Methionine enkephalin-like, substance P-like, and beta-endorphin-like immunoreactivity in human parotid saliva

These three neuropeptides were measured at daily baseline values by radioimmunoassay. Stimulated parotid saliva was collected from 31 subjects using a modified Carlson-Crittenden device affixed over Stenson's duct. Methionine enkephalin-like immunoreactivity ranged from 6.6 to 11.7 fmol/ml, with a mean of 9.3 fmol/ml. Substance P-like immunoreactivity ranged from 6.1 to 12.6 fmol/ml, with a mean of 9.3 fmol/ml. beta-Endorphin-like immunoreactivity ranged from 1.2 to 3.6 fmol/ml, with a mean of 2.6 fmol/ml. This is believed to be the first documentation of methionine enkephalin- and substance P-like activities in human parotid saliva and the first demonstration of beta-endorphin-like activity in any type of human saliva. Substance P-like activity was significantly higher in morning than evening samples; beta-endorphin-like activity also tended to be higher in the morning samples. Substance P and beta-endorphin-like immunoreactivities covaried in a significant positive manner, suggesting either common control mechanisms or similar responses to physiological variables.