An angiotensin (Ang) receptor homologous to the type 1 receptor (AT₁) has been cloned in chickens (cAT₁). We investigated whether cAT₁ expression in various tissues shows maturation/age-dependent changes. cAT₁ mRNA levels detected in renal glomeruli (in situ hybridization) and kidney extract (RT-PCR) are significantly (P < 0.01) higher in 19-d embryos (EB) than in chicks (CH, 2-3 wk) and pullets/cockerels (PL/CK, 14-16 wk). The levels in adrenal glands (concentrated in subcapsular regions) is high in EB and further increased in CH and PL/CK. cAT₁ mRNA is also detectable in smooth muscle (SM)/adventitia of EB and CH aortae, and in the adventitia, but not SM, from PL/CL aortae. The endothelia from small arteries and arterioles, but not from aorta, express cAT₁ mRNA (ISH). In all age groups, Ang II induces profound endothelium-dependent relaxation of abdominal aorta, partly (37-47%) inhibitable (P < 0.01) by N-nitro arginine methyl ester (L-NAME, 10^-4 M), suggesting the presence of Ang receptor in aortic endothelium. L-NAME-resistant Ang II relaxation, examined in a limited number of EB or CH aortae, was reduced by 125 mM K⁺ or apamin plus charybdotoxin. The results suggest that: 1) cAT₁ is present in kidney, adrenal gland, and vascular endothelium (heterogeneity exists among arteries) of EB, CH, and PL/CK, and in aortic SM/adventitia of EB/CH but only in adventitia of PL/CK, 2) levels of cAT₁ gene expression change during maturation in tissue-specific manner, and 3) Ang II-induced relaxation may be partly attributable to nitric oxide and potassium channel activation.