Uterine Steroid Hormone Receptors during the Estrous Cycle and during Hibernation in the Turkish Hamster (Mesocricetus Brandti)1

The Turkish hamster is a long-day breeder that hibernates for 4–5 mo if exposed to a short-day, cold environment. The objective of this study was to assess the uterine responsiveness of the hibernating animal to ovarian steroids. Our approach was 1) to characterize and determine uterine estrogen (E) and progesterone (P) receptors (R) during hibernation as compared to the levels observed in cycling females that had terminated hibernation, and 2) to assess the responsiveness of the uterus to E during hibernation by its ability to induce uterine P receptor. Females were exposed to short days (10L:14D) for 2 mo and then were placed in a cold-room (10L: 14D, 6 ± 1°C). After 2 or 4 mo in the cold, hibernating animals were killed and uterine steroid receptors were determined by 3H-steroid binding assay. Uterine receptors were also determined in cycling Turkish hamsters on each morning of the estrous cycle. Values for uterine receptors (pmol/g tissue, n=4–6) during the estrous cycle (estrus, diestrus I, diestrus II, proestrus) were: 4.3 ± 0.78, 3.9 ± 0.19, 4.1 ± 0.25, 3.7 ± 0.5 for cytosolic ER; 36.6 ± 5.8, 32.2 ± 6.8, 36.3 ± 1.5, 54.4 ± 1.9 for cytosolic PR; 0.59 ± 0.11, 0.54 ± 0.07, 1.06 ± 0.05, 1.42 ± 0.17 for nuclear ER. Hibernating (torpid) animals sampled after 2 mo in the cold showed a significant (p < 0.05) depression of cytosolic ER (2.6 ± 0.12, n=5) and cytosolic PR (19.0 ± 2.6, n=8) as compared to any day of the estrous cycle. Nuclear ER was low (0.55 ± 0.06, n=5) and was similar to the level observed on either estrus or diestrus I. No differences in steroid-binding specificity or sedimentation profile in linear sucrose-glycerol gradients were observed. No increase of uterine cytosolic PR was found 24 h after E treatment (5 µg/-animal, s.c.) of torpid animals, whereas a significant (p < 0.01) increase was observed in similarly treated hiberna¬ting animals on the first day of arousal from a bout of torpor. As expected, hibernating animals showed a significant regression of the uterus (102 ± 4 mg, n=16) compared to weights of 366 ± 36 on proestrus or 297 ± 18 on estrus. Toward the end of the hibernation season (4 mo in the cold), uterine weights of hibernating animals bad increased significantly (148 ± 13, n=8). At this time, both cytosolic ER (4.0 ± 0.42) and PR (33.9 ± 7.6) ap¬peared to increase as well. Despite the inability of the torpid animal to respond to E treatment, steroid stimula¬tion of the uterus during periods of arousal may occur in concert with a resumption of ovarian activity and secretion toward the end of the hibernation season. An increase in ovarian activity and uterine receptors for E and P toward the end of hibernation may ensure a coordinated return of reproductive competence with emergence from hibernation.