  We observe a property of orthogonality of the Mellin-Barnes transformation of
the triangle one-loop diagrams, which follows from our previous papers [JHEP
{\bf 0808} (2008) 106, JHEP {\bf 1003} (2010) 051, JMP {\bf 51} (2010) 052304].
In those papers it has been established that Usyukina-Davydychev functions are
invariant with respect to Fourier transformation. This has been proved at the
level of graphs and also via the Mellin-Barnes transformation. We partially
apply to one-loop massless scalar diagram the same trick in which the
Mellin-Barnes transformation was involved and obtain the property of
orthogonality of the corresponding MB transforms under integration over
contours in two complex planes with certain weight. This property is valid in
an arbitrary number of dimensions.
