Quantitation of secretory responsiveness in albino TH null mice. The number of active glands was determined by counting the pores formed in the two interdigital footpads of albino mice that were wild-type at the TH locus (+/+), heterozygous for the TH mutation (+/−) or TH null (−/−) at the ages indicated. At P15 and P18, fewer glands were active in the TH+/− mice than in wild-type mice. At all ages, fewer than one active gland on average was detected in the TH null mice. Four albino TH null pups were injected twice daily with 75 mg/kg l-DOPA dissolved in saline solution containing 0.25% ascorbic acid as an antioxidant. When secretory responsiveness was assayed in the DOPA-treated albino TH null mice at P21, 15 glands on average were active. Error bars represent SEM. ANOVA and post hoc pairwise comparisons with Sheffe's F test (α= 0.05 for all tests) indicated significant differences among all three genotypes at P15 and P18 and between TH null and TH wild-type, heterozygote mice at P21. Secretory responsiveness in the DOPA-treated TH null mice was significantly different from that in all three untreated groups at P21 (data not shown). Significant differences are indicated as ●, between +/+ and +/−; ∧, between +/+ and −/−; ∗, between +/− and −/−.