ALBERT

Notes: Summary 1. N-acetylglucosamine-l-14C or D-glucose-U-14C was given by injection into hemolymph orD-glucose-U-14C by means of stomach catheter to animals in premoult stage D4, about one day before moult. The distribution of radioactivity between the tissues and between the classes of body constituents was determined 3 hours after administration and about 22 hours after moult. These data are compared with published data on the fate of N-acetylglucosamine absorbed from the old exoskeleton via the integumental tissue (Speck and Urich, 1972b). 2. The distributions of radioactivity between the tissues and body constituents are very different in the four sets of observations (cf. Tables 1 and 2). 3. These differences are due primarily to the different chemical nature of the substances administered but are enhanced by the functional properties of the absorbing tissues. 4. Before moult the activity of administered N-acetylglucosamine is incorporated into shortlived polysaccharides and proteins especially within the integumental tissues. After moult this activity is found predominantly in CO2 and chitin. This indicates that specific polysaccharides and proteins function as storage substances for the N-acetylglucosamine absorbed from the old exoskeleton. After administration of glucose there is no synthesis of shortlived storage substances.

Notes: Summary Earlier data on the chemical conversion of glucose within the absorbing tissues in crayfish (Speck and Urich, 1972) are recalculated on the basis of the recently determined turnover constants for hemolymph constituents (HerzHübner, Urich and Speck, 1973). During glucose absorption, sugars, organic acids, and amino acids contribute one third each to the total substance transfer from absorbing tissues to hemolymph. Only 9 percent of absorbed glucose penetrates the absorbing tissues unchanged.

Notes: Summary 1. The turnover constants and half-lives of more than 20 important low molecular hemolymph constituents were determined from the decrease of radioactivity in the hemolymph after injection of14C-labeled substances (cf. Table 1). The turnover of amino acids is generally more rapid than that of sugars and organic acids. 2. With the poolsize in the hemolymph of a standard animal of 20 g body weight and the turnover constant the transfer from hemolymph to body tissues [μg/min] was calculated for each substance. The total transfer of hemolymph substances to tissues adds up to 390 μg/min, of which sugars make up 11 %, amino acids 32%, and organic acids, mainly lactate, 57% (of. Table 1). 3. When the concentration in hemolymph is experimentally increased the transfer of lactate is unaffected, that of glucose increased proportionally, and that of the amino acids examined enlarged subproportionally (cf. Table 2). 4. In premoult animals the turnover constant for N-acetylglucosamine is higher and that for trehalose and glutamine lower than in intermoult animals (cf. Table 3). This is consistent with the findings that before moult the synthesis of glucosamine from sugars, presumably by amino transfer from glutamine, is blocked, but a large amount of N-acetylglucosamine is absorbed from the old exoskeleton. 5. The accumulation of hemolymph substances in the organs and the transfers from hemolymph to the organs were calculated from the distribution of the14C-label in the organs (of. Tables 4 and 5). There are wide differences between the organs with regard to the degree of accumulation of substances, to the intensity of total transfer and to the contribution of the different substances or substance classes to this transfer. This indicates, that there are corresponding differences in the intensity of metabolic conversions. The degrees of accumulation of hemolymph substances and the specific activities of those enzymes that participate in the metabolism of these substances are well correlated (cf. Table 6).

Notes: Summary 1. U-14C-labelled glucose, amino acid mixture, palmitate, starch or protein were fed to the crayfish by means of a stomach catheter, 5 min to several hours after feeding determinations were made of the 14C-activity of sugars, polysaccharides, organic acids, amino acids, proteins, lipids and the most important components of the sugar fraction in the absorbing tissues (stomach, midgut, hepatopancreas and hindgut) and in hemolymph. 2. The absorbed nutrients were chemically converted within the absorbing cells very rapidly and extensively (cf. Tables 1 to 3). 3. The metabolites produced by the conversion of the nutrients were partially given off to the hemolymph (cf. Tables 3 and 4). An estimation of the relative rates of output showed that not much more than 20% of the absorbed glucose entered the hemolymph unchanged. The percentages for absorbed amino acids or palmitate were higher.

Notes: Summary 1. The quantitatively most important body constituents of freshly caught, male crayfish were determined at about monthly intervals from April 1969 until March 1971 except during the moulting period which occurs in summer (cf. Tables 1 to 3. 2. Every body constituent showed significant fluctuations of concentration during the course of the year. 3. The body weight of a “standard animal” increased from 20.0 g in October to 21.5 g in December and to 22.5 g from January to May. During the extremely cold winter and spring of 1969/70 there was at first an increase in protein content from 1700 mg in January to 2700 mg in March, followed by a decline to 2150 mg in May; all other constituents of the body displayed an increment from October to December–January (“winter accumulation”), followed by gradual decrement to the minimum in April–May. During the outstandingly warm winter and spring of 1970/71 these changes were less marked (cf. Fig. 1). 4. There were great differences in the composition of the tissues, especially in the amino acid patterns. The composition of tissues from animals in October differed only slightly from that of postmoult animals 1 to 4 hours after moult (cf. Tables 4 and 5).

Notes: Summary 1. With the intention of observing the metabolic fate of N-acetyl-glucosamine liberated from the chitin of the old exoskeleton N-acetyl-glucosamine-1-14C was injected into the space between old and new integument of premoult animals in stage D4, about 1 to 2 days before moult. At different time intervals after injection or after moult the14C-activities in chitin, protein, polysaccharide, lipid, low molecular weight metabolic products (“Intermediärprodukte”), free N-acetyl-glucosamine, free and polysaccharide-bound glucosamine were determined in all tissues. 2. Before moult the N-acetyl-glucosamine is accumulated preferentially in the integumental tissue, i. e. in the sample of this tissue from the carapax, the other parts of the exoskeleton (“Restkrebs”) and the gills (cf. Table 1). The abdominal muscle accumulates14C-activity very rapidly, but does not release it again. Maximal incorporation takes place in proteins and polysaccharides. Of the rapidly declining activity of low molecular weight products ≧40% are included in N-free sugars (+ organic acids), ≧20% in amino acids, ≦20% in N-acetyl-glucosamine, but about 2% only in glucosamine. In the polysaccharides 1/5 of the activity is incorporated in glucosamine. 3. 7 to 77 hours after moult 73% of14C-activity are found in CO2 and the chitin of “Restkrebs” and gills, 10% in abdominal muscle, but 17% only in the substances of other tissues. From this and from the correspondence of the specific activities of chitin and CO2 with that of the absorbed N-acetyl-glucosamine there must be concluded, that the absorbed N-actyl-glucosamine is not mixed with general metabolic pools, but is accumulated in specific pools to be re-used for chitin synthesis and energy metabolism.

Notes: Summary 1. Crayfish Orconectes limosus at the intermoult stage were fed by means of a stomach catheter with 0,1 to 5,0 mg of one of the following U-14C-nutrients: D-glucose, L-amino acid mixture, palmitate, starch, protein. At different times after feeding the 14C-activities were determined for the gut contents, hemolymph, body tissues and CO2. From these data inferences were drawn about the site and velocity of absorption and the distribution of absorbed nutrients among the body tissues. Gut contents and hemolymph have been labeled with 3H-inulin. 2. After 3H-inulin was fed into the stomach its kinetics of distribution among thedifferent parts of the gut lumen supports the view that the gut contents are mixed rapidly and completely. After only 5 min 3H was found in all parts of the gut lumen; within 15 min there was a specific and different concentration in each part of the gut lumen and these concentrations remained constant. 3. The main site of absorption is the hepato-pancreas, but stomach, midgut and hindgut are also capable of absorption. The quotient 14C/3H in the lumen of the hepato-pancreas is always lower than that in the lumen of the stomach or the midgut. Comparing all types of tissue, the 14C-activity rises most quickly and to the highest values in the gut tissues. The isolated, ligatured stomach transports 14C-glucose or -palmitate from the lumen toward the medium. Everted sacs of the hindgut are capable of accumulating glucose in their interior. 4. Palmitate can be absorbed by means of two different pathways: it is absorbed either in the hepato-pancreas and stored there in the form of lipids, or it is transformed within the stomach tissue into a water soluble intermediate and conveyed very rapidly by way of the hemolymph to the body tissues. 5. The velocity of absorption is surprisingly high. The initial velocity of absorption after feeding 5 mg glucose or amino acids amounts to 300–400 μg/min, with 1 mg palmitate the value is 60, with 5 mg starch or protein about 90 μg/min. 6. The distribution of absorbed 14C-activity among the body tissues is almost independent of the nature of the nutrient. Even in the last period of observation, 3 to 6 hours after feeding, the 14C-activities of the gut tissues are significantly higher than those of any other tissue. This is evidence that the gut and especially the hepatopancreas have a storage function. Heart and antennal gland always contain more, muscle and gills always less 14C-activity than would be expected from their proportions of the body weight. The hemolymph can, for short periods, accumulate up to 〉20% of supplied carbohydrate, but only a much smaller percentage (〈4%) of supplied amino acids. 7. The proportion of 14C-activity, that is incorporated within 3 hours into CO2, is significantly greater after feeding amino acids (16,9–18,6%) than after feeding glucose (2,6–12,5%) or palmitate (4,4–5,5%).