant correlation over 15 days (P less than 0.01). Serum cortisol and glucose were not apparently affected by starvation. Only cortisol provided a sensitive indicator of aquarium disturbance. Exposure of the fish to agitation or reduced O2 for 1 hr significantly elevated cortisol (P less than 0.001) but only the latter treatment elevated glucose (P less than 0.01); neither treatment affected the lipids.