Immunocytochemical localization of proANF 1-30, proANF 31-67 and atrial natriuretic factor in the kidney

ProANF [1-30 first 30 amino acids (a.a) of the 126 a.a atrial natriuretic factor (ANF) prohormone], ProANF 31-67 (a.a 31-67) as well as atrial natriuretic factor (a.a 99-126), of the ANF prohormone localized to the sub-brush border of the pars convoluta and pars rectus of the proximal tubules of hydrated and dehydrated rat kidneys with immunoperoxidase staining. Immunofluorescent studies revealed that each of these peptides and especially ProANF 31-67 had a strong predilection for the perinuclear region in the proximal and distal tubules. ProANFs 1-30, 31-67, and 99-126 (that is, ANF) also localized with both immunoperoxidase and immunofluorescent staining to the cortical collecting ducts, glomeruli, peritubular, and interstitial blood vessels. ProANF 31-67 immunoperoxidase staining was particularly striking in the elastica of the small and large interstitial arteries. The whole prohormone being present was suggested by immunological recognition in the rat kidney of both the N-terminus and C-terminus of the ANF prohormone by radioimmunoassays. The concentration of the N-terminus in the kidney was 1.0 +/- 0.03 ng/g of kidney weight, while the C-terminus of the ANF prohormone concentration was 0.4 +/- 0.01 ng/g of kidney tissue. These findings of a sub-brush border and perinuclear location of the N-terminal and C-terminal ANF prohormone peptides suggest that the atrial natriuretic factor prohormone may be synthesized in and/or the respective peptides are captured by the proximal tubules, but also to a lesser extent by the distal tubules of the kidney.