Distribution along the rat nephron of three enzymes of gluconeogenesis in acidosis and starvation

Methods were devised or modified which made it possible to measure phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase in seven defined parts of single nephrons and in patches from thin limb and papilla areas dissected from freeze-dried microtome sections of rat kidney. All three enzymes were essentially confined to the proximal tubule. In normal kidneys, the levels were highest in the proximal convoluted tubule. Glucose-6-phosphatase was 20 times higher in the early part of the convoluted segment than in the late part of the straight segment. With one exception, in acidosis, only phosphoenolpyruvate carboxykinase increased (fourfold in the proximal convoluted segment but much less in the straight portion). In starvation, phosphoenolpyruvate carboxykinase increased about as much as in acidosis in the proximal straight tubule, but not as much in convoluted portions, whereas glucose-6-phosphatase rose modestly in both parts of the proximal tubule and fructose bisphosphatase rose only in the straight tubule, especially the early segment. It is suggested that ammoniagenesis can accompany gluconeogenesis in the proximal convoluted tubule but not in the straight segment.

Gluconeogenic enzymes in defined structures of developing rat nephron

Three gluconeogenic enzymes, P-pyruvate carboxykinase (PPCK), fructose-1-6 bisphosphatase (FBPase), and glucose-6-phosphatase (G6Pase) were measured in identified structures of rat nephron from 2 days before birth to maturity. In the proximal convoluted tubule, the three enzymes increased from the earliest age assayed to +14 days (PPCK, 7-fold, FBPase, 2-fold and G6Pase, 50-fold). Among the 7 defined structures that were analyzed, highest levels at all ages were in the proximal convoluted tubule with almost no activity in the distal convoluted tubule. All three enzymes had negligible activity in the neogenic zone and mesenchyme. Supported by grants from the Public Health Service (HD 03891 and NS-05221) and the American Cancer Society (P-78).

Effects of nine N-nitroso compounds on the specific radioactivity of liver proteins after injection of [14C]leucine into rats

We compared the effect of nine N-nitroso compounds, given by gavage to adult rats, on specific radioactivity of the trichloroacetic acid-precipitable liver proteins, 1 hr after the injection of [14C]leucine. The specific radioactivity was decreased by dimethylnitrosamine, diethylnitrosamine, methyl-n-butylnitrosamine, and nitrosomorpholine 5 to 10 hr after their administration; was increased by nitrosopiperidine, dinitrosopiperazine, and methylnitrosourea 5 to 24 hr after gavage; and was unaffected by nitrososarcosine and nitrosodihydrouracil. With dimethylnitrosamine, specific radioactivity was decreased by 10 but not 5 mg/kg. In control rats and rats given injections of either of two nitrosamines, protein specific radioactivity at 60 min after the [14C]leucine injection was 76 to 87% of that at 30 min, indicating some degradation of the proteins at 60 min. The liver:blood ratio of [14C]cycloleucine concentration was unaffected by four nitrosamines, indicating no effect on leucine transport. The effect of the nine compounds was examined on total pool size of free leucine in the liver, at times close to those for the maximum specific radioactivity effect. For these data, we calculated "corrected specific radioactivity," adjusted for changes in pool size. This adjustment is only a first approximation since, for example, the free leucine pool is not uniform with respect to protein synthesis. The four N-nitroso compounds that decreased specific radioactivity also decreased corrected specific radioactivity, even though they enlarged the leucine pool. Of the remaining compounds, two enlarged the leucine pool and three increased corrected specific radioactivity. For all nine compounds, the decrease in specific and correlated with the ability to cause acute liver necrosis. When nitrosodihydrouracil was excluded, the decrease in specific and corrected specific radioactivity was significantly correlated with the reported liver carcinogenicity.

A Study of Fireflood Field Projects (includes associated paper 6504)

More than 40 domestic and foreign firefloods were reviewed. Regressionequations were developed for predicting production performanceof firefloods. Two screening guides were established for selecting reservoirs for the application of the fireflood process.

Introduction

Enhanced recovery methods that show most promise forcommercial application include hydrocarbon miscibleflood, carbon dioxide miscible flood, micellar flood, andthermal recovery methods. Since the first threeprocesses are applicable only to low-viscosity crudes (10 cpor less), the recovery of medium- to high-viscosity crudesdepends solely on thermal methods - steam stimulation, steamflood, and fireflood.

A recent domestic survey showed that, of the threethermal methods, steam stimulation has been practicedexclusively in California and steamflood has been usedpredominantly there. Fireflood projects, on the otherhand, cover a much wider area including California, Texas, Louisiana, Oklahoma, Arkansas, Illinois, Mississippi, Nebraska, and Wyoming. This wide geographical distribution of fields amenable to firefloods clearlyindicates that firefloods are applicable to a broader range ofreservoir and crude properties than steam stimulation andsteamflood.

More than 70 firefloods have been completed or are inprogress in the U.S. Firefloods also have been practicedin other countries such as Venezuela, U.S.S.R., Romania, and Japan. Varying information is available onmore than 40 domestic and foreign firefloods.The purpose of this paper is to review these firefloods and therebydevelop criteria for screening prospects for theapplication of the fireflood process.

This paper first gives a general description of firefloodand its variations and discusses variables characterizingthe performance of firefloods. Screening guides forfireflood prospects are developed by two different statisticalapproaches - the confidence-limits approach and theregression-analysis approach. The choice betweenfireflood and steamflood is also discussed.

Fireflood and Its Variations

The most commonly used form of the fireflood process isdry forward combustion. The process is called drycombustion because no water is injected along with air.The combustion is forward because ignition occurs near the injection well and the burning front moves forward fromthe injection well to the production well. The advantageof this process is that an undesirable fraction of the crudeis burned in the form of coke, leaving clean sand in theregion behind the burning front. However, it has twolimitations. First, the produced oil has to pass through acold region of the reservoir. If the oil is highly viscous, liquid blocking will occur, which may terminate theprocess. Second, heat stored in the burned-out region isnot utilized efficiently because injected air is notsufficiently effective to carry the heat forward.

Reverse combustion is a variation of the fireflood thatremedies the first limitation of the conventional fireflood.Ignition occurs near the production well and the burningfront moves countercurrent to the flow of the injected air.Since oil moves through a hot region toward the produced well, there is no upper limit to the viscosity of thereservoir crude. Reverse combustion is not as efficient asforward combustion because a desirable fraction of theoil is burned as the fuel, and the undesirable fraction remains in the region behind the combustion front.

JPT

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