Females with and without CF calculated their high– and low–E2 level days based on the onset of menses, and nasal PDs were recorded at these times. White bars represent low–E2 level days and black bars represent high–E2 level days. (A and B) Typical traces showing sequential addition of amiloride, a low Cl^– solution, and UTP on low and high days respectively. T, time. (C) Paired mean basal nasal PDs measured on low– and high–E2 level days (n = 12). (D) Paired mean changes in nasal PD in normal subjects on low- and high-level E2 days following amiloride addition and following perfusion of a low Cl^– solution and a low Cl^– solution containing 100 μM UTP added in the continued presence of amiloride to measure the UTP-activated Cl^– secretory response (n = 12). In a separate experiment, perfusion of a low Cl^– solution containing amiloride with 100 μM ISO in a subset of the subjects tested in A–C (n = 6). (E and F) Typical traces showing sequential addition of amiloride, a low Cl^– solution with 100 μM ISO, and UTP on low- and high-level E2 days, respectively, in CF subjects. (G) Paired mean basal CF nasal PDs measured on low– and high–E2 level days (n = 10). (H) Paired mean changes in nasal PD in CF patients following amiloride addition and following perfusion of a low Cl^– solution containing 100 μM ISO and a low Cl^– solution containing 100 μM UTP added in the continued presence of amiloride to measure the UTP-activated Cl^– secretory response (n = 10). *P < 0.05 difference in UTP secretion between low– and high–E2 level days. ^†P < 0.05 compared with non-CF.