Differential modulation of digestive enzymes and energy reserves at different times after feeding in juveniles of the marine estuarine-dependent flatfish Paralichthys orbignyanus (Valenciennes, 1839).

Integrative studies are lacking on the responses of digestive enzymes and energy reserves in conjunction with morphological traits at distinct postprandial times in marine estuarine-dependent flatfishes of ecological and economic importance, such as Paralichthys orbignyanus. We determined total weight (TW), hepato-somatic index (IH), activities of digestive enzymes in the intestine, and the concentration of energy reserves in the liver and the muscle at 0, 24, 72, and 360 h after feeding in juveniles of P. orbignyanus. Amylase activity decreased at 72 h (about 30%). Maltase, sucrose, and lipase activities reached peak at 24 h (67%, 600%, and 35%, respectively). Trypsin and aminopeptidase-N activities at 24 and 72 h, respectively, were lower than those at t = 0 (53% and 30%). A peak increase in the concentration of glycogen and triglycerides in the liver (24 h) (86% and 89%, respectively) occurred. In muscle, glycogen and triglyceride concentrations were unchanged at 24 h and higher at 72 and 360 h (100% and 60%). No changes were found in TW, IH, free glucose in the liver and muscle, and protein in the liver. The protein concentration in the muscle sharply increased at 24 and 360 h after feeding (60%). The results indicate a distinct and specific response of central components of carbohydrate, lipid, and protein metabolism that could be adjustments at the biochemical level upon periods of irregular feeding and even of long-term food deprivation inside coastal lagoons or estuaries. The distinct responses of digestive enzymes in the intestine and energy reserves in the liver and muscle suggest the differential modulation of tissue-specific anabolic and catabolic pathways that would allow the maintenance of physical conditions.

Trypsin and N-aminopeptidase (APN) activities in the hepatopancreas of an intertidal euryhaline crab: Biochemical characteristics and differential modulation by histamine and salinity.

No studies are available about biochemical characteristics and modulation (i.e. by endogenous and/or environmental cues) of trypsin (a key digestive endoprotease) in hepatopancreas of intertidal euryhaline crabs neither on the possible concomitant modulation of key ectoproteases such as aminopeptidase-N (APN) involved in final steps of protein digestion. Furthermore, nothing is still known in decapods crustaceans about the role of histamine as primary chemical messenger for modulation of main components of digestive process (i.e. proteases). We determined biochemical characteristics and investigated the effect of histamine injections; of histamine in vitro and of acclimation of individuals to low and high salinity on trypsin and aminopeptidase-N (APN) activities in the hepatopancreas of the euryhaline crab Cyrtograpsus angulatus (Dana 1851). Trypsin activity was maximal at pH7.4 and at 45°C. APN activity increased from pH6.6 to 7.6-9.0 and was maintained high at 37-45°C. Both activities exhibited Michaelis-Menten kinetics (apparent Km: trypsin=0.36mM; APN=0.07mM). The injection of 10-4M histamine decreased trypsin activity (about 40%) in hepatopancreas while did not affect APN activity. Similarly, in vitro 10-4M histamine decreased trypsin activity (about 52%) in hepatopancreas but not APN activity. Trypsin activity in the hepatopancreas was not affected by acclimation of crabs to low (10psu) or high (40psu) environmental salinity while APN activity was increased (about 200%) in 10psu. The results show the differential modulation of trypsin and APN by distinct cues and point to histamine as modulator of intracellular trypsin by direct action on the hepatopancreas.