The effect of ovarian steroids and photoperiod on body fat stores and uncoupling protein 2 in the marsupial Sminthopsis crassicaudata

To determine the effects of photoperiod and ovarian steroids on fat stores in the marsupial S. crassicaudata, animals were ovariectomised (OVX) or sha m operated, and maintained under either short-day (SD) or long-day (LD) pho toperiods for 104 days. Photoperiod had no effect on body weight in the sha m animals. In the LD OVX animals, body weight fell and remained below basel ine for about 45 days, whereafter it returned to baseline. In contrast, bod y weight of SD OVX animals increased over the first 45 days then returned t o baseline. Tail width (a reflection of body fat stores) increased in both sham and OVX animals exposed to SD. When exposed to LD, tail width increase d only in the OVX animals. There was no effect of either photoperiod or OVX on total cumulative energy intake. Leptin mRNA expression was increased in the LD OVX animals compared to the shams. Photoperiod had no effect on UCP 2 mRNA expression in any tissue; however, OVX decreased UCP2 mRNA expressio n in muscle. These data indicate that in S, crassicaudata: (a) fat mass inc reases in response to both SD photoperiod and OVX and they have additive ef fects; (b) the effects of photoperiod on fat mass are mediated by both gona dal steroid dependent and independent mechanisms: (c) alterations in UCP2 m RNA expression may mediate the effect of OVX, but not photoperiod; and (d) UCP2 mRNA is differentially regulated in muscle and fat. (C) 2000 Elsevier Science Inc. All rights reserved.