Claudin-15 and -25b expression in the intestinal tract of Atlantic salmon in response to seawater acclimation,smoltification and hormone treatment

In seawater fishes, osmotic homeostasis requires uptake of ions and water in the intestine and these processes are governed by the combined trans- and paracellular pathways. The current study examined mRNA expression of two tight junction proteins (claudin-15 and -25b) predominantly expressed in the intestine of Atlantic salmon. We examined the response in pyloric caecae, middle and posterior intestine to seawater challenge, during smoltification and after injection with osmoregulatory hormones. Seawater (SW) transfer elevated levels of claudin-15 and -25b while no change was induced throughout the smolt stage. In freshwater, cortisol and growth hormone inhibited claudin-15 expression in the two anterior segments. Claudin-25b was elevated in all intestinal segments by growth hormone, while cortisol had an inhibitory effect. In seawater, prolactin and cortisol inhibited claudin expression. The data suggest that claudin expression is involved in the reorganisation of intestinal epithelium and possibly change paracellular permeability during SW acclimation. The lack of preparatory change during smoltification suggests that this process is not completed during smolt development. The effects of the tested hormones cannot explain the sum of changes induced by salinity, which, like the smoltification data, suggests the importance of additional factors and possibly contact with the imbibed SW per se.     

Cortisol and hypothalamic–pituitary–gonadal axis hormones in follicular-phase women with fibromyalgia and chronic fatigue syndrome and effect of depressive symptoms on these hormones

We investigated abnormalities of the hypothalamic–pituitary–gonadal axis and cortisol concentrations in women with fibromyalgia and chronic fatigue syndrome (CFS) who were in the follicular phase of their menstrual cycle, and whether their scores for depressive symptoms were related to levels of these hormones. A total of 176 subjects participated – 46 healthy volunteers, 68 patients with fibromyalgia, and 62 patients with CFS. We examined concentrations of follicle-stimulating hormone, luteinizing hormone (LH), estradiol, progesterone, prolactin, and cortisol. Depressive symptoms were assessed using the Beck Depression Inventory (BDI). Cortisol levels were significantly lower in patients with fibromyalgia or CFS than in healthy controls (P < 0.05); there were no significant differences in other hormone levels between the three groups.     

Induction of a 'Periderm-like' Tissue in Excised Roots of the Fern Ophioglossum petiolatum Hook

Basal applications of plant growth regulators to excised rootsof Ophioglossum induce modifications in the outer cortical cells.Benzyladenine initiates periclinal divisions in these outercells producing a ‘periderm-like’ tissue while 2,4-Dcauses cell enlargement only. Walls of the outer cells of the‘periderm-like’ tissue are resistant to sulphuricacid and stain with Sudan IV and presumably are suberized.     

Regulation of Prolactin and Growth Hormone Production by Clonal Strains of Functional Pituitary Cells in Culture

This report describes the use of clonal strains of rat pituitarytumor cells to study the regulation of prolactin and growthhormone production. Emphasis is placed on the effects on prolactinproduction of the hypothalamic tripeptide pGlu-His-ProNH₂, alsocalled thyrotropin releasing hormone (TRH). TRH binds to specificcellular receptors and stimulates initially the release of previouslysynthesized prolactin; several hours later it stimulates thesynthesis of prolactin. Several kinds of experimental resultsare consistent with the hypothesis that cyclic AMP mediatesthe TRH-stimuIated release of prolactin. However, all of theeffects of TRH on these cells in culture are not mimicked bycyclic AMP analogs, for TRH decreases growth hormone productionwhile it increases the synthesis of prolactin, and the analogdibutyryl cyclic AMP increases the production of both hormones.     

Impedance Spectroscopy in Frost Hardiness Evaluation of Rhododendron Leaves

Impedance spectroscopy was used in studying frost hardinessof leaves of two diploid rhododendron cultivars, RhododendronL. ‘PJM’ and R. ‘Cunningham's White’,and their tetraploid derivatives, R. ‘Northern Starburst’(NSB) and CW4. After the growing season and initial hardeningin a greenhouse, plants were subjected to an acclimation regimein a phytotron: 3 consecutive weeks at +5, +1 and -2°C each.Hardiness was studied with controlled freezing tests beforeeach decrease in temperature and at the end of the experiment,based on data of extracellular resistance r_eand relaxation time of the frost-exposed leaves. The correlation of the two estimateswas 0.92. Generally, the diploid clones had better frost hardinessthan the tetraploid clones. At the end of the experiment, frosthardiness of the diploid ‘PJM’ was -28.7°C andthat of the tetraploid NSB -20.6°C. Leaves of the diploid‘Cunningham's White’ and of the tetraploid CW4 hardenedto -32.0°C and -20.9°C, respectively. Frost hardinessestimated by impedance spectroscopy correlated well with earlierresults based on visual scoring (r = 0.81–0.86) and electrolyteleakage tests (r = 0.84–0.90), but results from impedancespectroscopy indicated weaker hardiness than the other tests.The difference between the results from impedance spectroscopyand the other tests was smaller and more coherent within the‘Cunningham's White’ clones than within ‘PJM’and NSB. Changes in extracellular and intracellular resistanceof non-frozen leaves during the acclimation correlated withthe changes in frost hardiness of ‘Cunningham's White’clones, but not with those of ‘PJM’ and NSB, whichbelong to another subspecies.Copyright 2000 Annals of BotanyCompany Cold resistance, evergreen, frost hardiness, impedance spectroscopy, polyploid, Rhododendron, tetraploid     

Expression of glucocorticoid receptor in the intestine of a euryhaline teleost, the Mozambique tilapia (Oreochromis mossambicus): effect of seawater exposure and cortisol treatment

Cortisol plays an important role in controlling intestinal water and ion transport in teleosts possibly through glucocorticoid receptor (GR) and/or mineralocorticoid receptor. To better understand the role of GR in the teleost intestine, in a euryhaline tilapia, Oreochromis mossambicus, we examined (1) the intestinal localizations of GR; (2) the effects of environmental salinity challenge and cortisol treatment on GR mRNA expression. The mRNA abundance of GR in the posterior intestinal region of tilapia was found to be higher than that in the anterior and middle intestine. In the posterior intestine, GR appears to be localized in the mucosal layer. GR mRNA levels in the posterior intestine were elevated after exposure of freshwater fish to seawater for 7 days following an increase in plasma cortisol. Similarly, cortisol implantation in freshwater tilapia for 7 days elevated the intestinal GR mRNA. These results indicate that seawater acclimation is accompanied by upregulation of GR mRNA abundance in intestinal tissue, possibly as a consequence of the elevation of cortisol levels. In contrast, a single intraperitoneal injection of cortisol into freshwater tilapia decreased intestinal GR mRNA. This downregulation of the GR mRNA by cortisol suggests a dual mode of autoregulation of GR expression by cortisol.     

Cortisol and prolactin modulation of caudal neurosecretory system activity in the euryhaline flounder Platichthys flesus

Previous studies have shown roles for cortisol and prolactin in osmoregulatory adaptation to seawater and freshwater, respectively, in euryhaline fish. This study of the European flounder investigated the potential for these hormones to modulate activity of the caudal neurosecretory system (CNSS), which is thought to be involved in physiological adaptation to changing external salinity. Superfusion of isolated CNSS with either cortisol or prolactin (10 microM; 15 min) led to changes in firing activity in neuroendocrine Dahlgren cells, recorded extracellularly. Cortisol evoked a modest increase in overall firing activity, with the response delayed by 4 h after treatment. The response to prolactin was short latency, continued to build up over the subsequent 4-h wash period, and comprised increased firing activity together with recruitment of previously silent Dahlgren cells. Immunoreactivity for glucocorticoid and prolactin receptors was localised to Dahlgren cells. The CNSS expression level for glucocorticoid-2 receptor mRNA, measured by Q-PCR, was significantly lower in fish fully acclimated to freshwater, compared to seawater. No differences were seen between these two states for prolactin receptor mRNA expression. These results provide evidence for a modulatory action of both hormones on the neurosecretory function of the CNSS.     

The Effect of Bud Position on Branch Growth and Bud Abscission in Quercus petraea (Matt.) Liebl.

The time at which a bud began to expand was related to its positionnot only on an individual shoot but also within the crown. Thedistribution of buds and branches on the shoot was uneven; theshoot tip, where they were densely clustered, was termed the‘whorl; and the remainder of the shoot, where they werewidely spaced, the ‘interwhorl’ stem. In spring,the terminal bud started expanding before the ‘whorl’buds which preceded the ‘interwhorl’ stem buds;completion of the flush of growth, determined by the end ofleaf expansion, occurred in the reverse order, ‘interwhorl’> ‘whorl’ > terminal. Similarly bud expansionstarted at the top of the crown and progressed downwards, andthe first shoots to complete their flush were at the bottomof the crown. Approximately 60% of the buds on each shoot beganexpanding in spring but only about half of these formed branches.Bud abscission began in May and by Sep. 45% of buds originallypresent had abscised. Most of-the buds that did not abscisewere the small buds at the base of the shoot that were not originallyassociated with a leaf. Approximately 42% of ‘whorl’buds and 28% of MnterwhorP stem buds formed branches. ‘Whorl’branches were approx. 60% longer that ‘interwhorl’stem branches; buds on the lower surface of the shoot producedlonger branches than those on the upper surface. The implicationsof the results for the development of crown form and selectionof superior oak are discussed. Quercus petraea, oak, buds, branches, crown form     

Effects of cortisol, 17beta-estradiol and thyroliberin on prolactin and growth hormone production, cell growth and cell cycle distribution in cultured rat pituitary tumour cells.

Prolactin and growth hormone production were measured in a rat pituitary tumour cell strain (GH₃) after treatment with cortisol (5 × 10^?6 M), thyroliberin (2.5 × 10^?6 M) and 17β-estradiol (10^?6 M). The changes in hormone production were related to alterations in cell growth rate and cell cycle distribution. Cortisol inhibited prolactin production, stimulated growth hormone production and reduced the cellular growth rate measured two days after start of treatment (maximum about 40% inhibition). Flow-micro fluorometric analysis of DNA distributions showed that cortisol treatment reduced the relative number of cells in S phase (maximum effect about 50%) with a compensatory increase of the proportion of cells in G₁ phase. The lack of inhibition of prolactin production after three days of cortisol treatment may partly be related to the increased number of cells in G₁ phase. Thyroliberin and 17β-estradiol did not significantly affect cell growth after six days of treatment, although the fraction of cells in S phase was reduced by approximately 40% with a corresponding increase of cells in G₁ phase. For thyroliberin and 17β-estradiol, the stimulatory effect on prolactin production and the inhibitory effect on growth hormone production witin a period of treatment of six days cannot be explained by a shift in cell cycle distributions. None of the three hormones influenced the growth fraction which was equal to unity. In conclusion, thyroliberin and 17β-etradiol are able to change prolactin and growth hormone production without altering the cell cycle distribution. However, the effects of cortisol on prolactin and growth hormone production may partly be due to an alteration in cell cycle traverse resulting in an increased number of cells in the G₁ phase.     

Physiological and molecular endocrine changes in maturing wild sockeye salmon, <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis>, during ocean and river migration

Maturing adult sockeye salmon Oncorhynchus nerka were intercepted while migrating in the ocean and upstream in freshwater over a combined distance of more than 1,300 km to determine physiological and endocrine changes associated with ionoregulation. Sockeye migrating through seawater and freshwater showed consistent declines in gill Na⁺/K⁺-ATPase (NKA) activity, plasma osmolality and plasma chloride concentration. In contrast, plasma sodium concentration became elevated in seawater as fish approached the river mouth and was then restored after sockeye entered the river. Accompanying the movement from seawater to freshwater was a significant increase in mRNA for the NKA α1a subunit in the gill, with little change in the α1b subunit. Potential endocrine signals stimulating the physiological changes during migration were assessed by measuring plasma cortisol and prolactin (Prl) concentrations and quantifying mRNA extracted from the gill for glucocorticoid receptors 1 and 2 (GR1 and GR2), mineralocorticoid receptor (MR), growth hormone 1 receptor (GH1R), and prolactin receptor (PrlR). Plasma cortisol and prolactin concentrations were high in seawater suggesting a preparatory endocrine signal before freshwater entry. Generally, the mRNA expression for GR1, GR2 and MR declined during migration, most notably after fish entered freshwater. In contrast, PrlR mRNA increased throughout migration, particularly as sockeye approached the spawning grounds. A highly significant association existed between gill PrlR mRNA and gill NKA α1a mRNA. GH1R mRNA also increased significantly, but only after sockeye had migrated beyond tidal influence in the river and then again just before the fish reached the spawning grounds. These findings suggest that cortisol and prolactin stimulate ionoregulation in the gill as sockeye salmon adapt to freshwater.     

Hormonal responses to analgesic nitrous oxide in man

Analgesic concentrations of nitrous oxide were administered to 6 healthy male subjects, and blood samples were assayed for prolactin, ACTH, follicle stimulating hormone, luteinising hormone, growth hormone, cortisol and thyroid hormones. Analgesic nitrous oxide (mean concentration = 48.8%) produced statistically significant elevation of prolactin and depression of cortisol whilst not producing statistically significant changes in the other hormones assayed. The increase in prolactin and decrease in cortisol levels are similar to the hormonal changes associated with administration of opioids in man. We have also confirmed the findings of other workers that cortisol levels may not always be correlated with ACTH levels.     

Effects of environmental salinity and temperature on osmoregulatory ability, organic osmolytes, and plasma hormone profiles in the Mozambique tilapia (Oreochromis mossambicus)

The Mozambique tilapia, Oreochromis mossambicus, is capable of surviving a wide range of salinities and temperatures. The present study was undertaken to investigate the influence of environmental salinity and temperature on osmoregulatory ability, organic osmolytes and plasma hormone profiles in the tilapia. Fish were acclimated to fresh water (FW), seawater (SW) or double-strength seawater (200% SW) at 20, 28 or 35 degrees C for 7 days. Plasma osmolality increased significantly as environmental salinity and temperature increased. Marked increases in gill Na(+), K(+)-ATPase activity were observed at all temperatures in the fish acclimated to 200% SW. By contrast, Na(+), K(+)-ATPase activity was not affected by temperature at any salinity. Plasma glucose levels increased significantly with the increase in salinity and temperature. Significant correlations were observed between plasma glucose and osmolality. In brain and kidney, content of myo-inositol increased in parallel with plasma osmolality. In muscle and liver, there were similar increases in glycine and taurine, respectively. Glucose content in liver decreased significantly in the fish in 200% SW. Plasma prolactin levels decreased significantly after acclimation to SW or 200% SW. Plasma levels of cortisol and growth hormone were highly variable, and no consistent effect of salinity or temperature was observed. Although there was no significant difference among fish acclimated to different salinity at 20 degrees C, plasma IGF-I levels at 28 degrees C increased significantly with the increase in salinity. Highest levels of IGF-I were observed in SW fish at 35 degrees C. These results indicate that alterations in gill Na(+), K(+)-ATPase activity and glucose metabolism, the accumulation of organic osmolytes in some organs as well as plasma profiles of osmoregulatory hormones are sensitive to salinity and temperature acclimation in tilapia.     

Diurnal Phototropism in Leaves of Lavatera cretica L. under Conditions of Simulated Solar-Tracking

Diurnal laminar reorientation was followed in solar-trackingleaves of Lavatera cretica L. under simulated conditions. Asimulated ‘sun’ was moved over the lamina in a 180?arc in the vertical plane of the mid-vein, at an angular velocityof 15? h^–1 in a regime of 12-h photoperiods. In one groupof plants the petioles of the experimental leaves were arrangedto face ‘sunrise’, while in the other they werearranged to face ‘sunset’. At ‘sunrise’,the laminae in both groups, which were inclined towards theanticipated direction of ‘sunrise’, changed theirelevation towards the rising ‘sun’, resulting inprogressive reduction in the angle of incidence (AI) of lighton the laminar surface (AI= differential between laminar and‘solar’ elevation). As a result, laminar and ‘solar’elevation converged, and laminar reorientation gradually ceased,until the ‘solar’ elevation had passed the normalto the laminar surface (AI=0?). laminar reorientation was thenresumed, but its direction was reversed to follow the directionof ‘solar’ reorientation. During most of the remaining‘day’, laminar elevation (LE) trailed that of the‘sun’ by an average of 11?-14?. Laminar reorientationthen anticipated ‘sunset’ by starting to slow down60 to 90min in advance. During the 12-h dark period, the laminareoriented towards the anticipated direction of the subsequent‘sunrise’. The time-course of nocturnal reorientationwas qualitatively different in the two groups of experimentalplants. The time-course of diurnal phototropism under naturaland simulated conditions is analysed and compared and differencesand similarities between them are discussed. Key words: Diurnal phototropism, solar-tracking, vectorial excitation     

In vivo effects of thyroid hormone, corticosteroids and prolactin on cell proliferation and apoptosis in the anterior intestine of the euryhaline mudskipper (Periophthalmus modestus)

We have previously shown that anterior intestinal epithelium of the euryhaline mudskipper (Periophthalmus modestus) undergoes apoptosis during seawater (SW) acclimation, whereas elevated cell proliferation was observed in freshwater (FW)-acclimated fish. To understand the possible endocrine regulation of the gastrointestinal cell turnover during salinity acclimation, we examined the ratios of apoptotic and proliferating cells in the anterior intestine of one-third SW-acclimated mudskipper treated with triiodothyronine (T3), cortisol, 11-deoxycorticosterone (DOC, the putative teleostean mineralocorticoid), or prolactin (PRL). In situ nick end labeling of genomic DNA (TUNEL) and immunohistochemistry of proliferating cells nuclear antigen (PCNA) were used as indicators of apoptosis and cell proliferations, respectively. Cortisol significantly elevated apoptosis (P<0.05) in the epithelia and connective tissues and also stimulated the epithelial cell proliferation (P<0.05). PRL induced epithelial cell proliferation (P<0.05), but did not affect apoptotic status of the intestinal epithelium. Neither T3 nor DOC had any impact on cell proliferation or apoptosis. Together, our results suggest a role for cortisol and PRL in the regulation of anterior intestinal epithelial turnover during salinity acclimation in this species.     

The study of differentiative potential of the lactating mouse mammary gland in organ culture

Summary The organ culture of the mammary gland of lactating mice was used to examine the response of the differentiated gland to lactogenic stimuli, insulin, cortisol, and prolactin. Time course studies showed that casein synthesis in cultured tissue decreased rapidly during the first 2 d despite the presence of the three hormones, but on the 3rd d tissue cultured with either insulin and prolactin or all three hormones regained the ability to synthesize milk proteins, casein, and α-lactalbumin: a greater increase occurred in the three hormone system. The delayed addition of prolactin on Day 2 to the culture system containing insulin and cortisol also stimulated casein synthesis. The addition of cytarabine, which inhibited insulin-dependent cell proliferation in cultured explants, did not block the rebound of milk protein synthesis. The results indicate that in the presence of insulin, cortisol, and prolactin mammary epithelial cells in culture first lose and then regain the ability of synthesizing milk protein without requiring the formation of new daughter cells.     

Effects of Inorganic Phosphate on the Utilization of Sucrose by Suspension-cultured Catharanthus roseus Cells

The metabolic fate of [U-¹⁴C]sucrose in suspension culturesof Catharanthus roseus cells was monitored for 96 h after thecells were transferred to fresh complete (‘+Pi’)or to phosphate-deficient Murashige and Skoog (‘–Pi’)medium. Sucrose was hydrolysed extracellularly to glucose andfructose. The rate of uptake of sugars by the cells was 1.5–3times higher in ‘+Pi’ culture than in ‘–Pi’culture. Little difference in the rate of incorporation of radioactivityinto the ethanol-soluble fraction was found between the ‘+Pi’and ‘– Pi’ cultures during the initial 24h of culture, but after 48 h the rate in ‘ +Pi’cultures was higher than that in ‘–Pi’ cultures.Incorporation of radioactivity into ethanol-insoluble macromoleculeswas always significantly higher in the cells in ‘+Pi’cultures than in those in ‘–Pi’ cultures.The results suggest that Pi strongly affects the utilizationof sugars by cultured plant cells through the stimulation oftransport of sugars as well as through the activation of metabolism. Catharanthus roseus, Madagascar periwinkle, suspension culture, inorganic phosphate, sucrose, transport, metabolism     

Factors Affecting the Abscission of Reproductive Organs in Yellow Lupins (Lupinus luteus L.): III. ENDOGENOUS GROWTH SUBSTANCES IN VIRUS-INFECTED AND HEALTHY PLANTS AND THEIR EFFECT ON ABSCISSION

Extracts of small and mature-size lupin pods yielded four substancesaffecting the growth of wheat-coleoptile sections: one acidpromotor (A), two acid inhibitors(B and X), and one neutralinhibitor(Y). Inhibitor B was extremely active, however, coleoptile sectionsshowed no signs of toxic effects; they resumed growth at a rapidrate after rinsing them and adding ß-indolylaceticand (IAA) to the medium. 1 µg of IAA was required to counteractthe effect of ‘B’ extracted from 230 mg. Of tissue.On an equal fresh weight basis the inhibiting action of ‘B’in lupin pods was 500–1,500 times more potent than thatof ‘inhibitor ß’ in etiolated pea seedlings. Small pods of plants infected with pea-mosaic virus yielded3 times the amount of ‘A’ of healthy plants (equivalentto 1 µg. IAA 0.3 µg. IAA per 25 g. of tissue respectively),and approximately the amount of ‘B’. Mature podsof virus-infected plants again yielded more‘A’,but also 2? times more ‘B’ than pods of healthyplants. Healthy pods yielded more ‘A’ than virus-infectedpods, and there was no difference in ‘X’. A lupin abscission test was developed and the effects of proximaland distal application of -naphthyl acetic acid (NAA) are presented,and discussed with respect to results of other abscission tests. ‘A’ accelerated abscission when applied proximally,and delayed or prevented it when applied distally. ‘B’strongly accelerated abscission when applied in either way.A possible mechanism explaining the abscission-inducing effectof developing pods on later flowers is discussed in terms ofthe substances ‘A’ and ‘B’. The partlyprevented abscission observed on virus-infected plants was foundto agree well with the proposed mechanism.     

Concentration-dependent differntial effects of cortisol on synthesis of α-lactalbumin and of casein in cultured mouse mammary gland explants: Importance of prolactin concentration

Summary Cortisol was previously shown to elicit a concentration-dependent inhibition of α-lactalbumin accumulation in midpregnant mouse mammary gland cultured in medium containing optimal concentrations of 5 μg/ml prolactin and insulin. In contrast, casein accumulation under these conditions was progressively stimulated by addition of increasing amounts of cortisol (Ono, M.; Oka, T. Cell 19: 473–480; 1980). In the present study we found that in the presence of a suboptimal concentration of 0.5 μg/ml prolactin, 2.8×10⁻⁹ M to 2.8×10⁻⁷ M cortisol stimulated α-lactalbumin accumulation. Furthermore, higher concentrations of cortisol produced a smaller inhibition of α-lactalbumin accumulation as compared to that obtained in cultures containing 5 μg/ml prolactin. The maximal increase in α-lactalbumin accumulation attained in the presence of 1.4×10⁻⁸ M cortisol, 0.5 μg/ml prolactin, and insulin was comparable to that observed in culture containing 5 μg/ml prolactin and insulin. Similar results were obtained in a cortisol concentration-response study of α-lactalbumin accumulation in cultures containing a suboptimal concentration of 0.5 μg/ml human placental lactogen. Measurement of the rate of α-lactalbumin synthesis in cultured tissue indicated that the opposing effects of low and high concentrations of cortisol on α-lactalbumin accumulation involved an alteration in the rate of synthesis of the milk protein. In contrast to α-lactalbumin, the synthesis of casein was stimulated in a concentration-dependent manner by addition of cortisol that acted synergistically with either 0.5 μg/ml or 5 μg/ml prolactin. The maximal increases were obtained in the presence of 2.8×10⁻⁶ M cortisol. These results indicated that the action of cortisol on α-lactalbumin accumulation can be modulated by the concentration, of prolactin and suggest that the interplay between cortisol and prolactin in regulation of α-lactalbumin synthesis may be different from that involved in casein synthesis.     

Nitrogen Metabolism, Respiration, and Growth of Cultured Plant Tissue

Critical examination of the amino-acid composition of proteinsin fast-growing and slow-growing tissues reveals only very 8maUdifferences, indicating that some factor other than the amino-acidcomplement is responsible for, or reflects, the great increasein the mass of protein in the fast-growing tissues. Increases in fresh weight and total protein are exactly parallel,indicating that water uptake is an active process associatedwith growth. Respiration, on the other hand, increases far morein the fast-growing over the slow-growing tissues than doestotal protein. A given amount of protein in the fast-growingtissue will support a much greater respiration rate than thesame amount in slow-growing tissue. The incorporation of radioactivity into amino-acids of the proteinin4icates that there are two distinct types: those in whichincorporation is increased in fast-growing tissue much morethan the total protein, and to the same ezte as respiration(notably glutarnic acid, aspartic acid, and threonine); andthose in which the increased incorporation is much nafler, slightlyless than total protein (notably proline and hydroxyproline).It is concluded that there are two n protein fractions: the‘active’ moiety, which is undergoing rapid breakdownd resynthesis, giving rise to much of the CO through oxidationof its residues; a the ‘inactive’ moiety, whichonce synthesized is not reutilized or broken down. It is theformer, or ‘active‘ protein whose synthesis is greatlyincreased in the fast. growing tissues, and it is the pace,rather than the kind, of reactions which differ entiates betweenthe fast- and slow-growing tissues. The entire experimental data are discussed with reference toa number of cur rent theories and investigations. A number ofexperimental observations are noted which admit of interpretationalong the lines here developed.