Abstract
Antihypertensive and antidiabetic effects of stevia, Stevia rebaudiana
(Asteraceae), have been demonstrated in several human and animal models. The
current study aims to define steviaʼs role in modifying the
electrophysiological and mechanical properties of cardiomyocytes, blood
vessels, and gastrointestinal smooth muscle. Tissues from thoracic aorta,
mesenteric arteries, ileum, and left ventricular papillary muscles were
excised from 8-week-old healthy Wistar rats. The effects of stevia
(1 × 10−9 M to 1 × 10−4 M) were measured on these
tissues. Steviaʼs effects in the presence of verapamil, 4-AP, and L-NAME
were also assessed. In cardiomyocytes, stevia attenuated the force of
contraction, decreased the average peak amplitude, and shortened the
repolarisation phase of action potential – repolarisation phase of action
potential20 by 25 %, repolarisation phase of action
potential50 by 34 %, and repolarisation phase of action
potential90 by 36 %. Stevia caused relaxation of aortic
tissues which was significantly potentiated in the presence of verapamil. In
mesenteric arteries, incubation with L-NAME failed to block stevia-induced
relaxation indicating the mechanism of action may not be fully via nitric
oxide-dependent pathways. Stevia concentration-dependently reduced
electrical field stimulated and carbachol-induced contractions in the
isolated ileum. This study is the first to show the effectiveness of stevia
in reducing cardiac action potential duration at 20 %, 50 %, and 90 % of
repolarisation. Stevia also showed beneficial modulatory effects on
cardiovascular and gastrointestinal tissues via calcium channel antagonism,
activation of the M2 muscarinic receptor function, and enhanced
nitric oxide release.
Key words
Stevia rebaudiana (Asteraceae) - Wistar rats - cardiovascular function - electrophysiology - action potential duration - gastrointestinal smooth muscle
