ENDOCRINE CONTROL OF CARTILAGE GROWTH IN COHO SALMON - GH INFLUENCE IN-VIVO ON THE RESPONSE TO IGF-I IN-VITRO

Ceratobranchial cartilages from coho salmon (Oncorhynchus kisutch) par r, injected with growth hormone (GH) at 4 mug/g body weight or with sa line, were sampled monthly from February to July. Thymidine and sulfat e uptakes by cartilages were determined as measures of DNA and chondro itin sulfate synthesis, respectively. Cartilages were incubated with I GF-I at 0.01, 0.1 and mug/ml to examine the in vitro response to this hormone. GH injection increased cartilage thymidine and sulfate uptake s at least four-fold in all experiments. IGF-I treatment in vitro furt her increased sulfate but not thymidine uptake in cartilages from GH-i njected coho and increased uptake of both in cartilages from saline-tr eated coho. However, the IGF-stimulated uptakes were still significant ly below the uptakes in cartilages from GH-injected coho. The dual eff ector hypothesis of GH action [12] in mammals is supported at least in part in teleost fishes by the observation that addition of IGF-I in v itro was not equivalent to injection of GH in vivo.