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 ( approximately 10(-9) M) consistent with a role for ANF as a hypothalamic-pituitary regulator or modulator.