l-NAME differentially alters ventilatory behavior in Sprague-Dawley and Brown Norway rats

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Abstract
Nitric oxide (NO) is a regulating factor in respiration. The question was whether NO synthase (NOS) blockade would affect posthypoxic ventilatory behavior similarly in two rat strains with known differences in steady-state hypoxic and hypercapnic responses and in posthypoxic ventilatory behavior. Ventilatory behavior [respiratory frequency (f) and minute ventilation (V˙e)] was measured by body plethysmography on unanesthetized, unrestrained adult male Sprague-Dawley (SD; n= 8) and Brown Norway rats (BN; n = 8) at baseline and 1 min after rapid transition to 100% O2after 5 min of isocapnic hypoxia (10% O2-3% CO2-balance N2). Testing was performed 30 min after intraperitoneal injection of either saline (vehicle) or 100 mg/kg of NG-nitro-l-arginine methyl ester (l-NAME). Resting f and V˙e increased after l-NAME in both strains, more markedly in SD compared with BN (77 vs. 47% for f, and 42 vs. 16% for V˙e, respectively; P < 0.05). With vehicle, posthypoxic f and V˙e decline (Dejours phenomenon) was present only in BN and was absent in SD. With l-NAME, the Dejours phenomena were still present in BN but also were apparent in SD (f: 95.3 vs. 134.4 beats/min at baseline; V˙e: 66.3 vs. 88.8 ml/min at baseline; P < 0.05). Thus NOS blockade results in a strain-specific alteration in resting ventilation and uncovers the Dejours phenomenon in the SD strain.