Fig. 1.

Effect of an intra-arterial (ia) injection of the selective μ-opioid receptor agonist [d-Ala²,N-MePhe⁴,Gly-ol⁵]enkephalin (DAMGO) on reflex increases in mean arterial pressure (MAP; in mmHg) and heart rate [HR; in beats/min (bpm)] during static contraction. A: the peak increases of MAP and HR during static contraction in control rats were not affected by the intra-arterial injection of DAMGO. B: the augmented peak increases of MAP during static contraction in rats whose left femoral artery was occluded for 72 h previously were diminished by the intra-arterial injection of DAMGO (P = 0.008). The pressor response to contraction in the ligated rats was significantly greater (†P < 0.05) than that to contraction in their freely perfused counterparts in A. On the other hand, the peak increases of HR during static contraction in these rats were not affected by the intra-arterial injection of DAMGO (P = 0.073). Values are means ± SE. The pressor responses to contraction in each group were significantly increased from their respective baselines (*P < 0.05). The horizontal brackets signify that the responses were significantly different from each other (P < 0.05).