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Antagonistic Oxytocin/α 2 ‐Adrenoreceptor Interactions in the Nucleus Tractus Solitarii: Relevance for Central Cardiovascular Control

2000; Wiley; Volume: 12; Issue: 12 Linguagem: Inglês

10.1046/j.1365-2826.2000.00571.x

1365-2826

Zaida Dı x az-Cabiale, José Ángel Narváez, Rosario Garrido, Maria Petersson, Kerstin Uvnäs‐Moberg, Kjell Fuxé,

Receptor Mechanisms and Signaling

Abstract The modulation of the central cardiovascular effects of α 2 ‐adrenoceptor activation by oxytocin in the nucleus tractus solitarii has been evaluated by cardiovascular analysis and by quantitative receptor autoradiography. Microinjections in the nucleus tractus solitarii of a threshold dose of oxytocin effectively and significantly counteracted the vasodepressor and bradycardic actions of an ED50 dose of the α 2 −adrenoceptor agonist clonidine. The coinjection of a threshold dose of oxytocin with a threshold dose of clonidine did not produce any changes in the mean arterial pressure but a tachycardic response was observed. Receptor autoradiographical experiments showed that oxytocin (3 n M ) significantly increased the K d and B max values of [ 3 H] p ‐aminoclonidine binding sites in the nucleus tractus solitarii compatible with a possible antagonistic interaction with the α 2 ‐adrenoceptors, and this effect was blocked by the presence of the specific oxytocin receptor antagonist 1‐deamino‐2‐D‐Tyr‐(OEt)‐4‐Thr‐8‐Orn‐oxytocin. These findings suggest the existence of an antagonistic oxytocin/α 2 ‐adrenoceptor interaction in nucleus tractus solitarii that may be of relevance for the demonstrated modulation of α 2 −adrenoceptor induced cardiovascular responses by oxytocin.