Effect of 9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl)adenine on noradrenaline release from vascular sympathetic nerves

Attenuating effect of mexiletine hydrochloride on herpetic pain in mice infected with herpes simplex virus

The influence of mexiletine hydrochloride on herpes-related pain responses was examined using mice infected with herpes virus. BALB/c mice were inoculated with herpes simplex virus (HSV; 1 times 106 plaque-forming units) on the right hind paw, and the contralateral hind paw was without inoculation. The changes in nociceptive threshold were examined using electric von fray meter. BALB/c mice inoculated with HSV showed a decrease in nociceptive threshold. Intraperitoneal administration of mexiletine prevented the decrease in nociceptive threshold dose-dependently in HSV-inoculated mice, which was firstly observed at a dose of 15.0 mg kg−1, and peaked at doses more than 17.5 mg kg−1. This antinociceptive effect of mexiletine attained peaks at 60–90 min after administration and declined gradually to non-treated levels by 150 min. Intraperitoneal administration of mexiletine at a dose of 17.5 mg kg−1 (but not 10.0 mg kg−1) caused significant increase in β-endorphin levels in the mid brain and hypothalamus of HSV-inoculated mice. However, mexiletine scarcely affected noradrenaline (norepinephrine) levels in the pons and medulla oblongata, even when HSV-inoculated mice were treated with 17.5 mg kg−1 mexiletine. These results strongly suggested that mexiletine exerts antinociceptive effects on herpes-related pain through enhancement of β-endorphin levels in the central nervous system in HSV-inoculated mice. It is also suggested that mexiletine will be a good candidate for an antinociceptive drug in the treatment of acute herpetic pain in man.

Purinergic modulation of vascular sympathetic neurotransmission

It is generally agreed that the release of norepinephrine (NE) is inhibited by activation of prejunctional purinoceptor. We examined the pharmacological properties of purinoceptors on vascular sympathetic nerve terminals and the source of endogenous adenyl purines. Electrically (1 Hz) evoked NE-release was inhibited by not only P1-agonists but also P2-agonists. Although the inhibition induced by P2-agonists was blocked by P1-antagonists, P2-agonists-induced inhibition was not due to the breakdown to adenosine. Therefore, there may be a new class of purinoceptor that is activated by both P1- and P2-agonists and antagonized by P1-antagonists. Electrical stimulation at 8 Hz but not at 1 Hz evoked the release of adenyl purines such as ATP, ADP, AMP and adenosine, in addition to NE; and the purines-release was blocked by an alpha1-antagonist. Methoxamine, an alpha1-agonist, also evoked the release of purines. Electrically (1 Hz)-evoked NE-release was inhibited by methoxamine, and this inhibition was blocked by not only an alpha1-antagonist but also a P1-antagonist. Therefore, the activation of alpha1-adrenoceptor appeared to release purines, which in turn inhibited NE-release via prejunctional purinoceptors. From these results, it is suggested that the unique purinoceptor and the endogenous purines released from alpha1-adrenoceptor-sensitive sources participate in the antidromic transsynaptic modulation of vascular sympathetic neurotransmission.