Reduction in postsynaptic alpha 2-adrenoceptor activity by endogenous angiotensin III in the nucleus reticularis gigantocellularis of the rat.
We investigated in adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium the synaptic location of the interaction between endogenous angiotensin III (AIII) and the alpha 2-adrenoceptors in the medulla oblongata that are involved in cardiovascular regulation. The circulatory suppressant efficacy of a centrally acting alpha 2-adrenoceptor agonist, guanabenz, was used as the experimental index. Direct bilateral microinjection of AIII (40 pmol) into the nucleus reticularis gigantocellularis (NRGC), a medullary site believed to be intimately related to the cardiovascular inhibitory actions of guanabenz, attenuated, whereas the selective AIII receptor antagonist, Ile7-AIII (20 nmol), potentiated, the circulatory suppressant effects of guanabenz (100 micrograms/kg, i.v.). These two respective actions were essentially unaffected by immunocytochemically verified depletion of noradrenergic nerve terminals in the NRGC, elicited by a selective noradrenergic neurotoxin, DSP4. These data suggest that endogenous AIII may exert a tonic inhibitory action on the alpha 2-adrenoceptors located postsynaptically on neurons in the NRGC that are involved in central cardiovascular regulation.
Chan
J Y
JY
Department of Medical Research, Veterans General Hospital-Taipei, Taiwan, Republic of China.
Lee
H C
HC
Chan
S H
SH
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000805:Angiotensin III / Q000502:physiology*; D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D003864:Depression, Chemical; D006143:Guanabenz / Q000494:pharmacology; D006439:Hemodynamics / Q000187:drug effects; D007150:Immunohistochemistry; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D008845:Microinjections; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D013566:Sympathomimetics / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D001596:Benzylamines; D013566:Sympathomimetics; D000805:Angiotensin III; D006143:Guanabenz; C012102:DSP 4; D009638:Norepinephrine