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! i I I I I I I I i I I I I I I I I AUTHOR: SEPKOVIC, DANIEL W., MILTON V. MARSHALL, WALTER R. ROGERS, PATRICIA A. CRONIN, STEPHEN G. COLOSIMO, AND NANCY J. HALEY DATE; 1988 TITLE: THYROID HORMONE LEVELS AND CIGARETTE SMOKING IN BABOONS CITATION: PROCEEDINGS OF THE SOCIETY FOR EXPERIMENTAL BIOLOGY AND MEDICINE 187, 223-228 (1988) STUDY DESIGN= Two studies were undertaken to examine the effects of cigarette smoking on thyroid hormone levels. In study 1, mean total triiodothyronine (total T3) and mean total thyroxine (total T,) levels were measured in two groups of baboons who were taught to smoke cigarettes using operant conditioning techniques. The smokers were divided into established and na'(ve smokers according to pack-years of exposure. A control group of never-smoker baboon was included for comparison. Blood sampling was done after long term cigarette consumption and again 1 week after cigarette deprivation. In study 2, the same groups of baboons were divided into good and poor smokers by plasma'cotinine and blood carboxyhemoglobin (% COHb) levels during 28 weeks of cigarette smoking activity. Other indices of thyroid functions were assessed in this study. After examining T3 and T4 levels, the animals were deprived of cigarettes for 1 week and blood samples were obtained every other day during this period. RNDINGS/RESULTS: In study 1, in the na'~'ve smoker group, mean total T3 concentrations were reduced below control group, this reduction was significant. After cigarette deprivation for 1 week, mean total T3 values returned to normal. No significant differences in total T4 levels were observed in either group. In the second study, immediate fluctuations and reductions in total T3 levels were observed that were not accompanied by reductions in total T,~. After being deprived of cigarettes for one week, significant increases in total T3 concentrations were observed in poor smokers immediately after cessation. Both groups also exhibited significant reductions in T~ uptake and free T,~ index (FT41) when compared to control group values. CONCLUSIONS: The data suggest that poor smokers are more susceptible to thyroid hormone level shifts than more established smokers, since the established smokers become habituated to the compounds contained in cigarette smoke through repeated exposure.