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Effects of clomiphene citrate, cyclofenil and prostaglandins (PGE1 and PGF2α) on ovarian 32P uptake, on gonadotrophin levels in the pituitary gland and blood serum and on a gonadotrophin releasing hormone-like (GnRH-like) substance in the hypothalamus were investigated in Heteropneustes fossilis. These drugs were very effective in increasing the serum level of gonadotrophin with a subsequent increase in ovarian 32P uptake in sham-hypophysectomized recipients. All the drugs except cyclofenil failed to stimulate 32P incorporation by the ovary in hypophysectomized fish. Clomiphene citrate and cyclofenil also induced a significant increase in the GnRH-like factor in the hypothalamus of H. fossilis. Such a response was not obtained in fish treated with PGE1 and PGF2α. It seems likely that the action of clomiphene is routed through the hypothalamo-pituitary-ovarian axis and that of prostaglandins directly through the pituitary-ovarian axis. The action of cyclofenil is bimodal; one effect like that of clomiphene and the other direct upon the ovary probably by increasing its sensitivity to the available gonadotrophin.
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The effects of pesticides containing either an organophosphate malathion (Cythion) or an organochloride endrin (Hexadrin) on the survival, ovarian 32P uptake and the gonadotrophic potency of the pituitary gland and serum of Heteropneustes fossilis were studied for 96 h. Hexadrin was found to be more toxic than Cythion. Reduced ovarian 32P uptake and a significantly decreased level of total gonadotrophin in the pituitary gland and serum were seen when fish were placed either in a drug concentration that had been found to kill half the fish in 96 h or in a safe concentration of Hexadrin and Cythion in aquarium water. Administration of LH or homologous pituitary extract during the exposure of the fish to the pesticides increased the ovarian 32P uptake.
The data suggest that these pesticides retarded gonadotrophin secretion which in turn reduced ovarian 32P uptake. However, they did not interfere with the effects of exogenous LH or pituitary extract at the dose levels tested.
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SUMMARY
Gonadotrophin content in the pituitary gland and blood serum as well as ovarian 32P uptake were studied in response to methallibure treatment in H. fossilis. There was a marked reduction in the gonadotrophic activity of the pituitary gland and blood serum within 3 weeks of methallibure treatment (100 μg/g). A simultaneous significant reduction was also recorded in the ovarian activity of these fish. The fall in ovarian activity caused by methallibure could not be prevented by the administration of LH, FSH or LH + FSH. After cessation of methallibure treatment, LH + FSH (50 μg each) administration restored ovarian activity. It is evident from these results that methallibure alters the secretion of gonadotrophin, and also prevents its action on the ovary.
