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A fluid medium was developed to simulate the salient physical and chemical properties of human semen. The composition of the medium was based upon an extensive review of the literature on constituents of human semen. In choosing the ingredients for this medium, the goal was to emphasize properties that influence interactions of human semen with topical contraceptive, prophylactic, or therapeutic products. Among these properties, pH and buffering capacity, osmolarity, ionic strength, and rheological properties play dominant roles in the physico-chemical processes that govern drug release kinetics and delivery vehicle distribution. W hen therapeutic, contraceptive, or prophylactic formulations are applied to the vagina, they encounter a variety of fluids with widely varying physical and chemical properties. These fluids include those that originate in the vagina and those that flow into it (eg, cervical mucus and semen). The fluid actually present at any location within the vagina is a mixture, to a varying extent, of these fluids. The flow, retention, drug delivery kinetics, and bioactivity of vaginal formulations depend upon their interactions with these resident fluids. Work done by our group has determined that the physical and chemical properties of both the delivery vehicle and the surrounding environment are important factors in determining product performance (Katz et al, 1998;Owen et al, 1999aOwen et al, , 2000Owen et al, , 2001Owen et al, , 2003. Understanding of these interactions can, therefore, aid in the design and development of new and improved formulations.One component of such research is the in vitro testing of formulations with fluids representative of those that will be encountered within the vagina. Our laboratory has been developing and applying in vitro assays that focus on how the deployment and delivery of contraceptive and prophylactic compounds are affected by the properties of the delivery vehicle and its interactions with the surrounding fluids. To develop these assays using standardized materials of sufficient volume, we have found it useful to employ simulants of ambient biological fluids. Our for- mulation of a vaginal fluid simulant has been described in a previous publication (Owen and Katz, 1999b), and our semen simulant (and earlier versions) was presented in a number of studies of contraceptive and microbicidal gels (Owen et al, 2003(Owen et al, , 2004Geonnotti and Katz, 2004;Geonnotti et al, 2005a;Geonnotti et al, 2005b). Here we describe the formulation of a semen simulant embodying salient physical and chemical components and properties of human semen. This is based on a comprehensive review of the literature, and we present here, as well, an updated summary of the constituents of human semen. Materials and MethodsThe quantity and composition of human semen have been studied for a variety of reasons (eg, for the diagnosis of conditions such as prostatitis, infertility, and cancer), and the results of these studies were used in the development of our simulant. It i...

After insemination, mammalian sperm undergo a striking change in flagellar beat pattern, termed hyperactivation. In low-viscosity culture medium, nonhyperactivated sperm flagella generate relatively symmetrical, low-amplitude waves, while hyperactivated sperm flagella generate an asymetrical beating pattern that results in nonprogressive movement. Since sperm encounter highly viscous and viscoelastic fluids in the female reproductive tract, the progress of hyperactivated sperm was compared with that of nonhyperactivated and transitional sperm in media of increasing viscosity. Hamster sperm obtained from the caudal epididymis were incubated in a medium that promotes capacitation. After 0, 3, and 4 h of incubation, the majority of the sperm exhibited, respectively, activated, transitional, and hyperactivated motility. At each of these time points, aliquots of sperm were removed from incubation and added to solutions of 0, 5%, 10%, 20%, and 30% Ficoll in medium. Samples containing mostly hyperactivated sperm (4 h) maintained higher swimming and flagellar velocities and were able to generate greater forces in response to increased viscous loading than activated sperm (0 h). Transitional sperm (3 h) showed an intermediate response. The paths of hyperactivated sperm through solutions of 20% and 30% Ficoll were considerably straighter than those made through medium alone. This is the first demonstration that hyperactivation can confer a mechanical advantage upon sperm in the oviduct where they may encounter viscous oviductal fluid and a viscoelastic cumulus matrix.

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