  The threshold electrodisintegration of the deuteron at backward angles is
studied with a relativistic Hamiltonian, including a relativistic
one-pion-exchange potential (OPEP) with off-shell terms as predicted by
pseudovector coupling of pions to nucleons. The bound and scattering states are
obtained in the center-of-mass frame, and then boosted from it to the Breit
frame, where the evaluation of the relevant matrix elements of the
electromagnetic current operator is carried out. The latter includes, in
addition to one-body, also two-body terms due to pion exchange, as obtained,
consistently with the OPEP, in pseudovector pion-nucleon coupling theory. The
full Lorentz structure of these currents is retained. In order to estimate the
magnitude of the relativistic effects we perform, for comparison, the
calculation with a non-relativistic phase-equivalent Hamiltonian and the
standard non-relativistic expressions for the one-body and two-body
pion-exchange currents. Our results for the electrodisintegration cross section
show that, in the calculations using one-body currents, relativistic
corrections become significant ({\it i.e.}, larger than 10%) only at high
momentum transfer $Q$ ($Q^2 \simeq 40$fm$^{-2}$ and beyond). However, the
inclusion of two-body currents makes the relativistic predictions considerably
smaller than the corresponding non-relativistic results in the $Q^2$ region
(18--40) fm$^{-2}$. The calculations based on the relativistic model also
confirm the inadequacy, already established in a non-relativistic context, of
the present electromagnetic current model to reproduce accurately the
experimental data at intermediate values of momentum transfers.
