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 rol e in pituitary hormone release. Little is known about this system in t he 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 AC E inhibitor [I-125]351A revealed law levels of ACE throughout the hypo thalamus. Ang II- and vasopressin-immunoreactive neurons and fibers we re detected in the paraventricular, accessory magnocellulary, and supr aoptic nuclei, in the retrochiasmatic part of the supraoptic nucleus a nd in the median eminence. Autoradiography of Ang II receptors was per formed using [I-125]Sar(1)-Ang II binding. Ang II receptors were prese nt in the paraventricular, suprachiasmatic, arcuate and dorsomedial nu clei, and in the median eminence. In all areas [I-125]Sar(1)-Ang II bi nding was displaced by the AT(1) receptor antagonist losartan, indicat ing the presence of AT(1) receptors. In the paraventricular nucleus [I -125]Sar(1)-Ang II binding was displaced by Ang II (K-i = 7.6 x 10(-9) ) and losartan (K-i 1.4 x 10(-7)) but also by the AT(2) receptor ligan d PD 123319 (K-i = 5.0 x 10(-7)). In addition, a low amount of AT(2) r eceptor binding was detected in the paraventricular nucleus using [I-1 25]CGP42112 as radioligand, and the binding was displaced by Ang II (K -i = 2.4 x 10(-9)), CGP42112 (K-i = 7.9 x 10(-10)), and PD123319 (K-i = 2.2 x 10(-7)). ACE, Ang II, and AT(1) as well as AT(2) receptor subt ypes are present in the mouse hypothalamus. Our data are the basis for further studies on the mouse brain Ang II system.