Mechanisms of TRH-induced GH release (paradoxical response) in human somatotroph adenoma cells

The mechanisms of paradoxical TRH response in human somatotroph adenoma cells were investigated using intracellular calcium measurement and static incubation assay. Intracellular calcium measurement revealed that TRH induces a biphasic response: a transient increase followed by a sustained plateau. The transient phase was due to the calcium release from IP(3)-regulated intracellular calcium store and the subsequent sustained phase was due to the calcium influx through the voltage-gated calcium channels. The signal transduction mechanism of the calcium plateau involved protein kinase C. These calcium responses, especially the second phase, was responsible for the TRH-induced GH release.