Different acute effects of the tyrosine hydroxylase inhibitors alpha-methyl-p-tyrosine and 3-iodo-L-tyrosine on hypothalamic noradrenaline activity and adrenocorticotrophin release in the rat

Computerized gas chromatography-mass spectrometry techniques using selected ion monitoring and deuterated internal standards were used to assay simultaneously the medial basal hypothalamic concentrations of dopamine (DA) and noradrenaline (NA) and their major metabolites in individual rats 30 min after the administration of two different inhibitors of tyrosine hydroxylase, alpha-methyl-p-tyrosine (alpha-MT) and 3-iodo-L-tyrosine (MIT). Consistent with inhibition of DA synthesis, administration of both alpha-MT and MIT resulted in marked reductions (P less than 0.005) in the hypothalamic concentrations of DA and its metabolite homovanillic acid as well as in highly significant increases in prolactin secretion. alpha-MT administration, but not MIT, resulted in a highly significant decrease in NA concentration and a highly significant increase in the concentration of the NA metabolite 3,4-dihydroxyphenylethyleneglycol (DHPG). The hypothalamic ratio DHPG/NA was thus markedly increased (P less than 0.005) by alpha-MT indicating increased NA neuronal activity. alpha-MT administration also resulted in increased ACTH secretion (P less than 0.0005), an effect not observed following MIT. It is proposed that the effects on hypothalamic NA activity and ACTH secretion caused by alpha-MT are stress-mediated and unrelated to tyrosine hydroxylase inhibition. MIT is devoid of these effects but exhibits blockade activity, thus indicating it to be a preferable drug for the acute inhibition of tyrosine hydroxylase in neuroendocrine investigations.     

The use of graph theory in analysis of cells and cell nuclei in particular

Application of graph theory to morphological analysis of cells described by n parameters is presented. The analysis takes advantage of the possibility of describing structures in a multi-dimensional space. The method may be useful in determining similarity or differences between studied structures.     

The zinc-containing high Km cyclic nucleotide phosphodiesterase of bakers' yeast

The high Km cyclic nucleotide phosphodiesterase of Saccharomyces cerevisiae was purified by an improved procedure. Its amino acid composition is reported. Its pI is 5.85 +/- 0.1. Sedimentation equilibrium analysis of the native enzyme gave Mr = 88,000 +/- 6,000, whilst gel electrophoresis in the presence of dodecyl sulfate gave a molecular weight of 43,000, indicating that the enzyme is a dimer. Preparations of 94 +/- 4% purity contained about 2.4 atoms of zinc/43,000 daltons. Inactivation of the enzyme by 8-hydroxyquinoline was accompanied by removal of about 2 zinc atoms per monomer. Partially inactivated enzyme regained activity during dialysis against zinc, or, with less effect, cobalt salts. 8-Hydroxyquinoline (Ki = 1.1 mM) and 1,10-phenanthroline (Ki = 0.6 mM) were competitive inhibitors. The enzyme was also inhibited by the nonchelating 1,7-and 4,7-phenanthrolines and by thiols and KCN, but not by NaN3. These inhibitors probably act by binding to, but not chelating, enzyme-bound zinc.     

Transport theory for growing cell populations

The partial differential equation that describes the growth of cell populations whose maturation rate is random is developed. The equation resembles that used in classical transport theory but mitotic boundary conditions and the restriction of the maturation rate to non-negative values brings out new features and new problems. This is a generalization of a previously published formulation in which cells could make transitions at random between only two maturation velocities: a characteristic velocity and zero. Growth rates, cycle time distributions and pulsed labeled mitotic curves are calculated for a simple choice of parameters. A numerical algorithm that is suited to the solution of the transport equation is given.     

Determination of C distribution in photosynthetic serine and phosphoglycerate from grape leaves

Serine and phosphoglyceric acid are the classical marker intermediates of photorespiration and reductive carbon assimilation in C₃ plants. The present paper introduces a new and fast method for the determination of ¹⁴C distribution in these compounds by selective elimination of C-3 (NaIO₄) or C-1 (ninhydrin/ceric sulfate). Reproducibility of the procedure was found to be better than ±1% upon degradation of [U-¹⁴C]serine and [U-¹⁴C]glycerate standards.     

Spectroscopic characterization of extracts from humic and fulvic fractions: IR and1H NMR spectra

Summary Infrared and proton resonance spectra have been used to characterize fraction extracted sequentially from humic and fulvic acids by diethylether, acetone, dioxane, tetrahydrofuran, pyridine and dimethylformamide. The results showed that the same solvents extracted structurally similar components from both humic and fulvic acids. On the other hand, the spectra showed solvent-dependent differences, some being characteristic for a preponderance of aliphatic structures, others for aromatic structures.     

Low doses of X-rays decrease the risk of diploidy in mouse oocytes

Females from the NMRI/Han mouse strain ovulate a high number of diploid oocytes (about 12%) after gonadotrophin-stimulated ovulation. These oocytes can be fertilized and develop into triploid embryos subsequently. The exposure of such gonadotrophin-primed females to X-ray doses of 0.05, 0.10, 0.20 or 0.40 Gy during the preovulatory period (2 h after the HCG dose) significantly decreased the percentage of diploid oocytes. After the highest dose used, i.e. 0.80 Gy, however, the incidence was on the level from unirradiated females, again. We suggest that the observed negative hump-shaped dose response of diploidy is not caused by secondary modifications induced by irradiation, such as a selective killing of diploid oocytes before ovulation, or a (compensatory) super-ovulation of only normal oocytes, but rather is caused by a direct radiobiological interference of low doses in protecting from gonadotrophin-induced aneuploidy.     

The effect of soil water status on critical phosphorus concentrations inStylosanthes hamata cv. Verano

Summary The effect of soil water status on the critical phosphorus concentration (CPC) determined in apices and whole tops ofStylosanthes hamata cv. Verano was investigated in a glasshouse trial. The species was grown with six rates of P and three ranges of soil water potential and was harvested at 10 and 14 weeks after germination. The CPC of both whole tops and apices decliced between the two harvests. At the first harvest the CPC of both whole tops and apices increased as the soil water potential decreased but at the second harvest there was no effect of soil water potential on CPC. It is suggested that at the earlier harvest water stress was delaying physiological development, resulting in a CPC characteristic of chronologically younger tissue, but that by the second harvest the decline in CPC with age had ceased for all water treatments.