Plasma hyperosmolality increases G protein and 3',5'-cyclic adenosine monophosphate synthesis in the paraventricular...

Hyperosmotic stimuli produce profound changes in cellular morphology and biosynthetic activities within the hypothalamic paraventricular and supraoptic nuclei (SON) of the rat. The mechanisms by which osmoreceptive signals are transduced within these nuclei are poorly understood. We examined several components of the cAMP-associated second messenger system after giving rats 2% saline to drink for one week, a strong hyperosmotic stimulus. We found that mRNA levels for both the stimulatory and inhibitory guanine-nucleotide binding protein alpha-subunits were increased in the paraventricular nucleus and SON. In the SON, these changes were accompanied by increased basal cAMP levels, cholera toxin-stimulated adenylate cyclase, and Gs alpha. Our results suggest that Gs alpha levels are not saturated with respect to adenylate cyclase coupling and that osmoreception activates the cAMP second messenger system.