Thyroidal ANF: a possible mediator of autocrine regulation in the porcine thyroid gland

Atrial natriuretic factor immunoreactivity (ir-ANF) was examined in thyroid tissue sections and cultured thyroid cells using immunohistochemical staining with a monoclonal anti-ANF antibody. Localization of ir-ANF in perinuclear granules in cultured cells and in the basal region of follicular cells in sectioned tissue suggests that ir-ANF is a basally secreted product. Thyroidal ir-ANF was also characterized using reversed phase high performance liquid chromatography (RP-HPLC) of acidic thyroid extracts. An ir-ANF peak coeluting with synthetic rat ANF(99-126) suggests that thyroidal ir-ANF may be identical in form to circulating atrial ANF. However, the detection of ir-ANF in cultured thyroid cells confirms that the immunoreactivity is locally produced. Saturation analysis revealed high affinity ANF receptors (Kd = 0.1 nM; MBC = 17.2 fmol/mg protein) on these cultured cells, and a competition study demonstrated the ability of extracted thyroidal ir-ANF to inhibit 125I rat ANF binding to the membrane receptors. The evidence presented here suggests that ir-ANF in the thyroid may be secreted locally to exert an autocrine effect on neighboring follicular cells.