DEVELOPMENT OF A DOSE-RESPONSE BIOASSAY FOR STANNIOCALCIN IN FISH

Stanniocalcin (STC) is a polypeptide hormone that was first discovered in fish and recently identified in mammals. In fish, STC is released into the bloodstream in classical endocrine fashion and has well estab lished regulatory effects on calcium and phosphate homeostasis. Howeve r, there are no suitable dose-response bioassays for STC and consequen tly no methods for assigning units of potency to preparations of the h ormone. All the available in vitro bioassays are too complex from a te chnical standpoint to readily accommodate the large number of samples required in dose-response bioassays. Most in vivo bioassays are hamper ed by the fact that fish have natural rhythms governing plasma STC lev els which tend to make them variably sensitive to the injected hormone . In this report we have developed a new in vivo bioassay for STC usin g rainbow trout. The key feature of the bioassay involves suppressing plasma STC levels to the extent that fish are always receptive to inje cted hormone. This has been accomplished by phosphate-loading the anim als, which lowers their plasma calcium levels, removes the stimulus fo r STC secretion and brings about a reduction in resting plasma hormone levels. The net effect is an animal that is always responsive to inje cted STC. With this bioassay we have been able to obtain sensitive and reproducible, dose-related effects of salmon STC on gill calcium tran sport. (C) 1997 Elsevier Science Ireland Ltd.