Comparison of serum and salivary ghrelin in healthy adults, morbidly obese, and patients with metastatic carcinoma.

Background: Ghrelin, a known orexigenic hormone, has been demonstrated to be produced and released by salivary glands. Obtaining saliva for metabolism studies would be preferable for patients since the procedure is non-invasive.
Methods: The present study examined serum and salivary ghrelin levels in 41 morbidly obese subjects, 45 healthy controls, and 17 patients with metastatic carcinoma by using a commercial radioimmunoassay.
Results: When comparing serum and salivary levels under fasting conditions, ghrelin levels were significantly higher in saliva for morbidly obese and healthy subjects. A significant correlation between salivary and serum ghrelin could only be demonstrated for healthy subjects. Fasting serum ghrelin concentrations in morbidly obese patients were significantly lower compared with healthy controls and cancer patients, however the levels in whole saliva did not differ significantly between all groups. There was only a highly significant inverse correlation between BMI and serum ghrelin. Serum ghrelin correlated positively with age in morbidly obese. There was no significant difference in serum and saliva ghrelin concentrations between men and women. Following the standardized meal, no significant suppression of serum ghrelin levels in morbidly obese was observed, however salivary ghrelin concentrations were significantly decreased.
Conclusions: The results of the present study support the hypothesis that there is an autonomous production of ghrelin in the salivary glands. Further research should focus on factors involved in the regulation of salivary ghrelin. Until the mechanism of regulation is fully understood, the testing of ghrelin levels in saliva is too limited to recommend a switch from serum testing.