CHOLINERGIC CONTROL OF STANNIOCALCIN RELEASE IN THE RAINBOW-TROUT, ONCORHYNCHUS-MYKISS, AND THE AMERICAN EEL, ANGUILLA-ROSTRATA

An in vivo whole animal Ca-45 influx bioassay was used to study the cholinergic control of the release of stanniocalcin (STC) in the rainbow trout (Oncorhynchus mykiss) and the American eel (Anguilla rostrata). In both species calcium influx (J(in)(Ca2+)) was lowered in response to hypercalcemia induced by intravascular (trout) or intraperitoneal (eel) injections of CaCl2. In trout, this response was blocked by the cholinergic antagonist atropine (0.25 mu mol kg(-1)) and mimicked by the cholinoceptor agonist carbachol(0.25 mu mol kg(-1)). These observations are consistent with a cholinergic stimulation of STC release in response to hypercalcemia in trout. In eels, pretreatment with atropine did not block the lowering of J(in)(Ca+) in response to hypercalcemia. This suggests that cholinergic stimulation is not obligatory for stanniocalcin release in eels. However, carbachol treatment did elicit STC release as revealed by the lowering of J(in)(Ca2+). This response to carbachol was not observed in stanniectomized eels. Thus, in the American eel it appears that there is a potential for cholinergic control of STC release but that other factors such as the local plasma calcium concentration may also be involved, at least in response to severe acute hypercalcemia. (C) 1994 Academic Press, Inc.