Physiologic properties of contraction of the canine cremaster and cranial preputial muscles.

Contraction properties of the cremaster and the cranial preputial muscles of 11 mature intact male dogs were investigated. Isometric recordings of muscle contractile tension were performed in situ. Muscle contractions were elicited by stimulating the severed motor nerves. Contraction times of 73.8 ms and 103.2 ms were obtained for the cremaster and the cranial preputial muslces, respectively. Application of repetitive stiumuli produced summation of contractions at low stimulus frequencies. Apparent tetanic fusion and maximum tetanic tension were also observed at relatively low stimulus frequencies, 30 Hz for the cremaster muscle and 28 Hz for the cranial preputial muscle. Optimum length for the cremaster muscle was coincident with its observed in situ resting length (+/- 5 mm), but the optimum length for the cranial preputial muslce deviated by some 20 to 25 mm above the resting length. Possible artifactual errors regarding the cranial preputial muslce's length-tension relationship are discussed.