  We report on a relation between the decay constants of \rho-like
J^{PC}=1^{--} vector mesons, which arises solely from the perturbative analysis
of the VV, TT and VT correlators at order \alpha_s^0 in the large-N_c limit. We
find f_{V}^T/f_{V}=1/\sqrt{2} for highly excited states together with a pattern
of alternation in sign. Quite remarkably, recent lattice determinations
reported f_{\rho}^T/f_{\rho}=0.72(2), in excellent agreement with our large-N_c
result. This seems to suggest a pattern like f_{Vn}^T/f_{Vn}=(-1)^n/\sqrt{2}
for the whole (1^{--}) states. In order to test this conjecture in real QCD we
construct a set of spectral sum rules, which turn out to comply nicely with
this scenario.
