Facilitation of inspiration by intracerebroventricular injection of thyrotropin-releasing hormone in rabbits.

Effects of fourth cerebroventricular injection of thyrotropin-releasing hormone (TRH) on respiration were studied in vagotomized rabbits. Phrenic neural activity was recorded and integrated. TRH (1.0 microgram) injection facilitated phrenic neural activity and increased respiratory rate. Peak phrenic nerve activity increased slightly or showed no apparent changes when tonic activity appeared. Tidal phrenic neural activity either increased or decreased, depending on relations between peak phrenic activity and tonic activity. Results suggest that TRH facilitates central respiratory activity to induce tonic activity and increase respiratory rate.