Enhancing effect of temperature on the transmucosal penetration kinetics of 17 beta-estradiol

Human vaginal mucosa may be used as a model of buccal mucosa for in vitro permeability studies using various chemical compounds. Rectilinear temperature dependence of water flux across vaginal mucosa between 25 degrees C and 41 degrees C has been shown. The objective of this study was to examine the behaviour of the above barrier on fluxes of 17 beta-estradiol at various temperatures. Frozen vaginal mucosa specimens from a single patient were used (snap-frozen in liquid nitrogen and stored at -85 degrees C). The permeability to tritiated 17 beta-estradiol was determined using a continous flow-through perfusion system at temperatures of 20 degrees C, 25 degrees C, 30 degrees C, 37 degrees C and 41 degrees C. Histological examinations were performed before and after permeability experiments. Estimated steady state flux values were used at 20 degrees C, 25 degrees C and 30 degrees C. Estimated and true mean 17 beta-estradiol steady state flux rates (20-24 h) were found to be 415 +/- 27 standard error of the Mean (SEM), 848 +/- 60 SEM, 1355 +/- 77 SEM, 1436 +/- 37 SEM and 1482 +/- 35 SEM cpm.cm-2.min-1, at temperatures of 20 degrees C, 25 degrees C, 30 degrees C, 37 degrees C and 41 degrees C, respectively. A non-linear regression analysis and plot (R2 = 0.9941) displayed a curvilinear flux-temperature relationship. The results from this study showed that, notwithstanding cellular damage, the principal physical permeability barrier governing permeation kinetics was non-linearly temperature-dependent between the temperatures studied, providing further support for the concept that this barrier is lipoidal in nature.