Organ culture of rat kidney: A model for angiotensin II receptor ontogenic studies

Abstract

Angiotensin II (Ang II) exerts multiple renal effects on blood flow, glomerular filtration, tubular reabsorption of electrolytes, and renin secretion [1–4]. It also has growth factor properties in several cell culture models where it stimulates cell growth, expression of growth factors and proto-oncogenes [5–10]. The selective Ang II-receptor competitors Dup 753 and PD 123177 have been used to distinguish receptor subtypes in diverse tissues. Dup 753 inhibits binding to the AT1 receptor, the subtype mediating all biologically known actions of Ang II, whereas PD 123177 inhibits binding to the AT2 receptor, mainly expressed in fetal tissues and whose role is still unclear [11]. This pharmacological classification has been validated by the cloning of AT1 and AT2 cDNA. In the kidney of adult primate and rat, autoradiographic binding studies have shown that AT1 receptors are markedly predominant and mostly expressed in glomeruli, proximal tubules, inner stripe of the outer medulla and vasa recta bundles [12, 13], whereas the AT2 subtype is abundant and widely distributed in fetal kidneys [14–16]. In the rat, only a small proportion of glomeruli is functional at birth and nephrogenesis is not totally completed until about 10 days of age [17, 18]. The post-natal developmental period is characterized by a progressive increase in AT1 and a dramatic decrease in AT2 receptors [19]. The mechanisms that induce the disappearance of AT2 and the appearance of AT1 during development are unknown. We have analyzed the changes in Ang II receptor subtype expression in an in vitro system of nephrogenesis. We showed an early expression and rapid increase of AT1 receptors both at the protein and mRNA levels, suggesting that this model could be appropriate to probe the effects of candidate factors on the AT2-to-AT1 shift.