Atrial Natriuretic Factor is Released into Hypophysial Portal Blood: Direct Evidence that Atrial Natriuretic Factor may be a Neurohormone Involved in Hypothalamic Pituitary Control

Atrial natriuretic factor (ANF) is produced in atriomyocytes (1, 2), released as a 28 amino‐acid peptide into the systemic circulation and probably plays an important role in fluid and electrolyte balance (3, 4). The facts that immunoreactive ANF (ir‐ANF) is also present in nerve terminals in the external layer of the median eminence (ME) (5), ir‐ANF can be released from the hypothalamus in vitro by potassium depolarization (6) and specific ANF binding sites are present at a high concentration in rat pituitary tissue (7) suggest that ANF may be involved in hypothalamic‐pituitary regulation. We report here that ir‐ANF concentrations in hypophysial portal blood are about two to four times greater than in peripheral plasma from hypophysectomized as well as pituitary‐intact adult female rats. These results show for the first time that ir‐ANF is secreted from the hypothalamus into the hypophysial portal circulation at a concentration (≈10⁻⁹ M) consistent with a role for ANF as a hypothalamic‐pituitary regulator or modulator.