D1 receptors mediate dopamine stimulation of immunoreactive atrial natriuretic factor (ANF) release and pro-ANF messenger ribonucleic acid expression of rat hypothalamic neurons in culture.

Atrial natriuretic factor (ANF) and its smaller congeners are produced and released from rat brains to regulate the cardiovascular system, drinking behavior, and neurohormone release at the central level. In the hypothalamus, the adenylyl cyclase-cAMP system plays an important role in modulating the function of ANF neurons in the paraventricular nuclei and the periventricular regions that receive rich dopaminergic inputs. We report here a novel observation of a dopamine (DA) D1 agonist, SKF-38393, modulating immunoreactive (ir) ANF and pro-ANF messenger RNA (mRNA) expression in rat hypothalamic neurons. In long term primary cultures of neonatal rat hypothalamic cells, treatment with SKF-38393 increased irANF secretion in a time-related and dose-dependent manner, with an ED50 of approximately 10(-7) M and a concentration producing maximum effect of 10(-5) M. This stimulating effect of SKF-38393 was mimicked by 10(-5) M DA, a physiological ligand for D1 receptors. Furthermore, both of the stimulatory effects were abolished by SCH-23390, a D1 antagonist. These immunoassay findings were accompanied by corresponding changes in the abundance of pro-ANF mRNA in the cultures, as examined by colorimetric Northern blot analysis. By combining the techniques of in situ hybridization and immunocytochemistry, the mRNA of D1 receptor was colocalized in approximately 90% of the irANF-positive cells in the cultures. In addition, cholera toxin, an irreversible activator of adenylyl cyclases, markedly increased irANF secretion and cAMP production in a dose-dependent manner. This effect mimicked that of D1 agonist-stimulated ANF release, in that the latter also concurrently enhanced cAMP production in the hypothalamic cultures. Furthermore, the stimulatory effect of D1 agonist on irANF release was markedly suppressed by rp-cAMPS, a cAMP antagonist. We, thus, conclude that the release and gene expression of ANF in rat hypothalamic neurons are directly stimulated by DA acting through its D1 receptors on ANF neurons; this effect may operate at the genomic level and is mediated at least in part through activation of the cAMP-dependent kinase-A pathway.