Subplantar yeast injection induces a non-naloxone reversible antinociception in spontaneously hypertensive rats.
Spontaneously hypertensive (SH), Wistar Kyoto (WKY) or Sprague-Dawley (SD) rats were tested for their responsiveness to noxious mechanical pressure before and after a subplantar yeast injection to the right rear paw. Prior to the yeast injection, hypertensive animals were less responsive to pain relative to normotensive animals, as seen in the significantly greater pre-yeast latencies of SH compared to WKY or SD rats. Subplantar yeast injection produced hyperreactivity in the inflamed paws of WKY or SD rats, with no effect on the contralateral non-injected paw. However, identical subplantar yeast injections to hypertensive animals produced a robust, long-lasting antinociceptive effect in both rear paws of SH rats. This effect was not reversed by naloxone (opiate antagonist), labetalol (beta-blocker/vasodilator antihypertensive), or hydralazine (peripheral vasodilator antihypertensive); the antinociception was not potentiated by thiorphan (enkephalinase inhibitor). However, the alpha 2-receptor antagonist yohimbine (0.1-5 mg/kg s.c.), produced a dose-related reversal of the yeast-induced antinociception in SH rats. These results suggest that the subplantar yeast injection is triggering descending noradrenergic pain inhibitory pathways in SH rats.
D000818:Animals; D004723:Endorphins / Q000502:physiology; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D009270:Naloxone; D009638:Norepinephrine / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology; D015002:Yeast, Dried; D015016:Yohimbine
D004723:Endorphins; D015016:Yohimbine; D009270:Naloxone; D009638:Norepinephrine