Obtained from the seeds of Ricinus communis, castor oil has been used since ancient times as a laxative and a labor promoting drug. While the pharmacological properties of this vegetable oil are attributed to its main component – the ricinoleic acid, a hydroxylated unsaturated fatty acid –, its mechanisms of action were so far elusive. A group of researchers at Max Planck Institute for Heart and Lung Research and at Goethe University, both Germany, has solved the riddle.

The team, guided by Stefan Offermanns, discovered that the effects exerted by ricinoleic acid are due to its selective interaction with EP3 prostaglandin receptors expressed on smooth muscle cells of the intestine and of the uterus. The researchers observed that no contraction of the intestine occurred when they delivered castor oil to mice lacking EP3 receptors selectively on these cells. As a consequence, in EP3 deficient mice, castor oil did not promote any laxative effects. The scientist revealed that, in the absence of EP3 receptors, also the uteri of pregnant and non pregnant animals fail to contract upon ricinoleic acid administration.

While this study reveals a specific mechanism of action for an old drug still used in both traditional and alternative medicine, it also opens the doors to new therapeutic approaches. EP3 receptors could indeed be an important target for the development of novel laxative or labor inducing drugs, deprived of castor oil´s side effects such as nausea. Moreover, the discovery that ricinoleic acid interacts specifically with prostaglandin receptors, raises the possibility that also other hydroxylated fatty acid activate prostanoid receptors.

• Castor oil induces laxation and uterus contraction via ricinoleic acid activating prostaglandin EP3 receptors,
  S. Tunaru, T. F. Althoff, R. M. Nüsing, M. Diener, S. Offermanns.
  Proc. Natl. Acad. Sci. USA 2012.
  DOI: 10.1073/pnas.1201627109