Atrial natriuretic factor: assessment of its structure in atria and regulation of its biosynthesis with volume depletion
Atrial natriuretic factor (ANF) is a polypeptide that has been isolated from mammalian atrial tissue with potent natriuretic, diuretic and spasmolytic properties. Details of its biosynthesis, cleavage, storage and release are not yet fully defined. Using sequence-specific anti-peptide antisera in immunocytochemical and radioimmunoassay studies, we demonstrated the presence in atrial granules of sequences corresponding to both the large molecular weight ("prohormone") form of ANF and the carboxyterminal peptide believed to be responsible for its biological activity. However, a peptide sequence spanning the proposed site of cleavage of the "signal peptide" from preproANF was undetected. In volume-depleted rats, a 28% decrease in the relative concentrations of atrial ANF mRNA was observed as compared to that of controls (P less than 0.01). There was, however, no significant difference observed between the two groups of animals with respect to atrial levels of ANF, as measured by radioimmunoassay. We conclude from these studies that proANF, but not preproANF, is stored in atrial granules. The concentration of stored ANF remains constant in volume-depleted rats despite a 28% reduction in ambient levels of ANF mRNA. The physiologic significance of these findings is discussed.