Intake of dilute sweet solutions is influenced by stage of the rat's estrous cycle: Evidence for a shift in palatability.

Abstract

In female rats, endogenous and exogenous estradiol decrease intake of dilute sucrose solutions (e.g., 0.025 M), but fail to alter intake of concentrated sucrose solutions (e.g., 0.1 M) during brief (10-s) intake tests. Because the post-ingestive consequences of sucrose intake were negligible under these conditions, these data suggest that estradiol decreases the palatability of dilute sucrose solutions. The present study was conducted to better characterize this phenomenon and to determine whether it extends to other sweet solutions. Using a within-subjects design, female rats were first given access to sucrose (0.0125, 0.025, 0.05, and 0.1 M) and then saccharin (1.25, 2.5, 5.0, and 10 mM) solutions during daily intake tests conducted during diestrus (following low endogenous estradiol) and estrus (following high endogenous estradiol). The solutions were presented in an ascending concentration series. Intakes were measured after 5, 15, 30 and 60 min. Relative to diestrous rats, estrous rats consumed less 0.0125 M sucrose at each time point and less of all saccharin concentrations at 30 and 60 min. In contrast, intake of the more concentrated sucrose solutions was not influenced by stage of the estrous cycle. Thus, estradiol appears to selectively decrease intake of dilute sweet solutions. It is unlikely that this effect is secondary to estradiol's inhibitory effect on caloric intake, since diestrous and estrous rats consumed similar volumes of more concentrated sucrose solutions and intake of all concentrations of non-caloric saccharin was suppressed during estrus. A decrease in the palatability of these dilute sweet solutions appears to underlie this action of endogenous estradiol. Support: MH-63932 and DC-00044-10.