Effect of agents which alter the Na transport on the sodium appetite in rats

The effect of ouabain (OUA), ethacrinic acid (EA) and diphenylhydantoin (DPH) on sodium appetite was evaluated in sodium-depleted rats. These animals were injected with either OUA (50 pg) or EA (150 ng) into the third ventricle (3V), fourth ventricle (4V), lateral ventricle (LV), or lateral hypothalamus (LH). Decreased Na appetite was observed only after injections either into the 3V or LV. DPH injection (270 ng) enhanced sodium appetite in mildly depleted rats. These effects seem to be specific for Na appetite since EA and OUA injections into the 3V did not alter food intake in food-deprived rats. The drugs did not impair gustatory inputs since the water-glucose preference was not altered after OUA, EA or DPH administration. The decrease in Na appetite induced by a 3-hour infusion of OUA (1 microliter/hr) was reversed by a 3-hour infusion of DPH (1 microliter/hr), while a pretreatment with DPH prevented the inhibitory effect of OUA. The data show that agents which inhibit cellular Na efflux such as OUA and EA decreased sodium appetite while DPH, which inhibits cellular Na influx, induced the opposite effect, i.e., enhanced Na appetite. The results are consistent with the hypothesis that the Na content of sensor cells located on or near the walls of the 3V could be the signal for the central control of Na appetite.