Further evidence for a hypothalamic site of action of atrial natriuretic factor: inhibition of prolactin secretion in the conscious rat

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Abstract
The presence of atrial natriuretic factor (ANF) in the hypothalamus and pituitary gland suggests a possible neuroendocrine action of the peptide. Because ANF has been shown to alter the activity of hypothalamic neurons and to interact with brain dopamine systems, we examined the possibility that it might be involved in the hypothalamic control of prolactin (PRL) and thyroid-stimulating hormone (TSH) secretion. Neither basal not stimulated release of PRL or TSH from cultured dispersed anterior pituitary cells was altered by doses of ANF ranging from 10-11 to 10-6 M. Similarly, the in vitro inhibition of PRL release by dopamine was not affected by the presence of ANF (10-7 M). Plasma levels of PRL and TSH in conscious male rats infused for 30 min with 0.01 or 0.1 .mu.g ANF .cntdot. kg-1 .cntdot. min-1 did not differ significantly from those present in saline infused controls. Third-cerebroventricular injection of saline (2 .mu.L) or saline plus (0.02, 0.1, 1.0, or 2.0 nmol) did not significantly alter TSH secretion; however, injection of the two highest doses of ANF resulted in significant inhibition of PRL release. Levels of PRL remained significantly reduced for 90 min after injection of 2 nmol ANF. The results indicate that ANF can act centrally to alter the release of neural factors responsible for the hypothalamic control of lactotroph function.