Metabolic adjustments of Dentex dentex to prolonged starvation and refeeding.

The particular metabolic strategies of the common dentex (Dentex dentex) to face a period of prolonged starvation and subsequent refeeding were assessed. Plasma metabolites, endogenous reserves, and the activity of key enzymes of intermediary metabolism in liver, white muscle, and heart were evaluated. Plasma glucose, total lipid, triglycerides, total-, HDL- and LDL-cholesterol, and protein levels, liver, and white muscle glycogen, and perivisceral, and muscle fat were significantly reduced by starvation, whereas liver lipid content was surprisingly increased. Those enzymes involved in phosphorylation and oxidation of glucose and lipid synthesis, as well as alanine aminotransferase activity, were significantly depressed in liver of starved fish. The increase in ß-hydroxyacyl-CoA dehydrogenase (HOAD) indicated an enhanced fatty acid oxidation during starvation. Part of the acetyl-CoA generated by ß-oxidation was oxidized in the hepatic Krebs cycle, as reflected the increased citrate synthase (CS) activity. The oxaloacetate required for the reaction catalized by CS activity would be supplied by aspartate aminotransferase (ASAT) activity whose activity was also enhanced. Glutamate dehydrogenase also increased to deaminate the glutamate produced by transaminases, especially by the increased ASAT activity. Liver gluconeogenesis of starved fish was maintained at the same rate that in controls, with glycerol playing an important role as glucogenic substrate. The increased hepatic ß-hydroxybutyrate dehydrogenase (ß-OHBDH) activity indicates that part of the acetyl-CoA arriving from ß-oxidation was being diverted for ketone bodies production with dentex liver playing an important role in providing ketone bodies as fuels for other tissues under such circumstances. Most enzyme activities in white muscle of starved dentex were significantly depressed. In heart, starvation induced an important inhibition of those enzymes involved in glucose and protein metabolism, whereas CS, HOAD, and ß-OHBDH activities were maintained at control levels. Although several biomarkers assayed returned to control values after refeeding, many others did not, which indicate that after 3 weeks of refeeding, pre-starved dentex is still experiencing a transient period of metabolic adjustments directed toward the restoration of body mass.

Annual variations in the specific activity of fructose 1,6-bisphosphatase, alanine aminotransferase and pyruvate kinase in the Sparus aurata liver.

We determined the annual change in the intermediary metabolism of glucose through the variations of specific activity of fructose 1,6-bisphosphatase (FBPase), alanine aminotransferase (AAT) and pyruvate kinase (PK). Fish (average mass 330 g) were kept in cages under natural conditions of temperature and photoperiod and fed with a commercial diet. FBPase, AAT and PK increased their activity in June in different ways: AAT and PK increased V(max), and FBPase increased the velocity at subsaturating substrate concentrations, changing K(m). The reproduction period modified the annual tendency of changes in the enzyme activities in both parameters, K(m) and V(max), except for K(m) of PK which shows a circa-annual rhythm. No relation between the changes of enzymes activity and photoperiod or temperature has been found in this study, except for K(m) of AAT which presents a positive correlation with photoperiod and a negative correlation with temperature.

[Effects of partial hepatectomy on various blood and hepatic parameters in the rainbow trout (Salmo gairdnerii, Rich.)]. / Efectos de la hepatectomía parcial sobre algunos parámetros sanguíneos y hepáticos en la trucha arco iris (Salmo gairdnerii, Rich.).

After 36% of hepatic mass removal , rainbow trout recovered its initial liver weight in 20-30 days, i.e., with a regeneration rate clearly lower than in mammals. During early regeneration process hematocrit index and hemoglobin content were slightly decreased, but both parameters rapidly reached their normal values. The evolution of both glycaemia and hepatic glycogen content supported the idea of the existence of a late regeneration wave, which, in this case, could begin at about the 20th post-operative day.

Some functional consequences of partial hepatectomy in rainbow trout (Salmo gairdnerii).

A partial hepatectomy (an average of 36% of hepatic mass removed) was performed in rainbow trout. Thirty days after this partial hepatic removal, the liver had recovered its initial weight. During regeneration the remaining liver was unable to maintain normal blood levels of protein, cholesterol and, partially, lipids which decrease after surgery. The results obtained show that functional and liver weight regeneration proceed at different rates throughout a given time course, weight recovering faster than complete functional restoration.

Evolution of gluconeogenic enzyme activities during starvation in liver and kidney of the rainbow trout (Salmo gairdneri).

1. There was a general increase in the activities of enzymes involved in gluconeogenesis in liver and kidney of rainbow trout, Salmo gairdneri, during the second month of starvation. 2. The need of gluconeogenesis during the first month of the starvation period was probably minimal because of the utilization of liver glycogen as a source of blood glucose. 3. The decline of fat was more pronounced than that of protein total content in absolute values, suggesting that lipid reserved were the main sources of energy during starvation.

Hepatectomy in rainbow trout (Salmo gairdneri). A preliminary study.

1. Partial hepatectomy (25% of liver mass removed) has been performed on rainbow trout using a procedure allowing a high level of survival. 2. The liver regeneration was complete from the point of view of liver weight, at the 30th post-operative day. 3. During the first weeks after surgery, the NH-excretion rate in both hepatectomized and shamoperated trout was higher than in intact controls. Likewise, the food intake was lower in the operated animals. 4. Both facts can be attribute to the stress situation caused by the surgical manipulations rather than the removal of the liver.