In vivo interactions between prejunctional alpha 2- and beta 2-adrenoceptors at the level of the adrenal medulla.
The combined effect of a beta 2-antagonist and an alpha 2-agonist on the release of adrenal catecholamines was studied in the anaesthetized and vagotomized dog. The electrical stimulation of the splanchnic nerve (5-V pulses of 2 ms duration for 3 min at a frequency of 3 Hz) produced a significant rise in adrenal catecholamine release in the adrenal vein. Intravenous injection of a beta 2-antagonist significantly reduced this response and a subsequent injection of an alpha 2-agonist further reduced the release of catecholamines. However, if the alpha 2-agonist is injected first, the release is not different compared with the control stimulation, and the subsequent injection of the beta 2-antagonist also did not modify the release in response to electrical stimulation. These results suggest that the blockade of presynaptic beta 2-receptors reduces the release of adrenal catecholamines without interfering with the activation of the alpha 2-adrenoceptors. In contrast, the pretreatment with the alpha 2-agonist, which does not modify the release of catecholamine at 3 Hz, seems to interfere with the inhibitory effect of the beta 2-antagonist.
Foucart
S
S
Départment de physiologie, Faculté de médecine, Université de Montréal, Québec, Canada.
de Champlain
J
J
Nadeau
R
R
D000313:Adrenal Medulla / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure; D004285:Dogs; D004558:Electric Stimulation; D004837:Epinephrine / Q000097:blood / Q000378:metabolism*; D006339:Heart Rate; D007093:Imidazoles / Q000494:pharmacology*; D009638:Norepinephrine / Q000097:blood / Q000378:metabolism*; D010109:Oxymetazoline / Q000494:pharmacology*; D011412:Propanolamines / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D012016:Reference Values; D013153:Splanchnic Nerves / Q000502:physiology*; D014628:Vagotomy
D000319:Adrenergic beta-Antagonists; D007093:Imidazoles; D011412:Propanolamines; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; C026777:ICI 118551; D010109:Oxymetazoline; D009638:Norepinephrine; D004837:Epinephrine