Effect of Mirex on induced ovulation in immature rats (38550).

The chlorinated insecticide Mirex (dodecachlooctahdro-134metheno- 2H-cyclobuta(cd)pentalene) which is being used to control the fire ant in the southeastern U.S. was studied to determine the effect of Mirex on pregnant mare serum (PMS) induced ovulation in immature Long Evan rats and to provide evidence regarding the site of action. 45 IU PMS was given by injection in saline solution to immature female rats on Day 28 of age. Mirex was suspended in a carboxy methylcellulose vehicle and injected sc in doses of .2-50 mg. Animals were killed 72 hours after PM S injections. Oviducts were removed and ova recorded. The effect on ovulation was greater as the dose was increased to 25 and 50 mg (p less than .01). The 40-80% inhibition of PMS-induced ovulation by the injection of Mirex is thought to have resulted from the action of the compound on neural mechanisms controlling luteinizing hormone (LH) release. In a 2nd experiment human chorionic gonadotropin (HCG) was given after injections of 6 25 and 50 mg of Mirex. The HCG was suspended in saline 25 IU in .1 ml and given 60 hours after PMS injections. The HCG overcame the inhibitory effect of Mirex suggesting that the ovary is not the primary site of action of Mirex. In a 3rd experiment the Mirex was given at varying periods before and after the PMS-induced LH release. When Mirex was injected from 0 to 58 hours after PMS a significant inhibition of ovulation resulted. When Mirex was injected at 63 hours after PMS ovulation was unchanged.