Nitrogen and phosphorus dynamics in three central Texas impoundments

Summary The entrapment of nitrogen and phosphorus by three man-made impoundments in central Texas was studied from February, 1969 through January, 1970. Each impoundment was sampled at four-hour intervals during February, May, August, and November. During the other months, each station was sampled at midafternoon and between 2 A.M. and dawn.Annual nitrogen budgets for the three lakes show they all serve as nutrient traps. In general, retention of nitrogen is a function of increased autotrophic assimilation during the growing season.All three lakes lost phosphorus on an annual basis. This loss was attributed to the small demand by autotrophs and the addition of phosphorus from allochthonous sources around the lakes and from sewage plant effluents upstream. Based on nitrogen-phosphorus ratios, it is postulated that nitrogen is the nutrient factor which limits algal growth in all three impoundments.     

The Role of Glutathione in Protection against DNA Damage Induced by Rifamycin SV And Copper(II) Ions

Incubation of calf thymus DNA in the presence of rifamycin SV induces a decrease in the absorbance of DNA at 260 nm. The effect, was found to be proportional to the antibiotic concentration and enhanced by copper(II) ions. In the presence of rifamycin SV and copper(II), a significant increase in thiobarbituric acid-reactive (TBA-reactive) material is also observed. This effect is inhibited to different degrees by the following antioxidants: catalase 77%; thiourea 72%; glutathione (GSH) 62%; ethanol 52%; and DMSO 34%, suggesting that both hydrogen peroxide (H₂O₂) and hydroxyl radicals (OH·) are involved in DNA damage. Rifamycin SV-copper(II) mixtures were also found to induce the production of peroxidation material from deoxyribose and, in this case, glutathione and ethanol were the most effective antioxidant substrates with inhibition rates of 91% and 88% respectively.

Electrophoretic studies show that calf thymus DNA becomes damaged after 20 min. incubation in the presence of both agents together and that the damaged fragments run with migration rates similar to those obtained by the metal chelating agent 1,10-phenanthroline. Normal DNA electrophoretic pattern was found to be preserved by catalase, and GSH at physiological concentrations and by thiourea. No protection is observed in the presence of ethanol or DMSO. The results obtained indicate the involvement of different reactive species in the degradation process of DNA due to rifamycin SV-copper(II) complex and emphasize the role of reduced glutathione as an oxygen free radical scavenger.     

The cardioprotective effect of Mn-superoxide dismutase is lost at high doses in the postischemic isolated rabbit heart

The loss of protection by human recombinant (hr) Cu,Zn-superoxide dismutase (SOD) at higher doses reported previously may have been due to the weak peroxidase activity of this enzyme. To test this possibility we studied the dose-response relationship of hrMn-SOD, which lacks peroxidase activity. Isolated, buffer perfused rabbit hearts were subjected to 1 h of global ischemia followed by 1 h of reperfusion, and the percent recovery of developed tension (relative to preischemic) was measured via a left ventricular balloon connected through a pressure transducer to a polygraph recorder. The coronary effluent was assayed for lactate dehydrogenase (LDH) release. While hrMn-SOD almost completely protected against loss of function and LDH release at 2 and 5 mg/L (p < 0.01), it exacerbated the damage at 50 mg/L concentration (p < 0.05 against controls), thus giving an even sharper bell-shaped curve than seen with the hrCu,Zn-SOD. Therefore we conclude that, first, while the hrMn-SOD protects the reperfused heart at lower doses, it may exacerbate the damage at higher doses. Second, that the lack of protection seen at higher doses of hr-Cu,Zn-SOD is unlikely to be due only to its peroxidase activity.     

A fluorometric method for determination of actinomycin D in serum

A sensitive fluorometric method for the determination of actinomycin D in serum has been developed. The method is based on the fluorescence of the product obtained when actinomycin D is oxidized with alkaline hydrogen peroxide. The fluorescence is measured at 420 mμ with excitation at 370 mμ. The lower limit of detection for actinomycin D is 0.1 μg of actinomycin D per milliliter of serum. In this method, actinomycin D is totally recovered from serum by extraction with ethyl acetate.     

Enkephalins interfere with acquisition of an active avoidance response

Leu-enkephalin and Met-enkephalin at a dose of 400 μg/kg i.p. significantly impaired acquisition of a one-way active avoidance response. D-Ala-D-Leu-enkephalin also impaired acquisition but at a lower dose (4 μg/kg). D-Ala-Met-enkephalinamide in a wide dose range (0.04–400 μ/kg) did not alter acquisition of the response. A high dose of naloxone (100 mg/kg) blocked the impairing action of Leu-enkephalin. These results are discussed in terms of multiple opiate receptor species.