Lack of stimulation of renal (Na+ + K+)-ATPase by thyroid hormones in the rabbit

The effect of l-3,5,3′-triiodothyronine (T₃) and thyroxine (T₄) on (Na⁺ + K⁺)-ATPase activities was examined in rabbit kidneys because in this tissue almost 80% of the metabolism is connected to active sodium transport. T₃-receptor concentrations were estimated as 0.62 and 0.80 pmol/mg per DNA in the cortex and outer medulla, respectively. A dose of 0.5 mg T₃/kg body weight for 3 days increased basal metabolic rate by almost 60%, and the mitochondrial 1-α-glycerophosphate dehydrogenase activity was increased by 50% in both the cortex and medulla. (Na⁺ + K⁺)-ATPase activity in the liver was raised by almost 50%. However, no changes in (Na⁺ + K⁺)-ATPase activities or binding sites for [³H]ouabain in either the kidney cortex or medulla could be observed. T₄ at 16 mg/kg daily for 14 days was also without effect on renal (Na⁺ + K⁺)-ATPase activities. Furthermore, the response to T₃ was absent at high sodium excretion rates induced by unilateral nephrectomy and extracellular volume expansion. Thus, despite stimulation of basal metabolic rate and renal 1-α-glycerophosphate dehydrogenase activity by T₃ and T₄, the (Na⁺ + K⁺)-ATPase activity in the rabbit kidney is identical in euthyroid and hyperthyroid states. However, thyroid hormones prevent the normal natriuretic response to extracellular volume expansion.     

Intranuclear rodlets in a pulmonary neuroepithelial body of a rabbit

Summary Filamentous intranuclear rodlets were found in a majority of cells in a bronchiolar neuroepithelial body of a rabbit. These rodlets appear to be similar to structures that have been described primarily in neural tissues. They are composed of large bundles of microfibrils made up of smaller subbundles. No close association with any nuclear structure is seen. Although no function can as yet be ascribed to intranuclear rodlets, their demonstration in a neuroepithelial body may be of importance of the understanding of the function of both structures.Supported by N.I.H. Grant No. 20548 from the National Heart, Lung and Blood Institute     

The shape and distribution of astrocytes in the retina of the adult rabbit

Summary Astrocytes stained by antibodies to glial fibrillary acidic protein (GFAP) were examined in whole-mount preparations of retinae from adult rabbits and found to be restricted to the medullary rays. Astroglial cells exhibited a variety of shapes that varied between two extreme morphologies. One extreme was an astrocyte that possessed a few sturdy primary processes as well as finer processes and was strongly GFAP positive. The other extreme was an astroglial cell that displayed a star-shaped appearance; its perikarya gave rise to a few thin, radially oriented processes, which were rather weakly GFAP positive. The majority of astroglial processes were aligned with the ganglioncell axons, but some of their processes were in contact with capillaries. It has been proposed that astrocytes are specifically associated with ganglion-cell axons. Their restriction to the medullary rays in the retina of the rabbit suggests, however, that their physiological role is also concerned with the vascular system.     

The stimulatory effect of alloxan diabetes on citrulline formation in rabbit liver mitochondria

The effect of alloxan diabetes on citrulline formation from NH₄Cl and bicarbonate was studied in rabbit liver mitochondria incubated with glutamate or succinate as respiratory substrate, as well as with exogenous ATP in the presence of uncoupler and oligomycin. In contrast to ornithine transcarbamoylase, the activity of carbamoyl-phosphate synthetase (ammonia) was higher in mitochondria from diabetic animals than in those from normal ones. In diabetic rabbits the rates of citrulline synthesis were stimulated under all conditions studied. In contrast, levels of N-acetyglutamate, an activator of carbamoyl-phosphate synthetase (ammonia), were significantly increased only in the presence of glutamate, while the highest rates of citrulline formation occurred in uncoupled mitochondria incubated with exogenous ATP as energy source. Treatment of animals with alloxan resulted in an increase of both the intramitochondiral ATP level and the rate of adenine nucleotide translocation across the mitochondrial membrane. The results indicate that the stimulation of citrulline formation in liver mitochondria of diabetic rabbits is mainly due to an increase in carbamoyl-phosphate synthetase (ammonia) activity and an elevation of content of intramitochondrial ATP, a substrate of this enzyme.     

Effects of dietary plant polyphenols and seaweed extract mixture on male-rabbit semen: Quality traits and antioxidant markers

Feed additive consisting of polysaccharides from brown seaweeds plus phenolic acid, hydroxycinnamic acids, tannins, and flavonoids from plant extracts, was used as rabbit food supplement. Main aim of the study was to determine the effect of natural mix of marine and freshwater seaweed polyphenols on selected reproductive characteristics of male rabbits during the 90-days experiment. Natural mix was incorporated in feed-pellets for rabbits in two different concentrations – 0.3% (T1 group) and 0.6% (T2 group), compared with a control group (C group). In experimental groups a significant increase of concentration of calcium during first 30 days of supplementation was found. An increase of alanine aminotransferase, glutathione peroxidase and ferric reducing ability of plasma and a decrease in aspartate aminotransferase after 90 days were recorded in the same groups. Except for that we noticed decrease of semen distance of curved line and velocity of curved line after 30 days though only while being supplemented with 0.6% proportion of seaweed polyphenols in feed mixture. Based on the results it can be stated that the natural mix in the tested levels do not show adverse effect on male rabbit reproductive parameters, and an improvement of antioxidant status was observed. The feed additives can have a very important effect on growth, health and development of animals in general as it supplies the with the much-needed minerals, nutritional substances and antioxidants, on which we focused in our study.     

Interaction of BW A868C, a prostanoid DP-receptor antagonist, with two receptor subtypes in the rabbit isolated saphenous vein

In isolated rings of rabbit saphenous vein (RbSV) pre-contracted with 40 mM KCl, Prostaglandin E₂ (PGE₂), BW245C (a DP-receptor agonist) and PGD₂ caused concentration-dependent relaxations with mean potencies (EC₅₀) of 0.5, 38 and 114 nM respectively.The DP-receptor antagonist, BW A868C, antagonized BW245C concentration-effect ( ) curves, although the corresponding Schild plot had a slope less than unity and displayed a clear inflection. Analysis of the data yielded two pK_B estimates of 8.5 and 4.9, the higher estimate being consistent with antagonism at DP-receptors. The pA₂ estimate of 5.1 obtained for BW A868C against PGE₂ was not statistically different to the lower pK_B of 4.9 obtained against BW245C, and is probably indicative of antagonism at the EP₄-receptor. PGD₂ mediated responses were also antagonized by BW A868C, however the resultant curves were ‘bell shaped’ in nature. The weak EP₄-receptor antagonist AH23848B, also antagonized BW245C and PGD₂ responses, yielding pA₂ estimates of 5.6 and 5.5 respectively.These results suggest that in the RbSV, BW245C and PGD₂ are nonselective agonists mediating relaxations through DP- and EP₄-receptors. BW A868C also displayed an affinity for DP-receptors in this preparation, in addition to a second receptor subtype, presumably the EP₄-receptor.     

Pinealectomy Decelerates the Circadian Food Intake Rhythm of Cervically Sympathectomized Rabbits

Long-term records of the free-running food intake rhythms were obtained from 26 young adult blinded rabbits that were subjected in the course of recording to bilateral superior cervical ganglionectomy (sympathectomy). This always resulted in acceleration of the rhythm (mean λ r= - 0.35 h). Some 4 months afterwards, 12 rabbits were pinealectomized and after another 4 months sham pinealectomized also. In the other 14 animals, these operations were performed in the reverse order. It appeared that suctioning away part of the ventricular walls during sham pinealectomy was followed by a slight reduction in r (mean = - 0.07 h) that could be largely attributed to the spontaneous gradual reduction of r that occurred throughout all experiments. On the other hand, total pinealectomy in these already sympathectomized blinded rabbits always resulted in a substantial deceleration of the rhythms (mean λ r = + 0.23 h). These observations on blinded rabbits suggest that a sympathetically denervated pineal gland releases appreciable amounts of melatonin or of another hormone with a melatonin-like accelerating effect on the circadian pacemaker (SCN).     

Autoimmune recognition of thyroglobulin and thyroid hormones in rabbits

Two rabbits (RG-1, RG-2) were immunized with rabbit thyroglobulin (RTg) purified from thyroid glands of four other normal rabbits of the same strain, and bled serially. Antisera were obtained at different times after the first immunization and kept separately and studied. Production of anti-RTg as well as anti-thyroid hormone antibodies such as anti-thyroxine (T4) and anti-triiodothyronine (T3) antibodies was observed in both rabbits. Physicochemical parameters of anti-RTg antibodies with RTg, T4, and T3 were calculated in two selected antisera (70-day and 253-day) of each of the rabbits, using a Scatchard plot. Extraction of serial sera from both rabbits disclosed the presence of larger amounts of T3 and T4 in immune sera than in preimmune serum. Examination of pathology of thyroid glands and kidneys in both rabbits was negative for the lesions of autoimmune thyroiditis and immune nephritis. These results indicate that anti-Tg as well as anti-thyroid hormone autoantibodies can be raised without thyroid pathology in rabbit by immunization with autologous Tg.     

Expression of vimentin by rabbit corneal epithelial cells during wound repair

Summary Intermediate filaments of epithelial cells generally consist of specific combinations of keratins. However, cultured epithelial cells from certain tissues and some epithelial tumors have been shown also to express vimentin. In the present study, the expression of vimentin by epithelial cells in healing corneal wounds (partial thickness penetrating wounds) and in tissue culture was analyzed. Both immunohistochemical and immunotransblot analyses indicated that although vimentin was not detected in the normal rabbit corneal epithelium in vivo, cultured rabbit corneal epithelial cells co-express keratins and vimentin. At 1 day post-wounding, vimentin was not detectable in the epithelial cells that had covered the denuded stroma. However, at 2 days post-wounding, the epithelium at the base of the epithelial plug immunoreacted with both anti-vimentin and antikeratin monoclonal antibodies. Immunotransblot analyses of the extracts of the epithelial plugs confirmed the presence of vimentin (M_r=58k). The 58k band was not detected in the extract of normal rabbit corneal epithelium. At day/5, vimentin was no longer detectable in the epithelium. This study demonstrated that corneal epithelial cells transiently co-express vimentin and keratins in vivo during wound healing and in tissue culture. The time-course of the transient expression of vimentin suggests that the vimentin expression in the epithelial cells during healing is not linked to cell proliferation or to the centripetal migration of the epithelium during early stages (first 24 h) of healing, but may be linked to cell-matrix interactions or the migration of basal cells in the upward direction at the following stage of healing.