In vivo effects of putative crowding factors on Hymenolepis diminuta

Abstract

During in vitro incubation, Hymenolepis diminuta secretes substances into the medium that inhibit DNA synthesis in the germinative region of freshly isolated, uncrowded worms. Of the many substances that are released by H. diminuta into the medium, only succinate, acetate, glucosaminic acid and cGMP are apparendy responsible for the inhibition (Zavras and Roberts, 1985). These substances were referted to as "putative crowding factors" by Zavras and Roberts (1985). The effects of these crowding factors on worm development in \ivo were examined. At seven days post infection the proximal end of the hosts' intestine was catheterized and perfused with test solution. In some experiments 4.3 M succinate, 5.0 M acetate, or both were perfused by an Alzet® osmotic pump. In other experiments a solution containing 28 nM cGMP, 250 |LiM glucosaminic acid, 120 mM succinate, and 40 mM acetate was perfused by a peristaltic pump at a rate of 50 ml/day. At 2 weeks post infection, the worms were recovered for subsequent analysis. The test solutions in the osmotic pumps did not affect the wet weights of the worms. In the experiments using a peristaltic pump, worms exposed to the crowding factors were 53% less in wet weight than the control worms. Carbohydrate concentrations in worms from experimental groups were not different from those in control groups; therefore, the inhibition in growth was probably not due to carbohydrate deprivation. Worms from experimental groups had fewer immature, mature, and gravid proglottids than did worms from control groups. Attempts to measure succinate levels in the tat intestine were unsuccessful.