CONTROL OF CATECHOLAMINE AND SEROTONIN RELEASE FROM THE CHROMAFFIN TISSUE OF THE ATLANTIC HAGFISH

An in situ saline-perfused systemic heart/posterior cardinal vein prep aration of the Atlantic hagfish (Myxine glutinosa) was used to assess (1) the ability of the chromaffin tissue to release catecholamines in response to adrenocorticotropic hormone (ACTH; 7.5 i.u. kg(-1)), serot onin (250 nmol kg(-1)), carbachol (100 mu mol kg(-1)), [Asn(1)-Val(5)] angiotensin II (Ang II; 100 nmol kg(-1)), histamine (0.3-300 mu mol l( -1)) and a high-[K+] saline (60 mmol l(-1)), (2) whether serotonin is co-released with the catecholamines of the chromaffin tissues, and (3) the potential modulatory effects of NECA, an adenosine receptor agoni st, and DPSPX, an adenosine receptor antagonist, on catecholamine rele ase. Bolus injections of ACTH, serotonin or carbachol, or perfusion wi th high-[K+] saline, all elicited the release of both adrenaline and n oradrenaline. Pre-treatment with the serotonergic receptor antagonist methysergide or the cholinergic receptor antagonist hexamethonium abol ished the serotonin- and carbachol-mediated catecholamine releases, re spectively. Neither receptor antagonist affected the ACTH-mediated cat echolamine release, Bolus injections of Ang II or perfusion with a ran ge of histamine concentrations, two potent secretagogues in other vert ebrates, did not elicit catecholamine secretion in hagfish. While inje ctions of Ang II or perfusion with the high-[K+] saline both elicited the release of serotonin, treatments with ACTH, carbachol or histamine did not, Hence, corelease of catecholamines and serotonin was elicite d by non-specific cell membrane depolarization using K+, but not by th e specific secretagogues assessed in this study. The adenosine recepto r agonist NECA and antagonist DPSPX significantly modified the secreto ry responses elicited by ACTH, serotonin and carbachol. The results su ggest that adenosine may inhibit catecholamine release induced by sero tonin or carbachol, while stimulating ACTH-induced release. Although t he contribution of the different secretagogues identified in this stud y has yet to be explored in vivo, our results suggest that the control of catecholamine and serotonin release from the aneural chromaffin ti ssue of the Atlantic hagfish can be achieved through hormonal and/or p aracrine means.