Quantitative receptor radioautography in the study of receptor-receptor interactions in the nucleus tractus solitarii

RESUMO

The nucleus tractus solitarii (NTS) in the dorsomedial medulla comprises a wide range of neuropeptides and biogenic amines. Several of them are related to mechanism 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 alpha2-adrenoceptors in the NTS. Using quantitative recptor radioautography, we observed that NPY and Ang II receptors decreased the affinity of alpha1-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 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 alpha2-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 alpha2-adrenoceptors in the NTS. This receptor interaction may reduce the transduction over the alpha2-adrenoceptors which can be important in central cardiovascular regulation and in the development of hypertension.