The rate of loss of eyelid reflex following thiopental administration in hypo- and hypergonadism in rabbits.

ABSTRACT

BACKGROUND: The aim of this research was to explain whether different hormonal conditions caused by disturbed concentrations of estrogens and progesterone might lead to alteration of CNS reaction following administration of the hypnotic agent thiopental. The investigated factor was the rate of loss of the eyelid reflex after intravenous thiopental administration, since this corresponds with loss of consciousness. MATERIAL/METHODS: The investigation was performed in 24 sexually mature female Chinchilla 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-hydroxyprogesterone injections), or normal (sham surgery). Twelve weeks later, thiopental (40 mg/ml) was infused through the intravenous cannula at a constant rate (90 ml/hour) until loss of the eyelid reflex, at which time blood was sampled for determination of thiopental, b-estradiol, progesterone and 17 alpha-hydroxyprogesterone concentrations. The ANOVA and Tukey tests were applied in statistical analysis (p=0.05). RESULTS: Hyperprogesterone rabbits 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; hypoprogesterone rabbits 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 sleep induction 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 no effect. 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 barbiturate infusion.