Mechanical properties of isolated smooth muscle from rabbit sphincter of Oddi and duodenum

Isolated smooth muscle from rabbit sphincter of Oddi (SO) and duodenum were mounted in organ baths. The SO strips were obtained as transversal strips from the midsection of the SO. The duodenal strips were prepared as longitudinal (Dl) or circumferential (Dc) strips. Resting length was defined. Carbachol was used for activation of the contractile apparatus. By repeatedly increasing the length of the strips by 20% of the resting length and recording values of resting and active tension, length-tension relations for each muscle type were constructed. None of the strips developed active resting tension. Twelve of the Dl strips (75%) developed spontaneous contractions versus four of the Dc strips (10%) and one of the SO strips. The strips eventually reached a length (Lo) at which further elongation gave no additional increase in active tension development. The Lo from the Dc strips differed significantly from SO Lo (p greater than 0.02) and Dl Lo (p less than 0.02), indicating structural differences. SO Lo and Dl Lo did not differ significantly. Differential extension of these tissues should be applied in future experiments on smooth muscles from this area.