Stage-dependent accumulation of cadmium and induction of metallothionein-like binding activity in the testis of the dogfish shark, Squalus acanthias

Cadmium (Cd) is an established spermatotoxicant. Using the shark (Squalus acanthias) testis model, we investigated stage-related patterns of intratesticular Cd accumulation and effect. After a single injection of (CdCl2)-Cd-109, tracer was rapidly eliminated from plasma but accumulated and was retained in testis for at least 7 days. intratesticular Cd-109 was stage dependent, resulting in a 3- to 5-fold gradient: germinal zone (GZ) > premeiotic (PrM) > meiotic (M)> postmeiotic (PoM) stages. When measured as tissue:plasma ratios, the Cd-binding mechanism in CZ (71:1) was similar to that in liver (87:1) but lower than in kidney (381:1). The same intratesticular gradient was seen in untreated controls when tissue Cd levels were measured by atomic absorption spectroscopy, implying environmental exposure. A single CdCl2 injection (5 mg/kg i.v,) elevated testicular Cd > 160-fold in all stages but did not alter the direction or magnitude of the gradient. Intratesticular distribution of metallothionein-like Cd-binding protein was stage dependent (PrM = PoM > GZ = M), but the pattern differed from the Cd gradient. This binding component was Cd inducible in all but M stages, but induction did not alter the stage-dependent pattern of binding activity or Cd accumulation. Analysis of tissue subfractions after in vivo tracer injection indicated that the binding mechanism responsible for the intratesticular gradient is mainly cytosolic, but that a second less abundant component is associated with the nucleus. The functional significance of preferential Cd accumulation in GZ and PrM stages of spermatogenesis remains to be determined.