Elevation by Atrial Natriuretic Factors of Cyclic GMP Levels in Astroglia‐Rich Cultures from Murine Brain

Atrial natriuretic factors, peptide hormones originally found in the heart, slowly but strongly elevate the level of cyclic GMP in primary astrocyte-rich cultures derived from brains of newborn rats or mice but not in neuron-rich cultures prepared from embryonic rat brain. In the absence of a phosphodiesterase inhibitor, a plateau level of cyclic GMP is obtained within 10 min. In the presence of the inhibitor 3-isobutyl-1-methylxanthine, the concentration of cyclic GMP continues to rise, even after 30 min. The elevation of the level of cyclic GMP in response to atrial natriuretic factor is much more pronounced in the rat cultures than the mouse cultures. Even at peptide concentrations of 1 microM, plateaus of the concentration-response curves are not yet reached. The potencies of the active peptides vary over a range of approximately 1.5 orders of magnitude, with atriopeptins II and III and auriculin A being the most potent ones. These results suggest (a) that atrial natriuretic factors may regulate functions of glial cells, most likely of astrocytes, in brain and (b) that such cultures may be useful tools in defining such astroglial functions.