Localization of angiotensin-converting enzyme, angiotensin II, angiotensin II receptor subtypes, and vasopressin in the mouse hypothalamus

The hypothalamic angiotensin II (Ang II) system plays an important role in pituitary hormone release. Little is known about this system in the mouse brain. We studied the distribution of angiotensin-converting-enzyme (ACE), Ang II, Ang II receptor subtypes, and vasopressin in the hypothalamus of adult male mice. Autoradiography of binding of the ACE inhibitor ¹²⁵I]351A revealed low levels of ACE throughout the hypothalamus. Ang II- and vasopressin-immunoreactive neurons and fibers were detected in the paraventricular, accessory magnocellulary, and supraoptic nuclei, in the retrochiasmatic part of the supraoptic nucleus and in the median eminence. Autoradiography of Ang II receptors was performed using ¹²⁵I]Sar¹–Ang II binding. Ang II receptors were present in the paraventricular, suprachiasmatic, arcuate and dorsomedial nuclei, and in the median eminence. In all areas ¹²⁵I]Sar¹–Ang II binding was displaced by the AT₁ receptor antagonist losartan, indicating the presence of AT₁ receptors. In the paraventricular nucleus ¹²⁵I]Sar¹–Ang II binding was displaced by Ang II (K_i=7.6×10⁻⁹) and losartan (K_i=1.4×10⁻⁷) but also by the AT₂ receptor ligand PD 123319 (K_i=5.0×10⁻⁷). In addition, a low amount of AT₂ receptor binding was detected in the paraventricular nucleus using ¹²⁵I]CGP 42112 as radioligand, and the binding was displaced by Ang II (K_i=2.4×10⁻⁹), CGP 42112 (K_i=7.9×10⁻¹⁰), and PD 123319 (K_i=2.2×10⁻⁷). ACE, Ang II, and AT₁ as well as AT₂ receptor subtypes are present in the mouse hypothalamus. Our data are the basis for further studies on the mouse brain Ang II system.