Angiotensin II and angiotensin (1-7) excite neurons in the canine medulla in vitro

Our group showed previously that the heptapeptide angiotensin (1-7) [Ang-(1-7)] is a bioactive product of the renin-angiotensin system, and produces dose-dependent cardiovascular effects similar to those evoked by Ang II when microinjected into the nucleus tractus solitarii (nTS) of the rat. The effects of Ang II were compared with those of Ang-(1-7) on single neuron activity recorded from the medial nTS or dorsal motor nucleus of the vagus (dmnX) in perifused horizontal slices of the canine dorsomedial medulla. Ang II excited 48% of 31 medial nTS neurons, but only activated 14% of 22 dmnX cells. Ang-(1-7) also excited half of the medial nTS cells and 14% of the dmnXl neurons. Although most medial nTS neurons excited by Ang II were also activated by Ang-(1-7), two cells were excited by Ang II but not by Ang-(1-7), and one cell was excited by Ang-(1-7) but not by Ang II. Because Ang-(1-7) lacks direct vasoconstrictor effects, neurons in the dorsomedial medulla may have different receptor characteristics than peripheral tissues. The observation of a few medial nTS neurons excited by only one Ang peptide suggests that there may be a separate Ang-(1-7) receptor that participates in the physiological effects of Ang peptides mediated by the brain.