Shigui Liu

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The effects of different forms of stress on the American cockroach, Periplaneta americana (L.) have been systematically examined. This study demonstrated that at least two stress-related events occurred in the haemolymph of the American cockroach. First, the data clearly indicated that a large increase in hypertrehalosemic hormones occurred in the haemolymph of stressed cockroaches. Secondly, proteolytic activity in the haemolymph of stressed cockroaches was greatly increased. The increase of both hypertrehalosemic hormones and proteolytic activity in the haemolymph appeared to be a non-specific response to different forms of stress, including chemical poisoning with lindane, immobilization, forced movement, starvation, and elevated temperatures. The stress-related appearance of proteolytic activity and hypertrehalosemic hormones in the haemolymph could be blocked by neck ligation, suggesting the involvement of an unknown neurohormone or head factor in the release mechanism.;A major portion of this study deals with the isolation and in vitro characterization of the individual proteases present in the haemolymph. Two of these proteases have been purified to apparent homogeneity. The following properties of each of the isolated proteases were examined: (i) native molecular weight; (ii) optimal pH for activity; (iii) sensitivity to proteolytic inhibitors; (iv) cleavage specificity utilizing insulin B chain as substrate; (v) ability to degrade hypertrehalosemic hormones. The conclusion from these studies was that four distinct serine endoproteases appeared in the haemolymph in response to nonlethal forms of stress. These proteases were disappeared from the haemolymph when the stress was removed. One of these proteases was capable of clearing hypertrehalosemic hormones from the haemolymph both in vitro and in vivo. Under stress conditions leading to paralysis and death, two additional proteases, a serine and an aspartic endoprotease, appeared in the haemolymph, most likely of pathological origin.;These studies raise a number of important questions regarding the tissue of origin of the haemolymph proteases, the mechanisms involved in the release and/or activation of the proteases, the physiological role of these proteases, and the mechanisms involved in the clearing of these proteases from the haemolymph. The possible mechanisms involved, and the experimental approaches needed to prove or disprove such mechanisms, are discussed. The possible role of these haemolymph proteases in other stress-related events such as activation of prophenoloxidase, or clearance of FMRFamide-related peptides and proctolin, is discussed.



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