Some effects of substance P on central respiratory control in rabbit pups

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Abstract
Respiratory effects of substance P (SP) have been studied in rabbit pups (1–30 days). Rabbits were either anaesthetized with urethane or decerebrated at mid‐collicular level. Respiratory activity was measured with a pneumotachograph or in some cases as efferent phrenic nerve activity. SP applied to the exposed medulla oblongata from the dorsal side caused an increase of both tidal volume and respiratory frequency. The respiratory stimulation was more pronounced in decerebrate animals than in anesthetized ones. Moreover, this effect was most prominent in the youngest animals. A SP analogue (d‐arg1‐d‐Pro2,d‐Trp7, 9, Leu11)‐SP was found to block the ventilatory effects of SP and to decrease the hypoxic response, while the hypercapnic response was preserved. The results suggest that SP is involved in the control of respiration, possibly mediating the hypoxic response, and that this role is more important in the neonatal period.