滇黄芩甙A和B的结构

从龙胆科滇黄芩属植物滇黄芩(Veratrilla baillonii Franch)中分离得到两个新的酮二糖甙,经~1H NMR,~(13)C NMR,FAB-MS,MS,2D NMR,UV,IR等物理方法和化学反应,推定为:2,3,4,7-四甲氧基酮-1-O-β-D-葡萄糖(6←1)-β-D-木糖甙(1)和7-羟基-2,3,4-三甲氧基酮-1-O-β-D-葡萄糖(6←1)-β-D-木糖甙(2),分别命名为:滇黄芩甙A和滇黄芩甙B。     

Biochemistry and pharmacology of 7α-substituted androstenediones as aromatase inhibitors

The inhibition of aromatase, the enzyme responsible for converting androgens to estrogens, is therapeutically useful for the endocrine treatment of hormone-dependent breast cancer. Research by our laboratory has focused on developing competitive and irreversible steroidal aromatase inhibitors, with an emphasis on synthesis and biochemistry of 7α-substituted androstenediones. Numerous 7α-thiosubstituted androst-4-ene-3,17-diones are potent competitive inhibitors, and several 1,4-diene analogs, such as 7α-(4′-aminophenylthio)-androsta-1,4-diene-3,17-dione (7α-APTADD), have demonstrated effective enzyme-activated irreversible inhibition of aromatase in microsomal enzyme assays. One focus of current research is to examine the effectiveness and biochemical pharmacology of 7α-APTADD in vivo. In the hormone-dependent 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary carcinoma model system, 7α-APTADD at a 50 mg/kg/day dose caused an initial decrease in mean tumor volume during the first week, and tumor volume remained unchanged throughout the remaining 5-week treatment period. This agent lowers serum estradiol levels and inhibits ovarian aromatase activity. A second research area has focused on the synthesis of more metabolically stable inhibitors by replacing the thioether linkage at the 7α position with a carbon-carbon linkage. Several 7α-arylaliphatic androst-4-ene-3,17-diones were synthesized by 1,6-conjugate additions of appropriate organocuprates to a protected androst-4,6-diene or by 1,4-conjugate additions to a seco-A-ring steroid intermediate. These compounds were all potent inhibitors of aromatase with apparent K_is ranging between 13 and 19 nM. Extension of the research on these 7α-arylaliphatic androgens includes the introduction of a C₁---C₂ double bond in the A-ring to provide enzyme-activated irreversible inhibitors. The desired 7α-arylaliphatic androsta-1,4-diene-3,17-diones were obtained from their corresponding 7α-arylaliphatic androst-4-ene-3,17-diones by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). These inhibitors demonstrated enzyme-mediated inactivation of aromatase with apparent k_inacts ranging from 4.4 × 10⁻⁴ to 1.90 x 10⁻³ s⁻¹. The best inactivator of the series was 7α-phenpropylandrosta-1,4-diene-3,17-dione, which exhibited a T_1/2 of 6.08 min. Aromatase inhibition was also observed in MCF-7 human mammary carcinoma cell cultures and in JAr human choriocarcinoma cell cultures, exhibiting IC₅₀ values of 64-328 nM. The 7α-arylaliphatic androgens thus demonstrate potent inhibition of aromatase in both microsomal incubations and in choriocarcinoma cell lines expressing aromatase enzymatic activity. Additionally, the results from these studies provide further evidence for the presence of a hydrophobic binding pocket existing near the 7α-position of the steroid in the active site of aromatase. The size of the 7α-substituent influences optimal binding of steroidal inhibitors to the active site and affects the extent of enzyme-mediated inactivation observed with androsta-1,4-diene-3,17-dione analogs.     

Estrogen Enhances Performance of Female Rats during Acquisition of a Radial Arm Maze

Estrogen can influence the expression of behaviors not associated directly with reproduction, including learning and memory. However, the effects of estrogen on learning and memory in mammals are complex, dependent on a variety of factors. The radial arm maze is a traditional experimental task that takes advantage of the natural foraging strategy of rats and provides an appropriate measure for studying the effects of estrogen on working memory in this species. In the experiments reported here, ovariectomized rats were implanted subcutaneously with 5-mm Silastic capsules containing 25% estradiol diluted with cholesterol. Control females received 5-mm Silastic capsules containing 100% cholesterol. Results of three separate experiments demonstrated that estradiol administered by Silastic implants for 30 days prior to eight-arm radial maze training, during the 24 days of maze training, or both significantly improved working memory performance compared to females treated with cholesterol alone, as indicated by improved arm choice accuracy over trials. The positive effect of estradiol exposure prior to training suggests that estrogen may induce neuronal changes that persist beyond the period of exposure with functional consequences for behavior.     

Rate and composition of sweat fluid losses are unaltered by hypohydration during prolonged exercise in horses

Kingston, Janene K., Raymond J. Geor, and Laura JillMcCutcheon. Rate and composition of sweat fluid losses areunaltered by hypohydration during prolonged exercise in horses.J. Appl. Physiol. 83(4):1133-1143, 1997. Rate and ionic composition of sweat fluid losses and partitioning of evaporative heat loss into respiratory and cutaneous components were determined in six horses during three 15-km phases of exercise at ~40% of maximalO₂ uptake. Pattern of change insweat rate (SR) and composition was similar during each phase. SRincreased rapidly for the first 20 min of exercise but remained at~24-28ml · m² · min¹during the remainder of each phase. Similarly, the concentrations of Naand Cl in sweat increased until 30 min of exercise but were unchangedthereafter. Sweat osmolality and concentrations of Na and Cl werepositively correlated with SR. Sweat K concentration decreased duringexercise but was not correlated with SR. Fluid losses were 33.8 ± 1.5 liters, resulting in decreases of ~21% in plasma volume and~11% in total body water. The ~6% hypohydration was notassociated with an alteration in SR, sweat composition, or heatstorage. Respiratory and cutaneous evaporative heat loss represented~23 and 70%, respectively, of the total heat dissipated, and thepartitioning of heat loss was similar in each exercise phase. Weconclude that SR and the relative proportions of respiratory andcutaneous evaporative heat loss are unchanged in horses during prolonged low-intensity exercise despite moderate hypohydration.

     

Stereoselective hydroxylation at the aliphatic carbons of 7,8- and 9,10-dihydrobenzo[a]pyrenes by rat liver microsomes

Optically active 7-hydroxy-7,8-dihydrobenzo[a]pyrene and 8-hydroxy-7,8-dihydrobenzo[a]pyrene were identified as two of the major metabolites formed by incubation of 7,8-dihydrobenzo[a]pyrene with rat liver microsomes. Optically active 9-hydroxy-9,10-dihydrobenzo[a]pyrene and 10-hydroxy-9,10-dihydrobenzo[a]pyrene were similarly identified as two of the minor metabolites of 9,10-dihydrobenzo[a]pyrene. The formation of these metabolites was abolished either by prior treatment of liver microsomes with carbon monoxide or the absence of NADPH, but was not inhibited by an epoxide hydrolase inhibitor. The results indicate that the aliphatic carbons of dihydro polycyclic aromatic hydrocarbons may undergo stereoselective hydroxylation reactions catalyzed by the cytochrome P-450 system of rat liver microsomes.     

A high-pressure liquid chromatographic method for measuring 3', 5'-cyclic AMP in brain.

A method is described for the estimation of adenosine 3′,5′-monophosphate (3′,5′-cyclic AMP) in rat brain by high-pressure liquid chromatography (HPLC). The nucleotide is purified initially by being passed through two columns, alumina and AG-1X2. The peak in HPLC was identified by a number of methods. Optimum parameters for HPLC were obtained by using 1 mm KH₂PO₄ buffer, pH 4.8, at a flow rate of 57 ml/hr at room temperature. Using this technique the concentration of 3′,5′-cyclic AMP in rat brain was found to be 2.53 ± 0.40 nmol/g (mean ± SD, n = 5).     

Immunospecificity of nuclear antigens in chicken erythroid cells

Summary Specific antisera were produced against chicken reticulocyte dehistonized chromatin. The antisera reacts strongly with chicken reticulocyte chromatin, but only marginally with chicken erythrocyte chromatin. There is no reticulocyte antigen detected in chicken liver. Reticulocyte maturation is accompanied by a gradual decrease in the chromatin immunological activity and template capacity. The reduction of immunological activity is due to the change of chromatin conformation during erythrocyte maturation. Dehistonization and sonication of erythrocyte chromatin raises the erythrocyte chromatin immunological activity to levels similar to those of reticulocyte chromatin. The erythrocyte nuclear antigens are class specific, not being found in frog erythroid cell or murine Friend leukemia cell chromatins.     

Sexual development of patients with isochromosomes for the long arm of the X chromosome

Summary The sexual development of 14 girls with non-mosaic monocentric 46,X,iXq karyotype was studied. Seven out of eight girls were found to have immature secondary sexual characteristics and amenorrhoea, a finding greatly contrasting with that in Triplo-X girls. The relative ineffectiveness of the isochromosome Xq in maintaining fertility may be due to the absence of one short arm, which probably also carries a gonadal determinant. Alternatively, the presence of two inactivation sites on one isochromosome may render the gonadal determinants inactive at an important stage in gonadal development.