The processing and secretion of atrial natriuretic peptide (ANP) from neurons and the expression of high-affinity receptors on astroglia from primary cultures of fetal rat diencephalon have recently been demonstrated. Thus natriuretic peptides may play a role in neuronal-glial signaling, but a physiological role has not been characterized. In these studies, we show that ANP and brain natriuretic peptide significantly (P less than 0.05) decrease the incorporation of [3H]thymidine into astroglia in the presence of fetal bovine serum and inhibit the proliferation of these cells in the presence or absence of serum. These effects were evident at concentrations of natriuretic peptides (10(-10) M) characteristic of the receptor Kd and were not seen in cultured bovine brain capillary endothelial cells, another brain cell expressing high-affinity receptors for the natriuretic peptides. The antiproliferative effects were potently produced by ANP-(4-23), a ring-deleted analogue of ANP-(1-28), which at the concentrations used in this study binds only to the C or low-molecular-weight natriuretic peptide receptor. Thymidine incorporation was not affected by adenosine 3',5'-cyclic monophosphate (cAMP), the inhibition of which has been proposed to mediate postbinding signaling of the C receptor. Epidermal growth factor (10(-9) M) produced an 87% increase in thymidine incorporation, which was not significantly inhibited by either form of ANP. Thus natriuretic peptides in the brain may serve as antigrowth factors for glia through binding to a receptor previously felt to function solely in peptide clearance. The inhibitory effects are not the result of inhibiting the proliferative effects of an endogenous growth factor and are cAMP independent.