Depression Of Whole-Body Calcium Uptake During Acute Hypercalcaemia In American Eel, Anguilla Rostrata, is Mediated Exclusively by Corpuscles of Stannius

Abstract

1. The role of the corpuscles of Stannius (CS) in acute modulation of wholebody calcium influx (JinCa) in American eel, Anguilla rostrata, was investigated by (i) assessing the effects of stanniectomy on JinCa and plasma total calcium concentration ([Catot]), (ii) comparing the abilities of sham-operated and stanniectomized eels to reduce JinCa during artificially induced hypercalcaemia, and (iii) monitoring the effects of homologous hypocalcin (a 54×103Mr glycoprotein injection on JinCa 2. Stanniectomy (STX) caused a pronounced elevation of JinCa and hypercalcaemia measured 7 days after surgery. 3. When hypercalcaemia was induced by intra-arterial infusion of CaCl2, a treatment known to cause degranulation of the CS and the specific release of hypocalcin, JinCa was reduced significantly within 1 h in intact fish. NaCl infusion did not affect plasma [Catot] or JinCa in any group tested. 4. Stanniectomy prevented the reduction of JinCa associated with the hypercalcaemia induced by CaCl2 infusion. 5. Intra-arterial infusion of MgCl2 caused a significant elevation of plasma total magnesium concentration [Mgtot] but did not alter JinCa. 6. Intra-arterial infusion of hypocalcin (l8.5 nmolkg−1 body mass) into intact eels decreased JinCa to an extent similar to that seen following artificially induced hypercalcaemia. 7. We conclude that the rapid reduction of JinCa during experimental hypercalcaemia is mediated by hypocalcin released from the corpuscles of Stannius and suggest that calcitonin, another putative hypocalcaemic hormone, is not involved. The results are discussed with respect to the relative importance of hypocalcin and calcitonin as hypocalcaemic hormones in fish.