  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.
