Iberis amara L. desensitizes low-threshold mechano-sensitive afferents of the colon

Medicinal plants used in irritable bowel syndrome include Iberis amara L. (1). Its extract (STW 6) is component of the herbal combination preparation STW 5 (Iberogast^®) (2), for which an antagonizing effect on gastrointestinal hypersensitivity has been shown (3).

The colon of C57Bl6 mice was isolated and recordings of the mesenteric nerve were taken in an organ bath, while perfusing lumen and bath with Krebs solution (32°C, 10ml*min^-1) containing 1µM nifedipine to eliminate contractility. STW 5 (lyophilized, 57.1×10^-3µg*ml^-1) or STW 6 (lyophilized, 21.2×10^-3µg*ml^-1) were applied 10 minutes prior to stimulation with bradykinin (0.5µM), 5-HT (10µM) or luminal ramp distension from 0 to 80cm H₂0.

Intestinal afferent nerve discharge to 5-HT was reduced to 0.2±0.2imp*s^-1 after STW 6, compared to 5±2imp*s^-1 following vehicle and 3±1 imp*s^-1 following STW 5 (p<0.05 STW 6 vs. vehicle). The response to bradykinin was 36±5 imp*s^-1 after STW 6 and 38±6 imp*s^-1 after vehicle (n.s.). Following STW 5 it was reduced to 9±2 imp*s^-1 compared to vehicle (p<0.05). Values at 80 cmH₂O were 14±3 imp*s^-1 after STW 6, 22±3 imp*s^-1 after vehicle and 4±3 imp*s^-1 after STW 5 (p<0.05 for both versus vehicle).

The Iberis amara extract STW 6 has a particular desensitizing effect in low-threshold mechano-sensitive afferents, while STW 5 acts on both low- and high-threshold afferents. Therefore the broader profile of STW 5, possibly mediating its therapeutic effects in irritable bowel syndrome, is in part, but not entirely, based on the effects of STW 6.

Keywords: Iberis amara, Colon, Colon irritabile, Irritable bowel syndrome, Intestinal hypersensitivity, Bradykinin

References: 1. Reichling J, Saller R (2002) Klass Naturheilkd, 9 (Suppl. 1): 21–32; 2. Kroll U, Cordes C (2006) Phytomedicine, 13 (Supp. V): 12–19; 3. Müller MH et al. (2006) Phytomedicine 13: 100–106