p-chlorophenylalanine eliminates long-term modulation of the exercise ventilatory response in goats

Repeated hypercapnic exercise augments future exercise ventilatory response s, an effect termed long-term modulation. We hypothesized that serotonin de pletion with p-chlorophenylalanine (PCPA. 100 mg kg(-1) i.v.) would attenua te long-term modulation. Ventilation, CO2 production and arterial blood gas es were measured at rest and during exercise (4 km h(-1), 5% grade) in goat s before and after training (14 hypercapnic exercise trials). Six post-trai ning exercise trials were performed. Trials 1-3 and 4-6 were grouped for an alysis (post-training 1 and 2, respectively). Without PCPA, training exagge rated the Pa-CO2 decrease from rest to exercise (pre-training: 1.4 +/- ;0.3 mmHg; post-training 1: 3.1 +/- 0.3 mmHg, post-training 2: 2.3 +/- 0.3 mmHg P < 0.05), indicative of long-term modulation. The Pa-CO2 decrease from re st to exercise was unaffected by training following PCPA (pre-training: 1.4 +/- 0.1 mmHg; post-training 1: 1.4 +/- 0.3 mmHg, post-training 2: 1.1 +/- 0.5 mmHg: P > 0.05). Thus, PCPA abolishes long-term modulation, implicating serotonin in its underlying mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.