Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.
(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)
Effects of pregnancy and ovarian steroids on energy balance in Syrian hamsters
Abstract
In ovariectomized rats and Syrian hamsters, progesterone + estradiol treatment mimics the effect of pregnancy on energy balance. However, rats fatten, whereas hamsters lose body fat. Given this difference and paucity of information on the contribution of ovarian steroids to alterations in energy balance during pregnancy in laboratory species other than rats, I investigated the effects of pregnancy or progesterone and estradiol treatments (administered via subcutaneous implants) on fat metabolism (lipogenesis and fatty acid uptake) and energy expenditure (running wheel activity and nestbuilding activity) in Syrian hamsters. Fatty acid synthesis/uptake (incorporation of tritium into lipid from ($\sp3$H) $\sb2$O) was reduced in heart, liver, and white adipose tissue of late, but not early, pregnant hamsters. In ovariectomized hamsters, treatment with estradiol or progesterone alone was without effect, while treatment with both steroids decreased fatty acid synthesis/uptake in liver and white adipose tissue. When hamsters were pretreated with Triton WR-1339, which inhibits fatty acid uptake, but not synthesis, progesterone + estradiol treatment suppressed newly synthesized fatty acid levels in liver, not in white adipose tissue, suggesting that hamsters decrease adiposity during pregnancy partially from progesterone + estradiol suppression of hepatic lipogenesis. Pregnant hamsters did not reduce running wheel activity until late gestation, concomitant with substantial increases in conceptus weight. Consistent with this finding, estradiol or progesterone + estradiol treatments did not affect activity levels of ovariectomized hamsters, but ovariectomy also did not have a significant effect on running wheel activity. Running wheel activity varied with estrous cycle day, being increased across the nights prior to and during the time of estrus. Hamsters increased nestbuilding activity under conditions of chronically elevated estradiol or progesterone levels (late gestation, estradiol alone or with progesterone treatments) and increased energy demand (late gestation and cold exposure). Nestbuilding activity was not affected by lactation (characterized by low ovarian steroid levels and high energy demand) or estrous cycle day. In total, these results suggest that pregnant Syrian hamsters decrease adiposity partially from ovarian steroid effects on lipogenesis, but accompanying changes in running wheel activity and nestbuilding activity may be concerted responses to altered ovarian steroid levels, ovarian steroid metabolic effects, and the increased energy expenditure of late gestation.
Subject Area
Psychobiology|Physiological psychology
Recommended Citation
Bhatia, Anita J, "Effects of pregnancy and ovarian steroids on energy balance in Syrian hamsters" (1992). Doctoral Dissertations Available from Proquest. AAI9305802.
https://scholarworks.umass.edu/dissertations/AAI9305802