Meeting Abstract
Glucocorticoid (GC) hormones play important roles during pregnancy. They induce steps in fetal development, modulate energetic tradeoffs, and provide a signal to the fetus of the quality of the environment it will enter, adaptively altering its physiology. GCs circulate either bound to the carrier protein corticosteroid-binding globulin or unbound and biologically active (“free”). In many mammals, including humans and laboratory rodents, free GCs increase during pregnancy. However, this does not reflect the potential diversity in GC changes during pregnancy across Mammalia. We found that arctic ground squirrel (Urocitellus parryii) females emerge from hibernation with very high levels of free cortisol (51% unbound) but this is reduced markedly during pregnancy and lactation (5% and 10% unbound) due to an increase in corticosteroid-binding globulin. Total cortisol levels remained consistent across emergence and reproduction. We postulate that the high free cortisol just prior to visible pregnancy is related to the physiological changes or mobilization of body reserves involved in transitioning from hibernation to pregnancy. Thereafter, increased corticosteroid-binding globulin may shield the developing offspring from the negative effects of cortisol overexposure. These findings reveal a novel pattern in GC changes during pregnancy and underscore the importance of measuring corticosteroid-binding globulin levels in addition to total hormone concentrations.
