Time- and concentration-related effects of lindane on uterine contraction force (A) and frequency (B). Uterine strips were exposed to lindane (1, 10 or 100 μM) as described in Figure 1. The average peak force of contraction and the average frequency of contraction were calculated relative to basal (pretreatment) values, as described in Methods, over 30-min intervals of a 1-h exposure. Changes in contraction force and frequency were analyzed by separate repeated measures analysis of variance (ANOVA) for concentration, exposure duration, and interaction effects, with repeated measures on exposure duration. Lindane decreased uterine contraction frequency and force in concentration-dependent and time-dependent manners, with a significant interaction between concentration and exposure duration (ANOVA, p ≤ 0.001). Vertical bars with different letters have means that are significantly different from each other in pairwise comparisons (Student-Newman-Keuls, p ≤ 0.05). Values shown are mean ± SEM of 7 uterine strips. Error bars not visible are too small to be displayed graphically.