SEX AND DEPOT-SPECIFIC STIMULATION OF CREATINE-KINASE-B IN RAT ADIPOSE TISSUES BY GONADAL-STEROIDS

We report a sex- and depot-specific response of rat adipose tissues to gonadal steroids. The epididymal fat pad in male rats responded to an drogens (testosterone and dihydrotestosterone; DHT), but not to 17 bet a-estradiol (E-2), by increased specific activity of the brain type is ozyme of creatine kinase (CK). In female rats, the parametrial fat las well as the fat surrounding the spleen responded to E-2 but not to di hydrotestosterone. In both sexes, subcutaneous fat from the inguinal, abdominal or thigh region did not respond to any sex steroid. The para metrial fat showed increasing responsiveness to E-2 during postnatal d evelopment, in parallel to the response of the uterus. In cycling fema le rats, parametrial fat showed the highest basal activity of CK at es trus; stimulation by E-2 was achieved on all the other days of the cyc le. Both phytoestrogens and diethylstilbestrol stimulated CK activity in both parametrial and spleen fat, in parallel to their estrogenic po tencies; parametrial fat also responded to progesterone. The stimulati on of CK activity in parametrial fat by E-2 was completely blocked by actinomycin D or cycloheximide. Treatment with the antiestrogen, tamox ifen, caused moderate stimulation of CK activity in parametrial fat as well as partial inhibition of E-2 stimulation of CK activity; the ''p ure'' antiestrogen ICI 164,384 had no agonistic effect and completely blocked the E-2 effect. Ovariectomy caused an increased response to E- 2 without changes in the basal CK activity, but did not lead to any re sponse to DHT. As well as being a reliable response marker, the differ ential modulation of CK activity can thus serve to distinguish adipose cells from different sources. (C) 1997 Elsevier Science Ltd.