Central noradrenergic neurones and the cardiovascular actions of clonidine in the rabbit.
1. Clonidine (1 mug/kg), given by intracisternal injection to anaesthetized rabbits, lowered mean arterial blood pressure by 33 mmHg and heart rate by 32 beats/min.2. In animals pre-treated with 6-hydroxydopamine (6-OHD 500 mug/kg intracisternally) 7-10 days before, intracisternal clonidine (1 mug/kg) reduced mean arterial blood pressure by only 2.5 mmHg and heart rate by 4 beats/minute.3. The hypotensive action of intravenous clonidine was reduced to 49% of control by pre-treatment with intracisternal 6-OHD. In unanaesthetized normal animals intravenous clonidine (30 mug/kg) lowered mean arterial blood pressure by 19.3 mmHg, while after 6-OHD it fell only 9.4 mmHg.4. These studies suggest that the central hypotensive effect of clonidine is dependent on the integrity of central monoaminergic neurones.
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects*; D001923:Brain Chemistry; D002404:Catheterization; D003000:Clonidine / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005470:Fluorometry; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects*; D006892:Hydroxydopamines / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000502:physiology*; D009638:Norepinephrine / Q000032:analysis / Q000502:physiology*; D011817:Rabbits; D013223:Statistics as Topic; D013997:Time Factors
D006892:Hydroxydopamines; D003000:Clonidine; D001205:Ascorbic Acid; D009638:Norepinephrine