Male Holtzman rats with stainless steel cannula implanted into lateral ventricle and anaesthetized with urethane + ¦Á-chloralose were used.
Pilocarpine (500 nmol/1 ¦Ìl) injected i.c.v. Reduced SSG vascular resistance and increased arterial pressure, heart rate and mesenteric vascular resistance. Contrary to pilocarpine alone, the combination of moxonidine (20 nmol/1 ¦Ìl) and pilocarpine injected i.c.v. Increased SSG vascular resistance, an effect abolished by the pre-treatment with the ¦Á2-adrenoceptor antagonist yohimbine (320 nmol/2 ¦Ìl). The increase in arterial pressure, heart rate and mesenteric resistance was not modified by the combination of moxonidine and pilocarpine i.c.v.
These results suggest that the activation of central ¦Á2-adrenoceptors may oppose to the effects of central cholinergic receptor activation in the SSG vascular resistance.