Seasonal variation in platelet [H-3]paroxetine binding in healthy volunteers - Relationship to climatic variables

Recently, our laboratory has reported significant seasonal differences in [H-3]paroxetine binding to platelets in depressed subjects. This study aimed to examine the seasonal variation in [H-3]paroxetine binding to platelets and the relationships between [H-3]paroxetine binding and climatic variables in healthy volunteers. We took monthly blood samples during one calendar year from 26 healthy volunteers for assay of [H-3]paroxetine binding and analyzed the data by means of univariate and multivariate spectral and cosinor analyses. There was a statistically highly significant seasonal pattern in [3H]paroxetine binding to platelets with significant annual, 4-monthly and bimonthly rhythms, which were expressed as a group phenomenon. [H-3]paroxetine binding to platelets was significantly lower in fall and summer than in winter and spring; lows occurred in summer and peaks in spring. The peak-trough difference in this yearly variation, expressed as a percentage of the mean, was as large as 83.7%. A large part of the variance, that is, 32.5%, in [H-3]paroxetine binding could be explained by weather variables, such as ambient temperature, relative humidity and air pressure. Highly significant common annual rhythms were expressed in [H-3]paroxetine binding and ambient temperature or humidity (both inversely related) and changes in temperature the 2 weeks preceding blood samplings (positively related).