Another controller system for arterial pressure. AngII-vasopressin neural network of the parvocellular paraventricular nucleus may regulate arterial pressure during hypotension

In the parvocellular part of paraventricular nucleus, glutamatergic and GABAergic neurons mediate cardiovascular responses to AngII

Angiotensinergic, GABAergic, and glutamatergic neurons are present in the parvocellular region of the paraventricular nucleus (PVNp). It has been shown that microinjection of AngII into the PVNp increases arterial pressure (AP) and heart rate (HR). The presence of synapses between the angiotensinergic, GABAergic, and glutamatergic neurons has been shown in the PVNp. In this study, we investigated the possible interaction between these three systems of the PVNp for control of AP and HR. All drugs were bilaterally (100 nl/side) microinjected into the PVNp of urethane-anesthetized rats, and AP and HR were recorded continuously. Microinjection of AngII into the PVNp produced pressor and tachycardia responses. Pretreatment of PVNp with AP5 or CNQX, glutamatergic NMDA and AMPA receptors antagonists, attenuated the responses to AngII. Pretreatment of PVNp with bicuculline greatly attenuated the pressor and tachycardia responses to AngII. In conclusion, this study provides the first evidence that pressor and tachycardia responses to microinjection of AngII into the PVNp are partly mediated by both NMDA and non-NMDA receptors of glutamate. Activation of glutamatergic neurons by AngII stimulates the sympathoexcitatory neurons. We also showed that the responses to AngII were strongly mediated by GABA_A receptors, probably through activation of GABAergic neurons, which in turn inhibit sympathoinhibitory neurons.

Hypothalamic paraventricular nucleus augments baroreflex sensitivity, role of angiotensin II

The hypothalamic paraventricular nucleus (PVN) is an important brain region involved in control of the cardiovascular system. Direct injection of angiotensin II (AngII) into the PVN produces a short or long pressor response. This study was performed in anesthetized rats to find whether the parvocellular part of the paraventricular nucleus (PVNp) affects the baroreflex. And if so, what is the effect of AngII injected into the PVNp on the baroreflex? Drugs were microinjected into the PVNp while blood pressure and heart rate were recorded continuously. We found that microinjection of AT1 and AT2 receptor antagonists into the PVNp region did not affect the baseline mean arterial pressure (MAP) and heart rate (HR) indicating that under normal conditions AngII may not provide tonic activity, at least in anaesthetized animals. Bilateral microinjections of a synaptic blocker (CoCl₂) into the PVNp attenuated the baroreflex gains in responses to loading and unloading of baroreceptors, indicating that PVNp is involved in the baroreflex rate component. Microinjection of AngII into the PVNp increased MAP and HR. However, AngII slightly attenuated the baroreflex rate component using its two receptors AT1 and AT2. Collectively, these findings suggest that the PVNp as a whole is involved in the baroreflex. But AngII attenuates the heart rate response of the baroreflex through AT1 and AT2 receptors.

Cross-Talk between CB1, AT1, AT2 and Mas Receptors Responsible for Blood Pressure Control in the Paraventricular Nucleus of Hypothalamus in Conscious Spontaneously Hypertensive Rats and Their Normotensive Controls

We have previously shown that in urethane-anaesthetized rats, intravenous injection of the angiotensin II (Ang II) AT1 receptor antagonist losartan reversed the pressor effect of the cannabinoid CB1 receptor agonist CP55940 given in the paraventricular nucleus of hypothalamus (PVN). The aim of our study was to determine the potential interactions in the PVN between CB1 receptors and AT1 and AT2 receptors for Ang II and Mas receptors for Ang 1–7 in blood pressure regulation in conscious spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats. The pressor effects of Ang II, Ang 1–7 and CP55940 microinjected into the PVN were stronger in SHRs than in WKYs. Increases in blood pressure in response to Ang II were strongly inhibited by antagonists of AT1 (losartan), AT2 (PD123319) and CB1 (AM251) receptors, to Ang 1–7 by a Mas antagonist (A-779) and AM251 and to CP55940 by losartan, PD123319 and A-779. Higher (AT1 and CB1) and lower (AT2 and Mas) receptor expression in the PVN of SHR compared to WKY may partially explain the above differences. In conclusion, blood pressure control in the PVN depends on the mutual interaction of CB1, AT1, AT2 and Mas receptors in conscious spontaneously hypertensive rats and their normotensive controls.