Tissue distribution and subcellular localization of glutamate dehydrogenase in a freshwater air-breathing teleost, Heteropneustes fossilis

Alterations in nitrogen metabolism in freshwater fishes, Channa punctatus and Clarias batrachus, exposed to a commercial-grade λ-cyhalothrin, REEVA-5

In the present study, two freshwater fishes Channa punctatus and Clarias batrachus were exposed to sub-acute concentrations of a commercial-grade λ-cyhalothrin, REEVA-5, for 96 h to observe the changes in amino acid catabolism under pyrethroid-induced stress and to investigate the comparative mechanisms of ammonia detoxification in both fishes. The experiments included the estimation of levels of free amino acid, urea, ammonia and the specific activities of aspartate aminotransferase (AAT), alanine aminotransferase (AlAT), glutamate dehydrogenase (GDH), glutamine synthetase (GS) and arginase in different vital organs of fishes. λ-cyhalothrin caused significant decline in the levels of amino acids along with simultaneous significant increase in the activity of AAT, AlAT and GDH, which indicated amino acid catabolism as one of the important mechanisms to meet out immediate energy demand of fishes. The level of ammonia was observed to be enhanced considerably at lower concentrations of λ-cyhalothrin while higher concentrations caused remarkable decline. The λ-cyhalothrin treatment resulted in significant increase in the activities of GDH and GS with concomitant increase in the activity of arginase and level of urea, indicating activation of two different mechanisms of ammonia detoxification. The mechanism of ammonia detoxification through its conversion into glutamate and glutamine was more prominent in C. punctatus, while C. batrachus demonstrated ureogenesis as the major route. In fishwise comparison, C. batrachus was observed to be more sensitive with respect to the above-mentioned parameters. Another important finding was that unlike the liver, the kidney appeared as one of the primary sites of ureogenesis in fishes.

Cypermethrin induced alterations in nitrogen metabolism in freshwater fishes

In the present study, two fresh water fishes namely, Channa punctatus and Clarias batrachus, were exposed to three sub-acute concentrations of synthetic pyrethroid, cypermethrin, for 96 h to evaluate the role of amino acids in fulfilling the immediate energy needs of fishes under pyrethroid induced stress as well as to find out the mechanism of ammonia detoxification. The experiments were designed to estimate the levels of free amino acid, urea, ammonia and the activities of aspartate aminotransferase (AAT), alanine aminotransferase (AlAT), glutamate dehydrogenase (GDH), glutamine synthetase (GS) and arginase in some of the vital organs like brain, gills, liver, kidney and muscle of both fish species. The significant decrease in the levels of amino acids concomitant with remarkable increase in the activities of AAT, AlAT and GDH in these vital tissues of fish species elucidated the amino acid catabolism as one of the main mechanism of meeting out the immediate energy demand of the fishes in condition of cypermethrin exposure. The levels of ammonia were significantly increased at 10% of 96 h LC(50) of cypermethrin in the different organs such as brain, gills, liver, kidney and muscle of both fish species while 15% and 20% concentrations of 96 h LC(50) of cypermehrin registered remarkable decline in both fish species. The differential increment in the activities of GDH, GS and arginase and in the level of urea established three different alternative mechanisms of ammonia detoxification. The results indicated that in C. punctatus, the prevalent mode of nitrogen excretion is in the form of conversion of ammonia into glutamine and glutamate while in C. batrachus, the excessive nitrogen is excreted in the form of urea synthesized from ammonia.

In vitro testing of anthelmintic efficacy of Flemingia vestita (Fabaceae) on carbohydrate metabolism in Rallietina echinobothrida

The root tuber peel of Flemingia vestita has been in use in local traditional medicine against intestinal worm infections in Meghalaya (North-East India). In order to evaluate and authenticate the anthelminitc efficacy of the isoflavones of F. vestita, the root peel extract of this putative plant was tested against several helminth parasites, extensively on Rallietina echinobothrida, with respect to different parameters of these parasites. In this paper, we describe various methods to evaluate the anthelmintic efficacy of this medicinal plant with respect to carbohydrate metabolism in R. echinobothrida at paralytic time caused by the isoflavones of F. vestita. To meet the high energy demand by the parasite due to the anthelmintic stress, glucose breakdown follows the PEPCK-malate pathway in the parasite.

Cell volume changes affect gluconeogenesis in the perfused liver of the catfish Clarias batrachus

In addition to lactate and pyruvate, some amino acids were found to serve as potential gluconeogenic substrates in the perfused liver of Clarias batrachus. Glutamate was found to be the most effective substrate, followed by lactate, pyruvate, serine, ornithine, proline, glutamine, glycine, and aspartate. Four gluconeogenic enzymes, namely phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase (PC), fructose 1,6-bisphosphatase (FBPase) and glucose 6-phosphatase (G6Pase) could be detected mainly in liver and kidney, suggesting that the latter are the two major organs responsible for gluconeogenic activity in this fish. Hypo-osmotically induced cell swelling caused a significant decrease of gluconeogenic efflux accompanied with significant decrease of activities of PEPCK, FBPase and G6Pase enzymes in the perfused liver. Opposing effects were seen in response to hyperosmotically induced cell shrinkage. These changes were partly blocked in the presence of cycloheximide, suggesting that the aniso-osmotic regulations of gluconeogenesis possibly occurs through an inverse regulation of enzyme proteins and/or a regulatory protein synthesis in this catfish. In conclusion, gluconeogenesis appears to play a vital role in C. batrachus in maintaining glucose homeostasis, which is influenced by cell volume changes possibly for proper energy supply under osmotic stress.

Effects of phytochemicals of Flemingia vestita (Fabaceae) on glucose 6-phosphate dehydrogenase and enzymes of gluconeogenesis in a cestode (Raillietina echinobothrida)

The crude root-peel extract of Flemingia vestita, containing genistein as the major isoflavone, has a vermifugal/vermicidal effect. It acts by causing flaccid paralysis accompanied by alterations in the activities of several tegumental enzymes and other metabolic activities in the fowl tapeworm, Raillietina echinobothrida. To elucidate the mode of action of the putative phytochemicals on energy metabolism, crude root-peel extract, pure genistein and praziquantel were tested on glucose 6-phosphate dehydrogenase (G6PDH) and enzymes of gluconeogenesis--pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK) and fructose 1,6-bisphosphatase (FBPase)--in R. echinobothrida. The activities of G6PDH, PEPCK and FBPase were largely restricted to the cytosolic fraction, while PC was confined to the mitochondrial fraction. Following treatments, the G6PDH activity was decreased by 23-31%, whereas the activities of PC and PEPCK were increased by 32-44% and 44-49%, respectively. There was no significant effect by any of the treatments on FBPase activity. We hypothesize that the phytochemicals from F. vestita, genistein in particular, influence the key enzymes of these pathways, which is perhaps a function of high energy demand of the parasite under anthelmintic stress.

Role of ureogenesis in the mud-dwelled Singhi catfish (Heteropneustes fossilis) under condition of water shortage

The air-breathing Singhi catfish Heteropneustes fossilis was kept inside moist peat for 1 month mimicking their normal habitat in summer and the role of ureogenesis for their survival in a water-restricted condition was studied. The ammonia excretion rate by the mud-dwelled fish increased transiently between 6 and 12 h of re-immersion in water to approximately between eight and 10-fold, followed by a sharp decrease almost to the normal level at the later part of re-immersion. The urea-N excretion by the mud-dwelled fish increased to approximately 11-fold within 0-3 h of re-immersion, followed by a gradual decrease from 9 h onwards. The rate of urea-N excretion by the mud-dwelled fish, however, remained significantly higher (approx. threefold more) than the control fish even after 36-48 h of re-immersion. Although there was a significant increase of both ammonia and urea levels in the plasma and other tissues (except ammonia in the brain), the level of accumulation of urea was higher than ammonia in the mud-dwelled fish as indicated by the decrease in the ratio of ammonia: urea level in different tissues including the plasma. The activities (units/g tissue and /mg protein) of glutamine synthetase and three enzymes of the urea cycle, carbamyl phosphate synthetase, argininosuccinate synthetase and argininosuccinate lyase increased significantly in most of the tissues (except the brain) of the mud-dwelled fish as compared to the control fish. Higher accumulation of ammonia in vivo in the mud-dwelled Singhi catfish is suggested to be one of the major factors contributing to stimulation of ureogenesis. Due to this physiological adaptive strategy of ureogenesis, possibly along with other physiological adaptation(s), this air-breathing amphibious Singhi catfish is able to survive inside the moist peat for months in a water-restricted condition.