Interference of cadmium and copper with the endocrine control of ovarian growth, in the estuarine crab Chasmagnathus granulata

Abstract

The effects of cadmium and copper on the hormonal control of ovarian growth were evaluated on the estuarine crab Chasmagnathus granulata, by means of both in vivo (14 days exposure) and in vitro (24 h) assays. For both kind of assays, heavy metal concentrations of 0 (control), 0.5 mg/L of cadmium or 0.1 mg/L of copper were used. No significant ( P > 0.05) change of the gonadosomatic index was observed in the in vivo assays with intact females exposed to heavy metals, while eyestalk-ablated exposed females showed significantly ( P < 0.05) lower gonadosomatic index values than their respective controls. This latter result led us to consider the possibility that the interfered with extra-eyestalk hormones. In this sense, no differences were noted between control and heavy metals-exposed groups after co-incubating ovary with thoracic ganglion (the source of the gonad stimulating hormone). However, when ovary was incubated with methyl farnesoate or 17-hydroxyprogesterone, 3 H -leucine incorporation was significantly lower in the heavy metals-exposed groups than in the controls, indicating a possible interference of cadmium and copper with the transduction pathway of those hormones. On the other hand, ovaries co-incubated in vitro with eyestalk tissue and exposed to either heavy metal showed significantly higher 3 H -leucine incorporation than did the controls, suggesting an inhibitory effect of both heavy metals on the secretion of the gonad inhibiting hormone from the eyestalk tissue. Interference by copper and cadmium with the transduction mechanisms of gonad inhibiting hormone at the ovarian level does not appear to be a viable hypothesis, because the addition of eyestalk extracts to the incubation medium reversed the effect caused by each heavy metal. The results from the in vitro assays were in accordance with those obtained with the intact crabs in vivo.