Angiotensin receptor(s) in fowl

Maturation of the angiotensin II cardiovascular response in the embryonic White Leghorn chicken (Gallus gallus)

Angiotensin II (Ang II) is an important regulator of cardiovascular function in adult vertebrates. Although its role in regulating the adult system has been extensively investigated, the cardiovascular response to Ang II in embryonic vertebrates is relatively unknown. We investigated the potential of Ang II as a regulator of cardiovascular function in embryonic chickens, which lack central nervous system control of cardiovascular function throughout the majority of incubation. The cardiovascular response to Ang II in embryonic chickens was investigated over the final 50% of their development. Ang II produced a dose-dependent increase in arterial pressure on each day of development studied, and the response increased in intensity as development progressed. The Ang II type-1 receptor nonspecific competitive peptide antagonist [Sar(1) ile(8)] Ang II blocked the cardiovascular response to subsequent injections of Ang II on day 21 only. The embryonic pressure response to Ang II (hypertension only) differed from that of adult chickens, in which initial hypotension is followed by hypertension. The constant level of gene expression for the Ang II receptor, in conjunction with an increasing pressure response to the peptide, suggests that two Ang II receptor subtypes are present during chicken development. Collectively, the data indicate that Ang II plays an important role in the cardiovascular development of chickens; however, its role in maintaining basal function requires further study.

Maturation-dependent changes of angiotensin receptor expression in fowl

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 (ISH)] and kidney extract (RT-PCR) are significantly (P < 0.01) higher in 19-day 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) are 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 aorta and in the adventitia, but not SM, from PL/CK aortas. 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 Nomega-nitro-l-arginine methyl ester (l-NAME, 10(-4) M), suggesting the presence of ANG receptor in endothelium. l-NAME-resistant ANG II relaxation, examined in a limited number of EB or CH aortas, 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 a tissue-specific manner; and 3) ANG II-induced relaxation may be partly attributable to nitric oxide and potassium channel activation.

Autoradiographic analysis and regulation of angiotensin receptor subtypes AT(4), AT(1), and AT((1-7)) in the kidney

Receptor autoradiography revealed that angiotensin AT(4) receptors were abundantly expressed in normal mammalian (mouse, rat, gerbil, guinea pig, rabbit) and avian (sparrow, chicken, turkey) kidneys and were more extensively distributed than previously reported (including proximal and distal segments of the nephron, interstitium, renal artery, vein, and ureter). Angiotensin AT(4) receptors were generally found to be more abundant than angiotensin AT(1) receptors in mammalian kidneys, whereas angiotensin AT((1-7)) receptors were not detected in either mammalian or avian kidneys. Rats subjected to various chronic treatments were found to preferentially decrease kidney AT(4) receptor density (furosemide, puromycin aminonucleoside, nitro-L-arginine methyl ester), decrease kidney AT(1) receptor density (bilateral ureteral obstruction), or increase kidney AT(1) receptor distribution in the inner medulla (water diuresis). These results indicate that the AT(4) receptor can be expressed in numerous cell types within the normal kidney of several species. Furthermore, several models of renal dysfunction and injury have been identified that selectively alter kidney AT(4) density and may potentially aid in elucidating the role of this novel angiotensin receptor system in renal function.