BACKGROUND: The aim of this research was to explain whether different hormonalconditions caused by disturbed concentrations of estrogens and progesterone might lead to alterationof CNS reaction following administration of the hypnotic agent thiopental. The investigated factor wasthe rate of loss of the eyelid reflex after intravenous thiopental administration, since this correspondswith loss of consciousness. MATERIAL/METHODS: The investigation was performed in 24 sexually mature femaleChinchilla rabbits divided into 4 groups of 6 rabbits each. The animals were oophorectomized (hypoprogesterone/hypoestrogen),hyperestrogen (sham surgery plus estradiol injections), hyperprogesterone (sham surgery plus 17 alpha-hydroxyprogesteroneinjections), or normal (sham surgery). Twelve weeks later, thiopental (40 mg/ml) was infused throughthe intravenous cannula at a constant rate (90 ml/hour) until loss of the eyelid reflex, at which timeblood was sampled for determination of thiopental, b-estradiol, progesterone and 17 alpha-hydroxyprogesteroneconcentrations. The ANOVA and Tukey tests were applied in statistical analysis (p=0.05). RESULTS: Hyperprogesteronerabbits lost consciousness faster (138 +/- 34.6 sec), at a lower plasma thiopental concentration (46.3+/- 6.6 microg/ml), and required less thiopental (24.63 +/- 6.44 mg/kg) than controls; hypoprogesteronerabbits lost consciousness slower (207.5 +/- 30.9 sec), at a higher plasma thiopental concentration (129.2+/- 24.9 microg/ml), and required more thiopental (38.51 +/- 2.33 mg/kg) than controls. The time of sleepinduction in the control group was 190 +/- 25.7 sec.; the serum thiopental concentration was 77.8 +/-13.9 microg/ml, and the total thiopental consumption was 35.8 +/- 3.51 mg/kg. Estrogen status has noeffect. CONCLUSIONS: Various hormonal states are accompanied by different CNS reactions to thiopental.Among the studied groups of sex steroids, only progestins significantly modify the CNS response to barbiturateinfusion.

Keywords: 17-alpha-Hydroxyprogesterone, Anesthetics, Intravenous, Central Nervous System, Eyelids, Gonadal Disorders, Hypogonadism, Progestins, Reflex, Thiopental, Time Factors