ONTOGENY OF THE 2 ANGIOTENSIN-II TYPE-1 RECEPTOR SUBTYPES IN RATS

The two subtypes (AT(1A) and AT(1B)) Of the type 1 (AT(1)) angiotensin II receptor mRNA were localized by in situ hybridization in rat fetal tissues from day 11 to 19 of gestation and in the young rat from day 0 to 10 postpartum, by use of S-35-labeled cRNA probes. Both subtype mRNAs were present in the kidney and in the adrenal gland. Organs such as liver, lung, heart, and undifferentiated mesenchymes expressed only AT(1A) mRNA. In contrast to the adult, only AT(1A) subtype was expressed during fetal and postnatal periods in the pituitary gland. Large blood vessels (e.g., aorta and cerebral arteries) expressed exclusively AT(1A) mRNA during fetal stages. The expression of each subtype appears to be differentially regulated, in a tissue- and age-specific way. This spatiotemporal regulation of AT(1A) and AT(1B) expression suggests that angiotensin II could act as a differentiation factor during organogenesis in addition to its classical role as a regulator of the cardiovascular system.