GDNF is abundant in the adult rat gut

Glial derived neurotrophic factor (GDNF) is essential for the development of the enteric nervous system (ENS). Although previous work has measured GDNF mRNA levels, little is known about the concentration of GDNF protein produced in developing or adult tissues. The aim of this study was to quantitate the concentration of GDNF protein in various tissues of the developing and adult rat and in adult human gut. A two site antibody immunoassay was used to quantitate GDNF using recombinant rat GDNF as a standard. In the adult rat gastrointestinal tract the intestine contained the highest concentration of GDNF while the stomach and esophagus have the lowest concentrations. The isolated muscular wall of the intestine has approximately four times the GDNF concentration of the intact intestine. Other tissues with smooth muscle such as the aorta and urinary bladder contain moderate GDNF concentrations. In contrast, GDNF is barely detectable in the adult kidney and liver. High concentrations of GDNF were also detected in human colon and jejunum. As development proceeds in the rat, there is a tendency for the concentration of GDNF to increase in the intestine but decrease in other tissues. Treatment of the jejunum with the cationic surfactant benzyldimethyltetradecylammonium chloride (BAC) results in an increase in the number of smooth muscle cells, a decrease in myenteric neurons, and an increase in the concentration of GDNF in homogenates of intestine. The observations that GDNF concentrations are high in the adult intestine suggest that this growth factor may be important for the maintenance of the adult ENS.