Development of Nippostrongylus brasiliensis in gonadectomized and hormone-treated hamsters

Abstract

Gonadectomy of male hamsters from 2 weeks to 1 day (27–30 hours) prior to infection was followed by a significant decrease in the recovery of adult worms, whereas gonadectomy during the infection period had no apparent effect on adult worm burdens. Gonadectomy before infection did not increase the adult worm burdens of female hamsters. Testosterone propionate injections in doses of 5, 10, or 20 mg shortly before infection reversed the effects of gonadectomy in mature male hamsters; recoveries of adult worms varied with the dose. Testosterone injections also increased the susceptibility of normal male and gonadectomized and normal female hamsters. Preliminary studies indicated that progesterone was as effective as testosterone in increasing the susceptibility of normal female hamsters, whereas estradiol benzoate, cholesterol, and cortisone had no effect on adult worm burdens under the conditions studied. The effect of gonadectomy on the migration of larvae from the site of intracutaneous inoculation to the lungs and intestines generally supported the findings of the studies on adult worms, although it was found that the necropsy time selected was of importance. Significantly fewer larvae were recovered from the lungs of gonadectomized males than from those of sham controls at 15, 27, and 39 hours after infection; however, there was no significant difference in larval recoveries from the lungs of gonadectomized and sham-operated animals at 3, 6, and 9 days. After injections of testosterone at 16 and 8 hours prior to infection, larvae arrived more rapidly in the lungs of gonadectomized males and normal females than in those of the sesame oil controls, and considerable numbers reached the intestines by the third day of infection. The present findings strongly suggest that male gonadal hormones can act to condition the integument of the hamster, thereby facilitating the penetration and migration of Nippostrongylus brasiliensis larvae. Removal of the gonads from the male would remove the major source of androgens and permit changes in the integumentary structures (i.e., ground substances) sufficient to slow down initially the migration of larvae; injections of testosterone into the male or female would put the animal into a relatively highly susceptible state. The importance of the lung barrier in the gonadectomized host was also considered in relation to timing mechanisms and internal secretions. Whether testosterone can act directly on the worms or indirectly while the worms are still in the lungs is not yet known.