Developmental aspects of the effect of naloxone on control of breathing in piglets

The respiratory effects of a stereospecific opiate antagonist, naloxone, were studied in two groups of paralyzed and vagotomized piglets who were servoventilated on 100% oxygen. Phrenic neural activity was used as the index of respiratory output. In 7 piglets less than 10 days of age naloxone infusion caused phrenic minute output to increase 122±36% (P < 0.01). This change was accounted for by a significant increase only in peak phrenic activity, the neural equivalent of tidal volume. Frequency did not change significantly. In 7 piglets 20-34 days of age naloxone infusion caused phrenic minute output to increase 54±12% (P < 0.025). Both peak phrenic activity and frequency were significantly increased. The increase in respiratory output observed in the younger piglets was significantly greater than that of the older piglets (P < 0.05). These findings indicate that endogenous endorphins have a significant, though changing, role in control of breathing in the developing piglet.