摘要:

AbstractUrine of terrestrial and aquatic crabs generally is of neutral pH and contains negli‐gible waste nitrogen. Ammonia is added to urine during its reprocessing by the gills of some terrestrial species. The ghost crab,Ocypode quadrata, produces an acidic urine (pH100 mM). This prompted us to study the chemical changes which occur during urine reprocessing by this species. Urine and reprocessed urine were collected from fed animals maintained on sand moistened with diluted seawater, and several chemical variables were measured. During urine reprocessing, Cl−was reclaimed, and CO2concentration and pH increased. Evolution of gaseous ammonia was then measured in crabs which could and could not pass urine onto their gills. Animals with occluded nephropores released gaseous ammonia at a much lower rate (≈︁300 μmol·.kg−1·day−1) than animals with open nephropores (≈︁2,000 μmol·kg−·day−1). We hypothesize that the gaseous ammonia released by control crabs is predominantly due to degassing of NH3from the fluid (urine) upon the pH increase which occurs during reprocessing by the gill

ISSN:0022-104X    

DOI:10.1002/jez.1402670202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe investigated the influence of ambient temperature (Ta) and food availability on seasonal timing and extent of physiological responses to short photoperiod (SP), in particular daily torpor, in Djungarian hamsters (Phodopus sungorus). Exposure of hamsters to cold temperature (Ta= 5°C), relative to warm Ta(23°C), resulted in:(1)a significant advance (P<0.05) of the first occurrence of torpor among cold‐exposed hamsters (days 52–97 vs. days 83–99 in SP); (2) a higher (P<0.01) incidence of torpor (48% vs. 20% torpid animals/day);(3) a higher (P<0.05) degree of molt into the winter pelt; and (4) an accelerated reduction of body weights (P<0.001). However, within SP/cold‐Taexposed groups, individual hamsters clearly showed different tendencies for torpor (torpor on 0–95% of days observed). Therefore, we evaluated the effects of small changes in Taon torpor frequency and extension by subjecting the same SP‐adapted individuals to varying temperatures. Lowering of Tafrom 15°C to 10°C and 5°C caused significant (P<0.05) increases in the incidence of torpor (20%, 33%, and 40%, respectively) and lower minimal body temperatures during hypothermia (P<0.05). When the same animals were subjected to 24–48 h lasting periods of food restriction (60% of the ad libitum intake), torpor frequency further increased 1.8to 2.6‐fold at all Tas.These results show that Taand food availability are effective in modifying both seasonal timing and extent of photoperiodically controlled adaptations. This integration of multiple environmental cues, combined with a pronounced within‐species variability of winter adjustments, indicates that Djungarian hamsters are capable of flexible physiological responses towards unpredictable climatic changes in the environment.

ISSN:0022-104X    

DOI:10.1002/jez.1402670203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe insulin receptor, purified from the hepatopancreas of the shrimpPenaeus monodon, is a hydrophobic heterodimer of subunits with relative masses (Mr) of 70,000 and 58, 000, as estimated by FPLC on Superose™12 and SDS‐PAGE. Only the subunit of Mr 70,000 was autophosphorylated after the addition of insulin. The autophosphorylation occurred specifically at Tyr residues, as demonstrated by the specific subsequent dephosphorylation by the phosphotyrosyl protein phosphatase from the hepatopancreas of the shrimpPenaeus monodon. Proteins of Mr 44,000 and Mr 32,000 on the plasma membrane from the hepatopancreas of the shrimpPanaeus monodonwere phosphorylated by the autophosphorylated insulin receptor from the shrimp hepatopancreas, but not by that from the human placenta. The detergent, Triton X‐100, caused noticeable enhancement of the autophosphorylation of both shrimp and human insulin receptors. © 1993 Wiley‐L

ISSN:0022-104X    

DOI:10.1002/jez.1402670204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of differential rates of evaporative water loss on the survival capabilities of small aggregates (ca. 10 mg wet wt) ofAphelenchus avenaewere assessed. This was achieved using a comparative approach between rapid (direct transfer of preconditioned nematodes to successively compounds accumulated were also assessed during the induction process. Glyecrol and glucos levels remained low (<1% dry wt)) while trehalose levels increased dramatically during preconditioning (8–10% dry wt), but the elevated levels were unable to support survival during periods of rapid water loss. Survival was directly related to the rate of evaporative water loss, with the highest level of survival being afforded by the most gradual dehydration regime. In addition, the water loss curves identified a critical period where hydration levels ranged from 40% to 12% H2O. During this time, slow drying was essential if the nematodes were to successfully survive the dehydration process. Survival curves also revealed the existence of a transition phase in the dehydration process, where nematodes required further dehydration before revival could occur. These results are discussed in relation to the adaptive significance of polyhydroxy compound accumulation and the probable role that specific hydration levels play in the implementation of other adaptations at the cellular and subcellular levels. © 1993 Wiley‐Liss,

ISSN:0022-104X    

DOI:10.1002/jez.1402670205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe spleen of the newtTriturus cristatus carnifex(Laurenti) hoards erythrocytes when the animal is well oxygenated and releases these into circulation when the animal becomes hypoxic. This mechanism allows the newts, amphibians with prevalently cutaneous respiration, to adapt to both environmental and metabolic changes.Splenectomized specimens were anesthetized with chlorbutol (to eliminate movement and lung respiration) and observed in five different conditions: at 18°C in humid air, stirred water, and still water, and at 6°C and 33°C in humid air. The study demonstrates that the newt does not have substitute sites for erythrocyte accumulation. However, though the spleenless specimens are incapable of controlling their cutaneous oxygen supply, they can regulate their blood volume, which diminishes with decreasing temperature causing marked variations in the erythrocyte concentration and hematocrit value.The splenectomized specimens, raised for over a year at 18°C, present typically steatosic livers, with lipid droplets and extremely low hepatocyte glycogen levels, indicating a state of chronic hypoxia due to the prevalently aquatic habits of the newt. In fact, the spleenless newts have significantly fewer erythrocytes (P<0.001) than the unoperated animals‐‐a total volume of 2.27 ± 0.46 ml per 100 g of body weight compared to 2.74 ± 0.29 (mean ± standard deviation). The limited quantity of erythrocytes can provide adequate oxygen only at low temperatures and in an airy environment or in moving water, while an immobile animal in still water undergoes hypoxia due to the formation around it of an hypoxic =diffusion boundary layer= caused by the low coefficient of oxygen diffusion in water. © 1993 Wile

ISSN:0022-104X    

DOI:10.1002/jez.1402670206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractI found evidence of a morphological constraint on the food choice of young stages of a cichlid fish. The constraint is not a developmental one because it is not imposed by developmental changes. I found no evidence of developmental constraints. In gradual transitions developmental constraints may be rare, in contrast to their regular occurrence in sudden transitions. I suggest that flexible muscle activation and reserve capacity (structural capacity in excess of functional demand) provide organisms with mechanisms that buffer against the effects of form changes and as such facilitate ontogenetic and evolutionary changes.A mathematical model for piercing prey in the pharyngeal jaws is applied to a juvenile cichlid fish. The maximum possible biting forces and the best biting directions were calculated. Piercing forces were measured that were generated when natural prey were pierced. The results were compared with the feeding behaviour in the laboratory and in the field and with results from an adult. The model predicts great flexibility of the pharyngeal jaw apparatus. Furthermore, the model predicts that a shift in biting point, prey size, or predator size leads to changes in muscle recruitment. The m.transversus ventralis is predicted to play an important role in pharyngeal biting.The model explains why large fish can easily pierceChaoboruslarvae and pupae, whereas a fish of 2.5 cm is just able to pierce larvae (symmorphosis) and is unable to pierce pupae. The inability of small fish to pierce pupae is due to a morphological constraint. This constraint is imposed by the size of the cross‐sectional areas of the muscles that generate the biting force. © 1993 Wiley‐Liss,

ISSN:0022-104X    

DOI:10.1002/jez.1402670207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractGonadotropin‐releasing hormone (GnRH) binding sites were characterized in the goldfish testis using an analog of salmon GnRH ([D‐Arg6, Trp7, Leu8, Pro9‐NEt]‐GnRH; sGnRH‐A) as a labeled ligand. Binding of sGnRH‐A to goldfish testicular membrane homogenate was found to be saturable, reversible, and dependent on time, temperature, and tissue concentration. Addition of unlabeled sGnRH‐A displaced the bound125I‐sGnRH‐A in a dose‐related manner. Hill plot as well as Scatchard analysis indicated the presence of two classes of binding sites, a high affinity/low capacity site and a low affinity/high capacity site in the goldfish testis. Bound125I‐sGnRH‐A was also found to be displaceable by sGnRH ([Trp7, Leu8]‐GnRH) and cGnRH‐II ([His5, Trp7, Tyr8,]‐GnRH) which occur naturally in the goldfish brain. sGnRH‐A and cGnRH‐II were found to bind with greater affinity than sGnRH to the goldfish testicular GnRH binding sites. The findings provide the first characterization of testicular GnRH binding sites in a teleos

ISSN:0022-104X    

DOI:10.1002/jez.1402670208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractInterrenal and ovarian tissues ofRana esculentawere incubated in vitro during the preovulatory, ovulatory and postovulatory phases to study the basal release of prostaglandin E2(PGE2), prostaglandin F2α, (PGF2α), corticosterone, and cortisol. The effects of exogenous PGE2and PGF2αon interrenal and ovarian corticosteroid release were also studied. In addition, the plasma values of these four hormones were assessed during the same phases. During in vitro interrenal incubations, PGE2αPGF2α, corticosterone, and cortisol basal releases were higher in the postovulatory phase, PGE2, and PGF2αtreatment in vitro increased corticosteroids during the ovulatory phase. During in vitro ovarian incubations, PGE2basal release was higher in the preovulatory phase and PGF2αand corticosteroids in the ovulatory phase; PGE2treatment in vitro decreased corticosteroids in the ovulatory phase, and PGF2αincreased corticosteroids in the preovulatory and postovulatory phases. PGE2, corticosterone and cortisol plasma values were higher during the postovulatory phase, while PGF2α, was elevated during the ovulatory phase. These findings suggest that ovarian corticosteroids could be considered one of the factors inducing ovulation and that their synthesis may be modified by PGs. © 1993 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402670209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of periventricular nucleus (Pe) lesioning on the plasma growth hormone (GH) levels and the anterior pituitary (A.P.) and brain somatostatin (SRIF) receptors were studied. A transient significant increase in plasma GH level in lesioned rats was detected 1 day after the were paralleled by an increase in binding of125I‐Tyr11‐SRIF‐14 to the A.P. 1 day after lesioning. This result could further confirm that the SRIF inhibitory action on GH release takes place at the A.P. level. Also, a transient increase in binding of the radioligand was detected in some brain areas 1 and 4 days after the lesion. However, the mechanism by which this increase takes place remains to be elucidated. © 1993 Wiley‐L

ISSN:0022-104X    

DOI:10.1002/jez.1402670210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe wound epithelium of regenerating limbs of the American newt,Notophthalmus viridescens(Nv), up‐regulates a number of antigens, including those recognized by mAbs WE3 and WE4. In the present study, we show that the WE3 antigen is up‐regulated in a similar fashion in the wound epithelium of the European newt,Pleurodeles waltl(Pw). mAb WE3 and WE4 reactivities to secretory/transport body cell types, including integumentary glands, perineurium, endothelium, and conjunctiva, are also similar in these two species of newt. However, mAb WE4 reacts to both the epidermis and wound epithelium in Pw, whereas in Nv, mAb WE4 reacts only to the wound epithelium. Because the WE3 antigen is cytoskeleton‐associated and Western blots reveal a 43 kDa species, we compared mAb WE3 reactivity with that of rhodamine‐labeled phalloidin, a known actin‐binding compound. Phalloidin did not react preferentially to the wound epithelium, conjunctiva, or other cell types strongly reactive to mAb WE3. Pretreatment of sections and tissue extracts with DNAse 1, a protein known to bind to actin, nearly abolished mAb WE3 reactivity in tissue sections and both WE3 and WE4 reactivity in ELISA assays, respectively. The results lead to the hypothesis that the WE3 and WE4 antigens are actin‐binding proteins unique to the wound epithelium and other secretory/transport cell types. © 1993 Wil

ISSN:0022-104X    

DOI:10.1002/jez.1402670211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY