Central ventilatory effects of thyrotropin-releasing hormone in the conscious rat

Thyrotropin-releasing hormone was shown to exert potent ventilatory effects after central administration. These data, however, were derived from studies using anesthetized animal preparations. Since TRH elicits strong arousal reactions, the observed ventilatory effects of TRH under anesthesia may have been due to nonspecific reduction in the anesthetic state of the animals. In order to clarify the extent to which the reversal of anesthesia may change ventilatory parameters after TRH application, we investigated the effect of TRH on ventilation rate, relative tidal volume, relative respiratory minute volume, CO2 production CO2 consumption, and locomotor activity in the conscious, unrestrained rat. Intracerebroventricular application of TRH induced a dose-dependent, sustained increase in ventilation rate, relative tidal volume, and relative respiratory minute volume of maximally 128%, 890%, and 235%, respectively. In addition, CO2 production and O2 consumption were elevated by 4.6 and 11.7 fold, while no significant changes in locomotor activity were observed. The results suggest that TRH stimulates ventilation by a mechanism independent of its analeptic properties.