Tyrosine aminotransferase activity of frog (Rana esculenta) liver

1. The presence of tyrosine aminotransferase is reported both in particulate and soluble fractions of frog liver. 2. The activity of the soluble enzyme of frog liver was investigated with regard to its dose and time dependence, its substrate specificity and concentration dependence, its thermal sensitivity as well as pH and temperature dependence. 3. It appears that the properties of the soluble tyrosine aminotransferase of frog liver are in close agreement with those reported for the mammalian liver enzyme.     

Effects of Gramoxone and cooling on the antioxidant enzymes of frog (Rana esculenta)

The effects of paraquat, the active ingredient of Gramoxone, were studied on frogs (Rana esculenta) kept at 4 degrees C or 20 degrees C, to establish its effects on the survival, the antioxidant enzyme system and the lipid peroxidation of the tissues (liver and lung). The lower temperature was found to increase the survival. The activities of the antioxidant enzymes were decreased or not influenced by the LD50 of paraquat at the lower temperature, whereas the LD100 often resulted in a significant enzymatic activity increase. It was an important finding that the lipid peroxidation of the lipid decreased in response to paraquat at 4 degrees C, but increased at 20 degrees C. The lipid peroxidation of the lung increased at both temperatures.     

Ultrastructure of venom glands in the frog (Rana esculenta)

Electron microscopic study of skin venom glands in the frog, Rana esculenta, revealed the syncytial structure of the inner (secretory) wall which presents two distinct zones: a basal (juxtamuscular) one, which contains nuclei and major cytoplasmic organelles, and an apical one where large electron-dense granules form and accumulate. Granules are seen to arise inside clusters of tightly packed smooth endoplasmic reticulum (SER) elements, which suggests that the SER system is mainly involved in synthesis of this material. A high glutaraldehyde concentration (5%) also reveals a poorly defined material filling the intergranular cytoplasm. No apical limits to the syncytium could be traced, which suggests massive holocrine secretion. Nerves insinuate between the muscle cells and occur all along the internal face of the muscular layer, sometimes in close contact with the syncytium. The gland duct, the wall of which consists of epidermal cells, is blocked, in contact with the gland, by an epidermal bud linked externally to the muscle layer surrounding the gland. Thus, only strong muscle tension such as to expel all or part of the epidermal bud can trigger granule release. This phenomenon can be induced by the subcutaneous injection of epinephrine, but the high and distressing dose needed to provoke appreciable changes in venom glands renders unlikely any natural intense venom release triggered by epinephrine in the frog.     

Effect of some antibiotics on semi-circular canal activity in the frog (Rana esculenta)]

We have studied the action of two ototoxic antibiotics (streptomycin and gentamycin) on the activity of the horizontal semicircular canal in comparison with those of penicillin and 7 g/1 NaCl solution, all of them being injected into the labyrinthic cavity. Only streptomycin and gentamycin have a specific action, and the one of streptomycin is much more important than the one of gentamycin.     

Circannual variations in mevalonate utilization in frog (Rana esculenta)

1. The fate of mevalonate, the product of HMGCoA reductase, was studied in male and female frogs (Rana esculenta) in order to explain the circannual variations of enzyme activity. 2. The incorporation of 2-14C MVA into unsaponifiable lipids, cholesterol and dolichol in liver, plasma and eggs was followed. 3. Labeled MVA shows a different utilization depending on season and sex. In spring and summer cholesterol synthesis is related to hepatic reserve storage in both sexes, while the peak of enzyme activity, present only in females in fall, seems committed to cholesterol export into the blood and uptake by the oocytes. 4. The presence of a MVA-derived protein identifiable with vitellogenin and labeled on the lipid moiety, suggests that HMGCoA reductase activity in fall is committed to the lipidation of this protein essential for oocyte maturation.     

Photoreceptor layer composition in the retina of the frog (Rana esculenta)

Retinas of Rana esculenta frogs were studied by light and electron microscopy in order to establish the photoreceptor layer composition. We found 56% red rods, 9% green rods, 19% single cones, and 16% double cones. This work provides the morphological basis for electrophysiological investigations concerning the mass receptor potential of isolated Rana esculenta retinas.     

Tyrosine aminotransferase activity of frog (Rana esculenta) liver--II. Comparative aspects of intracellular distribution

1. A subcellular fractionation procedure for frog liver is reported and validated by the distribution pattern of several marker enzymes, also in comparison with rat liver. 2. The subcellular distribution of tyrosine aminotransferase was investigated in frog liver as compared to rat liver: a different distribution of the enzyme was observed, being the activity mostly recovered in mitochondrial and cytosolic compartments. 3. Results indicate that mitochondrial tyrosine aminotransferase of both frog and rat liver is a matrix enzyme, even if differences are observed concerning its release from the organelles upon detergent treatment.     

Haematological studies on the prewintering and wintering frog, Rana esculenta

1. A study of the haematology of the frog Rana esculenta including erythrocyte count (RBC), haemoglobin content (Hb), haematocrit (HCT), mean cell volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC) and erythrocyte size as a function of prewinter and winter was made. 2. The RBC count and Hb were significantly higher in contrast to MCV and MCH values during prewinter in both sexes. 3. The surface area to volume ratio was higher in prewinter whereas the length to width ratio (eccentricity) of the cytosome and nucleus was significantly higher during winter in both sexes. 4. Sexual differences in the erythrocyte count, Hb content and the surface area to volume ratio were also observed. 5. The physiological significance of these observations are reported for Rana esculenta.     

The adrenergic receptor subtypes present in frog (Rana esculenta) skin

Frog skin transports ions and water under hormonal control. In spite of the fundamental role played by adrenergic stimulation in maintaining the water balance of the organism, the receptor subtype(s) present in the skin have not been identified yet. We measured the increase in short-circuit current (ISC, an estimate of ion transport) induced by cirazoline, clonidine, xamoterol, formoterol, or BRL 37344, in order to verify the presence of alpha1, alpha2, beta1, beta2, or beta3 receptor subtypes, respectively. Only after treatment with formoterol, BRL 37344 and, to a lesser extent, cirazoline was measured a significant increase in ISC (57%, 33.2%, and 4.7%, respectively). The formoterol and BRL 37344 concentrations producing half-maximal effect (EC50) were 1.12 and 70.1 nM, respectively. Moreover, the formoterol effect was inhibited by treatment with ICI 118551 (antagonist of beta2 receptors) while SR 59230A (antagonist of beta3 receptors) had no effect; opposite findings were obtained when the BRL 37344 stimulation was investigated. Finally, by measuring the transepithelial fluxes of 22Na+ and 36Cl-, we demonstrated that Na+ absorption is increased by activation of beta2 and beta3 and is cAMP-sensitive, whereas the Cl- secretion is only increased by activation of beta2 receptors and is cAMP- and calmodulin-sensitive.     

Nociceptin binding sites in frog (Rana esculenta) brain membranes.

The recently discovered natural heptadecapeptide nociceptin (orphanin FQ) shares some homology with the opioid peptides but it binds to a distinct receptor type, termed nociceptin receptor. This study demonstrates the presence of specific nociceptin recognition sites in brain membrane fractions of an amphibian, Rana esculenta. Para-iodo-Phe(1)-nociceptin-amide was radiolabelled by catalytic dehalotritiation, resulting in p[(3)H]Phe(1)-nociceptin-amide of 25 Ci/mmol specific radioactivity. Specific binding of [(3)H]nociceptin-amide to frog brain membranes was found to be saturable and of high affinity with equilibrium K(d) values in the low nanomolar range. A single set of binding sites with about 180 fmol/mg protein maximal binding capacity was obtained in saturation and competition experiments. [(3)H]Nociceptin-amide binding could easily be inhibited by synthetic nociceptin compounds but not by opioid ligands. Both sodium ions and 5'-guanylylimidodiphosphate decreased the binding of the radioligand by transferring the receptor to a lower affinity state. Nociceptin dose-dependently stimulated the binding of the nonhydrolysable, radiolabeled GTP-analogue guanosine-5'-O-(3-thio)triphosphate ([(35)S]GTPgammaS) to G-proteins in frog brain membranes. Addition of 1 microM naloxone caused no significant change in the curves, indicating that nociceptin-mediated activation of G-proteins occurred through nonopioid mechanism.     

Hepatic respiratory compensation and blood volume in the frog (Rana esculenta)

In the frog, Rana esculenta (L.), the liver can change in volume by over 25%, depending on the respiratory conditions of the animal: in well-oxygenated specimens the organ can hoard about half of the total amount of erythrocytes in its sinusoids, and release them into the bloodstream under conditions of hypoxia. This phenomenon can be observed at a temperature of 6°C by comparing the liver volumes and haematic values of chlorobutanol-anaesthetized animals exposed to the air or submerged in still water (a condition which induces hypoxia): the blood volume remains constant, at about 5 ml per 100g of body weight, but red blood cell count and haematocrit value differ by as much as 50%. At 18°C there is an increase in oxygen demand and in anaesthetized animals, which rely totally on cutaneous respiration, the compensatory liver mechanism can no longer be observed, since all the available erythrocytes are already circulating in a blood volume which, depending on respiratory conditions, can vary between about 7 and 8ml/100g. At 30°C, cutaneous respiration alone does not allow the anaesthetized animals to survive long enough to stabilize their haematic parameters.     

Fine structure of the fungiform papilla in a ranid frog (Rana esculenta)

The freetop of the fungiform papilla shows a sensorial area about 100 micron in diameter, surrounded by a ring of ciliated cells. Externally to the ciliated cells, i.e., in the lateral wall, numerous large goblet cells can be seen devoid of their mucous content. The sensorial area is composed by three types of cells: mucous, supporting, and neuroepithelial cells. Mucous cells form the most superficial layer, while the cell bodies of the other two are deep, and from them basal and apical processes arise. The above mentioned cells are connected by desmosomes preferentially located between the mucous and the supporting cells, rather than between the supporting and the neuroepithelial cells. The lateral wall of the papilla is made up of a multilayered epithelium that comprises two types of cells: the first type contains electron-dense granules and an abundant rough endoplasmic reticulum, the others are ciliated cells. In the connective axis of the papilla, numerous fenestrated capillaries with endothelial vesiculated cells and nerve fibers are found.     

Intermitochondrial junctions in the heart of the frog,Rana esculenta

Summary In muscle fibers of the frog heart, junctions between outer membranes of adjacent mitochondrial profiles are occasionally found. In thin sections of embedded tissue and of mitochondrial pellets, the intermitochondrial junctional space is 5.4±0.15 nm; the external leaflets of the membranes are joined by periodic structures separated from each other by 16.3±0.29 nm. There are 65.3±2 periodic structures per m of membrane measured on a section perpendicular to the junction. After cryofracture, the outer membrane is cleaved into two parts. Closely packed, parallel rows of large particles and furrows are found either on the P-, or on the E-faces. The rows of particles are 11±0.3 nm thick and are separated from each other by 16.5±0.46 nm, their density being 65±2.28 per m of the membrane. In junctional areas, rows of particles on one membrane correspond with the furrows on the other membrane. Intermitochondrial junctions appear to be real structures and not artifacts due to preparation procedures. The conditions of their occurrence are discussed.     

Cytological and histochemical investigations on the pineal organ of the adult frog (Rana esculenta)

Cell and Tissue Research -     

Intratesticular control of spermatogenesis in the frog, Rana esculenta.

Adult intact and hypophysectomized (PDX) frogs, Rana esculenta, were treated with a gonadotropin releasing hormone agonist (GnRHA, HOE 766) and/or cyproterone acetate (CPA), the antiandrogen, in order to investigate the regulation of primary spermatogonial (I SPG) multiplication in vertebrates. Treatment with GnRHA (injections containing 900 ng administered for 12 days on alternate days) caused a significant increase of the mitotic index (MI) of I SPG in PDX animals and a further MI increase of SPG was observed when 0.66 mg CPA was given concomitantly with GnRHA. The treatment with 0.66 mg CPA in combination with GnRHA also increased secondary spermatocyte (II SPC) appearance. Moreover, number of nests containing spermatids (SPT) decreased as CPA, in combination with GnRHA, was administered in increasing doses (0.33 and 0.66 mg/injection). Intact animals treated with CPA (0.66 mg/injection) showed a time-dependent I SPG multiplication increase which reached highest values after 28 days. Secondary SPC also proliferated until day 28; meanwhile the number of nests containing SPT decreased. Neither testosterone nor R5020 (a progestin which is not converted to androgens) modified the basal and GnRHA-induced spermatogonial proliferation. These results confirm that in the frog, Rana esculenta, spermatid formation is impaired by CPA treatment and that I SPG multiplication is enhanced by a direct effect of GnRHA; moreover, we suggest that the absence of spermatids constitutes a signal promoting spermatogonial proliferation.     

Autoregulation of apical sodium entry in the colon of the frog (Rana esculenta)

1. Na transport (INa) in the K-depolarized colon of the frog was investigated by electro-physiological current-voltage analysis. 2. INa and the intracellular Na activity [(Na)c] increased with increasing mucosal Na concentration ([Na]m), whereas the apical Na-permeability (PNam) and the transepithelial resistance (RT) decreased. 3. The results are consistent with a Na self-inhibition mechanism; however, a feedback inhibition of INa by intracellular Na must also be considered.