Acute footshock stress and decreases in serum total and high-density lipoprotein cholesterol in male and female rats
Coco, Michael L.
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The effects of acute stress on serum total and high-density lipoprotein cholesterol (total- and HDL-C) were studied in male and female rats. The results of the two experiments suggest that, although rats fed high fat diets may show increased blood cholesterol levels in response to chronic stress, acute stress lowers the levels in male and female rats on regular stock diet. In the first experiment, male and female rats, aged about 160 days and maintained on standard lab chow, were stressed by jugular blood sampling (ether anesthesia, jugular venipuncture, 1.5 ml blood withdrawn) and either a 20-min or 120-min session of footshock beginning 15 min later (2-sec footshocks every 60 sec at a moderate intensity). A second jugular blood sample was taken following the footshock session, and for rats in the 20-min condition a third sample was taken 3 hr 40 min after the session. Serum total-C levels were significantly reduced from baseline by the end of the 20-min or 120-min footshock session in both male and female rats. For the 20-min condition, total-C levels 3-hr 40-min post-session did not differ from the values obtained immediately following the session. Serum HDL-C levels were similarly depressed in males (21%) and females (32%) following the 120-min session. However, HDL-C levels were not down at the end of the 20-min session, although females (but not males) did show a 45% decline from baseline by 3 hr 40 min following the 20-min session of footshock. In the second experiment, male and female rats (n's = 14) were randomly divided into pairs. Each pair consisted of a yoked-control and a same-sex experimental rat. The pairs were trained and 9 days later tested in an apparatus designed in another laboratory to engender a doubleavoidance conflict in the experimental rat. The test session was 120 min long and resulted in the rats being footshocked approximately the same amount of time as rats in the 120-min condition in Experiment 1. Both male and female rats showed significant drops in serum total-C and HDL-C at the end of the session, comparable to those seen with the 120-min session in Experiment 1. Levels in experimental and yoked-control rats did not differ. Possible explanations for the failure of the doubleavoidance conflict to result in additional depressions are discussed.