Comparative Biochemistry and Physiology Part A: Physiology最新文献

Coenzyme Q and trace element contents of two antarctic fishes (Pagothenia bernacchii and Chionodraco hamatus) were investigated and compared with that of one temperate marine fish (Mugil cephalus). In particular, muscle and erythrocyte concentrations of coenzyme Q, vitamin E, selenium, copper and zinc were determined. Antarctic fishes showed, at the level of their muscles, higher levels of selenium, zinc and copper compared with M. cepalus. In antarctic fishes, in the place of Q₁₀, the coenzyme Q form generally observed in temperature fishes, only the homolog coenzyme Q₉ was found. This particular finding has been related to the difference in the crystallization temperature existing between CoQ₁₀ and CoQ₉. Moreover, the high levels of zinc and selenium, observed in C. hamatus, correlate very well with a recent report on the presence, in the liver of this fish, of a zinc-binding protein that, in addition, is characterized by an amino acid sequence closely similar to that of a selenium-containing protein isolated from ovine heart. All together, the results indicate, for the antarctic species, a high level of antioxidant defenses with respect to the mediterranean fish and may be considered as a stimulating basis for further studies on the oxidative metabolism of Antarctic organisms.

The capacity for glucose synthesis in Chasmagnathus granulata hepatopancreas, associated with phosphoenolpyruvate carboxykinase activity, argues in favor of this tissue as a site for gluconeogenesis. In order to obtain more information on the gluconeogenic capacity in crabs, we investigated the effects of different diets on the incorporation of ¹⁴C-alanine or ¹⁴C-lactic acid into glucose in Chasmagnathus granulata hepatopancreas, as well as on the phosphoenolpyruvate carboxykinase activity in this organ. In contrast to what occurs in vertebrates, in Chasmagnathus granulata, the intrinsic capacity of the hepatopancreas to synthetize glucose from alanine or lactic acid, and its phosphoenolpyruvate carboxykinase activity, was not influenced by high-protein or carbohydrate diets. The amount of labelled glucose recovered from ¹⁴C-alanine was significantly higher than that recovered from ¹⁴C-lactic acid, and 40 mM of alanine is not a saturated concentration for the gluconeogenic pathway. Phosphoenolpyruvate carboxykinase activity was detected into the mitochondrial (10,000 × g) and cytosol (100,000 × g) fractions. The data suggest that gluconeogenesis from ¹⁴C-alanine in the hepatopancreas from Chasmagnathus granulata fed a high-protein or carbohydrate-rich diet is equally subject to end-point inhibition by glucose, as has been found in vertebrates.

Lipoproteins are involved in transport of exogenous and endogenous lipids. For this reason, the lipoprotein pattern undergoes drastic variation during fasting. In D. labrax, observed variations concern, the relative content of the five lipoproteins and their composition, both in lipid and apolipoprotein content. These data indicate the presence of a cascade mechanism of maturation involving very-low-density lipoprotein, (VLDL), low-density lipoprotein (LDL)-1 and LDL-2. In addition, a metabolic correlation involves VLDL and high-density lipoprotein (HDL). VLDL are functionally comparable with mammalian chylomicrons; in fact, they disappear rapidly after feeding from the chromatographic pattern and are composed of almost 80% triglycerides. From the evolutionary point of view, HDL represent the most conserved lipoproteins and are involved in transportation of endogenous lipids, mobilized from accumulation tissues. Their apolipoprotein pattern is dominated by two apolipoproteins, apo A1 (26,000 Da) and apo A2 (12,000 Da).

Cell clusters containing rhabdomeric structures and screening pigments are located in the optic lobes of pupae and adult beetles of Tenebrio molitor and Hylotrupes bajulus. Due to their resemblance with the compound eyes, the cell clusters were called cerebral extraocular photoreceptors (CEPs) and can readily be detected macroscopically as black spots spread between the lamina and medulla. CEPs of T. molitor responded to bright light with a transient depolarisation followed by a sustained plateau. In contrast, CEPs of H. bajulus responded to bright light either with small depolarisations or did not respond to the range of light intensities presented. CEP cells labelled with Lucifer yellow had axons projecting toward the medullar region. The maximum spectral sensitivity of CEPs was broadly tuned to the green region (λ_max at 524 nm). The role of CEPs in insects is still a matter of wide speculation, due to the lack of consistent systematic behavioral studies about insects carrying photoreactive CEPs. Here we suggest that the scattered distribution of CEPs in the optic lobes could allow a temporal pooling of information about the surrounding illumination, thereby entraining some rhythmic photobehavioural responses.

Vitellogenin of matrotrophic viviparous eelpout (Zoarces elongatus) was purified from estradiol-17β (E₂) treated immature male sera by gel chromatography and anion exchange chromatography. Isolated vitellogenin has a molecular weight of 540 kDa estimated by gel chromatography. Serum levels of vitellogenin in females were measured during oocyte development and gestation by single radial immunodiffusion. Serum vitellogenin level was low (less than 0.2 mg/ml) during the early vitellogenic period, increased in the late vitellogenic period to a peak level (6.4 ± 2.1 mg/ml) at the beginning of gestation. After that it rapidly decreased to a low level (0.1 ± 0.1 mg/ml) during the early gestation period. Levels of vitellogenin remained low throughout the gestation period. Serum E₂ levels in females showed increased from 1.3 to 3.0 ng/ml during the late vitellogenic period, and declined to 0.4 ng/ml during the early gestation period. Serum levels of E₂ showed good correlation with serum vitellogenin levels, suggesting that the vitellogenin synthesis is controlled by E₂ in this species. These results combined with the matrotrophic growth of embryo during gestation suggest that there is a shift in the synthesis of maternal nutritional products for embryos from the yolk to other nutrients.

Renal lithium transport was studied at different hydration levels in five species of anuran amphibians (Bufo bufo, B. danatensis, B. viridis, Rana ridibunda, and R. temporaria), two species of urodeles (Triturus vulgaris and T. cristatus) and four species of reptiles (lizards Eremias multiocellata, Lacerta vivipara, Trapelus sanguinolentus, and Teratoscincus scincus). Under dehydration conditions, Li⁺ was reabsorbed in the kidneys of amphibians and reptiles, but to a lesser degree than in mammalian kidneys: the ratio of lithium clearance (C_Li) to glomerular filtration rate (GFR)—fractional lithium excretion—in dehydrated animals was in the range 0.5–0.8. The transition to the hydrated state resulted in a cessation of net renal lithium reabsorption. Under condition of high hydration, all the animals studied, except for urodeles, showed net renal secretion of Li⁺, i.e., C_Li exceeded GFR. The ratio $\text{C}{}_{\mathrm{Li}}\text{GFR}$ was 1.2–1.3 in hydrated anurans and 1.7–2.3 in hydrated lizards. In urodeles, this ratio was approximately unity. It is suggested that renal lithium secretion in hydrated amphibians and reptiles reflects fluid secretion in the proximal tubule, which is additional to the glomerular filtration mechanism of fluid delivery to nephron under water loading.

Urinary protein excretion by red jungle fowl (Gallus gallus) was examined by measuring total protein concentrations in the ureteral urine and by comparing the proteins in the urine with plasma proteins. Protein concentration in the ureteral urine did not differ between males and females, and averaged 2.01 mg/ml. Gel electrophoresis showed many plasma proteins (30–149 kD) also present in the urine. Serum albumin is the most abundant protein, comprising approximately 50% of the total protein concentration in the plasma and 60% of the total protein concentration in the urine. Urinary protein, and particularly serum albumin, may be important in packaging uric acid in spheres, which facilitates excretion of uric acid without formation of large crystals that could block renal tubules.

Histological studies have detected nitric oxide (NO) synthase in the central nervous system of all vertebrates examined, from lampreys to mamals. However, there are still very few comparative physiological studies on the function of NO synthase in the brain of non-mammalian vertebrates. So far, we know that acetylcholine can cause an NO-dependent increase in brain blood flow in turtles and some fish species (crucian carp and rainbow trout), whereas some other fishes appear to lack such a mechanism. Hypercapnia can induce NO-dependent cerebral vasodilation in mammals, but such a mechanism appears to be lacking in the ectothermic vertebrates examined. The number of species studied needs to be expanded before we can draw any firm conclusions about the origin of NO-dependent brain blood flow regulation: if it has evolved more than once or if it has been occasionally lost during evolution. We conclude that NO synthase may be present in all vertebrate brains but that its functions can vary, as judged from its role in cerebral blood flow regulation. The diversity of functions that NO has proven to have within the mammalian brain is likely to be paralleled by the same degree of diversity of function between vertebrate groups.