Dehydroepiandrosterone regulation of the hepatic glucocorticoid receptor in the zucker rat. The obesity research program

Dehydroepiandrosterone (DHEA) decreases the activity of hepatic tyrosine aminotransferase (TAT), a glucocorticoid-inducible enzyme, in the obese, hypercorticosteronemic Zucker rat. To investigate the mechanism of this antiglucocorticoid action, the effect of exogenous DHEA on hepatic glucocorticoid receptor (GC) number and affinity was quantitated. Food supplementation with DHEA (0.6% w/w) for 1 or 7 days had no effect on either receptor number or affinity in obese Zucker rats. After 28 days, however, DHEA treatment resulted in a nearly 40% decrease in cytosolic hepatic receptor content (B_max; fmol/mg cytosolic protein) without any change in affinity (K_d) in both lean and obese rats. DHEA treatment for 28 days also resulted in an increased liver size and cytosolic protein content. When the hepatic GC receptor content was normalized based on the change in liver size and protein content, the apparent number of GC binding sites per liver was not affected by DHEA treatment. This observation suggests that DHEA's effect on GC receptor content may not be a specific action and that downregulation of the GC receptor is not the mechanism of DHEA action on GC induced TAT activity. This is supported by the effect of DHEA on obese rat TAT activity in the same experiment where the greatest inhibition occurred after only 1 day of treatment. From these experiments it is concluded that although long-term DHEA treatment may decrease the relative concentration of GC receptors in rat liver, this change is not the mechanism through which DHEA mediates its acute antiglucocorticoid action.     

Factors affecting the rate of ingestion of liquids by the locust, Chortoicetes terminifera

Neither the overall rate of intake of liquids by adults of Chortoicetes terminifera, calculated over the course of a whole meal, nor the rate of consumption during the first half of meals was dependent upon the stimulating power of the liquid, water being taken at the same rate as a veriety of more powerfully stimulating sucrose solutions. Rates of intake tended to decrease towards the end of meals, the greatest decreases occurring when the locusts consumed large volumes of liquid. When locusts were given alternate drops of water and 1·0 M sucrose, the rates of consumption of the two kinds of drops were similar for most of the meal, but towards the end of the meal drops of sucrose solution were consumed more rapidly than those of water.