Adrenal grafting for Parkinson's disease: a role for substance P

Parkinson's disease (PD) is a progressive neurodegenerative disorder in which the primary pathology is thought to be a loss of dopaminergic neurons in the substantia nigra (SN). The mainstay of treatment has been the use of the drug L-DOPA, a drug that crosses the blood-brain barrier and is converted to dopamine. Recently, intracerebrally implanted grafts of adrenal tissue to promote functional recovery in nigral-damaged recipient animals and patients have been successfully performed. The recovery in these cases is said to be due to the dopamine present in the grafted adrenal tissue. This explanation has several fallacies, however. It is the contention of this paper that substance P is the active agent in the grafted tissue. This raises the possibility of improving the treatment for PD by the use of grafted tissue that is a purer source of SP or SP agonists.