Influences of gender and region on responses to 5-HT in the rat small intestine.

The aim of this study was to obtain more information regarding the 'atypical' 5-HT7 receptor of the rat jejunum. 5-HT7-induced contractions of the jejunum were elicited by 5-HT in the presence of ondansetron. Maximal responses were slightly larger in tissues from male compared to female rats of comparable age, with Emax values of 97.2 +/- 3.3 and 84.25 +/- 4.3% respectively compared to acetylcholine as an internal standard. However, the pEC50 values for 5-HT were not significantly different. The mRNA expression levels of the 5-HT7 receptor were similar in whole jejunum and longitudinal muscle tissues taken from males and females. It was also shown that the maximal response of the jejunum from male rats was larger than the responses from mid intestine and ileum. However, in female tissues, the Emax of the mid intestine was significantly larger than the ileum, but not different from the jejunum. The results provide further insights into the 'atypical' 5-HT7 receptor of the rat jejunum and are also useful in optimising the preparation for further studies. Copyright (c) 2004 S. Karger AG, Basel.