Antifertility Effects of SC-20775 in Norway and Polynesian Rats

Abstract

SC-20775 (17a-ethynyl-llp-methylestradiol-3-cyclopentyl ether), a synthetic estrogen, showed promise as a chemosterilant for Norway rats (Rattus norvegicus) and Polynesian rats (R. exulans) in three preliminary laboratory studies. When females of both species were offered single feedings of 0.0012 or 0.012 percent SC-20775 in bait and then paired with males, birth of litters was 5-18 days later than for control females. When lactating female Norway rats were treated by gavage with 0.1, 1, or 10 mg/kg SC-20775, nursing young showed a significant percentage of gonadal abnormalities at 120 days; these effects, particularly testis weight in males, appeared dose-dependent. When small colonies of Polynesian rats (5 females and 2 males each) were offered SC-20775 in bait five times during a 70-day period, bait aversion reduced consumption (average SC-20775 per baiting, 0.56 mg/kg), but only 4 of 17 treated females became pregnant versus 13 of 20 control females. J. WILDL. MANAGE. 39(1):26-29 In the state of Hawaii, rats do major damage to sugarcane crops; the heaviest losses are caused by Norway and Polynesian rats, particularly the latter (Hood 1968). In a search for methods to alleviate this problem, one of the techniques this laboratory is investigating is the chemical inhibition of reproduction; we have screened a number of compounds for this purpose. One, SC20775, a synthetic estrogen provided by G. D. Searle & Company (reference to trade names does not imply endorsement of commercial products by the U.S. Government), showed promise as a control agent for both Norway and Polynesian rats in three preliminary tests described here.