In vivo and in vitro effect of naloxone on prolactin response to TRH in rat

In adult male Wistar rats submitted to a standardized noise stress, intravenous TRH induced a prolactin (PRL) secretory response. Prior IV naloxone administration not only lowered plasma PRL levels in those stressed rats but abolished also the stimulatory action of TRH. This effect was further studied by superfusion experiments on enriched PRL cell suspensions (70% lactotrophs) from female adult Wistar rats. Naloxone kept unaffected the basal PRL secretion but lowered significantly that induced by TRH. These experiments suggest a dual effect of naloxone on rat PRL secretion, one exerted on central opioid receptors lowering stress-related increased basal PRL levels, the other inhibiting the TRH-dependent PRL secretion exerted at the lactotroph level itself.     

Recent advances in chemiluminescence-based immunoassays for steroid hormones

Several formats of solid-phase separation techniques for the measurement of steroids and urinary steroid conjugates using chemiluminescence as an end point are described. These formats include: (1) immunoadsorption of second antibodies directed against the first antibody on solid support; (2) specific immunoadsorbents consisting of primary antibodies covalently coupled to polymer beads; (3) second antibody coupled to a polymer containing magnetic particles. In these assays a steroid-chemiluminescent marker conjugate serves as the labelled ligand, and highly specific homologous monoclonal antibodies are used to provide optimal specificity and rigorous standardization. These techniques enabled the direct measurement of steroid glucuronides in diluted urine and of steroids in plasma.     

Chromosomal aberrations induced in human cultured cells by liposome-encapsulated deoxyribonuclease I

Experiments of incorporation of a nucleolytic enzyme into human cells cultured in vitro have been carried out with the aim of inducing structural chromosome variations. Human heteroploid cells, either as asynchronous populations or enriched in mitoses, and PHA-stimulated lymphocytes were used as recipients. We found that all these cells when exposed to pancreatic DNAase I encapsulated in liposomes, either of multilamellar (MLV) or of small unilamellar (SUV) type, show an incidence of chromosome damage higher than that induced by the enzyme free in the incubation buffer. Our results indicate that liposomes are suitable vehicles for the transfer of an exogenous nuclease into human cultured cells. The enzyme remains functionally active and interacts with nuclear DNA, giving rise to chromosome lesions.     

Comparison of the effect of excessive light on chlorophyll fluorescence (77K) and photon yield of O2 evolution in leaves of higher plants

High-light treatments (1750–2000 mol photons m^–2 · s^–1) of leaves from a number of higher-plant species invariably resulted in quenching of the maximum 77K chlorophyll fluorescence at both 692 and 734 nm (F _M, 692 and F _M, 734). The response of instantaneous fluorescence at 692 nm (F _O, 692) was complex. In leaves of some species F _O, 692 increased dramatically in others it was quenched, and in others yet it showed no marked, consistent change. Regardless of the response of F _O, 692 an apparently linear relationship was obtained between the ratio of variable to maximum fluorescence (F _V/F _M, 692) and the photon yield of O₂ evolution, indicating that photoinhibition affects these two variables to approximately the same extent. Treatment of leaves in a CO₂–free gas stream containing 2% O₂ and 98% N₂ under weak light (100 mol · m^–2 · s^–1) resulted in a general and fully reversible quenching of 77K fluorescence at 692 and 734 nm. In this case both F _O, 692 and F _M, 692 were invariably quenched, indicating that the quenching was caused by an increased non-radiative energy dissipation in the pigment bed. We propose that high-light treatments can have at least two different, concurrent effects on 77K fluorescence in leaves. One results from damage to the photosystem II (PSII) reaction-center complex and leads to a rise in F _O, 692; the other results from an increased non-radiative energy dissipation and leads to quenching of both F _O, 692 and F _M, 692 This general quenching had a much longer relaxation time than reported for pH-dependent quenching in algae and chloroplasts. Sun leaves, whose F _V/F _M, 692 ratios were little affected by high-light exposure in normal air, suffered pronounced photoinhibition when the exposure was made under conditions that prevent photosynthetic gas exchange (2% O₂, 0% CO₂). However, they were still less susceptible than shade leaves, indicating that the higher capacity for energy dissipation via photosynthesis is not the only cause of their lower susceptibility. The rate constant for recovery from photoinhibition was much higher in mature sun leaves than in mature shade leaves, indicating that differences in the capacity for continuous repair may in part account for the difference in their susceptibility to photoinhibition.Abbreviations and symbols kDa kilodalton - LHC-II light-harvesting chlorophyll-protein complex - PFD photon flux density (photon fluence rate) - PSI, PSII photosystem I, II - F _O, F _M, F _V instantaneous, maximum, variable fluorescence emission - absorptance - _a photon yield of O₂ evolution (absorbed light) C.I.W.-D.P.B. Publication No. 925     

Specific Inhibition of Lignification in Bryonia dioica: Effects on Thigmomorphogenesis

Rubbing-induced lignification in Bryonia dioica internodes is significantly impaired by N(o-hydroxyphenyl) and N(o-aminophenyl) sulfinamoyl tertiobutyl acetate, specific inhibitors of cinnamyl alcohol dehydrogenase, an enzyme which is strictly associated with lignin monomer synthesis. Along with the reduction of lignification, these inhibitors counteract the inhibition of elongation due to rubbing. These results indicate that lignification participates in the thigmomorphogenetic growth response of Bryonia dioica internodes. In a general way, the data point to the causal role of lignification in the limitation of plant growth.     

Characterization of cyclic nucleotide phosphodiesterase activity in Phaseolus vulgaris

Cyclic nucleotide phosphodiesterase (3',5'-cyclic nucleotide nucleotidohydrolase, EC 3.1.4.17) activity isolated from Phaseolus vulgaris L. cv. Limberg seedlings was partially purified and characterized by fractional (NH₄)₂SO₄ precipitation, DEAE-cellulose chromatography, chromatography on 3',5'-cAMP-agarose, gel permeation chromatography and chromatofocusing. A crude enzyme preparation, a 30–65% (NH₄)₂SO₄ pellet, showed an acidic pH optimum. The enzyme activity was stimulated by imidazole and divalent cations such as Ca²⁺, Mg²⁺ and Mn²⁺, whereas NaF, PP_i and Fe³⁺ were inhibitory. Isobutylmethylxanthine had no significant effect on the plant enzyme. An M_I of 42 000 was estimated by gel permeation high performance liquid chromatography. By chromatography on 3',5'-cAMP-agarose a phosphodiesterase was resolved that produced 5'-AMP as sole reaction product.     

Biphasic fluence-response curves for phytochrome-mediated kalanchoë seed germination : sensitization by gibberellic Acid

The fluence-response curves for the effect of two red pulses separated by 24 hours on the germination of Kalanchoe blossfeldiana Poelln. cv Vesuv seeds, incubated on gibberellic acid (GA₃) are biphasic for suboptimal concentrations. The response in the low fluence range corresponds with a classical red/far-red reversible phytochrome mediated reaction. GA₃ induces an additional response in the very low fluence range, which is also phytochrome mediated. The sensitivity to phytochrome-far-red absorbing form (Pfr), however, is increased about 20,000-fold, so that even far-red fluences become saturating. Both in the very low and low fluence response range, the maximal responses induced by saturating fluences are modulated by the GA₃ concentration. GA₃ having no direct influence on the phytochrome phototransformations, alters the Pfr requirement and determines the responding seed population fraction in the very low and low fluence range. The effet of GA₃ appears to be on the transduction chain of the phytochrome signal.     

Elicitation of Necrosis in Vigna unguiculata Walp. by Homogeneous Aspergillus niger Endo-Polygalacturonase and by alpha-d-Galacturonate Oligomers

Endo-polygalacturonase (PG) was purified from a commercial preparation of Aspergillus niger pectinase by means of carboxymethylcellulose chromatography, preparative isoelectric focusing, and gel permeation through Sephadex G-50. The enzyme was electrophoretically homogeneous and consisted of a single polypeptide chain with a molecular weight of 33,500. The enzyme exhibited a specific activity significantly higher than those of purified polygalacturonases from phytopathogenic fungi. Galacturonate oligomers with a degree of polymerization higher than four appeared quickly as products of the enzymic hydrolysis of Napolygalacturonate. The oligomers were later degraded to di- and monogalacturonate. The homogeneous enzyme and growing mycelium of Aspergillus niger separately elicited a necrotic response in cowpea (Vigna unguiculata Walp.) pods. Heat-inactivated PG and PG inactivated with specific antibodies did not elicit necrosis, suggesting that the catalytic activity of the enzyme is necessary for its function as an elicitor. The PG-released oligosaccharides from Vigna cell wall and the galacturonides with a degree of polymerization greater than four separately elicited necrosis, whereas di- and monogalacturonate did not.     

Spinach ferredoxin is a calcium-binding protein

Spinach-leaf ferredoxin was identified as a calcium-binding protein by ⁴⁵Ca autoradiography on nitrocellulose membranes and with the cationic carbocyanine dye 1-ethyl-2-[3-(1-ethylnaphtho[1,2-d]thiazolin-2-ylidene)-2-methylpropenyl] naphtho[1,2-d]thiazolium bromide (stains-all). Binding of ⁴⁵Ca was observed at pH 6.8 and pH 7.8 and in the presence of 5 mM and 20 mM MgCl₂. At the higher MgCl₂ concentration the Ca²⁺-binding capacity is reduced. Only micromolar concentrations of LaCl₃, however, are required to achieve a similar effect. Both the oxidized and reduced forms of ferredoxin bind calcium.Abbreviations PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate - stains-all 1-ethyl-2-[3-(1-ethylnaphtho[1,2-d]thiazolin-2-ylidene)-2-methylpropenyl] naptho[1,2-d]thiazolium bromide     

Relative biological effectiveness (RBE) of neutrons produced by 50 MeV deuterons and by 34, 45, 65 and 75 MeV protons

RBE of p(34) + Be, p(45) + Be, p(65), + Be, p(75) + Be and d(50) + Be neutron beams produced at the cyclotron "Cyclone" of Louvain-la-Neuve were measured. The biological criterion was the regeneration of the crypts of the intestinal mucosa (50 regenerated crypts per circumference) after abdominal irradiation in mice. Taking the p(65) + Be neutrons as reference, RBE values were found equal to 1.12, 1.07, 1.00 (Ref.), 0.96 and 1.02 respectively. These results are consistent with those published for cell lethality in vitro. However, the RBE variation is smaller than this previously obtained in the laboratory for growth inhibition in Vicia faba.