ANGIOTENSIN-II RECEPTOR SUBTYPES AND ANGIOTENSIN-CONVERTING ENZYME INTHE FETAL-RAT BRAIN

Angiotensin II (ANG II) receptor subtypes (AT(1), displaced by losarta n, and AT(2), displaced by CGP 42112A) were characterized by quantitat ive autoradiography after incubation with the ANG II agonist [I-125]Sa r(1)-ANG II, in specific brain nuclei of 19-day-old rat embryos. Bindi ng to AT(1) receptors, located in the subfornical organ, paraventricul ar nucleus, nucleus of the solitary tract and choroid plexus, was sens itive to incubation with GTP gamma S. The sensitivity of AT(2) recepto rs to GTP gamma S was heterogeneous. In the ventral thalamic, rostral hypoglossal and medial geniculate nuclei, and in the locus coeruleus, binding to AT(2) receptors was sensitive to GTP gamma S and these area s belong to the AT(2A) subgroup. Conversely, in the inferior olive, me dial (fastigial) cerebellar nucleus and caudal part of the hypoglossal nucleus, areas belonging to the AT(2B) subgroup, binding was insensit ive to GTP gamma S. AT(2) receptors were also present in cerebral arte ries. In the fetal anterior pituitary, AT(1) receptors predominated. T he angiotensin-converting enzyme (ACE; EC 3.4.15.1) was studied by aut oradiography with the selective inhibitor [I-125]351A. In I9-day-old e mbryos, ACE was highly expressed in choroid plexus, with high concentr ations in subfornical organ, posterior pituitary and cerebral arteries . No ACE binding was detected in extrapyramidal structures or anterior pituitary in 19-day-old embryos.