What treatment is there for cats in pain when in heat?

My cat very definitely has pain when she is in heat. Similar to female cramps. It is not just a horniness reaction like I have read elsewhere. She keeps her abdomen close to the ground and will allow a gentle rubbing of the upper area where her ovaries are if she isn't in too much pain. We have had cats in the past who have not had these symptoms I can only assume is is similar to other females, some who get cramps that hurt and others who never seem phased by their cycles.