Epidemiological research and studies in wildlife have reported an increase in male reproductive abnormalities, including increases in testicular cancer and declining sperm counts. These reports have stimulated a debate as to the role of environmental chemicals, but clear cause-and-effect relationships remain to be established. What has hampered attempts to elucidate factors and mechanisms that control spermatogenesis is the complex organization of the testis of man and conventional laboratory and domestic animals. In these species, the number of different somatic elements that support spermatogenesis (Leydig, Sertoli, and peritubular myoid cells), and the arrangement and spacing between successive germ cell stages, make it technically difficult to analyze and experimentally manipulate a single discrete stage without disrupting germ cell clones, somatic elements, and the privileged germinal compartment. For the same reason, attempts to develop an in vitro spermatogenesis system for routine chemical testing and mechanistic studies have had only limited success. Future progress in understanding human health effects, as well as the impact of environmental factors on normal spermato-genic efficiency and survival of animal species, has been linked to the acquisition of new experimental models and test systems. proventil inhaler
The strategy of seeking simpler animal models is justified on the basis that spermatogenesis has been fundamentally conserved throughout the vertebrates, especially at the cellular and molecular levels. Where phyletic and species differences do occur is in the organization of the testis. Studies in this laboratory have shown that the spiny dogfish shark (Squalus acanthias) is an ideal model for the step-wise analysis of spermatogenesis.