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System and organ-selectivity of smooth muscle relaxants on in vitro spontaneously contracting preparations
Abstract:
The effects of verapamil, papaverine and octylonium bromide on amplitude and frequency of spontaneous contractions of rabbit duodenum and rat colon, portal vein and right atria have been investigated. Myogenic nature of spontaneous contractions was demonstrated by their resistance to tetrodotoxin (100 micrograms/ml) and hexamethonium (10(-4) M). Verapamil (10(-7) - 5 X 10(-6) M) reduced, in a concentration-dependent manner, amplitude and frequency of spontaneous contractions with a certain degree of selectivity for duodenal preparations. Automaticity of rat right atria was affected by concentrations of verapamil higher than those required to modify automaticity of intestinal preparations. Papaverine (3 X 10(-6) - 3 X 10(-4) M), was almost equipotent in reducing the amplitude of spontaneous contractions of each preparation but inhibited the frequency of contractions in the following order: colon greater than duodenum greater than atrium. Octylonium bromide (10(-6) - 10(-4) M) was characterized by its greater effectiveness in reducing frequency and amplitude of spontaneous contractions of rat colon as compared to the other preparations. All three smooth muscle relaxant drugs, in spite of concentration-related reduction in amplitude, determined a parallel enhancement of frequency of spontaneous contractions in rat portal vein. Differences in drug selectivity are discussed in terms of different roles played by various Ca++-dependent processes (which constitute the cellular target of action of these smooth muscle relaxant drugs) in the genesis of frequency and amplitude of myogenic contractions in the various preparations.
Insights
Verapamil, papaverine, and octylonium bromide relax smooth muscles by affecting calcium channels. These drugs show varying selectivity across rabbit duodenum, rat colon, portal vein, and atria, impacting contraction amplitude and frequency differently.
Area of Science:
- Pharmacology
- Physiology
- Smooth Muscle Biology
Background:
- Spontaneous smooth muscle contractions are crucial for organ function.
- Understanding the mechanisms of smooth muscle relaxation is key for therapeutic development.
- Calcium-dependent processes play a significant role in regulating smooth muscle contractility.
Purpose of the Study:
- To investigate the effects of verapamil, papaverine, and octylonium bromide on spontaneous contractions.
- To compare the selectivity of these drugs on different smooth muscle preparations.
- To elucidate the role of calcium-dependent mechanisms in drug-induced smooth muscle relaxation.
Main Methods:
- Studied spontaneous contractions of rabbit duodenum, rat colon, portal vein, and right atria.
- Utilized tetrodotoxin and hexamethonium to confirm the myogenic nature of contractions.
- Administered verapamil, papaverine, and octylonium bromide in concentration-dependent ranges.
Main Results:
- Verapamil reduced amplitude and frequency concentration-dependently, with selectivity for duodenal preparations.
- PapaverineEqually reduced amplitude across preparations but inhibited frequency in the order: colon > duodenum > atrium.
- Octylonium bromide was most effective on rat colon, reducing both amplitude and frequency. All drugs increased rat portal vein frequency despite reducing amplitude.
Conclusions:
- Verapamil, papaverine, and octylonium bromide exhibit differential selectivity in relaxing various smooth muscles.
- Drug effects are linked to the varying roles of Ca++-dependent processes in myogenic contraction generation.
- These findings provide insights into the pharmacological modulation of smooth muscle activity.