EFFECTS OF ORCHIECTOMY AND HORMONE REPLACEMENT ON RAT HEPATIC HEXOSE-MONOPHOSPHATE PATHWAY ENZYMES

This study was designed to determine if the attenuated starvation-refe ed (SRF) over shoot response of hepatic G6PDH and 6PGDH observed in ad ult female rats is due to the presence of high levels of estrogen or l ower levels of testosterone in the female. Male rats were castrated as weanlings, then allowed to reach adulthood before initiation of the r emainder of the study. Ten days prior to the dietary study, when the r ats were 9 weeks old, they began to receive daily injections of one of the following preparations: carrier only, 17-beta-estradiol or testos terone propionate. Next, the rats were starved for 2 days and refed ei ther a nonpurified diet or a purified 65% carbohydrate diet (sucrose, fructose, glucose or cornstarch) for 3 days. Castration suppressed the magnitude of the SRF overshoot response by 40% compared to that obser ved in intact males. Testosterone injections did not restore the SRF r esponse. In fact, the enzyme activities of testosterone-injected, cast rated rats were indistinguishable from those of castrated, carrier-inj ected controls. Estrogen injections doubled basal G6PDH and 6PGDH acti vities, but decreased the SRF overshoot response by 60% compared to ca strated carrier injected rats. These results suggest that estrogen pro motes higher basal enzyme activities and suppresses the magnitude of t he SRF overshoot response in adult female rats.