Among the published reports on invertebrate biochemistry is a study by Robin (1954) using Arenicola marina L. Robin hypothesized that taurocyamine, a sulfur-containing guanidine derivative, was formed from taurine. Although the hypothesis has not been demonstrated experimentally, it constitutes a major part of the information presently available on sulfur metabolism in invertebrates. Taurine in invertebrates generally has been regarded as a metabolically inactive compound. In Arenicola, however, since taurocyamine appears to be the phosphagen involved in energy transfers related to muscular activity, Robin's hypothesis requires an active metabolic role for taurine. Relatively high levels of taurine have been reported from a diversity of marine invertebrates. The fact that no definite role has been demonstrated for these high levels suggests that an organism, such as Arenicola, which presumably both synthesizes and metabolizes taurine, might be a useful experimental tool for studying sulfur metabolism in invertebrates. The present study was undertaken to determine the biochemical pathway leading to taurine formation in Arenicola cristata Stimpson, and to determine whether taurocyamine is synthesized by the route suggested by Robin or by some other mechanism.

In addition to dramatic effects on the primary and secondary sexual characteristics, there are several responses to castration and testosterone administration in the male mammal which indicate this hormone to be at least indirectly a controlling factor in some of the body's fundamental metabolic processes. In the case of the albino rat infected with Hymenolepis diminuta, these effects in turn cause changes in the normal activities of this tapeworm, indicating the far-reaching influence of this sex hormone as well as the intimacy of the host-parasite relationship. The present investigation represents an attempt to analyze further one part of this relationship: namely, some of the metabolic responses of the tapeworm to changes in the testosterone level of the host.

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The studies reported herein are part of an overall program devoted to the task of providing sufficient factual information for a more complete understanding of the physiology of the rat tapeworm, Hymenolepis diminuta, and the relationships that it has with its host. There are essentially two lines of attack that such a program may take. First, a knowledge of the basic constituents of the parasite is necessary in order to know the type of material with which one is dealing. An essential adjunct to this knowledge is an understanding of the factors, within and without the organism, that control the quantitative levels of these various constituents. A second way by which it is possible to obtain information on the physiological and chemical activities of the parasite is through experiments designed to test or assay the metabolic capabilities of the organism in terms of a particular enzyme system or a sequence of enzyme systems.

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The present work involves the examination of parathyroid tissue, histologically and cytologically, and an extension of the findings to the submicroscopic level with the aid of the electron microscope. Primary interests in the study are to elucidate factors in the process of secretion by the tissue cells; to examine changes in different states of secretory activity; and ultimately to use these as criteria for estimating secretory rate in response to altered physiological conditions in an attempt to clarify the mechanism responsible for stimulating hormone production.

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