Meeting Abstract

P2.16  Tuesday, Jan. 5  Local steroid levels in brain: effect of saline perfusion and comparison with plasma versus whole blood levels TAVES, MD*; SCHMIDT, KL; RUHR, IM; KAPUSTA, K; SOMA, KK; Univ of British Columbia taves@zoology.ubc.ca

The brain and other organs locally synthesize steroids, and such local synthesis is suggested when steroid levels are higher in tissue than blood. Plasma steroid levels are considered to be representative of blood levels, but plasma and blood concentrations may not be the same. Additionally, blood contamination in tissues may affect measurement of tissue steroid levels. To avoid this problem, saline perfusion may be used to remove blood. Here, in Study 1, we measured corticosterone in zebra finch (Taeniopygia guttata) plasma, whole blood, and red blood cells (RBC) at baseline and after 60 min restraint stress. In Study 2, we quantified corticosterone, dehydroepiandrosterone (DHEA), testosterone (T), and 17β-estradiol (E₂) in the brain of saline- or sham-perfused animals. In Study 1, corticosterone concentrations were highest in plasma, intermediate in whole blood, and lowest in RBC. Corticosterone levels in all 3 sample types were higher at 60 min than at baseline, with a greater increase in plasma than whole blood or RBC. In Study 2, saline perfusion unexpectedly increased corticosterone levels in rostral telencephalon but had no effect on corticosterone levels in caudal telencephalon, diencephalon, or cerebellum. In contrast, saline perfusion decreased DHEA levels in caudal telencephalon and diencephalon but not in rostral telencephalon or cerebellum. Saline perfusion did not affect T levels in caudal telencephalon but increased E₂ levels in caudal telencephalon. Thus, using plasma samples can overestimate circulating steroid levels in blood, and this can impair detection of high local steroid levels in tissue. In addition, blood contamination has little effect on measurement of brain steroid levels, and saline perfusion to remove blood might have its own effects on neural steroid synthesis.