1. When
NG-nitro-L-arginine methyl ester (L-NAME, 0.1-10 nmol) or
NG-monomethyl-L-arginine (
L-NMMA, 10 nmol-1 mumol) was intradermally administered with
bradykinin (BK, 3 nmol) into the instep of rat hind-paws, a dose-related suppression of BK-induced
hyperalgesia, assessed by the paw-pressure test, was produced. 2.
L-Arginine (1 mumol) but not D-
arginine (1 mumol) reversed the suppressive effects of
L-NAME (10 nmol) and
L-NMMA (1 mumol) on BK-induced
hyperalgesia. 3. Concomitant intradermal administration of BK (3 nmol) with haemoglobin (1 nmol) significantly suppressed BK-induced
hyperalgesia in the paw-pressure test. The BK-induced
hyperalgesia was abolished by concomitant intradermal administration of either a
guanylate cyclase inhibitor,
methylene blue (10 nmol), or
LY83583 (1 nmol). In addition,
KT5823 (1 nmol) or Rp-8-bromoguanosine-3':5'-cyclic monophosphothioate (Rp-8-Br-cGMPS; 1 nmol), an inhibitor of
cyclic GMP-dependent protein kinase, also significantly suppressed BK-induced
hyperalgesia. 4. The
carrageenin-induced
hyperalgesia was significantly attenuated by
L-NAME in a dose-dependent manner. 5.
L-Arginine (1 mumol),
sodium nitroprusside (1 mumol),
dibutyryl cyclic GMP (1 mumol) or 8-bromo
cyclic GMP (1 mumol) all failed to produce any significant relieving effect on the nociceptive threshold of rodent hind-paws. Concomitant administrations of each agent with a sub-threshold dose (0.1 nmol) of BK induced significant
hyperalgesia. 6. Rp-
adenosine 3':5'-cyclic monophosphothioate (
Rp-cAMPS; 1 nmol), an inhibitor of
cyclic AMP-dependent protein kinase, significantly suppressed BK-induced
mechanical hyperalgesia. Concomitant administration of
forskolin (1 nmol) with 8-bromo
cyclic GMP (100 nmol) induced significant
hyperalgesia. 7. In the superfusion experiment of a
blister base on the instep of rodent hind-paws, intradermally administered BK (3 nmol) significantly increased the outflow of both
cyclic GMP and
cyclic AMP from the
blister base. Concomitant administrations of
L-NAME (10 nmol) with BK significantly reduced the BK-induced outflow of
cyclic GMP without affecting the
cyclic AMP content. 8. These results suggest that the NO-
cyclic GMP pathway is involved in the mechanism of BK-induced
hyperalgesia, and an activation of both
cyclic GMP-and
cyclic AMP-second messenger system plays an important role in the production of peripherally induced
mechanical hyperalgesia.