Administration of recombinant enkephalinase (neutral endopeptidase) prevents capsaicin-induced miosis in the rabbit eye in vivo.
Substance P induced a dose-dependent contraction of iris sphincter muscles when applied in the presence of atropine to the isolated rabbit iris in vitro as evidenced by a decreased pupil diameter. Pretreatment of the iris with 20 micrograms of recombinant enkephalinase (neutral endopeptidase; EC 3.4.24.11) totally abolished the contractile response to substance P. Injection of 10 micrograms of capsaicin into the anterior chamber of atropine-treated rabbit eyes in vivo induced an immediate and intense miosis. Injection of 100 micrograms of recombinant enkephalinase, 1 or 5 min before capsaicin injection, significantly inhibited this miosis. This effect of enkephalinase was totally abolished by preincubating the enzyme with thiorphan, a high-affinity enkephalinase inhibitor. These results show that enkephalinase, which is known to hydrolyze substance P in vitro with high efficiency, also hydrolyzes endogenously released substance P in vivo. Furthermore, our results suggest that enkephalinase application may represent a novel therapeutic approach to treat substance P-mediated pathologies.
Department of Pharmacological Sciences, Process R&D Genentech, Inc., South San Francisco, California.
B
B
Malfroy
D
D
Liggitt
J
J
McCabe
R
R
Baughman
H
H
Kado-Fong
K
K
Mulholland
R
R
Bridenbaugh
J
J
Anderson
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D015260:Neprilysin / Q000494:pharmacology*; D011680:Pupil / Q000187:drug effects*; D011817:Rabbits; D011994:Recombinant Proteins / Q000494:pharmacology; D013373:Substance P / Q000494:pharmacology
D011994:Recombinant Proteins; D013373:Substance P; D015260:Neprilysin; D002211:Capsaicin