The effective chiral Lagrangian of the strong and electromagnetic
interactions of the pseudoscalar mesons at low energies depends on a
set of low energy constants. We determine the contributions to the
electromagnetic coupling constants at order $O(e^2 p^2)$, which arise
from resonances within a photon loop. We give some implications of our
results, in particular we discuss in detail the effects on the
corrections to Dashen's theorem.