Studies conducted by researchers at Case Western Reserve on the biocompatibility, or biological response testing, of silicone rubber and its inherent characteristics as a component of Norplant, have led to the conclusion that it is not immune system reaction but polymer supply and availability of biomaterials that constitute the greatest challenge to the contraceptive industry. Years of tort litigation about silicone rubber used in the production of medical devices have culminated in what is now a crisis in the availability of biomaterials for many implant technologies. When the major chemical companies finally and totally discontinue production and sales of silicone rubber and related products, the small quantities of silicone materials that are needed for contraceptive implants will no longer be available. Some of the ''mirror image" silicone rubbers now being tested by companies are inadequate in the chemical properties that, for a 5-year implant like Norplant, are integral to its success since it is the maintenance of the integrity of the shell that sustains its perfusion properties. Reform of tort laws concerning silicone should continue to include provisions for holding accountable the company producing a given device; the problem of supply stems from the fear that accountability is not limited to that company alone, but often extends to the suppliers of raw materials.
Preston A. Marx, Ph.D.
Aaron Diamond AIDS Research Center
A rhesus macaque monkey model was developed to investigate progesterone's effect on vaginal simian immunodeficiency virus (SIV) transmission. As estrogen and progesterone influence the fitness of the vaginal epithelium, the hypothesis was that progesterone will diminish the vaginal barrier and increase vaginal transmission of SIV. The model was initially developed to get a clearer understanding of the early pathogenesis of SIV transmission. During these experiments, cell-free SIV was inserted into the vagina without trauma, since trauma was unnecessary as the virus transmits across intact vaginal epithelium.
One of the first findings from these studies was that the intact vaginal epithelium was a strong barrier to infection. Intravenous transmission of SIV proves to be the most sensitive way to introduce an HIV-like virus into a monkey or HIV into a human. Intravenously, the virus simply needs to come in contact with a susceptible lymphoid cell to initiate infection; it has very few barriers to cross. The vaginal mucosa therefore required 1,000 times more virus to elicit an