Time-synchronized continuous wave laser-induced fluorescence on an oscillatory xenon discharge.

A novel approach to time-synchronizing laser-induced fluorescence measurements to an oscillating current in a 60 Hz xenon discharge lamp using a continuous wave laser is presented. A sample-hold circuit is implemented to separate out signals at different phases along a current cycle, and is followed by a lock-in amplifier to pull out the resulting time-synchronized fluorescence trace from the large background signal. The time evolution of lower state population is derived from the changes in intensity of the fluorescence excitation line shape resulting from laser-induced fluorescence measurements of the 6s(')[1/2](1)(0)-6p(')[3/2](2) xenon atomic transition at λ = 834.68 nm. Results show that the lower state population oscillates at twice the frequency of the discharge current, 120 Hz.

Nutritional regulation of IGF-II, but not IGF-I, is age dependent in sheep.

In post-natal animals, plasma concentrations of IGF-I are tightly regulated by nutritional status. The current study reports that plasma levels of IGF-II in sheep are also regulated by nutrition, but whether plasma IGF-II is increased, decreased or remains the same, depends on the age of the animal. Ewe lambs, ranging in age from 2 days to 2 years, were fed or fasted for lengths of time between 24 and 72 h. Blood samples were taken at intervals of 24 h throughout the treatment period and immediately before slaughter. Plasma concentrations of IGF-I increased with advancing age in fed animals (P<0.001) and were reduced by fasting in all age groups (P<0.001). Plasma concentrations of IGF-II also increased as animals matured (P<0.001), but did not show an overall effect of the fasting treatment. An interaction between age and nutrition (P<0.001) resulted from a decrease in plasma IGF-II in response to fasting in neonatal animals (P<0.01) and, conversely, increased levels of plasma IGF-II in fasted mature animals (P<0.01 or P<0.001). Fasted sheep of peripubertal age showed no change in plasma levels of IGF-II. The nutritional sensitivity of serum IGF-binding proteins (BPs) also changed with age. The 29 kDa BP, which we presume to be BP1, was elevated by fasting in young animals and reduced slightly in older animals. BP2 was increased to a similar magnitude by fasting at all ages. BP3 was depressed by fasting in young animals and showed little change in adults. In contrast, a 24 kDa BP, which is probably BP4, showed little change in young animals and was reduced substantially in older sheep. In conclusion, the response of plasma IGF-II to fasting suggests that this peptide has functions in mediating nutritional stress which depend on the age of the animal, and also that the role of IGF-II may differ from that of IGF-I in adults.

Synthesis and transsulfuration of homocysteine in blood.

Interest in total plasma homocysteine (homocyst[e]ine) as a risk factor for atherosclerosis is expanding. However, the origin of plasma homocyst(e)ine has not been defined. Our studies examined the metabolism of homocyst(e)ine by blood cells as a potential contributor to the homeostasis of homocyst(e)inemia. Incubation of blood for 24 hours at 37 degrees C produced a threefold increase in the level of plasma homocyst(e)ine. In samples of fractionated blood cells incubated in vitro, increases in total plasma homocysteine were limited to incubated erythrocyte fractions and were influenced by addition of methionine. Anticoagulants had no significant effect. Incubation of blood in the presence of methionine tagged with sulfur 35 demonstrated incorporation of label into homocysteine and transsulfuration products. Similar incubations of blood cell fractions suggested that synthesis of homocysteine occurred in erythrocytes, whereas leukocytes both synthesized and transsulfurated homocysteine. These findings demonstrated a possible interaction of different blood cells in the metabolism of methionine, as well as their potential role as a source of total plasma homocysteine in plasma.