Mechanical properties of the mammalian vas deferens. II. In the active state.

The mechanical response of the vas induced by field stimulation is described in this paper. The experiments were performed, in vitro, on vasa from Sprague-Dawley albino rats. In the maintained ac tetanic stimulation, the active force achieves the peak magnitude in about 1 to 1.2 sec; thereafter, it relaxes gradually. For a given stimulus voltage (amplitude), a maximal response is elicited at 60 Hz. At 6000 Hz, and greater, no response is elicited. The ability to respond to stimulus dies out in 2 hr at 5 degrees C above the normal temperature of 37 degrees C; the ability to respond to stimulus remains unaffected at 5 degrees C below the normal temperature. The active force is always larger than the passive force when the vas is subjected to titanic stimulation near its in situ length.

Mechanical properties of the mammalian vas deferens. I. In the passive state.

Knowledge of the mechanical properties of the vas deferens is important in order to understand the mechanical interaction between an intravasal device (IVD) and the vas deferens--a necessary step for successful long-term implantation. It is equally important in order to understand the mechanism of sperm transport through the vas, with or without an IVD implant, by means of quantitative mechanical models. Experiments were performed, in vitro, on vas deferens from rat, bull, and rabbit, to determine its mechanical properties in the passive state. The data consist of (1) load response to simple extension and cyclic extension, (2) extensional response to cyclic loading, and (3) stress relaxation response at constant extensions. The load-elongation behavior is characterized by Fung's exponential model T = (T* + beta)e alpha(lambda-lambda*) - beta quantitatively, where T is the Lagrangian or engineering stress (current force in the specimen divided by the original area of cross section) (dyn/cm2), T* is a convenient stress value (dyn/cm2), alpha is a parameter characterizing material elasticity (dimensionless), beta is a second material parameter (dyn/cm2), lambda is a stretch ratio (dimensionless) equal to l/l0, where l is the instantaneous length of the specimen (cm) and l0 is its reference length measured at 2-gram-force (1 gram force = 981 dyn) applied load (cm), and lambda* is the stretch level corresponding to T* (dimensionless). The vas appears to behave as a viscoelastic material and its reduced relaxation function may be dependent on the initial level of stretch. The cyclic-loading and cyclic-extension data give evidence of internal damping mechanisms, which make the loading curves different from the unloading curves (hysteresis). Also, the mechanical behavior of the vas is found to be altered by repeated loadings in quick succession. It is likely that cyclic loadings, in vivo, occur at much lower levels of stress and thus cause negligible damage, or that there are natural mechanisms which repair the damage. The behavior of tissue from different species of animals are qualitatively similar, although the tissue from the larger-size animal is likely to be stronger and stiffer. Due to very little interweaving between the muscle fibers of the longitudinal and circumferential layers, the data reported reflect the properties of the longitudinal layers only. Because the muscular structure of the three layers is very similar, the properties of the circumferential layer may be extrapolated.

Applicability of hydrodynamic analyses of spermatozoan motion.

This paper investigates the applicability of a simple hydrodynamics theory due to Gray & Hancock (1955), and extended by Brokaw (1970), to the analysis of the motions of sea urchin, rabbit, and bull spermatozoa. Experimental procedures for filming and analysing the swimming motions are presented. A detailed discussion of the agreement between the experimental and theoretical results is given, and the limitations of the theory in analysing the motion of mammalian spermatozoa are discussed.

A mathematical model of the human menstrual cycle.

A mathematical model for the hormonal interactions of the human menstrual cycle is presented. The feedback effects of estrogen on the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are considered, including a mechanism describing the midcycle LH peak. Computer simulation with this model yields results which are periodic and in good agreement with physiological data.