The nucleus tractus solitarii (NTS) in the dorsomedial medulla comprises a wide range of neuropeptides and biogenic amines. Several of them are related to mechanisms of central blood pressure control. Angiotensin II (Ang II), neuropeptide Y (NPY) and noradrenaline (NA) are found in the NTS cells, as well as their receptors. Based on this observation we have evaluated the modulatory effect of these peptide receptors on <FONT FACE="Symbol">a</font>2-adrenoceptors in the NTS. Using quantitative receptor radioautography, we observed that NPY and Ang II receptors decreased the affinity of <FONT FACE="Symbol">a</font>2-adrenoceptors for their agonists in the NTS of the rat. Cardiovascular experiments agreed with the in vitro data. Coinjection of a threshold dose of Ang II or of the NPY agonists together with an ED50 dose of adrenergic agonists such as NA, adrenaline and clonidine counteracted the depressor effect produced by the <FONT FACE="Symbol">a</font>2-agonist in the NTS. The results provide evidence for the existence of an antagonistic interaction between Ang II at1 receptors and NPY receptor subtypes with the <FONT FACE="Symbol">a</font>2-adrenoceptors in the NTS. This receptor interaction may reduce the transduction over the <FONT FACE="Symbol">a</font>2-adrenoceptors which can be important in central cardiovascular regulation and in the development of hypertension
quantitative radioautography; nucleus tractus solitarii; alpha-2-adrenoceptors; neuropeptide Y receptors; angiotensin II receptors
