Catechol concentrations in the hemolymph of the scallop, Placopecten magellanicus

Catecholamines have previously been detected in numerous tissues and are th ought to control a nide variety of physiological functions in bivalve mollu scs. In the present study, alumina extraction and high-performance liquid c hromatography reveal the presence of significant concentrations of 3,4-dihy droxyphenylalanine (DOPA), dopamine, and 3,4-dihydroxyphenylacetic acid (DO PAC) in the hemolymph of the sea scallop, Placopecten magellanicus. The con centration of dopamine in the hemolymph averaged 223.8 ng/ml, (+/-48.4, SEM ), equivalent to 10(-7) to 10(-6) M. Neither epinephrine nor norepinephrine was reliably detected in significant quantities. Previous studies have dem onstrated physiological responses to dopamine with thresholds of 10(-9) to 10(-6) M, thus suggesting that this catecholamine may have an endocrine fun ction. Furthermore, monitoring hemolymph concentrations of catechols might provide a sensitive measure of the physiological status of bivalves. For ex ample, drugs known to affect catechol concentrations in other tissues also effect hemolymph levels. Administration of monoamine oxidase inhibitors suc h as pargyline, deprenyl, and clorgyline at 10(-4) M for 1 day of incubatio n followed by a 2-day wash resulted in decreased hemolymph concentrations o f DOPAC and increased concentrations of its precursors, DOPA and dopamine. Incubation in 10(-4) M 3,5-dinitrocatechol, a catecholamine-O-methyl transf erase blocker, for 1 day followed by a 2-day wash significantly increased t he concentration of dopamine and DOPAC in the hemolymph. Scallops incubated in 10(-5) M alpha-methyl-p- tyrosine, a blocker of tyrosine hydroxylase, f or 1 day followed by a 3-day wash in artificial seawater had significantly reduced concentrations of DOPA, dopamine, and DOPAC in the hemolymph. In ad dition to responding to pharmacological agents, dopamine levels also decrea sed significantly following thermal induction of spawning, thus suggesting that hemolymph concentrations of catechols might provide indices of reprodu ctive activity and/or stress. (C) 2000 Academic Press.