Treatment of
intractable pain with parenteral, subarachnoid, or epidural
narcotics is often unsatisfactory due to tolerance and other systemic complications that accompany increasing dosages of these drugs. Other disadvantages include the potential
infections with implantable pumps and the inconvenience of repeated
narcotic administration. During the past several years, studies at the author's laboratory indicated that
transplantation of adrenal medullary tissue or isolated chromaffin cells into the spinal subarachnoid space can significantly reduce
pain in several rodent models without resulting in development of tolerance. Adrenal medullary chromaffin cells were selected because they produce high levels of both
opioid peptides and
catecholamines, agents that independently, and possibly synergistically, reduce
pain when injected locally into the spinal subarachnoid space. The adrenal medullary transplants survive for prolonged periods, and continue to produce high levels of both
catecholamines and
met-enkephalin. These transplants reduce
pain in two rodent
chronic pain models, an
arthritis model and a
peripheral neuropathy model, both of which closely resemble human
chronic pain syndromes. The success of the animal studies has led to initiation of human clinical trials in patients with chronic
cancer pain; results are promising.