Bioactive atrial natriuretic factor-like peptides in rat anterior pituitary

The presence of biologically active atrial natriuretic factor (ANF)-like peptides was demonstrated in rat anterior pituitary. ANF-like immunoreactivity was detected in rat anterior pituitary by specific radioimmunoassay and was extracted from rat anterior pituitary homogenates by heat-activated Vycor glass beads; extracts were purified by reverse-phase high performance liquid chromatography. Two peaks containing ANF immunoreactive material were obtained. The first peak was eluted from the C18 mu Bondapak column at a position similar to the 28-amino acid carboxy terminal peptide (Ser99-Tyr126)-ANF of prohormone. The second peak had the same pattern of elution as the 126-amino acid prohormone, (Asn1-Tyr126)-ANF. The biological activity of the smaller molecular weight peptide (28 amino acid) was assessed by its inhibitory effect on 10(-8) M ACTH-stimulated aldosterone secretion in rat zona glomerulosa cell suspension. This ANF-like material also displaced I125-labelled ANF from rat glomerular receptors with a potency similar to synthetic (Arg101-Tyr126)-ANF. Immunocytochemical localization revealed a distribution of ANF-stained cells similar in pattern and location to that of gonadotrophs. These results suggest the existence of biologically active ANF-like peptides and ANF prohormone within the anterior pituitary. However, their role remains to be elucidated.