Ontogeny of the two angiotensin II type 1 receptor subtypes in rats.

The two subtypes (AT1A and AT1B) of the type 1 (AT1) 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 35S-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 AT1A mRNA. In contrast to the adult, only AT1A subtype was expressed during fetal and postnatal periods in the pituitary gland. Large blood vessels (e.g., aorta and cerebral arteries) expressed exclusively AT1A mRNA during fetal stages. The expression of each subtype appears to be differentially regulated, in a tissue- and age-specific way. This spatotemporal regulation of AT1A and AT1B 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.