Angiotensin II receptor subtypes and angiotensin-converting enzyme in the fetal rat brain

Abstract

Angiotensin II (ANG II) receptor subtypes (AT 1, displaced by losartan, and AT 2, displaced by CGP 42112A) were characterized by quantitative autoraography after incubation with the ANG II agonist [ 125I]Sar 1-ANG II, in specific brain nuclei of 19-day-old rat embryos. Binding to AT 1 receptors, located in the subfornical organ, paraventricular nucleus, nucleus of the solitary tract and choroid plexus, was sensitive to incubation with GTPγS. The sensitivity of AT 2 receptors to GTPγS 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 GTPγS and these areas belong to the AT 2A subgroup. Conversely, in the inferior olive, medial (fastigial) cerebellar nucleus and caudal part of the hypoglossal nucleus, areas belonging to the AT 2B subgroup, binding was insensitive to GTPγS. AT 2 receptors were also present in cerebral arteries. In the fetal anterior pituitary, AT 1 receptors predominated. The angiotensin-converting enzyme (ACE; EC 3.4.15.1) was studied by autoradiography with the selective inhibitor [ 125I]351A. In 19-day-old embryos, ACE was highly expressed in chroid plexus, with high concentrations in subfornical organ, posterior pituitary and cerebral arteries. No ACE binding was detected in extrapyramidal structures or anterior pituitary in 19-day-old embryos.