Histamine in the Phylum Platyhelminthes

Six members of the phylum Platyhelminthes have been examined for histamine content. The free-living species studied contained no histamine, whilst the parasitic species studied contain appreciable amounts of histamine. No correlation could be found between the histamine content of a parasite and that of its host tissue. Particularly high values of histamine were found in Mesocoelium monodi; this species also possesses an exceedingly high histidine decarboxylase activity. No ability to form histamine could be detected in the other members of the phylum examined. The distribution of histamine has been studied extensively in the vertebrates, and it is well established that the amine is present in greater or lesser amount in almost every mammalian organ, tissue, and fluid (Guggenheim, 1951; Feldberg, 1956). Among the invertebrates, high concentrations of histamine have been found in various stings and venoms (Marcou, Derevici, and Derevici, 1937; Jaques and Schachter, 1954; Rothschild and Parsons, 1962), in the gnat (Eckert, Paasonen, and Vartiainen, 1951), in two coelenterates (Mathias, Ross, and Schachter, 1960), and in a sponge (Ackermann and List, 1957). It is not known, however, whether histamine is of general as opposed to isolated occurrence among the lower invertebrate phyla. It has recently been suggested that histamine plays an important role in the general process of growth (Kahlson, 1960; Kahlson, Rosengren, and White, 1960), and it therefore seemed of particular interest to establish whether the distribution of the amine is widespread among the invertebrate species. During the course of such work, representatives of the classes Turbellaria, Trematoda, and Cestoda were examined both for histamine content and histidine decarboxylase activity. MATERIALS AND METHODS Animals: Free-living marine turbellarians (Stylochus megalops and Styloplanocera fasciata) were extracted for histamine within 1 hr of collection. Large numbers of Lytechinus variegatus were kept Received for publication 5 March 1963. in aerated tanks of seawater and examined for Syndesmis franciscana on the day of collection. Specimens of Fasciola hepatica were obtained from livers of cows derived from the Kingston Municipal Slaughter House; whole livers were brought to the laboratory and examined within 1 hr of the animals' being killed. Large numbers of Bufo marinus and Ameiva dorsalis were collected, killed singly, and immediately examined for Mesocoelium monodi and Oochoristica ameivae respectively. Extraction of histamine: Groups of freshly collected organisms were cleaned and weighed, and extracted with 10% (w/v) trichloroacetic acid (5 ml/g tissue) for 24 hr. Excess acid was removed by shaking the supernatant with 4 vol of anesthetic ether 5 times, the ethereal layers being discarded. After gentle heating to remove dissolved ether the aqueous residue was assayed for its histamine content. Each result is the mean of three experiments. Measurement of histidine decarboxylase activity: The method of Waton (1956), slightly modified and described in detail by Telford and West (1961a), was used. Briefly, groups of freshly collected organisms were cleaned and weighed, and ground in a glass mortar with a little sand and physiological saline solution (5 ml/g tissue). The supernatant fluid was incubated for 3 hr with L-histidine (15 mg) in the presence of phosphate buffer, aminoguanidine (to inhibit inactivation of histamine), and benzene (a catalyst). The amount of histamine formed from histidine was then determined by biological assay. In each experiment, mixtures with and without the substrate, and mixtures containing boiled homogenate or no homogenate, were incubated and assayed for histamine. The mean histamine content of mixtures incubated in the presence of histidine less the mean histamine content of mixtures incubated in the absence of histidine gave the amount of histamine formed from histidine. Each result is the mean of three experiments. Assay of histamine: Biological assays of all