LH concentrations in two cattle with XY gonadal dysgenesis

Two animals with XY gonadal dysgenesis both had a reproductive tract similar in size to that found in sexually immature heifers, but neither had normal testicular or ovarian tissue. All cells examined in both animals contained XY chromosomes and spinal cord neurones were sex chromatin negative. Basal LH concentrations averaged 3.1 ng/ml in Animal 1 and 2.4 ng/ml in Animal 2 but increased within 12 h of injecting oestradiol to peak concentrations of 125 and 11 ng/ml respectively. Animal 1 displayed a distinct pulsatile LH release pattern with a highly repeatable decline phase at each pulse. A GnRH injection produced a rapid rise in plasma LH in both animals, sustained in Animal 1 at greater than 500 ng/ml for more than 2 h. Each animal displayed behavioural symptoms of oestrus within 12 h of being injected with 3 mg oestradiol benzoate and was repeatedly served by a bull. These studies indicated that both animals differed from freemartins and had some hypothalamic and pituitary response patterns resembling those reported for female cattle.     

Compartmentation of glutamate metabolism in brain. Evidence for the existence of two different tricarboxylic acid cycles in brain

1. (14)C from [1-(14)C]glucose injected intraperitoneally into mice is incorporated into glutamate, aspartate and glutamine in the brain to a much greater extent than (14)C from [2-(14)C]glucose. This difference for [1-(14)C]glucose and [2-(14)C]glucose increases with time. The amount of (14)C in C-1 of glutamate increases steadily with time with both precursors. It is suggested that a large part of the glutamate and aspartate pools in brain are in close contact with intermediates of a fast-turning tricarboxylic acid cycle. 2. (14)C from [1-(14)C]acetate and [2-(14)C]acetate is incorporated to a much larger extent into glutamine than into glutamate. An examination of the time-course of (14)C incorporated into glutamine and glutamate reveals that glutamine is not formed from the glutamate pool, labelled extensively by glucose, but from a small glutamate pool. This small glutamate pool is not derived from an intermediate of a fast-turning tricarboxylic acid cycle. 3. It is proposed that two different tricarboxylic acid cycles exist in brain.     

Survival of six species of African ticks in relation to saturation deficits

The survival of unfed males and females of six species of African ticks was monitored at five different saturation deficits at constant temperature (25°C). The survivorship curves for each species comprised a pre-mortality period, prior to when ticks started to die and a mortality period corresponding to a rapid increase in the mortality rate. Longevity was defined as pre-mortality plus mortality. A negative correlation between the longevity of the ticks and the saturation deficits was found with ticks surviving longer at lower deficits. The survival of males and females was similar. At low saturation deficits (2–4 mmHg) Amblyomma hebraeum survived the longest periods (74 weeks). Some correlation was found between the tick survival under dehydrating conditions and habitat associations. Rhipicephalus appendiculatus and Haemaphysalis leachii, the most mesic in distribution, had the shortest longevity (21 and 13 weeks, respectively) at high saturation deficits (7–21 mmHg). Hyalomma marginatum rufipes, the most xerophilic in distribution, had the longest survival (39.3±10.5 weeks) at high saturation deficits. Other factors apart from the adult survival should be taken into account when accounting for the tick distribution, in particular the tolerance of earlier developmental stages to desiccation.     

The effects of tick numbers and intervals between infestations on the resistance acquired by guinea-pigs to adults of Rhipicephalus evertsi evertsi (Acari: Ixodidae)

Guinea-pigs were infested three times at short (1 week) intervals or long (10 week) intervals between successive infestations with low (1), medium (8) and high (15) numbers of adult Rhipicephalus evertsi evertsi. To compare the resistance developed by the hosts at short and long intervals between infestations, a challenge (fourth) infestation was performed with the high number of ticks. Resistance was assessed by comparing the mean weight of engorged female ticks that dropped from the hosts. Concentrations of beta globulins in the host sera were also monitored. Different tick Ioads (low, medium and high) and infestation intervals had a similar influence on the reduction in weight of the females which was between 60–70% after the final challenge. However, the concentration of beta globulins, was highest in the guinea-pigs exposed to medium and high numbers of ticks with long infestation intervals, probably because of an increase in the production of protective antibodies in response to more intensive antigenic challenge. The relationship between engorgement weight and beta globulin levels in host sera is discussed.     

An effect of elevated postirradiation pH on the yield of double-strand breaks in DNA from irradiated bacterial cells

Exposure of DNA isolated from irradiated cells of Escherichia coli to a pH of 9.6 caused a marked increase in the yield of double-strand breaks (dsb). The dsb were measured by sedimentation analysis of E. coli chromosomal DNA using neutral sucrose gradients. After incubation for 4 hr at 37 degrees C and pH 9.6 the dsb yields were 95% and 71% higher than when incubation was at pH 7.0 for irradiation under oxic and anoxic conditions, respectively. This effect was not apparent when dsb were induced enzymatically and it was linearly related to radiation dose. After oxic irradiation, the increase in dsb at pH 9.6 was consistent with first-order kinetics over greater than 2 half-lives (t1/2 = 1.6 hr at 37 degrees C). The effect of elevated pH was largely additive to a previously reported increase in dsb yield caused by ethanol. It is proposed that the effects of elevated pH and of ethanol revealed the presence in intracellularly irradiated DNA of previously unidentified sites where both strands of the DNA were damaged as a result of single radiation events. The possible nature of the proposed sites and the relevance of these findings to the "neutral" elution technique are discussed.     

Evidence for catalytic dismutation of superoxide by cobalt(II) derivatives of bovine superoxide dismutase in aqueous solution as studied by pulse radiolysis.

By using the technique of pulse radiolysis to generate O2-., it is demonstrated that Co(II) derivatives of bovine superoxide dismutase in which the copper alone and both the copper and zinc of the enzyme have been substituted by Co(II), resulting in (Co,Zn)- and (Co,Co)-proteins, are capable of catalytically dismutating O2-. with 'turnover' rate constants of 4.8 X 10(6) dm3.s-1.mol-1 and 3.1 X 10(6) dm3.s-1.mol-1 respectively. The activities of the proteins are independent of the pH (7.4-9.4) and are about three orders of magnitude less than that of the native (Cu,Zn)-protein. The rate constants for the initial interaction of O2-. with the Co-proteins were determined to be (1.5-1.6) X 10(9) dm3.s-1.mol-1; however, in the presence of phosphate, partial inhibition is apparent [k approximately (1.9-2.3) X 10(8) dm3.s-1.mol-1]. To account for the experimental observations, two reaction schemes are presented, involving initially either complex-formation or redox reactions between O2-. and Co(II). This is the first demonstration that substitution of a metal into the vacant copper site of (Cu,Zn)-protein results in proteins that retain superoxide dismutase activity.     

Exceptionally low blood glucose response to dried beans: comparison with other carbohydrate foods.

Normal volunteers took 50-g carbohydrate portions of eight varieties of dried legumes and 24 common foods drawn from grains, cereals and pasta, breakfast cereals, biscuits, and tuberous vegetables. Both the mean peak rise in blood glucose concentrations and mean area under the glucose curve of the subjects who ate beans were at least 45% lower than those of subjects who ate the other foods. These results suggest a potentially valuable role for dried leguminous seeds in carbohydrate exchanges for individuals with impaired carbohydrate tolerance.     

Radiosensitization of hypoxic mammalian cells in vitro by some 5-substituted-4-nitroimidazoles

The efficiencies of various 5-substituted-4-nitroimidazoles as radiation sensitizers have been determined in hypoxic Chinese hamster cells irradiated in vitro. Compared with published data on the sensitizing properties of substituted 2-nitro- and 5-nitroimidazoles, some of the 4-nitro derivatives show unusually high sensitizing efficiencies defined as the concentrations required to give an enhancement ratio of 1.6. The equilibrium one-electron reduction potentials of the compounds (E17) were measured by a pulse radiolysis technique and the results show that although sensitizing efficiencies are unexpectedly high, based on considerations of electron affinity, they still increase with increasing values of E17. Enhancement ratios were determined in two V79 cell lines for combinations of one of these compounds (a 4-nitroimidazole containing the group SO2.O.phenyl in the 5-position, NSC 38087) with various concentrations of misonidazole. The sensitization observed suggests that the two compounds may be operating by different mechanisms.     

Selective destruction of amino acid residues in irradiated solutions of superoxide dismutase.

Amino acid analyses of irradiated bovine superoxide dismutase solutions showed that only a few types of residues are destroyed by H and Br₂^? radicals and confirmed the indications obtained from work on free amino acids. Furthermore destruction of lysine - unexpected on the basis of data obtained in free solutions of amino acids exposed to Br₂^? - was observed in the copper-containing protein. Different extent of amino acid losses were observed depending on pH and presence or absence of copper. Correlation of these losses with residual enzymic activity permitted identification of some vital residues.