Involvement of adrenergic and angiotensinergic receptors in the paraventricular nucleus in the angiotensin II-induced vasopressin release.
The role of hypothalamic paraventricular adrenoceptors and angiotensin II (ANG II)-AT 1 receptors in mediating the vasopressin (AVP) release into the plasma in response to i.c.v. and local paraventricular ANG II injections was investigated in conscious chronically instrumented rats. Noradrenaline (NA) administered bilaterally into the paraventricular nucleus (PVN) dose-dependently stimulated AVP release. Bilateral PVN microinjections of the alpha 1 adrenoceptor agonists methoxamine and phenylephrine, or of the alpha2 adrenoceptor agonist clonidine, did not affect plasma AVP when given alone, but increased plasma AVP when methoxamine and clonidine were given in combination. In contrast, PVN microinjections of both the beta 1 adrenoceptor agonist dobutamine and the beta 2 adrenoceptor agonist salbutamol significantly reduced basal plasma AVP. Bilateral PVN pretreatment with the alpha 1 and alpha 2 adrenergic antagonists prazosin, idazoxan and rauwolscine, but not of the beta 1 and beta 2 adrenoceptor antagonists atenolol and ICI 118 551, significantly attenuated the i.c.v. ANG II-induced AVP release. ANG II injected bilaterally into the PVN dose-dependently increased plasma AVP. Bilateral PVN pretreatment with the specific ANG II-AT 1 receptor antagonist losartan partially inhibited the i.c.v. ANG II-induced AVP release. We conclude: 1) Beta 1 and beta 2 adrenoceptors in the PVN exert an inhibitory action on basal AVP secretion. 2) ANG II can release AVP by directly stimulating its ANG II-AT 1 receptors in the PVN. 3) PVN mediated AVP release in response to periventricular ANG II-AT 1 receptor stimulation is at least partially effected through ANG II-AT 1 receptors in the PVN impinging on alpha adrenergic terminals.
Veltmar
A
A
Department of Pharmacology, University of Heidelberg, Germany.
Culman
J
J
Qadri
F
F
Rascher
W
W
Unger
T
T
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism*; D004146:Dioxanes / Q000494:pharmacology; D019329:Idazoxan; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects*; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000187:drug effects* / Q000502:physiology; D011945:Receptors, Angiotensin / Q000187:drug effects* / Q000502:physiology
D004146:Dioxanes; D011941:Receptors, Adrenergic; D011945:Receptors, Angiotensin; D000804:Angiotensin II; D001127:Arginine Vasopressin; D009638:Norepinephrine; D011224:Prazosin; D019329:Idazoxan