Objective: 

Angiotensin II (Ang II) has a potent contractile effect on smooth muscles in the gastrointestinal tract (GIT). The present study was designed to compare the registered responses to Ang II of different segments from GIT by application of time-parameters.

Methods: 

Longitudinal strips from Wistar rats' stomach and intestine were prepared and influenced by Ang II. The recorded force-vs.-time curves permit determination of amplitudes, area under the curve (AUC) of the smooth muscle contraction, as well as defining of time-parameters: half-contraction time (Thc), contraction time (Tc), half-relaxation time (Thr), contraction plus half-relaxation time (Tchr).

Results: 

There is a gradual increase in the amplitude of the Ang II - provoked muscle contraction along the rat intestine. The analysis of time-parameters indicated that the stomach response to Ang II required more time to develop - Tc-78.18±5.87 s and Tchr-224.90±18.45 s. All of the recorded intestinal contractions showed similar values for each of the time-parameters with exception of the ileum, which Thr (106.33±9.89 s) and Tchr (141.08±9.48 s) were significantly prolonged.

Conclusions: 

The use of time-parameters enables a detailed study of smooth muscle contractions. These parameters significantly contribute to the analysis of the contraction process and permit a good comparison of the Ang II – induced responses. The observed differences in the duration of gastrointestinal contractions may be due to variations in the Ang II receptor subtypes distribution and the corresponding interaction of Ang II with them.