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 less than 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 less than 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 less than 0.05). These findings indicate that endogenous endorphins have a significant, though changing, role in control of breathing in the developing piglet.