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The possible cyclic AMP-dependence of an early prereplicative event that determines mitosis in regenerating rat liver 总被引:1,自引:0,他引:1
The beta-adrenergic blocker dl-propranolol prevented a large proportion of regenerating rat liver cells from entering the mitotic phase of their first cell division cycle without affecting their ability to initiate or complete DNA replication. The drug, at a dose of 20 or 50 mg/kg of body weight, was most effective in reducing mitosis when injected between 1 and 2 hours after the proliferatively activating partial hepatectomy, which was 22 to 23 hours before the peak of DNA-synthetic activity. Propranolol also inhibited the early prereplicative surge of total liver cyclic AMP, which occurs shortly after partial hepatectomy, but this effect was not correlated to the mitosis-inhibiting activity. However, cyclic AMP or dibutyryl cyclic AMP completely reversed propranolol's mitosis-inhibiting action when injected between 1.5 and 2 hours (but not sooner or later) after partial hepatectomy, which was just before the total liver cyclic AMP content began to rise. Thus, there appears to be a transient, propranolol-inhibitable, probably cyclic AMP-initiated event in the early prereplicative development of rat hepatocytes that determines entry into mitosis rather than the initiation of DNA replication. 相似文献
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Antoni Lombarte Ana Gordoa Alan K. Whitfield Nicola C. James Víctor M. Tuset 《Environmental Biology of Fishes》2012,94(4):601-614
Ecomorphological changes as a result of natural perturbations in estuarine fish communities were investigated in two South African estuaries (Swartvlei and East Kleinemonde), both before and after the loss of aquatic macrophyte beds in these systems. The fish communities were analysed using an ecomorphological diversity index (EMI) and the results compared to a traditional index, the Shannon-Wiener diversity index. The EMI revealed that the major changes in fish community composition recorded in both estuaries were associated with quantitative variations at the species level. Both estuaries essentially lost their macrophyte beds and ended up with the same type of bottom habitat (bare sediment). In both cases the fish morphological variability decreased immediately after aquatic macrophyte loss and then increased to end above the initial value. The ecomorphological analysis appeared to be sensitive to major ecological disturbances that occurred during the study period and this was confirmed by the morphospace configuration. The results indicate that the ecomorphology of the fish community responds to habitat changes and that this change corresponds to alterations in the representation of the different feeding types. These findings therefore contribute to the measurement of morphological changes in estuarine fish assemblages as a result of habitat changes within the ecosystem and we propose that ecomorphological analyses add another dimension to the information provided by existing diversity indices in studying changing fish communities. 相似文献
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Although some waders (Charadrii) are known regularly to attempt to rear 2 broods in some summers (e.g. Ringed Plover Charadrius hiaticula, Little Ringed Plover Charadrius dubius l), this ability is not associated with Palearctic waders breeding at higher latitudes, except where one or more clutches are left in the sole care of previous mates. This note documents an attempt made by a male Dotterel to raise a second brood after its first brood of young became independent. 相似文献
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