I definitely think that the tolerance of pain can be trained and even manipualted to bring pleasure to the receiver. Just think of the whole 'Pavlov's dogs' experiment. The dogs were trained to be fed after hearing the ring of a bell. After time, the dogs drooled simply upon hearing the sound of the bell as they knew that a meal would soon follow. Why wouldn't converting pain into pleasure work in the same way? If you inflict pain upon your partner and follow it with an act that you know will bring on a wave of pleasure for her, then over time, she ought to associate pain with pleasure and actually get off on the pain because of the anticipation of the pleasure to come...i think, hehe.