Bacterial Flora, a Possible Source of Serotonin in the Intestine of Adult Female Ascaris suum

Abstract

The effect of intestinal bacteria on 5-hydroxytryptamine (5-HT, serotonin) level and 5-HT turnover rates in Ascaris suum intestine are presented. Ascaris suum were incubated in media containing antibiotics for 24 hr, and the bacterial flora in the anterior regions of the intestine of A. suum was eliminated. The bacteria were significantly reduced (> 99%) but not eliminated in the middle and posterior segments of the worm. The 5-HT level decreased in the intestine after 24 hr incubation in antibiotics, whereas the 5-HT turnover rate increased (131 ng/mg protein/hr). Two possible sources of 5-HT from the intestine were examined: the intestinal tissue itself and the microflora inhabiting the intestine. The 5-HT level in the microflora was 30% higher (72.6 ng/g) than the intestinal tissue (43.3 ng/g) in control samples (0 hr, no antibiotics). These values decreased significantly after 24 hr incubation in A. suum saline. The 5-HT values decreased to 18.6 ng/g in the presence and 28.6 ng/g in the absence of antibiotics. The 5-HT turnover rate during this time period indicated that as the number of bacteria declined, the 5-HT turnover rate also declined in the microflora, but the 5-HT turnover rate in the intestinal tissues increased. Results from these studies suggest that bacterial 5-HT may be contributing to the 5-HT level in A. suum intestinal tissue.