The effect of alfalfa saponins on the contractility of bovine isolated abomasum and duodenum preparations

Abstract

Saponins, a vast group of secondary plant metabolites, occur naturally in plants that are commonly present in ruminants’ diet or plants that are used as phytogenic feed additives. They have gained particular attention among ruminant nutritionists due to numerous health benefits resulting in improved animal performance and feed conversion efficiency. Despite the broad knowledge of saponins’ effects of on cattle, little is known about their impact on gut motility. Therefore, the effect of two structurally divergent alfalfa saponins on the contractility of abomasum and duodenum smooth muscle was examined.The study was conducted on tissues obtained from routinely slaughtered, healthy cows. The experiments were carried out on longitudinal and circular smooth muscle preparations under isometric conditions. The effect of hederagenin and medicagenic acid in a concentration range of 0.001–100µM was verified in a non-cumulative manner on acetylcholine-precontracted smooth muscle specimens. The results are expressed as percentage of the control contraction induced by acetylcholine.Generally, both triterpenoid saponins caused significant enhancement of acetylcholine-induced contraction of abomasum and duodenum preparations. Hederagenin generated dose-dependently significant increase of acetylcholine-evoked contraction of abomasum strips. The strongest contraction caused by hederagenin in a concentration of 100µM was observed in abomasal circular smooth muscle and amounted to 184.1±15.5% of the control treatment. Similarly, in case of duodenum hederagenin increased smooth muscle contractility dose-dependently. Hederagenin applied in the highest tested concentration doubled the force of acetylcholine-induced contraction in duodenal longitudinal smooth muscle. Medicagenic acid caused a remarkable increase of abomasum but not duodenum smooth muscle contractility. The contractile effect of medicagenic acid was observed in a concentration range of 0.001–10µM. The highest contractions of abomasal longitudinal and circular smooth muscle generated by medicagenic acid exceeded 150% of the control treatment with acetylcholine. All reactions caused by hederagenin and medicagenic acid were reversible and did not abolish the spontaneous motoric activity of specimens.Taking into consideration the physicochemical properties of saponins it is postulated that the contractile effect of hederagenin and medicagenic acid results from their impact on the fluidity or plasticity of the membrane and subsequently the ion flow through cell membrane. The increased ability of cells to depolarize can explain the enhancement of the response to acetylcholine. The reversibility of induced contractions, preserved spontaneous contractility and remained reactivity of smooth muscle after saponin treatment indicate that the effect caused by alfalfa saponin does not result from cell membrane damage.