The Tl 2 Mn 2 O 7 pyrochlore system, pure or doped at the Tl position (Cd, Bi, Sc) or at Mn position (Sb, Te, Cr, Pb), present interesting magnetotransport properties characterized by the Colossal Magnetoresistance (CMR) effect. Our data for Tl 2 Mn 2 O 7 and Tl 1.9 Bi 0.1 Mn 2 O 7 indicate a decrease of the ordering temperature, measured from resistivity and magnetic susceptibility up to 70-90 kbars, with a clear increase of T C for higher pressures (up to 120 kbars). By contrast, in the case of Tl 2 Mn 1.8 Sb 0.2 O 7 , T C increases with pressure in the explored pressure range. A recent theory from Nuñez-Regueiro and Lacroix explains this dependence in terms of the existence of a second coupling mechanism between Mn ions, mediated by the conduction band (Tl (6s)). The doping at the Mn position (Sb) strongly increases the charge carrier density, so that this second coupling mediated by the conduction band, is strongly enhanced, in such a way that T C increases with pressure.