Various monoamines released as neurohormones from the pericardial organs of crab hearts were found to potentiate the oxygen affinity of haemocyanin from Cancer magister. Of the compounds tested, the catechol dopamine was the most active. Preincubation of the haemocyanin with a dopamine antagonist abolished the effect, indicating a specific site. Haemocyanin may also retard the rapid auto-oxidation of dopamine that normally occurs at physiological pH.
The neurohormonal regulation of physiological processes in decapod crustaceans has received some attention, but the role played by monoamines is still incompletely understood (for reviews, see Cooke and Sullivan, '82; McMahon and Wilkens, '83; Wilkens, '87). Similarly, advances have been made in the molecular physiology of haemocyanin, the respiratory pigment of many crustaceans. It has been realised for some time that haemocyanin oxygen affinity was strongly influenced by a number of inorganic ions (see Mangum, 1983a, for overview). Until recently, however, the modulation of haemocyanin function by organic ions was believed to be restricted to Llactate (Truchot, '80; Mangum, '83b; Graham et al. '83, Bridges et al., '84; Morris and Bridges '85). Uric acid has now been found to have a similar potentiating effect (Morris et al., 1986). Despite these findings, it is apparent that further, unidentified factors with similar properties occur in crustacean haemolymph (Bridges and Morris, '86; Morris and Bridges, '86). This study examines and discusses the role of neurologically active molecules in controlling haemocyanin oxygen affinity. The commonly accepted pathway for the formation of monoamines in crustaceans precludes the formation of norepinephrine and epinephrine (Kennedy, '78; Cooke and Sullivan, '82). There are reports that do indicate, however, that these and other compounds may occur in crustaceans (Marmaras et al., '71; Fingerman et al., '78), but dopamine is likely the most important product formed (Zatta, '87).