Compounds of Formula I: ##STR1## wherein: X.sub.1, and X.sub.2 are each independently either O.sup.- or S.sup.- ;X.sub.3 and X.sub.4 are each independently either --H or --OH, with the proviso that X.sub.3 and X.sub.4 are not simultaneously --H;R.sub.1 is selected from the group consisting of O, imido, methylene and dihalomethylene;R.sub.2 is selected from the group consisting of H, halo, alkyl, substituted alkyl, alkoxyl, nitro and azido;R.sub.3 is selected from the group consisting of H, alkyl, acyl, aryl, and arylalkyl; andR.sub.4 is selected from the group consisting of --OR', --SR', --NR', and --NR'R", wherein R' and R" are independently selected from the group consisting of H, alkyl, substituted alkyl, aryl, substituted aryl, arylalkyl, alkoxyl, and aryloxyl, with the proviso that R' is absent when R.sub.4 is double bonded from an oxygen or sulfur atom to the carbon at the 4-position of the pyrimidine ring, are used in methods of hydrating lung mucus secretions and treating lung disorders such as cystic fibrosis, ventilator-associated pneumonia, chronic bronchitis, chronic obstructive pulmonary disorder and primary ciliary dyskinesia. Pharmaceutical compositions containing compounds of Formula I, and novel compounds of Formula I are also described.