Release of Atrial Natriuretic Factor from Intact and Hypophysectomized Rat Hypothalamic Expiants

Experiments examined release of atrial natriuretic factor (ANF), measured by radioimmunoassay, from acutely prepared explants of rat hypothalamus maintained in vitro by intra-arterial perfusion of artificial cerebrospinal fluid. Perfusates collected from intact preparations contained 6.1 +/- 0.6 pg (mean +/- SEM) of ANF per 2-min sample. Following a 3-min infusion of noradrenaline (60 muM), ANF release increased significantly (P<0.05) to 11.4+/-1.4 pg/sample. Media collected from hypophysectomized preparations showed the same basal ANF release (6.8 +/- 0.9 pg/sample) as intact preparations, but demonstrated no significant increase after noradrenaline infusions. Levels of spontaneous ANF release were not appreciably affected by the absence of the paraventricular nuclei and/or the anteroventral third ventricle area. Extracted material from the perfusate by reverse-phase high performance liquid chromatography revealed two main peaks of immunoreactive ANF: a small molecular weight form that coeluted with synthetic ANF (99-126) and with similar biological activity in a radioreceptor assay, and a larger molecular weight form with the same elution profile as the ANF (1-126) prohormone. These observations indicate that the ANF released from perfused rat hypothalamic explants contains distinct contributions from the hypothalamus (sites undetermined) and the neurointermediate lobe.