RT Journal Article
SR Electronic
T1 Effects of Met-enkephalin on the substance P-ergic and cholinergic responses in the rabbit iris sphincter muscle.
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 507
OP 511
VO 226
IS 2
A1 N Ueda
A1 I Muramatsu
A1 H Hayashi
A1 M Fujiwara
YR 1983
UL http://jpet.aspetjournals.org/content/226/2/507.abstract
AB In the rabbit iris sphincter muscle, transmural electrical stimulation produces a substance P-ergic response, in addition to a cholinergic one. The substance P-ergic response was selectively attenuated or abolished by (D-Pro2, D-Trp7,9) substance P or trigeminal denervation. In the present work, the effects of Met-enkephalin on these two neurogenic responses were examined. Met-enkephalin (10(-7) to 10(-5) M) inhibited the substance P-ergic and cholinergic responses, in a dose-dependent manner and the inhibitory action of Met-enkephalin was greater in the case of low frequency stimulation. These inhibitory effects of Met-enkephalin were antagonized by naloxone (10(-5) M). On the other hand, Met-enkephalin had no effects on the responses to exogenously applied substances P and carbachol. These results suggest that the trigeminal, substance P-ergic neurons as well as cholinergic nerves have opiate receptors and that enkephalin inhibits the neuronal responses presynaptically, probably the release of substance P or acetylcholine, through such opiate receptors.