title: The effect of urethane on pituitary-adrenal function of female rats.
abstract: Urethane anaesthesia resulted in rapid and sustained increase in plasma corticosterone levels of adult female rats both in the (a.m.) AM and (p.m.) PM. Initial corticosterone levels of non-injected control rats showed marked AM-PM differences (i.e., 28.3 micrograms/dl and 52.6 micrograms/dl, respectively), but by 10 min post-injection, the morning corticosterone levels were increased (76.2 micrograms/dl) such that AM-PM differences were not observed. By 30 min post-injection, PM plasma corticosterone levels had increased significantly (88 micrograms/dl) but were not different from AM values for the remainder of the 2 h experiment. Saline injected controls showed the expected response to stress; plasma corticosterone levels were increased (P less than 0.01) at 10 min but were back to baseline by 45 min (9.0 micrograms/dl). Dexamethasone (100 micrograms/kg, sc) markedly suppressed both AM and PM urethane-stimulated corticosterone levels. However, diurnal differences in dexamethasone suppression were noted; whereas morning plasma corticosterone levels averaged 24.8 micrograms/dl over the five sampling times corresponding PM values averaged 54.3 micrograms/dl. Plasma corticosterone levels of non-anaesthetized, hypophysectomized ACTH-primed and injected rats were not different from those similarly treated and anaesthetized with urethane and urethane-induced increases in corticosterone were not abolished by hypothalamic isolation (HI). However, plasma corticosterone levels of HI rats were less than those of sham-operated controls (i.e., 58 micrograms/dl and 74 micrograms/dl, respectively). Collectively, these data indicate that urethane evokes a sustained increase in pituitary-adrenal activity, that the increased activity is dexamethasone sensitive and that a site of action for pituitary-adrenal activation is, at least in part, at the level of the hypothalamo-hypophyseal complex.
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000494:pharmacology; D000818:Animals; D002940:Circadian Rhythm; D003345:Corticosterone / Q000097:blood*; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D007016:Hypophysectomy; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D010913:Pituitary-Adrenal System / Q000187:drug effects*; D051381:Rats; D014520:Urethane / Q000494:pharmacology*
chemical_list: D014520:Urethane; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D003345:Corticosterone