Estradiol phase-shifts circannual rhythms of golden-mantled ground squirrels.
Ovariectomized golden-mantled ground squirrels (Spermophilus lateralis) were implanted with estradiol benzoate (EB)-filled or empty capsules. Body weight was monitored for at least 1 yr before, during, and after hormone treatment. EB treatment of 6-7 mo duration, restricted to the weight-gain phase, decelerated weight gain and delayed attainment of peak weight by 34 days; the period of the circannual rhythm, measured between successive trough weights, was 36 days longer in squirrels treated with estradiol than in untreated animals. EB treatment of 2- to 4-mo duration, restricted to the weight-loss phase, accelerated weight loss, advanced attainment of trough weights by 57 days, and decreased the period of the circannual rhythm by 66 days. Estradiol-induced phase delays and advances were preserved in the year after discontinuation of hormone treatment. These results favor the existence of circannual phase-response curves to hormones and provide a system for pharmacological manipulation of circannual rhythms.
Lee
T M
TM
Department of Psychology, University of California, Berkeley 94720.
Zucker
I
I
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D010507:Periodicity; D012589:Sciuridae
D004958:Estradiol