The observed intratesticular Cd gradient cannot be ascribed to a dilution effect related to the pattern of vascular flow. In sharks, blood from the genital artery first perfuses the EO and then passes successively from mature to immature regions, which is the reverse of the gradient. Also, in contrast to the rapid elimination of 109Cd from plasma, testicular 109Cd increases progressively in the 3-day interval after injection and then persists unchanged for an additional 4 days.Data reported here reveal an intratesticular stage-related gradient of Cd uptake and retention. Cd accumulated preferentially in GZ, with decreasing levels in succeeding developmental stages. The direction (immature > mature) and magnitude (3- to 5-fold) of the intratesticular gradient were essentially the same whether Cd was measured as radioactivity after a single injection of 109Cd or by atomic absorption spectrophotometry after administration of radio-inert CdCl2. Buy Advair Diskus Online
Moreover, the same pattern was seen in untreated controls, indicating that the gradient was not a treatment artifact and implying that animals are exposed to Cd in their environment. Cd occurs in nature in ores and minerals, but levels in seawater are generally low. Because Cd undergoes bioaccumulation and biomagnification in the food chain, and sharks are apex feeders, tissue Cd is likely to be dietary in origin. Identifying the source of this exposure would be difficult, however, because Squalus migrates annually between the North and South Atlantic.