Abstract
In adult rats, opioids administered into the pulmonary circulation produces an apnea and given systemically turns the phenylbiguanide (PBG)‐evoked rapid shallow breaths (RSBs) to an apnea by stimulating and facilitating PCFs, respectively. Fentanyl, an opioid μ‐receptor agonist, clinically has a lesser inhibitory effect on ventilation in children (< 3 years old) than in adults (Barker, Pediatric Anesthesia 2007). Thus, we tested if the modulatory effect of opioids on the PCF‐mediated VE responses in rats were age‐dependent. VE responses to a right atrial bolus injection of PBG (before and after systemic administration of fentanyl) or fentanyl were recorded in anesthetized rat pups (3 week‐old) and adults. We found that: 1) PBG (5 μg/kg) evoked 5–10 RSBs in adults, but caused no change or 2–3 rapid breaths in pups; 2) systemic fentanyl (6 μg/kg, iv) reduced VE more greatly in adults (60%) than pups (27%, P < 0.01) and switched the PBG‐induced RSB to an apnea in adults, but failed to alter the PBG effects on VE in pups; 3) right atrial injection of fentanyl (2 μg/kg) alone produced an apnea in adults but not in pups; and 4) the VE responses to right atrial injection of PBG or fentanyl were eliminated by bilateral vagotomy. Our data suggest that the PCF‐mediated RSBs and inspiratory inhibition in response to PBG and fentanyl are age‐dependent in rats, indicating a plasticity of PCFs as development. (ALA RT‐83131‐N).
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