Trbovic, Sinisa M., Miodrag Radulovacki, and David W. Carley. Protoveratrines A and B increase sleep apnea index in Sprague-Dawley rats. J. Appl. Physiol. 83(5): 1602-1606, 1997.The action of protovertarines A and B, which stimulate carotid sinus baroreceptors and vagal sensory endings in the heart as well as pulmonary bed, were assessed on spontaneous and postsigh central sleep apneas in freely moving Sprague-Dawley rats. During the 6-h recording period, animals were simultaneously monitored for sleep by using electroencephalogram and electromyogram recordings, for respiration by single-chamber plethysmography, and for blood pressure and heart period by using radiotelemetry. After administration of 0.2, 0.5, or 1 mg/kg sc of protoveratrines, cardiopulmonary changes lasting at least 6 h were observed in all three behavioral states [heart period increased up to 23% in wakefulness, 21% in non-rapid-eye-movement (non-REM) sleep, and 20% in REM sleep; P < 0.005 for each]. At the same time, there was a substantial increase in the number of spontaneous (375% increase; P = 0.04) and postsigh (268% increase, P = 0.0002) apneas. Minute ventilation decreased by up to 24% in wakefulness, 25% in non-REM, and 35% in REM sleep (P < 0.05 for each). We conclude that pharmacological stimulation of baroreflexes promotes apnea expression in the sleeping rat.