Immunoassay of 6-hydroxymelatonin sulfate in human plasma and urine: abolition of the urinary 24-hour rhythm with atenolol

An assessment of the rhythmic characteristics of melatonin secretion in man and other species requires the determination of 24-h secretion profiles. Measurement of a major excreted metabolite would allow noninvasive study of pineal function, applicable in particular to pediatric and long term circadian rhythm studies. This report describes a simple and rapid RIA for 6-hydroxymelatonin sulfate in human plasma and urine. Physiological studies revealed that both plasma and urinary levels of 6-hydroxymelatonin sulfate were closely related to plasma melatonin, and that the urinary 24-h rhythm was abolished by the beta 1-adrenergic anagonist atenolol.

How our food affects our hormones

Food can affect the production and secretion of hormones by direct actions on the gut, by nervous reflexes, through changes in the concentration of various metabolites in the blood, or secondary to changes in circulating gut hormone levels. Not only is the composition of the diet important but also its texture, quantity and duration. GIP and insulin are used as examples of hormones whose production and secretion are diet-dependent. Their possible involvement in the pathogenesis of obesity and non-insulin-dependent (type II) diabetes is discussed.

Chronopharmacology

The time of day that drugs are given can have a profound effect upon both their pharmacodynamics, i.e. their effectiveness and toxicity, and their pharmacokinetics, i.e. the way they themselves behave in the body. The chronopharmacokinetics of relatively few drugs have been investigated and are mostly those used for the treatment of cancer. We have shown that the toxicity and chronopharmacokinetics of drugs can be altered by pretreatment with steroids or melatonin.

The effect of guar gum on carbohydrate-, fat- and protein-stimulated gut hormone secretion: modification of postprandial gastric inhibitory polypeptide and gastrin responses

The effect of incorporating guar gum into predominantly single-component meals of carbohydrate, fat or protein on liquid gastric emptying and on the secretion of gastric inhibitory polypeptide (GIP), gastrin and motilin, was studied in healthy human volunteers. Volunteers were given either 80 ml Hycal (carbohydrate meal), 150 g cooked lean minced beef (protein meal) or 200 ml double cream (fat meal) either with or without 5 or 6 g guar gum. Liquid gastric emptying was monitored in the fat and protein meals by taking 1.5 g paracetamol, consumed in water, with the meals and monitoring its appearance in circulation. Postprandial insulin and GIP levels were both significantly reduced by addition of guar gum to the carbohydrate meal. Postprandial GIP secretion was also reduced by addition of guar gum to the protein meal, but protein-stimulated gastrin secretion was enhanced by guar gum. There was a significant negative correlation between peak circulating gastrin levels and the corresponding GIP levels. Postprandial GIP secretion and plasma motilin levels were unaffected by addition of guar gum to the fat meal. 5 and 10 g guar gum/l solutions in water possessed buffering capacities between pH 2.75 and 5.5. Guar gum at 5 g/l caused no detectable change in liquid gastric-emptying time. The observed augmentation of gastrin secretion by guar gum following a protein meal could be due either to the buffering capacity of guar gum or to the attenuation of GIP secretion. It is possible that the chronic use of guar gum could be associated with changes in gastric acid secretion.

Tissue disposition and excretion of gold and 14C in rats treated with sodium aurothio[1,4-14C]malate or thio [1,4-14C] malic acid

In rats injected intramuscularly with sodium aurothio[1,4-14C]malate, 80% of the 14C was excreted in the urine, mostly in 24 h, 2% in the faeces and 10% as 14CO2 in the expired air during the first six hours with none thereafter. Urinary and faecal gold represented 5% and 2.5% of the dose, respectively. In rats given thio[1,4-14C]malic acid, 50% of the 14C was excreted in the urine, 10% in the expired air as 14CO2 and 2% in the faeces. Radioactivity was found in all tissues with distribution similar for the two compounds, the major sites of accumulation being bone, kidney and liver. Significantly higher amounts of 14C were found in the 14C-aurothiomalate-dosed animals, notably in bone and kidney. Gold was located principally in kidney, liver, lung and spleen with smaller amounts elsewhere. At least seven radioactive metabolites (including sodium aurothiomalate and thiomalic acid) were present in the urine of rats given 14C-aurothiomalate. Urine from 14C-thiomalic acid-treated rats contained at least five radiolabelled compounds, one of which was thiomalic acid. Results show that most of the gold was removed from the thiomalate moiety, however, the 14C distribution and the radioactive metabolites in urine demonstrated that some intact aurothiomalate remains.

The role of immunoassay in the analysis of microcontaminants in water samples

Concentrations of natural and synthetic steroids and an anticancer drug (methotrexate) have been determined in water by adapting established immunoassay procedures. The limits of detection for the assays used were 10 ng/liter for norethisterone, 5 ng/liter for ethinyl estradiol and progesterone, and 6.25 ng/liter for methotrexate. Results below the level of detection were obtained in all the samples examined (8 river samples and 6 potable supply samples) except for 2 river samples (17 ng/liter) for norethisterone, and 1 river sample and 1 potable water sample for progesterone (6 ng/liter). A concentration of 1 microgram/liter of methotrexate was found in a sample of hospital effluent. There appears to be no evidence of adverse effects from reused water resources which may be contaminated from the normal use of such highly active therapeutic agents.

High-dose methylprednisolone sodium succinate (pulse therapy) in the treatment of renal disease: plasma and urine concentrations

Methylprednisolone hemisuccinate (MPS) and methylprednisolone (MP) concentrations in plasma and urine were monitored in renal transplant and glomerulonephritis patients who were given i.v. infusions of 0.5 g or 1 g of MPS. A marked individual variation of peak plasma levels of both MPS and MP was observed after the same dose and MPS disappeared from plasma more rapidly than MP. Their clearances from the circulation, however, did not appear to be significantly influenced by the peak plasma levels of the drug, creatinine clearance, administration of previous pulses of MPS or the urinary excretion of unconjugated MPS and MP. Even in patients with profoundly reduced renal function, no accumulation of the drug was apparent when repeated doses of MPS were administered at 48-h intervals.

Passive inhalation of cannabis smoke

Six volunteers each smoked simultaneously, in a small unventilated room (volume 27 950 litre), a cannabis cigarette containing 17.1 mg delta 9-tetrahydrocannabinol (THC). A further four subjects - passive inhalers - remained in the room during smoking and afterwards for a total of 3 h. Blood and urine samples were taken from all ten subjects and analysed by radioimmunoassay for THC metabolites. The blood samples from the passive subjects taken up to 3 h after the start of exposure to cannabis smoke showed a complete absence of cannabinoids. In contrast, their urine samples taken up to 6 h after exposure showed significant concentrations of cannabinoid metabolites (less than or equal to 6.8 ng ml-1). These data, taken with the results of other workers, show passive inhalation of cannabis smoke to be possible. These results have important implications for forensic toxicologists who are frequently called upon to interpret cannabinoid levels in body fluids.

Plasma immunoreactive gastric inhibitory polypeptide in obese hyperglycaemic (ob/ob) mice

Gastric inhibitory polypeptide (GIP), a recognized component of the enteroinsular axis, is raised in the plasma and intestine of obese hyperglycaemic (ob/ob) mice. To evaluate the control of plasma GIP and its role in the hyperinsulinaemia of the ob/ob syndrome, GIP and insulin were determined at different ages in fed mice, and at 10-12 weeks of age after fasting/refeeding and administration of GIP, different nutrients and insulin to mice fasted for 18 h. Plasma GIP and insulin were raised in adult (10- and 20-week-old) compared with younger (3- and 5-week-old) mice, although GIP was not increased in the presence of hyperinsulinaemia at 3 weeks of age. Fasting suppressed and refeeding promptly restored plasma GIP and insulin concentrations. Administration of GIP to mimic postprandial concentrations evoked a marked but transient insulin response which was protracted in the presence of rising hyperglycaemia. Orally administered fat, glucose and amino acids raised GIP concentrations with fat having a particularly strong effect. Glucose and amino acids also evoked prominent increases of insulin, but fat produced only a small rise in insulin in the absence of increasing glucose concentrations. Consistent with glucose-potentiation, a mixture of all three nutrients greatly augmented the insulin response without further increase of plasma GIP. Glucose-induced increase in endogenous insulin and doses of exogenous insulin up to 100 units/kg did not suppress basal, fat-stimulated or glucose-stimulated GIP release. The results indicate that raised GIP concentrations make an important contribution to the hyperinsulinaemia and related metabolic abnormalities of the ob/ob syndrome.

Measurement of plasma caffeine concentrations by substrate labelled fluoroimmunoassay

Abuse or misuse of caffeine has been implicated in the pathogenesis of a variety of clinical disorders and measurement of its plasma concentration is likely to become important in clinical laboratories in the future. A rapid, sensitive and easily performed method for the measurement of caffeine in biological fluids by the technique of fluoroimmunoassay is described. The results produced are precise and agree well with those obtained by radioimmunoassay or HPLC. Cross-reactivity of the antiserum with other substituted xanthines and uric acids is negligible for the major metabolites of caffeine but there is significant cross-reactivity with theophylline at concentrations likely to be found when this drug is being administered therapeutically. The measurement of caffeine by fluoroimmunoassay has a place in the clinical laboratory particularly where small batches of samples are to be analysed.

The differential effect of intragastric and intravenous tryptophan on plasma glucose, insulin, glucagon, GLI and GIP in the fasted rat

L-tryptophan was given to fasted rats intragastrically or intravenously at a dose of 500 of 166 mg/kg b.w., respectively. Mean (+/- SEM) plasma insulin levels rose after both stimuli and at 10, 30 and 45 min were 63 +/- 26, 86 +/- 25, 48 +/- 7 mU/l after oral, and 28 +/- 4, 25 +/- 6, 19 +/- 6 mU/l after intravenous administration, respectively; plasma tryptophan levels at the above intervals during the oral study were 27%, 60% and 128%, respectively of those during the intravenous study. Plasma GIP levels rose only after intragastric tryptophan administration, and plasma GLI levels did not change in response to either intragastric or intravenous tryptophan. Intragastric tryptophan consistently raised plasma pancreatic glucagon levels which were significantly higher than those observed in control rats given saline, 5, 10, 30 and 45 min after administration. The rise in plasma glucagon was attributed to the glucagonotropic effect of GIP.

Determination of caffeine, theophylline and theobromine in serum and saliva using high-performance liquid chromatography

A method is described for the measurement of theobromine, theophylline and caffeine in serum and saliva by high-performance liquid chromatography (HPLC). A chloroform/isopropanol extract (85:15, v/v) is evaporated to dryness and chromatographed on a 100 X 4.5 mm id Hypersil octadecylsilane column with UV detection at 280 nm. Theobromine, theophylline, caffeine and the internal standard proxyphylline are satisfactorily resolved with an elution system of acetonitrile/tetrahydrofuran/50 mM acetate buffer, pH 4.0, (4:1:95, v/v). No interference is observed from the presence of xanthine metabolites or any of a number of common drugs examined. A good correlation was observed between the concentrations of caffeine in serum and in saliva suggesting that salivary measurements may be useful for the study of caffeine pharmacokinetics in man. Caffeine levels determined by the HPLC procedure described here agreed well with those obtained by a radioimmunoassay method. The method is also suitable for determining the xanthine content of beverages by direct injection of diluted samples.

Effects of physical training on insulin, connecting peptide (C-peptide), gastric inhibitory polypeptide (GIP) and pancreatic polypeptide (PP) levels in obese subjects

Ten severely obese women were subjected to physical training for three months on ad libitum diet. Under metabolic ward conditions oral glucose tolerance test was performed before and after the training period with the same energy intake quantitatively and qualitatively, and glucose, insulin, connecting (C)-peptide, gastric inhibitory polypeptide (GIP) and pancreatic polypeptide (PP) were determined. In confirmation of previous work, physical training caused no decrease in body fat in these severely obese subjects, and no change in body cell mass or glucose tolerance, while insulin and blood pressure decreased. The control of dietary conditions demonstrated that the latter phenomena were not due to quantitative or qualitative changes in the diet. C-peptide concentrations decreased also, indicating effects of physical training in obesity on insulin production. GIP is believed to be a gastrointestinal factor facilitating insulin secretion (Incretin). Previous work has indicated that gastrointestinal factor(s) are involved in the insulin lowering effect seen after physical training. It is possible that GIP is contributing to this phenomenon.

Serum levels and response to amitriptyline in depressed out-patients

Serum levels of amitriptyline plus nortriptyline were measured by radioimmunoassay at 1 and 6 weeks in depressed out-patients treated with amitriptyline for 6 weeks. Serum concentrations at 6 weeks were higher in older patients. Serum levels showed no relationship to clinical response at 6 weeks, and a week inverse relationship with response at 2 weeks. Routine monitoring of serum levels appears to be of little value in depressed out-patients treated with amitriptyline.

Measurement of serum theophylline concentrations using a modified Ames TDA system

Results are presented which show that the Ames TDA Theophylline kit provides an accurate and reliable method of measuring the concentration of theophylline in plasma. It may be used with a shortened incubation time (5 min) without loss of accuracy, and a single calibration curve can be used over a 3-week period. There is an acceptable precision at all assayed levels (coefficient of variation, 3.3%) and results obtained for patients' samples correlate well with those obtained using liquid chromatography (y = 0.02 + 1.06x, r = 0.99) and enzyme immunoassay (y = 0.58 + 1.03x, r = 0.99).

A critical evaluation of a new fluorescence immunoassay system for the measurement of serum phenytoin concentrations

Results are presented which show that the Ames TDA tm phenytoin kit may be used with a shortened incubation time (5 minutes) and that, using a Fluorostat tm instrument, a single calibration curve can be stored and used effectively over a three-week period. The importance of temperature control when using a single calibration curve is emphasised. An unexplained finding was that higher results were obtained for phenytoin concentrations up to about 15 mg/l with increasing incubation temperature. There was acceptable precision of measurement at all levels of phenytoin concentration, and there was no significant interference by haemoglobin, bilirubin, or lipids. The TDA results correlated well with those obtained using liquid chromatography (y = 0.39 + 0.98x, r = 0.98, where y = TDA and x = HPLC) and enzyme immunoassay (y = 0.08 + 0.93x, r = 0.96, where y = TDA and x = EIA).

Plasma levels and response to prednisolone therapy in rheumatoid arthritis

Plasma prednisolone levels were measured in parallel with clinical and laboratory assessments in seven patients with rheumatoid arthritis on single daily doses of prednisolone which were reduced at weekly intervals from 10 mg. to 7, 6 and 5 mg. A significant negative rank correlation was observed between prednisolone dose and the duration of morning stiffness (p less than 0.05). No significant correlation was observed between plasma prednisolone levels, other clinical assessment criteria or laboratory indices.