TEMPORAL SYNERGISM OF CORTICOSTERONE AND PROLACTIN IN THE SYRIAN-HAMSTER, MESOCRICETUS-AURATUS

To augment the limited work reported in the literature regarding testi ng of the hormonal temporal synergism hypothesis in Syrian hamsters (J oseph MM, Meier AH. Proc Soc Exp Biol Med. 1974;146:1150-5), a large e xperiment with female hamsters was conducted. Forty-eight received cor ticosterone at 18:00 h on January 21, 23, 25, 27, and 29 and ovine pro lactin at one of six times of day beginning January 22 for 8 days; 36 received saline (at 18:00) and prolactin at one of the six times of da y for 8 days; 35 received only prolactin at one of the six times of da y for 8 days; and 16 received no injections. Twelve hamsters receiving corticosterone and prolactin and eight uninjected hamsters were on ru nning wheels. The corticosterone and prolactin group not on wheels had a body weight gain and no circadian rhythm of weight gain, but did ha ve circadian rhythms of response in organ weight, per 100 g of body we ight, and in weights of fat pads and uteri. The corticosterone and pro lactin group with access to running wheels gained in body weight and h ad larger ovaries and smaller fat pads. Hamsters receiving saline and prolactin had a body weight gain, but had no circadian rhythms of resp onse in organ weights. The hamsters receiving only prolactin gained in body weight but had no rhythms of response, except for unexpected cir cadian rhythms in body weight gain and weights of fat pads. The uninje cted hamsters had a modest weight gain. Most or all hamsters with acce ss to running wheels free-ran, and the corticosterone injections did n ot appear to synchronize the locomotor activity rhythms. In conclusion , corticosterone does interact with the injection time effect of prola ctin on weights of fat pads, paired ovaries, and uteri. The mechanism of that effect, in terms of circadian rhythm theory, is unclear.