Effect of fasting on free and esterified carnitine levels in human serum and urine: correlation with serum levels of free fatty acids and beta-hydroxybutyrate.

Serum levels of free L-carnitine, acylcarnitines, creatinine, beta-hydroxybutyrate, free fatty acids, cholesterol, triglycerides, and glucose were determined in healthy volunteers during a 24-36-hr fast. The effect of oral administration of free L-carnitine (1 g/person) on these parameters was studied. Urinary excretion of carnitine and creatinine was monitored throughout. Serum and urine levels of free carnitine and its renal clearance decreased during the fast. However, the serum concentration and urinary excretion of acylcarnitines increased during the same interval. Following the ingestion of free L-carnitine, both serum and urinary levels of free L-carnitine rose. Within 6 hr of ingestion, 10% of the administered dose could be accounted for by urinary excretion. No significant effect on the other serum constituents under study was seen following the oral L-carnitine dose. A significant negative correlation was found between serum levels of free L-carnitine and beta-hydroxybutyrate and free fatty acids (r equal -0.567, p less than 0.001 and r equal -0.607, p less than 0.001, respectively) during the fast.

Comparison of four commercial methods for the determination of fast hemoglobins.

The performance of three commercial kits, based on microchromatographic techniques for the determination of glycosylated hemoglobins (fast hemoglobins) has been evaluated. All three kits showed good precision, provided the laboratory temperature remained constant. Temperature variations of even one degree C had a profound effect on the kits from Helena Laboratories and Isolab Inc., while the one from BIO-RAD Laboratories was less influenced. The use of the temperature correction tables provided by Helena Laboratories and Isolab Inc., improved the reproducibility of their results significantly. Since there is no designated reference method, an evaluation of accuracy was not possible. The absolute values for fast hemoglobins, as measured by the three microchromatographic kits, differed from each other. Also, when a series of specimens from diabetic patients and from healthy control subjects were compared, the relative ratios of the results obtained from the three kits differed from specimen to specimen. However, there was no overlap between results from diabetic and control specimens. The performance of the electrophoretic method of Corning Medical Co. was also evaluated.

Serum UDP-galactose: glycoprotein galactosyltransferase in diabetics with microangiopathy.

1. Levels of serum UDP-galactose:glycoprotein galactosyltransferase in 117 unselected diabetics were compared with those in 60 non-diabetic healthy controls. 2. Enzyme activity (mean +/- 2 S.D.) of control sera was found to be 90.2 +/- 21.5 etamoles/ml/hr at 37 degrees. In 30 of the 117 diabetic sera (26%) enzyme activity was elevated (greater than mean + 2 S.D. of the controls). Sixteen of 19 (84%) patients with retinopathy, 16 of 26 (62%) patients with peripheral vasculopathy and 13 of 26 (50%) patients with neuropathy had higher levels of serum enzyme. When serum enzyme levels of groups of diabetics with retinopathy, peripheral vasculopathy and neuropathy were compared with the enzyme level in all diabetics, there was a significant difference with p values of 0.001, 0.05 and 0.05 respectively.

Serum enzymes in the BB rat before and after onset of the overt diabetic syndrome.

As part of a six-month prospective study of the effects of neonatal thymectomy in the spontaneously diabetic BB Wistar rat, activities of the following enzymes were determined: alkaline phosphatase (AP), lactate dehydrogenase (LDH), creatine phosphokinase (CPK), glutamic-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT) and UDP-galactosyltransferase (UDPG). In prediabetics, AP and LDH levels were higher than in sham-operated, non-diabetic controls; however, this increase was seen in nearly all diabetes-prone BB rats, diminishing the usefulness of these changes in discerning potential diabetics from asymptomatic, diabetes-prone rats. After onset of the syndrome, there was a striking elevation of AP values in all diabetics with no similar alteration in asymptomatic, diabetes-prone rats suggesting this was a diabetes-related phenomenon. By contrast, UDPG was the only enzyme to decrease immediately following the onset of the syndrome. Both UDPG and AP levels correlated with blood glucose, the former negatively and the latter positively, suggesting a close relationship with changes occurring after onset of the syndrome. The remaining enzymes increased only in a portion of diabetics alone (GOT, GPT) or in a portion of both diabetics and asymptomatic, diabetes-prone BB rats (LDH, CPK).

Transfer constants for blood-brain barrier permeation of the neuroexcitatory shellfish toxin, domoic acid.

The cause of the toxic mussel poisoning episode in 1987 was traced to a plankton-produced excitotoxin, domoic acid. Experiments were undertaken to quantitate the degree to which blood-borne domoic acid can permeate the microvasculature to enter the brain. Pentobarbital-anesthetized, adult rats received an i.v. injection of 3H-domoic acid which was permitted to circulate for 3-60 min. Transfer constants (Ki) describing blood-to-brain diffusion of tracer were calculated from analysis of the relationship between brain vs plasma radioactivity with time. Mean values (mL.g-1.s-1 X 10(6] for permeation into 7 brain regions (n = 10 rats) ranged from 1.60 +/- 0.13 (SE) to 1.86 +/- 0.33 (cortex, pons-medulla respectively), and carrier transport or regional selectivity in uptake were not evident. Nephrectomy prior to domoic acid injection resulted in the elevation of circulating plasma tracer level and brain uptake. The Ki values are comparable to those for other polar compounds such as sucrose, and indicate that the blood-brain barrier greatly limits the amount of toxin that enters the brain. Together with absorbed dosage, integrity of the cerebrovascular barrier and normal kidney function are important to the outcome of accidentally ingesting domoic acid.

Effect of analgesic nephropathy in women on the metabolism and excretion of 14C-acetaminophen.

Nephropathy due to excessive consumption of phenacetin-containing analgesic mixtures has been a problem in Canada. Following the withdrawal of phenacetin it seems probable that acetaminophen consumption will increase and this study investigated the metabolism of 14C-Acetaminophen in patients with nephropathy and in healthy women. The respective alpha T1/2s of excretion of Acetaminophen and its metabolites were 2.58 h in the controls, 4.28 h in patients with analgesic nephropathy and 6.53 h in patients with nephropathy due to causes other than analgesic abuse. Both groups of patients had T1/2s that were significantly longer than the controls. The total 12 h recovery of 14C was highly positively correlated with creatinine clearance. (R = 0.92, P less than 0.001). No significant shifts in metabolism were discernable. It is concluded that patients with either analgesic nephropathy or nephropathy due to other causes metabolise Acetaminophen normally but excretion is delayed in proportion to the degree of renal impairment.

Determination of phosphodiesterase I activity in human blood serum.

Phosphodiesterase I (EC 3.1.4.1) activity was detected in normal human blood serum. The enzyme is stable at laboratory temperature for three days, but is inactivated at pH less than 7. The pH for optimum activity increases with the substrate concentration (under the conditions used, from pH 9.0 to 10.2) and, conversely, the Km increases with pH and buffer concentration. The enzyme is inhibited by ethylenediaminetetraacetate but not by phosphate (0.1 mol/liter). We developed a simple quantitative method for its determination, based on hydrolysis of the p-nitrophenyl ester of thymidine 5'-monophosphate and subsequent measurement of the liberated p-nitrophenol at 400 nm in NaOH (0.1 mol/liter). Normal values (mean +/- 2 SD) were determined to be 33 +/- 6.4 U/liter. Preliminary studies indicate that phosphodiesterase I activity is greater than normal in serum of patients with necrotic changes in the liver or kidney or in cases of breast cancer, but not in that of patients with myocardial infarction, bone cancer, lung cancer, or chronic liver cirrhosis.

An immunofluorescence study of anti-pancreatic islet cell antibodies in the spontaneously diabetic BB Wistar rat.

Sera from BB Wistar rats and Wistar control rats were evaluated for the presence of islet cell antibodies in a prospective study using an indirect immunofluorescence assay on pancreatic islet cell suspensions from cultured rat islets. Islet cell surface antibodies were detected in sera from all animals of the spontaneously diabetic BB Wistar rat colony. The antibody could be detected well before the clinical onset of the disease and was present throughout the course of study of all diabetic animals. Sera from control Wistar rats were negative when tested for this antibody.

Time course of serum glucoregulatory variables and lipids following neonatal thymectomy of diabetes-prone and control BB Wistar rats fed a defined diet.

The acute diabetic syndrome in the BB Wistar rat resembles human type 1 (insulin-dependent) diabetes, including a possible association with T cell-mediated, (auto)immune processes. In most previous studies 'normoglycemic' littermates of diabetic BB rats have been used as controls and little attention has been paid to the role of diet. It now appears that asymptomatic/diabetes-prone littermates of diabetics have immune system defects as well as metabolic abnormalities. Since there are also indicators that the disease process starts before animals become symptomatic, we looked for prospective metabolic changes in prediabetic, asymptomatic/diabetes-prone and control (diabetes-free) BB rats following intervention in the immune system while maintaining the animals on a defined diet (AIN-76). The results reported here confirm and extend the finding of Like et al. (1982) that neonatal thymectomy reduces the frequency of the syndrome and emphasize the role of diet in modifying its expression. In contrast to previous reports of hyperglucagonemia only after onset of diabetes, asymptomatic/diabetes-prone animals had periodic increases of plasma glucagon values up to 3-fold those of diabetes-free controls; prediabetics displayed a similar pattern. Asymptomatic/diabetes-prone rats also tended to have slightly higher blood cholesterol levels. The low incidence and delayed onset of the syndrome in rats fed a modified AIN-76 diet (27%, 127 +/- 21 days) compared to the previous chow-fed generation (60%, 93 +/- 18 days) and chow-fed littermates (38%, 87 +/- 16 days) suggested that diet can modify expression of the syndrome.

Carnitine content of blood and amniotic fluid.

Free carnitine levels were determined in amniotic fluids between the 10th and 40th week of gestation. They were found to decrease significantly with gestational age. Blood levels of carnitine were lower in pregnant than in nonpregnant women. Levels were found to be higher in cord blood than in maternal blood and usually were higher in the umbilical artery than vein. Intra-arterial injection of L-carnitine into a pregnant ewe did not cause a rise in the fetal blood level of carnitine, which, in contrast to human fetal blood, contained less than half the level of carnitine in maternal blood.

Interlaboratory testing of the transferability of a candidate reference method for total cholesterol in serum.

In 1975 the Centers for Disease Control, in cooperation with the American Association for Clinical Chemistry Cholesterol Reference Method Study Group, began an investigation to develop a reference method for total cholesterol. Five potential reference methods were compared with the definitive method developed by the National Bureau of Standards before the chemical method of Abell et al. (J Biol Chem 1952;195:357-66) was selected as the recommended reference method. Because acceptance of a proposed reference method depends so greatly on the method's capability for transfer to other laboratories by written specifications and instructions, a transferability testing study was designed and conducted with 14 laboratories. The study consisted of preliminary testing of readiness of equipment, reagents, and personnel followed by transferability testing with eight runs on 10 serum pools. Laboratoires that did not meet readiness specifications had higher CVs in the transferability testing. The study demonstrated that the proposed method permits laboratories to attain a CV of less than 1.5% for one laboratory and of less than 3.0% among laboratories. The mean percent bias value was less than 1.0% for six of the 14 laboratories, less than 1.5% for 12, and less than 3.0% for all 14 laboratories.