摘要:

AbstractThe biocalcification of Mediterranean red coralCorallium rubrum(Anthozoa, Octocorallia) was investigated by using45Ca as a tracer to follow calcium transport and deposition. Kinetic experiments were performed by tracing the appearance of radioisotope in the three studied compartments of the apical part of the red coral: tissue fraction, spicules, and axial skeleton. The results demonstrate that calcium is absorbed by tissue before being deposited in the skeletal structures. The interval of time required by calcium to reach the site of calcification is about 1 hour. The spicule fraction represents the most important site of45Ca deposition in comparison with the other two compartments.By using different kinds of inhibitors, we demonstrate that calcium enters the cell along its electrochemical gradient via verapamil‐sensitive calcium channels and is concentrated in spicule‐forming vesicles or exported to the site of axis formation by an energetic process whose activation energy is 12 Kcal/mol for both skeletal structures.Modifications of the CO2/HCO3−buffering system were used to examine the possible origins of inorganic carbon for CaCO3formation. Our results suggest that metabolic CO2may serve as a main source. The carbonic anhydrase enzyme appears to be involved in the hydratation of CO2to HCO3, this latter ion being subsequently transported to the calcification site by a Cl−/HCO3−exchanger. © 1992 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402620302

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn carp exposed to pH 5.2 in fresh water, the Ca2+influx from the water is reduced by 31% when compared to fish in water of neutral pH. At pH 5.2, the Ca2+influx but not Na+uptake is decreased by aluminum (Al). Al reduces Ca2+influx dose‐dependently: a maximum 55% reduction was observed after 1–2 h exposure to 200 μg·1−1(7.4 μM) Al. Branchial Ca2+efflux is less sensitive to Al and affected only by exposure for more than 1 h to high Al concentrations. Na+influx is not affected by concentrations Al up to 400 μg·1−1. Na+efflux, similarly to Ca2+efflux, increased when fish were exposed for more than 1 h to 400 μg·l−1Al. © 199

ISSN:0022-104X    

DOI:10.1002/jez.1402620303

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

年代:1992

数据来源: WILEY

摘要:

AbstractVitamin D3(20 I.U./100 g body wt) was administered to the freshwater snakeNatrix piscatorfor 15 days. Elevation of serum calcium and inorganic phosphate levels was observed after the treatment. The ultimobranchial body became active whereas the parathyroid glands exhibited reduced activity. © 1992 Wiley‐Liss, I

ISSN:0022-104X    

DOI:10.1002/jez.1402620304

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

年代:1992

数据来源: WILEY

摘要:

AbstractAdministration of L‐thyroxine (T4) to thyroidectomizedCalotes versicolorsignificantly increased the activity of glucose‐6‐phosphatase (G‐6‐Pase) (liver and kidney), the concentrations of blood glucose and total protein (liver and kidney), and decreased hepatic cholesterol when compared to thyroidectomized lizards. Propranolol injections in thyroidectomized lizards increased the cholesterol concentration and did not change the other parameters. The activity of G‐6‐Pase and blood glucose content was stimulated, whereas the total protein and cholesterol contents were decreased after alloxan treatment. Administration of T4to thyroidectomized animals pretreated with propranolol or alloxan significantly elevated the activity of G‐6‐Pase, the concentrations of blood glucose, and total protein, and reduced hepatic cholesterol level when compared to drug‐treated lizards. From the results, it is evident that thyroid hormone has an independent stimulatory influence on intermediary metabolism inC. versicolorirrespective of the involvement of adrenaline or insulin. ©

ISSN:0022-104X    

DOI:10.1002/jez.1402620305

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

年代:1992

数据来源: WILEY

摘要:

AbstractRecent studies have shown that agents that increase intracellular calcium content (calcium ionophore A23187) and activate protein kinase C (phorbol 12‐myristate 13‐acetate; PMA) modulate basal and cAMP‐stimulated steroid production by goldfish preovulatory ovarian follicles. This report describes studies evaluating sites in the steroidogenic cascade (pre‐ and postadenylyl cyclase) influenced by calcium and protein kinase C. PMA (12.5–400 nM) inhibits hCG stimulated cAMP production, whereas phorbol 12, 13‐dideconate, an inactive phorbol ester that does not activate protein kinase C, was without effect. Earlier studies suggested that PMA also acts post cAMP formation, but this action was shown to be exerted prior to cholesterol side‐chain cleavage as metabolism of 25‐hydroxycholesterol to testosterone was not inhibited by PMA. A high dosage of A23187 (4000 nM) inhibited the stimulatory action of hCG on cAMP and testosterone production; lower dosages of A23187 were without effect. In contrast, a wide range of A23187 dosages (250–4,000 nM) enhanced conversion of 25‐hydroxycholesterol to testosterone. This effect appears to be exerted at the level of the cholesterol side‐chain cleavage enzyme as A23187 did not affect conversion of exogenous pregnenolone to testosterone. These data demonstrate specific regulatory actions of calcium and protein kinase C at multiple sites in the steroidogenic cascade both proximal and distal to cAMP generation.

ISSN:0022-104X    

DOI:10.1002/jez.1402620306

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

年代:1992

数据来源: WILEY

摘要:

AbstractCalcitonin‐like immunoreactivity has been found in blood and tissues of the marine blue crab,Callinectes sapidusRathbun. The activity in blood rises significantly during the immediate premolt (D4) stage, but tissue immunoreactivity does not vary significantly with molt stage. The immunoreactivity to antisalmon calcitonin serum is due to a 27.2 kDa protein that shows strong similarities in amino acid composition to a similar protein in a lobster and to human calcitonin precursor. The protein is most abundant in the midgut glands (hepatopancreas), but is also found in significant quantities in several other tissues. Immunoreactivity in the blood appears to be primarily due to the same molecular weight fraction, with secondary contributions from smaller molecules, closer in size to vertebrate calcitonin. A physiological function of the calcitonin‐like substance in calcium transport during or after molt has yet to be demonstrated. © 1992 Wiley‐Lis

ISSN:0022-104X    

DOI:10.1002/jez.1402620307

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

年代:1992

数据来源: WILEY

摘要:

AbstractA recombinant human IGF‐I (rhIGF‐I) was applied to primary cultures of rainbow trout pituitary cells. In wells containing 3 × 104and 6 × 104cells/well, rhIGF‐I inhibited basal GH release both in short (6 h) and long (12 and 24 h) exposures. The decline in GH release was dose‐dependent over the range of 0.01 and 100 mM. The combination of rhIGF‐I and low concentrations of synthetic somatostatin14(SRIF) enhanced the inhibitory effect of rhIGF‐I in an additive manner. Any appreciable effect of rhIGF‐I on PRL release was not evidenced. To our knowledge, this report demonstrates for the first time the participation of IGFs on the inhibitory component of fish GH regulation. © 1992

ISSN:0022-104X    

DOI:10.1002/jez.1402620308

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

年代:1992

数据来源: WILEY

摘要:

AbstractFertile eggs from the domestic fowl were incubated under normobaric normoxic (21% O2), hypoxic (14% O2), and hyperoxic (40% O2) conditions in order to examine the influence of the prevailing oxygen level on the growth and maturation of the chorioallantoic memorane. Eggs were sampled at regular stages throughout incubation for morphometric analysis. Under normoxic conditions, maturation of the capillary plexus occurred in two distinct stages, both of which contributed to a reduction in the thickness of the air‐blood barrier. Between days 6 and 10, the capillaries sprouted and fused to form a dense plexus. Subsequently, between days 10 and 14, this plexus invaginated into the chorionic epithelium. Differentiation of the chorioallantoic membrane appeared maximal by the end of this period. Hypoxia resulted in diminished growth of the embryo and chorioallantoic membrane, but in accelerated maturation of the capillary plexus. Hyperoxia had a less marked effect but appeared to retard the final invagination of the plexus, resulting in a thicker air‐blood barrier. © 1992 Wiley‐Lis

ISSN:0022-104X    

DOI:10.1002/jez.1402620309

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

年代:1992

数据来源: WILEY

摘要:

AbstractTime‐lapse video light microscopy was used to study the emergence and maturation of the migratory slug from aD. discoideumaggregate. The anterior part, the tip of this simple multicellular organism, establishes migration prior to the definition of the rear, and hence the length of the slug. It was found that newly formed slugs of wild‐type strain WS380B can reach lengths greater than 1 cm, yet mature slugs of this strain are rarely longer than 2–3 μmm. Often the tip extended out of the aggregation mound upon an arching pillar of cells. After the tip first touched the substratum, it commenced migration with a rapid succession of movement steps. Here we show that at the initiation of migration, a differential rate of cell movement along the developing slug axis results in a series of complicated changes, before the stable and mature shape of the slug is formed. Our results lead to new conclusions aboutD. discoideumslug formation and shape maintenance. Evidence is presesnted for regulation of slug length. © 1992 Wiley‐

ISSN:0022-104X    

DOI:10.1002/jez.1402620310

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe marine hydroidHydractiniais a model system for study of historecognition in invertebrates. Present knowledge of this system comes from fusibility studies involving intraspecific (i.e., isogeneic and allogeneic) encounters of adult‐stage stolonal tissues. Little is known about the ability ofHydractiniato recognize and respond to xenogeneic tissue, about allorecognition by tissues other than stolonal, and about the ontogeny of historecognition. We have investigated these questions with stolonal‐encounter and grafting experiments, using the speciesH. echinataandH. symbiolongicarpus.We find that (a)Hydractiniaemploys the nematocyst effector system against the closely related hydroidPodocoryneand the more distantly relatedEirene; (b) unlike intraspecific encounters, these interspecific encounters elicit nematocyst discharge byHydractiniaover a distance of up to 50 μm prior to stolonal contact; (c) the capability for historecognition is not restricted to stolonal tissues; (d) the capacity to display incompatibility, or rejection, arises between the late larval stage and early post‐metamorphosis; and (e) embryo grafts ofH. symbiolongicarpus, but not those ofH. echinata, appeared to show limited tolerization. © 1992 Wiley‐

ISSN:0022-104X    

DOI:10.1002/jez.1402620311

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

年代:1992

数据来源: WILEY