Disaccharidases and alanyl aminopeptidase activities in intestine of a marine estuarine-dependent fish: differential responses to dopamine and histamine in juveniles of Mugil liza (Actiopterygii: Mugilidae)

Abstract

Information about the modulation by chemical messengers of key digestive enzymes in the intestine of fishes is both scarce and fragmentary. Moreover, nothing is known in groups of ecological and economic importance such as marine estuarinedependent fishes. Furthermore, no studies are available about the role of the biogenic amines dopamine and histamine as regulators of digestive enzyme activities in the intestine of fishes. We determined the in vitro effect of dopamine and histamine on maltase, sucrase and alanyl aminopeptidase activities in the intestine of juveniles of Mugil liza. Dopamine (10 -4 M) increased maltase, sucrase and alanyl aminopeptidase activities (about 86%, 98% and 73% respectively). Histamine (10 -4 M) increased (about 57%) alanyl aminopeptidase activity but it had no effect on either maltase or sucrase activity. The in vitro modulation by dopamine and histamine suggests a role of these biogenic amines in the regulation of digestive enzymes in the intestine. The fact that histamine, unlike dopamine, appeared not to affect maltase or sucrase activity suggests a differential and specific modulation of disaccharidases and alanyl aminopeptidase by distinct chemical messengers. The stimulation of alanyl aminopeptidase activity by both dopamine and histamine further suggests that this enzyme is under control of distinct modulation pathways in the intestine of juveniles of M. liza. To our knowledge, this work is the first to show the stimulation of dopamine and histamine of a digestive enzyme activity by direct effect on the intestine of fish.