High-performance wobbling subreflector for the Millimetre and Infrared Testa Grigia Observatory 2.6-m telescope.

The Millimetre and Infrared Testa Grigia Observatory 2.6-m Cassegrain telescope has been designed to allow high-sensitivity observations in the millimeter spectral range. For this purpose, in order to reduce unwanted contributions from local foregrounds, we adopted a sky-chopping technique, by wobbling the telescope subreflector. We describe the design and performance of the wobbling system, which can endure external forced two and three fields square-wave modulation and includes features such as high frequency, high amplitude, high duty cycle, low microphonics, and high stability.

In vivo inhibition of N-nitrosodimethylamine metabolism by 4-methylpyrazole: a model for endogenous nitrosation.

The endogenous formation of N-nitrosodimethylamine (NDMA) was investigated in the ferret by inhibiting metabolism and monitoring urinary NDMA levels. The addition of 1.0 mg/ml of 4-methylpyrazole (4-MP) to the drinking water was sufficient to allow a 13% urinary recovery of a 4.0 nmol oral dose of NDMA to be made in 24 h. Without 4-MP, no NDMA could be detected in urine. There was no detectable urinary NDMA when dimethylamine (DMA) alone was given but when as little as 5 mumol of nitrite and 0.75 mmol of DMA were given, the urine contained approximately 0.3 nmol NDMA/day. Nitrite doses of 0-100 mumol along with 0.75 mmol of DMA resulted in a dose-dependent excretion of less than 0.1-2.5 nmol NDMA/day. When 10 mumol of aminopyrine was substituted for DMA and 40 mumol of nitrite given, the excretion of NDMA was 10 nmol day. Administration of ascorbic acid inhibited NDMA excretion and thiocyanate increased NDMA formation. Consumption of foods containing trace amounts of NDMA resulted in the excretion of NDMA but in most cases at levels that were lower than those ingested in the food. These data suggest that mumol amounts of nitrite can result in the endogenous formation of nmol amounts of NDMA in the acidic environment of the stomach. It also suggests that short-term ingestion of 4-MP might be an approach to studying the possible endogenous formation of NDMA in humans.

Nitrite-cured meats as a source of endogenously and exogenously formed N-nitrosoproline in the ferret.

Nitrite-cured meat containing 120 mg Na15NO2/kg was fed to male ferrets (Mustela putorius furo). During consumption of the meat, the animals were dosed orally with 0.87 mmol [2-2H]proline. All urine was collected throughout the study and analysed for total N-nitrosoproline (NPRO) and isotopic enrichment of NPRO by mass spectrometry. The cured-meat diet increased the urinary excretion of NPRO 14-fold. Isotope analyses indicated that approximately 70% of the NPRO came from the cured meat, the majority of which was analytically unavailable or 'bound' NPRO in the meat. A small portion of the excreted NPRO appeared to be formed in the stomach as a result of ingesting the cured meat. A minor amount of the excreted NPRO did not contain any isotopically labelled atoms. The administration of ascorbic acid did not significantly alter NPRO excretion. Animals dosed orally with 11.4 mumol of a peptide in which the N-terminal proline was nitrosated increased their excretion of NPRO by 385 nmol over the following 48 hr. These data indicate that nitrite-cured meat contains bound NPRO which contributes to the total amount of NPRO in the urine.

The effects of fractionated thermally oxidized corn oil on drug-metabolizing enzyme systems in the rat.

Corn oil samples were heated, with aeration, to 210 degrees C for a total of 5 hr. Both fresh and oxidized samples were urea-fractionated and the individual fractions were administered to male Sprague-Dawley rats by gastric intubation. The effects of urea adducts, adduct-free fractions, non-saponifiable fractions and unfractioned fresh and thermally oxidized oil samples on hepatic, intestinal and colonic drug-metabolizing enzymes were determined. The treatments had no significant effects on hepatic or intestinal drug-metabolizing or mixed-function oxidase activities. There was a significant (P less than 0.05) increase in colonic UDP-glucuronyltransferase activity in rats treated with thermally oxidized corn oil, while the non-saponifiable fraction of the same sample decreased (P less than 0.1) the activity of this enzyme. There was also a significant increase in the activity of colonic benzo[a]pyrene hydroxylase in rats treated with the non-adduct fraction or with urea adducts of the thermally oxidized corn oil. These data suggest the colon as a possible specific site for the alteration of mixed-function oxidase activities by products of thermally oxidized oils.