Naloxone effects on the blood pressure response induced by thin-fiber muscular afferents

Naloxone effects on the blood pressure level and on the blood pressure responses induced by thin-fiber muscular afferent stimulation were studied in anesthetized, bilaterally vagotomized and carotid sinus nerve-denervated dogs under artificial ventilation. Repetitive pulses of 8 Hz with various intensities were applied to the gastrocnemius nerve for 1 min while monitoring the compound action potentials. The mean arterial pressure significantly (P less than 0.001) rose by 10.95 +/- 1.78 mmHg (mean +/- S.E.) about 5 min after a naloxone injection. Compared with the reflexive response in the control period, the depressor effect significantly decreased by 3.80 +/- 1.06 mmHg, and the pressor effect significantly increased by 3.63 +/- 0.73 mmHg for 30 min after the injection of naloxone. No correlation was found between naloxone effects on the blood pressure level and on the reflex response, indicating an involvement of different mechanisms with these naloxone effects. We suggest that endogenous opiates might participate in the regulation of the blood pressure level, as well as of the blood pressure responses caused by thin-fiber muscular afferents.