CELLULAR AND ULTRASTRUCTURAL LOCATION OF ANGIOTENSINOGEN IN RAT AND SHEEP KIDNEY

Cellular and ultrastructural location of angiotensinogen in rat and sh eep kidney. Recent evidence suggests the involvement of a local renin- angiotensin system in some renal actions of angiotensin II (Ang II). I n this study the renal distribution of the precursor to angiotensin fo rmation, angiotensinogen, was investigated in rats and sheep using imm unohistochemistry, immunoelectron microscopy and non-isotopic hybridiz ation histochemistry. Immunostaining for angiotensinogen was seen in p roximal tubules (PCT) of both rat and sheep kidneys. In the rat the st rongest immunostaining was found in the kidneys of neonatal (1 day old ) rats. Staining declined after birth. Non-isotopic hybridization hist ochemistry using oligodeoxynucleotide probes labeled with biotin confi rmed the presence of angiotensinogen mRNA expression in PCT of the rat renal cortex. Electron microscopic immunohistochemistry using antibod ies raised against rat angiotensinogen showed weak staining in the adu lt of granule-like structures close to the apical membrane of PCT cell s. In the neonatal rat kidney, angiotensinogen immunostaining was foun d throughout the PCT cells and was markedly stronger than that seen in adult rat kidney. In sheep, angiotensinogen immunostaining with an an tibody raised against purified ovine angiotensinogen showed staining o f PCT in fetal, newborn and adult sheep kidney. The strongest immunost aining seen was in fetal sheep kidney with a decline seen after birth. Reverse transcription polymerase chain reaction (RT-PCR) showed that angiotensinogen mRNA was expressed in the sheep kidney at all ages stu died. Angiotensinogen expression was higher in fetal sheep kidneys (77 day and 141 day gestation) than in adult sheep kidney. In conclusion, angiotensinogen mRNA expression was detected in both rat and sheep ki dneys. Immunostaining showed angiotensinogen protein in PCT cells of t he renal cortex. Angiotensinogen staining and mRNA expression is highe st during development and declines in the adult.