There was no significant difference in 24-h water intake (data not shown) among treatment groups on the pre-drug day. During the 5 treatment days there was an error in 24-h water intake determinations for day 5, so the 24-h intake analyses included only days 1–4. For these 4 treatment days there was a significant effect of dose [F(4,46) = 60.20, p < 0.001] but no significant dose × day interaction (average water intake for the vehicle-treated or 10, 20, 40, or 80 µg/kg clonidine-treated group was 35.0 ± 1.2, 32.5 ± 1.5, 38.4 ± 1.2, 50.9 ± 2.1, or 64.1 ± 2.2 mL/kg/24 h, respectively). Pairwise comparisons using the Fisher’s LSD test revealed that 24-h water intake was increased (p < 0.001) by clonidine at doses of 40 or 80 µg/kg relative to treatment with vehicle, independent of day. On post-treatment days 3 and 4, there was no significant effect of dose or day and no significant dose × day interaction (average 24-h water intake for the vehicle-treated or clonidine 10, 20, 40, or 80 µg/kg clonidine-treated group was 29.8 ± 2.7, 28.7 ± 1.6, 33.5 ± 1.6, 27.4 ± 3.6, or 35.5 ± 3.0 mL/kg/24 h, respectively).
