THE INTERPLAY BETWEEN PATENCY, MICROSOMAL NA+ K+ ATPASE ACTIVITY AND JUVENILE-HORMONE, IN TENEBRIO-MOLITOR PARASITIZED BY HYMENOLEPIS-DIMINUTA/

Beetles infected with metacestodes of the rat tapeworm, Hymenolepis di minuta, exhibit reduced fecundity, due to alterations in vitellogenesi s, Follicle cell patency is retarded and inefficient vitellogenin upta ke ensues. Here, we have reassessed patency and its stimulation by JH III at day 3 post-infection, when the most detrimental changes are obs erved in other ovarian processes, In Rhodnius prolixus, patency is bel ieved to be brought about by the action of a JH-dependent membrane-hou nd Na+/K+ GTPase (EC 3.6.1.3); however, this had not been established in Tenebrio molitor. Therefore, the properties of the enzyme, with res pect to optimal assay conditions and juvenile hormone dependency, are reported, Maximal stimulation occurred between 50 and 500 nM JH III, a range over which greatest increases in patency were also observed, In infected insects, a 35% reduction in Na+/K+ ATPase activity was noted , but exposure to 50 nM JH III is sufficient for stimulation to a spec ific activity 89% that of JH-treated controls, In a similar fashion, p atency in infected insects is reduced, but can be 'rescued' by 50 nM J H III, Moreover, in the absence of exogenous hormone, patency in infec ted beetles can be elevated to control levels after in vitro culture ( 6 h), with exchange of medium every 2 h, The possibility that such rev ersible decreases in enzyme activity and patency are caused by a JH bi nding inhibitor molecule is discussed. (C) 1997 Elsevier Science Ltd.