Bovine TSH-stimulation of fish thyroid peroxidase activity and role of thyroxine thereon

bTSH augmented the fish thyroid peroxidase activity in a dose-response manner. Thyroxine could not modulate the effect of exogenous bTSH, but it decreased the peroxidase activity in a control system when administered alone. The data therefore suggest similar negative feedback control system for TSH-regulation as operative in the case of mammals.