Natural Compound Schisandrin A Suppresses Intestinal Contraction

— Revealing a Mechanism Underlying the Antidiarrheal Effects of Schisandra chinensis fruits—

A research team from the Departments of Chemical Pharmacology and Pharmacognosy at the Faculty of Pharmaceutical Sciences, Toho University, has found that Schisandrin A, a natural compound found in the traditional medicinal plant Schisandra chinensis, suppresses intestinal smooth muscle contraction. The study shows that Schisandrin A inhibits calcium (Ca²⁺) influx through L-type calcium channels, thereby reducing intestinal contractions triggered by various stimuli (Fig. 1). These findings help explain why Schisandra chinensis fruits have long been used to treat diarrhea and other gastrointestinal disorders. The results were published online on April 9, 2026, in Biological and Pharmaceutical Bulletin.

A research team from the Departments of Chemical Pharmacology and Pharmacognosy at the Faculty of Pharmaceutical Sciences, Toho University, has found that Schisandrin A, a natural compound found in the traditional medicinal plant Schisandra chinensis, suppresses intestinal smooth muscle contraction.
The study shows that Schisandrin A inhibits calcium (Ca2+) influx through L-type calcium channels, thereby reducing intestinal contractions triggered by various stimuli (Fig. 1). These findings help explain why Schisandra chinensis fruits have long been used to treat diarrhea and other gastrointestinal disorders.
The results were published online on April 9, 2026, in Biological and Pharmaceutical Bulletin.

Key Points

Schisandrin A is a major active compound in Schisandra chinensis fruits, a traditional herbal medicine used to treat gastrointestinal symptoms such as diarrhea, although its mechanism of action has remained unclear.
The study demonstrated that Schisandrin A suppresses contractions of guinea pig ileal smooth muscle induced by acetylcholine, histamine, and prostaglandin F_2α in a concentration-dependent manner, mainly by inhibiting Ca²⁺ influx through L-type calcium channels.
These findings provide new insight into the mechanism underlying the antidiarrheal effects of Schisandra chinensis fruits, highlighting the role of calcium channel inhibition.

Background

Schisandrin A is a major lignan component of the fruits of Schisandra chinensis, a medicinal plant widely used in East Asia. Previous studies have reported a range of pharmacological effects, including antioxidant, anti-inflammatory, and hepatoprotective activities.

In addition to these effects, Schisandra chinensis fruits have traditionally been used to treat gastrointestinal disorders such as diarrhea. However, the molecular mechanisms responsible for its antidiarrheal effects have not been fully understood. In particular, the direct effects of Schisandrin A on intestinal smooth muscle contraction have remained unclear.

Research Findings

To investigate how Schisandrin A affects intestinal function, the researchers conducted pharmacological studies using guinea pig ileal longitudinal smooth muscle.

They found that Schisandrin A concentration-dependently inhibited contractions induced by acetylcholine, histamine, and prostaglandin F_2α, all of which are known to stimulate gastrointestinal smooth muscle. It also suppressed contractions triggered by membrane depolarization using high potassium.

These contractile responses were completely abolished by the L-type calcium channel blocker diltiazem, suggesting that Schisandrin A acts by interfering with Ca²⁺ influx pathways.

Further experiments using fluorescence-based calcium imaging in A7r5 smooth muscle cells showed that Schisandrin A significantly reduced increases in intracellular Ca²⁺ levels induced by high potassium. This supports the idea that Schisandrin A functionally inhibits Ca²⁺ entry through L-type calcium channels.

In addition, molecular docking analysis using the structure of the human Ca_V1.2 channel suggested that Schisandrin A may bind within the channel pore, potentially interacting with specific amino acid residues such as Tyr1508 (Fig. 1). This provides structural insight into how Schisandrin A may directly inhibit calcium influx.

Overall, the study indicates that Schisandrin A suppresses intestinal smooth muscle contraction by inhibiting Ca²⁺ influx through L-type calcium channels, particularly Ca_V1.2, affecting both receptor-mediated and depolarization-induced pathways (Fig. 1).

However, the plasma concentration of Schisandrin A after oral administration is relatively low and may not reach the effective levels observed in this study. This suggests that local effects within the intestinal lumen may be more relevant, although further investigation is needed.

These findings help explain the traditional use of Schisandra chinensis as an antidiarrheal remedy.

Figure 1. Proposed mechanism by which Schisandrin A inhibits intestinal smooth muscle contraction.

Contractile stimuli such as acetylcholine activate L-type calcium channels via receptor-mediated pathways, leading to Ca²⁺ influx from the extracellular space and subsequent contraction of intestinal smooth muscle. Intestinal motility is regulated by this contraction, and excessive contraction can contribute to diarrhea. Schisandrin A inhibits Ca²⁺ influx through L-type calcium channels (particularly Ca_V1.2), thereby suppressing intesContractile stimuli such as acetylcholine activate L-type calcium channels via receptor-mediated pathways, leading to Ca²⁺ influx from the extracellular space and subsequent contraction of intestinal smooth muscle. Intestinal motility is regulated by this contraction, and excessive contraction can contribute to diarrhea. Schisandrin A inhibits Ca²⁺ influx through L-type calcium channels (particularly Ca_V1.2), thereby suppressing intestinal smooth muscle contraction and motility. In addition, molecular docking analysis suggests that Schisandrin A may bind within the channel pore.

Journal:
Biological and Pharmaceutical Bulletin (April 9, 2026)

Title:
Schisandrin A suppresses guinea pig ileal longitudinal smooth muscle contraction through functional inhibition of L-type Ca²⁺ channels

Authors:
Qianghaodi Hong, Tomoya Ohta, Kouharu Otsuki, Wakaba Kinami, Teppei Sato, Takashi Kikuchi, Wei Li, Kento Yoshioka, Keisuke Obara, Yoshio Tanaka

DOI: 10.1248/bpb.b26-00055

Abstract URL: https://doi.org/10.1248/bpb.b26-00055

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