Analysis of 6-mercaptopurine in human plasma with a high-performance liquid chromatographic method including post-column derivatization and fluorimetric detection

A relatively simple assay with improved reliability and sensitivity for measuring levels of 6-mercaptopurine in human plasma is presented. After extraction of the compound and the added internal standard with phenyl mercury acetate, samples were separated by ion-pair reversed-phase high-performance liquid chromatography. On-line the analytes were oxidized to fluorescent products and detected in a flow-fluorimeter. The within-day coefficient of variation was 3.8% at a concentration of 25 ng/ml. The lower detection limit was 2 ng/ml when 1.0 ml of plasma was used. Mercaptopurine concentration versus time curves of two subjects after a single oral dose of azathioprine are shown.     

Immune response of mice exposed to cis-diamminedichloroplatinum

Summary The effects of cis-diamminedichloroplatinum (CDDP) on lymphoid organs and the immune response of young and older adult mice were studied histologically and by functionally assessing the activity of various subpopulations of immune cells. Young adult mice (6–8 weeks old) treated with 2 mg/kg CDDP mounted an enhanced splenic plaque-forming cell (PFC) response to both sheep erythrocytes, a helper T-cell-dependent antigen (HD), and pneumococcal polysaccharide type III a helper T-cell-independent antigen (HI). Older adult mice (18–22 weeks old) treated in the same way exhibited an equally enhanced PFC response to HD antigen and even a more pronounced response to HI antigen. Treatment of mice with 12 mg/kg CDDP resulted in immunosuppression. Thymus, lymph nodes, and spleen of animals treated with the higher dose of CDDP showed a marked cell depletion from both T and B areas, confirming that the immunosuppression was due to an indiscriminate elimination of both T and B lymphocytes. The immunosuppression and the cell depletion from lymphoid organs were more pronounced in younger mice. Thus, the effects of CDDP on the lymphoid organs and the immune response depend both on the age of the animals and on the dose of the drug. CDDP given in small doses enhances the PFC response, whereas a reduced PFC response is obtained following high-dose treatment. Abbreviations used: CDDP, cis-diamminedichloroplatinum; PFC, plaque-forming cell; HD, helper T-cell dependent; HI, helper T cell-independent; SIII, pneumococcal polysaccharide type III; SRBC, sheep red blood cells; TNP, trinitrophenyl; KLH, keyhole limpet hemocyanin; TNBS, 2, 4, 6-trinitrobenzene sulfonic acid; BBS, borate-buffered saline     

Water use efficiency as a function of leaf age and position within the cotton canopy

The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention in recent years. However, insufficient information exists on the coordination of transpiration and CO₂ uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration (E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO₂ mmol⁻¹ H₂O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in stomatal conductance (g_s·H₂O) since decreases in g_s·H₂O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these findings are presented in relation to light competition within the plant canopy during development.     

The Y deletion gr/gr and susceptibility to testicular germ cell tumor

Testicular germ cell tumor (TGCT) is the most common cancer in young men. Despite a considerable familial component to TGCT risk, no genetic change that confers increased risk has been substantiated to date. The human Y chromosome carries a number of genes specifically involved in male germ cell development, and deletion of the AZFc region at Yq11 is the most common known genetic cause of infertility. Recently, a 1.6-Mb deletion of the Y chromosome that removes part of the AZFc region—known as the “gr/gr” deletion—has been associated with infertility. In epidemiological studies, male infertility has shown an association with TGCT that is out of proportion with what can be explained by tumor effects. Thus, we hypothesized that the gr/gr deletion may be associated with TGCT. Using logistic modeling, we analyzed this deletion in a large series of TGCT cases with and without a family history of TGCT. The gr/gr deletion was present in 3.0% (13/431) of TGCT cases with a family history, 2% (28/1,376) of TGCT cases without a family history, and 1.3% (33/2,599) of unaffected males. Presence of the gr/gr deletion was associated with a twofold increased risk of TGCT (adjusted odds ratio [aOR] 2.1; 95% confidence interval [CI] 1.3–3.6; P = .005) and a threefold increased risk of TGCT among patients with a positive family history (aOR 3.2; 95% CI 1.5–6.7; P = .0027). The gr/gr deletion was more strongly associated with seminoma (aOR 3.0; 95% CI 1.6–5.4; P = .0004) than with nonseminoma TGCT (aOR 1.5; 95% CI 0.72–3.0; P = .29). These data indicate that the Y microdeletion gr/gr is a rare, low-penetrance allele that confers susceptibility to TGCT.     

Physiologic and Yield Responses of Shaded Cotton to the Plant Growth Regulator PGR-IV

The plant growth regulator PGR-IV has been reported to improve the growth, boll retention, and yield of cotton (Gossypium hirsutum L.) under optimum growing conditions. However, little is known about the response of cotton to PGR-IV under low light stress. A 3-year field study was conducted to determine if applying PGR-IV before an 8-day period of shade (63% light reduction) benefitted the growth and yield of shaded cotton. Shading during early squaring did not affect yield. Shading after the first flower stage significantly increased leaf chlorophyll concentration and fruit abscission and decreased the leaf photosynthetic rate, nonstructural carbohydrate concentrations, and lint yield. Foliar application of PGR-IV at 292 mL ha⁻¹ at early squaring and first flower did not improve the leaf photosynthetic rate of shaded cotton. However, shaded plants receiving PGR-IV had higher nonstructural carbohydrate concentrations in the floral buds and significantly lower fruit abscission than the shaded plants without PGR-IV. Applying PGR-IV to the foliage before shading resulted in a numeric increase (6–18%) in lint yield compared with shaded plants without PGR-IV. The decreased fruit abscission from the application of PGR-IV was associated with improved assimilate translocation. The yield enhancement from foliar application of PGR-IV was attributed to increased fruit retention. However, the average boll weight of shaded plants with PGR-IV tended to be lower than that of shaded plants without PGR-IV. Lint percentage was not affected by PGR-IV. Foliar application of PGR-IV appears beneficial for increasing the fruit retention of shaded cotton. Received June 12, 1997; accepted January 19, 1998     

Decline in photosynthesis as related to alterations in chloroplast ultrastructure of a cotton leaf during ontogeny

Field studies were conducted to investigate ontogenic changes in leaf photosynthesis and chloroplast ultrastructure of a single cotton (Gossypium hirsutum L.) leaf subtending the fruit. A 20-d old leaf was the most physiologically active with net photosynthetic rate (PN) of 16.5 mol m-2 s-1 and nitrogen (N) concentration of 168 mmol m-2. These values declined with leaf age and a close relationship existed between them. Concurrent with declines in PN, ultrastructural alterations occurred in the chloroplast: the 20-d old leaf had increased grana number and thylakoids per granum and a few plastoglobuli. Afterwards, the grana number and thylakoids per granum declined with leaf age indicating disintegrated grana and stroma lamellae. Concomitant with disintegrated membrane system was the presence of numerous large plastoglobuli. The PN was closely related to grana number and thylakoids per granum suggesting that the decline in PN with leaf age was associated with ultrastructural changes in the chloroplast.     

Pressure chamber measurements using two wheat leaves

Summary The most widely used technique of leaf water potential measurements is with the Scholander pressure chamber. Representative leaf water potential values require many determinations on individual leaves and this can be time consuming in large fields or experiments with multiple treatments. This paper describes a method of obtaining a mean value more rapidly, by using two leaves in the pressure chamber at the same time, but recording the end point of each leaf separately.     

Scale-down and optimization studies of the gluconic acid fermentation by Gluconobacter oxydans

To simulate production-scale conditions of gluconic acid fermentation by Gluconobacter oxydans, different experimental setups are presented in this study. From the determination of the time constants of a production-scale reactor, it can be concluded that mixing and oxygen transfer are the rate-limiting mechanisms. This results in oxygen concentration gradients which were simulated in a one-compartment reactor in which the oxygen concentration was fluctuated by a fluctuated gassing with air and nitrogen. It could be concluded that only very long periods of absence of oxygen (ca. 180 s) results in lower specific oxygen uptake rates by Gluconobacter oxydans. From scale-down studies carried out in a two-compartment system to simulate a production-scale reactor more accurately, it could be concluded that not only the residence time in the aerated part of the system is important, but the liquid flow in between the different parts of the reactor is also an essential parameter. It could also be concluded that the microorganisms are not influenced negatively by the fluctuated oxygen concentrations with respect to their maximal oxidation capacity. The two-compartment system can also be used for optimization experiments in which the "aerated" compartment was gassed with pure oxygen. From these experiments it was concluded that also a short residence of the cells at high oxygen concentrations diminished the growth and product formation rates. These experiments show the necessity of the scale-down experiments if optimization is carried out. The two-compartment system presented in this study is a very attractive tool for reliable scale-down experiments.