Potentiation of [Met5]enkephalin-induced antinociception by mixture of three peptidase inhibitors in rat

Abstract

The present data, together with those of earlier studies, clearly demonstrate that amastatin-, captopril-, and phosphoramidon-sensitive enzymes play an important role in inactivation of opioid peptides at the spinal level.

Sialorphin Potentiates Effects of [Met5]Enkephalin without Toxicity by Action other than Peptidase Inhibition

“…A previous study demonstrated that pretreatment with i.t. administration of a combination of 10 nmol each of amastatin (A), captopril (C) and phosphoramidon (P) completely inhibited peptidase-induced degradation of ME (Murata et al, 2014). In the present study, i.t.…”

“…accordance with the method in earlier studies by the present group (Kitamura et al, 2000;Takahashi et al, 2007;Akahori et al, 2008;Murata et al, 2014;Ajimi et al, 2015;Matsuda et al, 2017), nociceptive stimulation was achieved by immersing the tail of each rat in hot water (55ºC) for a maximum of 5 sec. This time limit was set to prevent injury to the animal in accordance with the result from earlier studies by the present group showing that persistent pain occurs when the tail is placed in hot water for more than 5 seconds (data not shown).…”

“…Based on a method described in an earlier study (Murata et al, 2014), intathecal (i.t.) catheters were implanted in male Wistar rats (7-8 weeks-old) under inhalation anesthesia with nitrous oxide, oxygen, and isoflurane (2%).…”

“…However, one earlier study found that i.t. administration of ME at a dose of 20 nmol had no antinociceptive effect (Murata et al, 2014). This dose can be taken to correspond to approximately 200 !M based on the finding that the amount of cerebrospinal fluid was approximately 100 !l in rat (200-300 body weight) (Consiglio and Lucion, 2000).…”

“…The membrane-bound three enzymes, aminopeptidase N (APN), dipeptidyl carboxypeptidase, and neutral endopeptidase (NEP), play an essential role in the degradation of [Met 5 ]enkephalin (ME) in three different types of isolated preparation: guinea pig ileum (Aoki et al, 1984), mouse vas deferens (MVD) (Aoki et al, 1986) and rat vas deferens (Cui et al, 1986). A mixture of the following three peptidase inhibitors (PIs) significantly increased the antinociceptive effects of ME: amastatin (A), an aminopeptidase inhibitor; captopril (C), a dipeptidyl carboxypeptidase inhibitor; and phosphoramidon (P), an endopeptidase-24.11 inhibitor (Murata et al, 2014). This finding was in good agreement with those of earlier studies employing high performance liquid chromatography (HPLC) that showed that a mixture of these PIs almost completely inhibited the degradation of ME (Hiranuma and Oka, 1986).…”