The response of C19- and some C21-steroids during Synacthen and insulin tolerance test.

Testing of the adrenal function with ACTH 1-24 (Synacthen test) or insulin (insulin tolerance test-ITT) is commonly used. The question of ongoing debate is the dose of Synacthen. Moreover, it may be important from the physiological point of view besides measurement of cortisol levels and 17α-hydroxy-progesterone to know also the response of other steroids to these test. The plasma levels of 24 free steroids and their polar conjugates were followed after stimulation of 1 µg, 10 µg and 250 µg of ACTH 1-24 and after insulin administration in thirteen healthy subjects. The study aimed to describe a response of steroid metabolome to various doses of ACTH 1-24 and to find the equivalency of these tests. The additional ambition was to contribute to understanding of physiology of these stimulation tests and suggest an additional marker for HPA axis evaluation. No increase of most conjugated steroids and even decrease of some of them during all of the Synacthen tests and ITT at 60th min were observed. The levels of steroid conjugates decreased in ITT but did not during all of the Synacthen tests by 20 min of each test. Testosterone and estradiol did not increase during the Synacthen tests or ITT as expected. The results suggest that the conjugated steroids in the circulation can serve as reserve stock for rapid conversion into free steroids in the first minutes of the stress situation. Various doses of ACTH 1-24 used in the Synacthen tests implicate earlier or later occurrence of maximal response of stimulated steroids. The equivalent dose to ITT and standard 250 µg of ACTH 1-24 seemed to be dose of 10 µg ACTH 1-24 producing the similar response in all of the steroids in the 60th min of the test.

The Response of C19 Δ5-steroids to ACTH Stimulation and Hypoglycemia in Insulin Tolerance Test for Adrenal Insufficiency.

Studies on the time course of ACTH- or insulin-induced hypoglycemia stimulating adrenal androgens are usually limited to dehydroepiandrosterone and/or its sulphate. Our data on dehydroepiandrosterone (DHEA) and its hydroxylated metabolites clearly show that measurements of DHEA and its sulphate (DHEAS) are valuable markers of the integrity of the HPA (hypothalamus-pituitary-adrenal) axis. Assessments of HPA function should rely on measurements of baseline and/or stimulated serum cortisol concentrations, and C19 Δ5-steroids may provide additional information. The art of stimulation of 7- and 16-hydroxylated metabolites of DHEA can help our understanding of the formation sequence of these compounds.

A Comparison of Salivary Steroid Levels during Diagnostic Tests for Adrenal Insufficiency.

Numerous diagnostic tests are used to evaluate the hypothalamic-pituitary-adrenal axis (HPA axis). The gold standard is still considered the insulin tolerance test (ITT), but this test has many limitations. Current guidelines therefore recommend the Synacthen test first when an HPA axis insufficiency is suspected. However, the dose of Synacthen that is diagnostically most accurate and sensitive is still a matter of debate. We investigated 15 healthy men with mean/median age 27.4/26 (SD±4.8) years, and mean/median BMI (body mass index) 25.38/24.82 (SD±3.2) kg/m2. All subjects underwent 4 dynamic tests of the HPA axis, specifically 1 µg, 10 µg, and 250 µg Synacthen (ACTH) tests and an ITT. Salivary cortisol, cortisone, pregnenolone, and DHEA (dehydroepiandrosterone) were analysed using liquid chromatography-tandem mass spectrometry. During the ITT maximum salivary cortisol levels over 12.5 nmol/l were found at 60 minutes. Maximum cortisol levels in all of the Synacthen tests were higher than this; however, demonstrating that sufficient stimulation of the adrenal glands was achieved. Cortisone reacted similarly as cortisol, i.e. we did not find any change in the ratio of cortisol to cortisone. Pregnenolone and DHEA were higher during the ITT, and their peaks preceded the cortisol peak. There was no increase of pregnenolone or DHEA in any of the Synacthen tests. We demonstrate that the 10 µg Synacthen dose is sufficient stimulus for testing the HPA axis and is also a safe and cost-effective alternative. This dose also largely eliminates both false negative and false positive results.

Transgenic barley overexpressing a cytokinin dehydrogenase gene shows greater tolerance to drought stress.

Together with auxins, cytokinins are the main plant hormones involved in many different physiological processes. Given this knowledge, cytokinin levels can be manipulated by genetic modification in order to improve agronomic parameters of cereals in relation to, for example, morphology, yield, and tolerance to various stresses. The barley (Hordeum vulgare) cultivar Golden Promise was transformed using the cytokinin dehydrogenase 1 gene from Arabidopsis thaliana (AtCKX1) under the control of mild root-specific ß-glucosidase promoter from maize. Increased cytokinin degradation activity was observed positively to affect the number and length of lateral roots. The impact on morphology depended upon the recombinant protein's subcellular compartmentation. While assumed cytosolic and vacuolar targeting of AtCKX1 had negligible effect on shoot growth, secretion of AtCKX1 protein to the apoplast had a negative effect on development of the aerial part and yield. Upon the application of severe drought stress, all transgenic genotypes maintained higher water content and showed better growth and yield parameters during revitalization. Higher tolerance to drought stress was most caused by altered root morphology resulting in better dehydration avoidance.

Extra- and intracellular distribution of cytokinins in the leaves of monocots and dicots.

The plant hormones cytokinins are a convenient target of genetic manipulations that bring benefits in biotechnological applications. The present work demonstrates the importance of the subcellular compartmentalization of cytokinins on the model dicot plant Arabidopsis thaliana and monocot crop Hordeum vulgare. The method of protoplast and vacuole isolation combined with precise cytokinin analysis and recovery assay of a vacuolar marker protein were used to quantify the contents of individual cytokinin forms in the leaf extracellular space, cell interior and vacuole. The data obtained for wild type plants and in each case a specific mutant line allow comparing the effect of genetic manipulations on the hormone distribution and homeostatic balance of cytokinins in the modified plants.

How smoking cessation influence hormonal levels in postmenopausal women?

Smoking represents the most widespread substance dependence in the world. Nicotine alters women hormonal homeostasis. Women smokers have higher testosterone and lower estradiol levels throughout life compared to nonsmokers. We monitored the effect of smoking discontinuation on steroid spectrum with 25 postmenopausal women smokers. They had been examined before discontinuation of smoking and after 6, 12, 24 and 48 weeks of abstinence. Blood was collected to determine steroid spectrum (measured by GC-MS), luteinizing hormone, follicle stimulating hormone and sex hormone binding globulin (measured by IRMA). Repeated measures ANOVA model was used for evaluation of the data. In postmenopausal women, an increase in testosterone, dihydrotestosterone, dehydroepiandrosterone and other androgens occurred. Neither nicotine replacement therapy nor weight changes nor age play a role in androgen level increase. The higher androgens levels correlated with failure in smoking cessation. Women smokers have higher androgen levels, which might play a role in smoking dependence development. Women successful in smoking cessation, compared to the non-successful ones, have lower androgen levels initially and also after smoking discontinuation.

Overexpression of cytokinin dehydrogenase genes in barley (Hordeum vulgare cv. Golden Promise) fundamentally affects morphology and fertility.

Barley is one of the most important cereal crops grown worldwide. It has numerous applications, but its utility could potentially be extended by genetically manipulating its hormonal balances. To explore some of this potential we identified gene families of cytokinin dehydrogenases (CKX) and isopentenyl transferases, enzymes that respectively irreversibly degrade and synthesize cytokinin (CK) plant hormones, in the raw sequenced barley genome. We then examined their spatial and temporal expression patterns by immunostaining and qPCR. Two CKX-specific antibodies, anti-HvCKX1 and anti-HvCKX9, predominantly detect proteins in the aleurone layer of maturing grains and leaf vasculature, respectively. In addition, two selected CKX genes were used for stable, Agrobacterium tumefaciens-mediated transformation of the barley cultivar Golden Promise. The results show that constitutive overexpression of CKX causes morphological changes in barley plants and prevents their transition to flowering. In all independent transgenic lines roots proliferated more rapidly and root-to-shoot ratios were higher than in wild-type plants. Only one transgenic line, overexpressing CKX under the control of a promoter from a phosphate transporter gene, which is expressed more strongly in root tissue than in aerial parts, yielded progeny. Analysis of several T1-generation plants indicates that plants tend to compensate for effects of the transgene and restore CK homeostasis later during development. Depleted CK levels during early phases of development are restored by down-regulation of endogenous CKX genes and reinforced de novo biosynthesis of CKs.

Genetic engineering of cytokinin metabolism: prospective way to improve agricultural traits of crop plants.

Cytokinins (CKs) are ubiquitous phytohormones that participate in development, morphogenesis and many physiological processes throughout plant kingdom. In higher plants, mutants and transgenic cells and tissues with altered activity of CK metabolic enzymes or perception machinery, have highlighted their crucial involvement in different agriculturally important traits, such as productivity, increased tolerance to various stresses and overall plant morphology. Furthermore, recent precise metabolomic analyses have elucidated the specific occurrence and distinct functions of different CK types in various plant species. Thus, smooth manipulation of active CK levels in a spatial and temporal way could be a very potent tool for plant biotechnology in the future. This review summarises recent advances in cytokinin research ranging from transgenic alteration of CK biosynthetic, degradation and glucosylation activities and CK perception to detailed elucidation of molecular processes, in which CKs work as a trigger in model plants. The first attempts to improve the quality of crop plants, focused on cereals are discussed, together with proposed mechanism of action of the responses involved.

Root-synthesized cytokinins improve shoot growth and fruit yield in salinized tomato (Solanum lycopersicum L.) plants.

Salinity limits crop productivity, in part by decreasing shoot concentrations of the growth-promoting and senescence-delaying hormones cytokinins. Since constitutive cytokinin overproduction may have pleiotropic effects on plant development, two approaches assessed whether specific root-localized transgenic IPT (a key enzyme for cytokinin biosynthesis) gene expression could substantially improve tomato plant growth and yield under salinity: transient root IPT induction (HSP70::IPT) and grafting wild-type (WT) shoots onto a constitutive IPT-expressing rootstock (WT/35S::IPT). Transient root IPT induction increased root, xylem sap, and leaf bioactive cytokinin concentrations 2- to 3-fold without shoot IPT gene expression. Although IPT induction reduced root biomass (by 15%) in control (non-salinized) plants, in salinized plants (100 mM NaCl for 22 d), increased cytokinin concentrations delayed stomatal closure and leaf senescence and almost doubled shoot growth (compared with WT plants), with concomitant increases in the essential nutrient K(+) (20%) and decreases in the toxic ion Na(+) (by 30%) and abscisic acid (by 20-40%) concentrations in transpiring mature leaves. Similarly, WT/35S::IPT plants (scion/rootstock) grown with 75 mM NaCl for 90 d had higher fruit trans-zeatin concentrations (1.5- to 2-fold) and yielded 30% more than WT/non-transformed plants. Enhancing root cytokinin synthesis modified both shoot hormonal and ionic status, thus ameliorating salinity-induced decreases in growth and yield.

Cigarette smoking and progesterone and androgen metabolites in premenopausal women.

BACKGROUND: Smoking represents the most widespread substance dependence in the world. Several studies show nicotine's ability to alter women hormonal homeostasis. Women smokers have higher testosterone and lower estradiol levels throughout life compared to women non-smokers. This negatively affects women's reproductive function. Furthermore, alteration of neuroactive and neuroprotective steroids occurs in women smokers, and this plays an important role in the activity of the central nervous system, cognition, mental condition, and degree of substance dependence. METHODS: We monitored the effect of smoking discontinuation on steroid spectrum in 40 premenopausal women heavy smokers. These women were examined before they began to discontinue smoking, and after 6, 12, 24 and 48 weeks of abstinence. In each examination, blood was collected to determine steroid spectrum, LH, FSH, and SHBG; basic anthropometric data were also measured using GC-MS or immunoanalysis. Repeated-measures analysis of variance (ANOVA) model was used for evaluation of the data. RESULTS: Given the small number of women who persisted in not smoking, only the data after 6 weeks could be analyzed. No changes were found in C21 steroids, and a slight increase in androgens occurred after the discontinuation of smoking. CONCLUSION: Chronic smoking causes hyperandrogenism in fertile women; after smoking discontinuation, it increases further. Longer-term monitoring is necessary to show the effect of smoking discontinuation on steroid spectrum.

Free testosterone and free dihydrotestosterone throughout the life span of men.

OBJECTIVE: The dihydrotestosterone/testosterone ratio seems to be an important factor in the expression of androgenic activity, especially in the prostate and pilosebaceous unit. Whereas the decline of testosterone in aging men is well known, controversial data can be found concerning the age dependence of dihydrotestosterone levels. Hormonal values from our database served for the construction of the life span curve of free dihydrotestosterone/free testosterone ratio. METHODS: The results of testosterone, dihydrotestosterone and SHBG determination obtained by immunoassays from 13,152 male patients were used for the calculation of free steroid content and the construction of the age dependence curves. RESULTS: After initial high free dihydrotestosterone: free testosterone ratio in infancy it decreases at the start of puberty and remains practically without change from approx. 20 years of age till senescence. CONCLUSION: The course of free dihydrotestosterone/free testosterone ratio demonstrates the role of dihydrotestosterone for androgen functions especially in prepubertal age.

Hydrolytic cleavage of N6-substituted adenine derivatives by eukaryotic adenine and adenosine deaminases.

Homogeneous adenine deaminases (EC 3.5.4.2) from the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe and a putative ADA (adenosine deaminase; EC 3.5.4.4) from Arabidopsis thaliana were obtained for the first time as purified recombinant proteins by molecular cloning of the corresponding genes and their overexpression in Escherichia coli. The enzymes showed comparable molecular properties with well-known mammalian ADAs, but exhibited much lower k(cat) values. Adenine was the most favoured substrate for the yeast enzymes, whereas the plant enzyme showed only very low activities with either adenine, adenosine, AMP or ATP. Interestingly, the yeast enzymes also hydrolysed N6-substituted adenines from cytokinins, a group of plant hormones, cleaving them to inosine and the corresponding side chain amine. The hydrolytic cleavage of synthetic cytokinin 2,6-di-substituted analogues that are used in cancer therapy, such as olomoucine, roscovitine and bohemine, was subsequently shown for a reference sample of human ADA1. ADA1, however, showed a different reaction mechanism to that of the yeast enzymes, hydrolysing the compounds to an adenine derivative and a side chain alcohol. The reaction products were identified using reference compounds on HPLC coupled to UV and Q-TOF (quadrupole-time-of-flight) detectors.The ADA1 activity may constitute the debenzylation metabolic route already described for bohemine and, as a consequence, it may compromise the physiological or therapeutic effects of exogenously applied cytokinin derivatives.

Aminohydrolases acting on adenine, adenosine and their derivatives.

BACKGROUND: Adenine and adenosine-acting aminohydrolases are important groups of enzymes responsible for the metabolic salvage of purine compounds. Several subclasses of these enzymes have been described and given current knowledge of the full genome sequences of many organisms, it is possible to identify genes encoding these enzymes and group them according to their primary structure. METHODS AND RESULTS: This article is a short overview of the enzymes classified as adenine and adenosine deaminase. It summarises knowledge of their occurrence, genetic basis and their catalytic and structural properties. CONCLUSIONS: These enzymes are constitutive components of purine metabolism and their impairment may cause serious medical disorders. In humans, adenosine deaminase deficiency is linked to severe combined immunodeficiency and as such the enzyme has been approved for the first gene therapy trial. The role of these enzymes in plants is unclear, since the activity was has not been detected in extracts and putative genes have not been yet cloned and analyzed. A literature search and amino acid identity comparison show that Ascomycetes contain only adenine deaminase, but not adenosine deaminase, despite the fact that corresponding genes are annotated in databases as the adenosine cleaving enzymes because they share the same conserved domain.