Ventilatory and cardiovascular responses of the unanaesthetized chicken, Gallus domesticus, to the respiratory stimulants etamiphylline and almitrine.

The ventilatory and cardiovascular effects of i.v. administration of the respiratory stimulants etamiphylline and almitrine were investigated in conscious or decerebrate adult female domestic fowl. Infusion of etamiphylline (100 mg . kg-1) or injection of almitrine (2 mg . kg-1) evoked a potent long-lasting stimulation of ventilation in both conscious and decerebrate fowl. The pattern of the respiratory response was characteristically different to that observed in mammals in that the increased minute volume of ventilation was attained by large increases in respiratory frequency accompanied by a reduction in tidal volume. The pattern of respiration following drug-induced stimulation was, in some birds, typical of thermal panting although neither etamiphylline nor almitrine caused significant increases in body temperature. Differences in the pattern of responses of the rate and depth of breathing may be attributed in part to the differences in pulmonary receptor systems involved in the control of breathing in birds and mammals.