Organ distinctive mutagenicity in MutaMouse after short-term exposure to PhIP

We have investigated PhIP-induced mutagenicity in various tissues (kidney, liver, large and small intestine) using a transgenic mouse model (MutaMouse). In addition to tissue specific mutagenesis, we measured the binding of [14C]PhIP to MutaMouse mice blood proteins (haemoglobin and albumin), to obtain a quantitative estimate of carcinogen exposure and activation and their relationship to mutagenesis. Short-term (4 days) treatment of MutaMouse mice with [14C]PhIP by oral gavage resulted in the dose-dependent accumulation of radiolabelled material bound to haemoglobin and serum albumin. PhIP, at the highest dose (20 mg/kg), caused a 5.9-fold increase in the mutation frequency in the large intestine, a 4.2-fold increase in the mutation frequency in the small intestine but only a marginal 1.6-fold increase in the liver. However, there was no significant increase in mutations in the kidney at this dose. In contrast, there were no significant differences in any of these tissues between the vehicle control and the two lower doses (2.0 and 0.2 mg/kg respectively). These results are discussed in relationship to those previously reported for PhIP at the Dlb-1 locus.

Duration-dependent increase in striatal glutamate following prolonged fluphenazine administration in rats

Chronic neuroleptic administration has been shown to selectively increase striatal extracellular glutamate concentration. In the current study, age-matched female rats were administered chronic oral fluphenazime or no drug via their drinking water for 3 or 32 weeks. Microdialysis probes were inserted into the ventrolateral caudate putamen and the medial nucleus accumbens and dialysis samples were analyzed for glutamate and gamma-aminobutyric acid (GABA) concentrations Glutamate levels were significantly increased only in the ventrolateral caudate putamen after 32 weeks. No significant effects were seen for GABA levels. Neuroleptic-induced enhancement of striatal glutamate levels thus appears to increase with chronic exposure and this increase may relate to late onset motor side effects.

Heterocyclic amines: evaluation of their role in diet associated human cancer

1. Heterocyclic amines are formed in parts per billion levels when meat is cooked. 2. The heterocyclic amines MeIQx and PhIP are efficiently absorbed into the systemic circulation after ingestion of cooked food. 3. We have shown that MeIQx and PhIP, both in vitro and in vivo, are substrates for human hepatic CYP1A2, which exclusively and efficiently catalyses their conversion to genotoxic hydroxylamines. 4. MeIQx and PhIP are promutagens. MeIQx is a very powerful bacterial mutagen whereas PhIP is a more potent mammalian cell mutagen. Using a mammalian cell target gene, hprt, we have shown that PhIP induces a characteristic mutational 'fingerprint'. 5. MeIQx and PhIP are carcinogenic in bioassays. The PhIP mutational 'fingerprint' has been detected in the Apc gene of 5/8 colonic tumours induced by PhIP in rats.

Subchronic administration of clozapine, but not haloperidol or metoclopramide, decreases dopamine D2 receptor messenger RNA levels in the nucleus accumbens and caudate-putamen in rats

The effects of unique profile antipsychotic drugs on dopamine D2 receptors and D2 receptor messenger RNA were assessed following subchronic administration in rats. Male, Sprague-Dawley rats were administered oral haloperidol, clozapine, metoclopramide or no drug for three weeks via their drinking water. Tissue from the medial nucleus accumbens and dorsolateral caudate-putamen was dissected and analyzed by Northern blot analysis for levels of dopamine D2 receptor messenger RNA and binding assays conducted with [3H]spiperone for dopamine D2 receptors. Haloperidol and metoclopramide, but not clozapine, significantly increased [3H]spiperone in the caudate-putamen, but not the nucleus accumbens. Clozapine significantly decreased D2 messenger RNA levels in the caudate-putamen and the nucleus accumbens, while metoclopramide and haloperidol had no significant effect in either brain region. The finding of decreased D2 receptor messenger RNA levels produced by subchronic clozapine may account for the lack of striatal D2 receptor up-regulation, which was robustly observed after subchronic haloperidol and metoclopramide. Furthermore, since haloperidol and metoclopramide have a high liability for motor side effects, the current results relate favorably to the low motor side effect profile of clozapine.

Physical enhancement of dermatologic drug delivery: iontophoresis and phonophoresis

Iontophoresis and phonophoresis are emerging technologies capable of enhancing drug penetration through the stratum corneum, the principal barrier to percutaneous absorption. With utilization of applied electric current or ultrasonic waves, respectively, iontophoresis and phonophoresis have shown efficacy in an increasing number of clinical applications. This article reviews the underlying principles, current status, and potential of iontophoresis and phonophoresis in dermatologic therapy.

Enzymic and interindividual differences in the human metabolism of heterocyclic amines

Heterocyclic amines (HAs) present in cooked meat (PhIP and MeIQx) are activated only by CYP1A2 in the liver of most species, including man. This enzyme exhibits marked interindividual differences in its expression, due to induction and possibly also genetically. The absence of CYP1A2 appears to protect from HA-(PhIP and MeIQx) induced cancer, as exemplified by results in the cynomolgus monkey. Differences in the potency of these HAs are not due to differences in the kinetics of their activation. The catalytic efficiency of CYP1A2 towards HAs and their oxidative fate varies amongst species, in both cases increasing the susceptibility of humans compared to that of the rat. Interindividual and inter-organ differences in the further metabolism of N-hydroxy-HAs appear to be important determinants of cancer susceptibility, as does the glutathione S-transferase catalysed detoxication of esters of N-hydroxy-PhIP. There is a need for an effective means of quantifying the in vivo activation of HAs in man to enable the possible risk posed by these compounds to be assessed effectively.

Chronic haloperidol-induced changes in regional dopamine release and metabolism and neurotensin content in rats

Chronic neuroleptic administration has previously been shown to alter in vivo measures of dopaminergic function and lead to regionally selective increases in neurotensin levels. In the current study, female rats were administered chronic haloperidol for 6 months via subcutaneous silastic implants. After 24 weeks of administration, microdialysis probes were inserted into the lateral caudate putamen and the medial prefrontal cortex. Basal samples were collected prior to infusion of a high K+ concentration (100 mM KCl). Extracellular concentrations of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid were assessed using HPLC. Chronic haloperidol-treated rats showed increased basal dopamine metabolite levels in the caudate putamen and an altered response to the effects of high K+ on 3,4-dihydroxyphenylacetic acid; no significant differences were seen with other analytes in the caudate putamen. Although basal concentrations were not different between groups in the prefrontal cortex, haloperidol-treated rats showed a significant attenuation of response to the effects of high K+ infusion on dopamine metabolite concentrations. Radioimmunoassay measurement of tissue neurotensin content showed highly significant elevations of neurotensin concentrations in the caudate putamen and nucleus accumbens, but not in other brain regions analyzed. These results suggest a confluence of altered dopamine and neurotensin function in the caudate putamen which may be related to motor side effects of haloperidol, whereas changes in prefrontal dopamine function are not associated with altered neurotensin levels.

Longitudinal measurement of anticardiolipin antibodies during normal pregnancy: a prospective study

We have previously shown that elevation of anticardiolipin antibodies (aCL) at the first prenatal visit is associated with increased fetal loss in normal pregnancy. The variation in aCL levels during normal pregnancy has not been established. To examine this question we measured IgG, IgM and IgA aCL levels five times during pregnancy at weeks 5-15, 16-25, 26-35, 36-37 and at delivery. Data were analyzed to determine: (a) the within and between subject variability of aCL during pregnancy; (2) the temporal trend of aCL; and (3) the relation of serial measures of aCL with maternal complications of pregnancy. We divided our cohort of 354 subjects into two groups. Group A included those subjects with consistently normal levels of aCL and group B those subjects with at least one elevated level of aCL. In group A the within subject variability was relatively low (28-34%). In group B we found wide fluctuations in aCL levels and a within subject variability of 88-91%. Subjects in group B had no increase in maternal complications of pregnancy. The present data suggest that aCL may fluctuate significantly during normal pregnancy and there is little clinical value in measuring aCL on a serial basis during pregnancy.

Chronic haloperidol potentiates stimulated glutamate release in caudate putamen, but not prefrontal cortex

Rats were given haloperidol continuously for 6 months via subcutaneous implants. Extracellular concentrations of basal and high K(+)-stimulated GABA and glutamate in the lateral caudate putamen and the medial prefrontal cortex were then assessed using microdialysis. While there were no significant differences in basal extracellular concentrations in either brain region, chronic haloperidol-treated rats showed significantly greater increases in glutamate following stimulation with high K+ in the caudate putamen, but not the prefrontal cortex. This effect was accompanied by an attenuation of K(+)-stimulated GABA overflow in the caudate putamen. These results suggest regionally selective alterations in amino acid transmitter function which may be related to chronic neuroleptic-induced motor side effects.

Tolerance-like attenuation to contingent and noncontingent cocaine-induced elevation of extracellular dopamine in the ventral striatum following 7 days of withdrawal from chronic treatment

Time-dependent changes in mesolimbic dopamine (DA) function are believed to play a role in behavioral sensitization and drug craving experienced during withdrawal from chronic cocaine administration. The present study utilized intravenous (IV) cocaine self-administration coupled with intracranial microdialysis in rats to investigate time dependent changes during withdrawal from chronic cocaine exposure. Following 2 weeks of IV cocaine self-administration, rats were allowed contingent access to cocaine at 1 and 7 days of withdrawal while extracellular levels of DA were measured from the ventral striatum. A second group of animals received yoked, noncontingent cocaine for 2 weeks and were then administered noncontingent cocaine on days 1 and 7 of withdrawal. In addition, a third group of animals received 2 weeks of yoked saline followed by noncontingent cocaine 1 day after withdrawal. There were no significant differences between groups for the overall cocaine dosage or temporal pattern of infusions on days 1 and 7 of withdrawal. Basal extracellular DA concentrations did not differ between any treatment groups at either withdrawal time. Extracellular DA levels were increased throughout the session on both days; however, the increases at day 7 were significantly less than day 1 for both contingent and noncontingent conditions. DA overflow on day 1 did not differ between animals receiving chronic yoked cocaine or saline. These results suggest that tolerance-like attenuation to the DA-elevating effects of cocaine is not apparent early in withdrawal, but does develop by later time points.(ABSTRACT TRUNCATED AT 250 WORDS)

CYP1A2-catalyzed conversion of dietary heterocyclic amines to their proximate carcinogens is their major route of metabolism in humans

The contribution of CYP1A2 to the metabolism of the dietary heterocyclic amines, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in vivo in humans, has been determined with furafylline, a highly selective inhibitor of this enzyme. The inhibitory potential of furafylline in vivo was first assessed by determining its effect on clearance of phenacetin to paracetamol by the model CYP1A2-dependent O-deethylation pathway. Furafylline inhibited this reaction by > 99% in all subjects, thus demonstrating its applicability to determining the contribution of CYP1A2 to a given reaction in vivo. A group of 6 healthy male volunteers received either placebo or 125 mg furafylline, in a double-blind balanced crossover design, 2 h prior to consuming a test meal of fried beef containing a known amount of amines. The excretion of PhIP and MeIQx in urine was determined during the subsequent 28 h, using gas chromatography-mass spectrometry. Following furafylline, the excretion of unchanged MeIQx increased 14.3-fold, while that of PhIP increased 4.1-fold (P < 0.01, paired t test). Elimination of both amines was first order and very rapid, with half-lives of < 5 h. The elimination rate constants did not change following furafylline, suggesting that total clearance is limited by hepatic blood flow. Because the elimination of the amines was first order, it was possible to calculate the contribution of CYP1A2 to the clearance of the amines. CYP1A2-catalyzed metabolism accounts for 91% of the elimination of ingested MeIQx and 70% of ingested PhIP, most likely via N-hydroxylation.

Quantification of the carcinogens 2-amino-3,8-dimethyl- and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in food using a combined assay based on gas chromatography-negative ion mass spectrometry

A gas chromatographic-mass spectrometric assay has been developed for the measurement of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in food. Stable isotope-labelled analogues of MeIQx and PhIP are used as internal standards and the synthesis of deuterated PhIP is described. The mass spectrometer is operated in the electron-capture negative ion chemical ionisation mode and the amines are chromatographed as their di-3,5-bistrifluoromethylbenzyl derivatives. All three compounds can be measured in a single chromatographic run and detection limits of 0.05, 0.1 and 0.2 ng/g for MeIQx, DiMeIQx and PhIP, respectively, in food are obtained. Various home-cooked and commercially prepared foodstuffs were analysed with this assay and several were found to contain measurable amounts of one or more of the three amines. These results are presented and discussed.

The cytochalasin-B micronucleus/kinetochore assay in vitro: studies with 10 suspected aneugens

An in vitro micronucleus assay in low passage Chinese hamster Luc2 cells capable of detecting numerical and structural chromosome changes was developed. Chromosome loss was inferred by indirect visualisation of human CREST antikinetochore antibodies bound to centromeres in chemically-induced micronuclei of cytochalasin-B arrested binucleated cells. The assay was used to evaluate 10 chemicals which had been selected for their known or suspected effects upon various components of the cell-division apparatus. These chemicals were colchicine (COL), vinblastine (VBL), thiabendazole (TBZ), chloral hydrate (CH), thimerosal (TM), diazepam (DZ), pyrimethamine (PYR), hydroquinone (HQ), cadmium chloride (CdCl2) and econazole nitrate (EZ). Mitomycin-C (MMC) was used as a positive control for the induction of micronuclei. 8 of the core chemicals induced micronuclei in Chinese hamster Luc2 cells. 4 of the chemicals (COL, VBL, TBZ, CH) increased levels of micronuclei which were positive for kinetochore antibody labelling and hence chromosome loss. 3 of the chemicals (DZ, PYR, HQ) and the positive control (MMC) increased the levels of Mn which were negative for kinetochore antibody labelling. The results with TM were equivocal and EN was negative. The results of these studies suggest that the cytochalasin-B Mn/k assay is a cost-effective, simple and rapid alternative to classical cytogenetic assays for the detection of chemically induced aneuploidy.

Molecular dosimetry of the food-borne carcinogen MeIQx using adducts of serum albumin

Incubation of mouse serum albumin with the food borne carcinogen [2-14C]-Amino-3,8,-dimethylimidazo[4,5-f]quinoxaline (14C-MeIQx) in the presence of mouse hepatic microsomes and an NADPH-regenerating system in vitro resulted in the formation of adducts of MeIQx with albumin, which increased proportionately with time for at least 120 min (approximately 1 pmol equivalents/mg of protein/min). We have previously shown in male Swiss Webster mice in vivo that 14C-MeIQx bound covalently to serum proteins and that the formation of adducts was dose dependent. 14C-MeIQx (100 mg/kg, i.p.) was administered to male (MF1) mice which were killed 24 h later. Serum albumin was purified by affinity chromatography and covalent binding of 14C-MeIQx was assessed. Total covalent binding of MeIQx to albumin was 14.0 +/- 5.2 pmol per mg albumin, which was 5-fold greater than to haemoglobin. Following mild acid hydrolysis, 1.25 pmol MeIQx per mg albumin was liberated as free amine, as determined by gas chromatography negative ion mass spectrometry (GC-MS). This represents 9% of total MeIQx adducted to albumin in vivo (cf 1.3% adducted to haemoglobin). These results suggested that adducts of MeIQx with serum albumin should provide a significantly more sensitive dosimeter than those with haemoglobin. We therefore investigated this approach with serum protein samples from three volunteers. Human serum albumin and non-serum albumin protein fractions were separated by affinity chromatography, before being subjected to GC-MS analysis for hydrolysable adducts of MeIQx. The levels of MeIQx in control samples, and from the release of the putative sulphinamide adducts in hydrolysed samples were below the limits of detection of the GC-MS assay (29 +/- 2.6 amol MeIQx/mg albumin). Despite an increase of 2 orders of magnitude in sensitivity, compared with haemoglobin, it is unlikely that the sulphinamide adduct of MeIQx with human serum albumin can be used as a dosimeter for human aminoimidazoazaarene exposure.

Intra- and interindividual variability in systemic exposure in humans to 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl- 6-phenylimidazo[4,5-b]pyridine, carcinogens present in cooked beef

During the cooking of beef, the genotoxic heterocyclic aromatic amines 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are formed. Little is known about the fate of these compounds in humans or the factors affecting it. We have developed assays based on capillary column gas chromatography-negative ion mass spectrometry capable of the simultaneous measurement of MeIQx, DiMeIQx, and PhIP in cooked meat and in human urine using stable isotope labeled analogues. Ten normal, healthy male volunteers were invited to consume a standard cooked meat meal (400-450 g lean beef, cooked as patties on a griddle hotplate) on four separate occasions over a period of 14 months. Following consumption of the test meals, urine was collected from 0 to 8 h, during which time all free amines were excreted and analyzed for MeIQx, DiMeIQx, and PhIP. Subjects ingested 240 +/- 9 (SEM) g cooked meat, which contained 2.2 +/- 0.2 ng MeIQx/g meat, 0.7 +/- 0.1 ng DiMeIQx/g meat, and 16.4 +/- 2.1 ng PhIP/g meat. The variability in relative systemic bioavailability was assessed from the percentage of ingested amine excreted unchanged in the urine. Subjects excreted 2.1 +/- 1.1% of MeIQx and 1.1 +/- 0.5% of PhIP ingested as unchanged amine in the urine. Levels of DiMeIQx in urine, if present, were below the sensitivity of our assay (20 pg/ml) and could not be detected in any of the samples analyzed. Irrespective of dose, urinary excretion of unchanged MeIQx or PhIP (expressed as a percentage of the ingested dose) remained constant for each individual subject. The intraindividual coefficients of variation for MeIQx (28.4%) and PhIP (23.7%) were low and the pooled interday (intrasubject) coefficients of variation for both compounds were only 19 and 3.4%, respectively. In contrast, inter-subject (intraday) variation was greater, with pooled coefficients of variation of 145% for MeIQx and 71% for PhIP. Based on these studies, it should be possible to use the percentage excretion of MeIQx and PhIP to assess the relative bioavailability of these compounds in humans.

Distribution of substance P-like immunoreactivity in guinea pig central nervous system

The distribution of substance P-like immunoreactivity (SP-LI) in the guinea pig brain has been studied by immunohistochemistry and the results compared with the distribution in similar regions in the rat brain. In both species, dense SP-LI staining was found in the median eminence, arcuate hypothalamic nucleus, substantia nigra, dorsal raphe and dorsal tegmental nuclei, nucleus of the solitary tract, substantia gelatinosa of the spinal trigeminal nucleus, and spinal cord. Less dense staining was found in the caudate putamen, globus pallidus, nucleus accumbens, habenula, hypothalamic areas, and central grey. SP-LI cell bodies were found in areas previously described for the rat brain including several hypothalamic areas, limbic areas, central grey, and dorsal raphe and solitary tract nuclei. The major difference between the two species was found in the cortex and hippocampus. The guinea pig cortex contained many more SP-LI cells and fibres, distributed in layers II-VI, than the rat cortex. The guinea pig hippocampus contained marked staining, particularly in the pyramidal cell layer of CA1-3 fields of Ammon's horn and in the granular layer of the dentate gyrus, and SP-LI cells in the hilus of the dentate gyrus, whereas rat hippocampus contained few cells and no regions of dense staining. It is concluded that because the guinea pig brain has an extensive distribution of SP-LI in the cortex and hippocampus it resembles the primate brain more closely than does the rat brain.

The measurement of MeIQx adducts with mouse haemoglobin in vitro and in vivo: implications for human dosimetry

We have investigated covalent binding of radiolabelled [14C]2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) to mouse haemoglobin in vitro and in vivo. Furthermore, we report the development of a capillary column gas chromatography negative ion mass spectrometry (GC-MS) assay capable of detecting MeIQx liberated from haemoglobin after acid or base hydrolysis. Following microsomal activation, the amount of radiolabelled material associated with haemoglobin in vitro increased with incubation time to 0.67 +/- 0.15 nmol/mg haemoglobin at 2 h (initial concentration 0.47 mM [14C]MeIQx, mean +/- SD, n = 6). Hydrolysis of these samples with acid revealed that 47-60% of the radiolabelled material covalently bound to haemoglobin was acid labile. Of this, 7.2-9.8% was recovered as MeIQx as determined by GC-MS. This liberated fraction should reflect the amount of sulphinic acid amide present which is formed when N-hydroxy-MeIQx reacts with sulphydryl-containing amino acids present in haemoglobin. In vivo, no radiolabelled material bound to haemoglobin could be detected in animals treated with the lowest dose of MeIQx (0.2 mg/kg). At higher doses, there was a dose-dependent increase in the covalent binding of radiolabel to haemoglobin (2.0-200 mg/kg). However, the GC-MS assay for hydrolysable adducts of MeIQx yielded detectable quantities of MeIQx (32.2 +/- 17.5 fmol MeIQx/mg haemoglobin) only at the highest dose used. Application of the GC-MS assay to human haemoglobin samples showed that acid-labile adducts of MeIQx, if present, were below the limit of detection of the assay. These results show that levels of sulphinamide adducts of the dietary aromatic amine MeIQx, with haemoglobin, are very low and the implications for future human dosimetry of this carcinogen are discussed.

Imipenem resistance in a case of AIDS with relapsing Pseudomonas meningitis

We describe an AIDS patient who had a recurrence of Pseudomonas meningitis to illustrate three points. First, the use of sulfamethoxazole-trimethoprim in AIDS patients for prophylaxis of Pneumocystis carinii pneumonia may cause the various body sites to be colonized with resistant species such as P aeruginosa. Second, Pseudomonas meningitis can recur in a patient with AIDS after a month of appropriate therapy. Finally, imipenem is a poor choice for Pseudomonas meningitis, even when alternative therapies appear much less attractive. High doses of imipenem should not be used for fear of seizures, and lower doses only produce resistant organisms in the CSF.

Glucose increases cytosolic calcium concentration and inositol lipid metabolism in HIT-T15 cells

We have investigated the effects of glucose on cytosolic free calcium concentration in the insulin-secreting cell line HIT-T15. Addition of glucose (10 mM) caused a 20-75% increase in cytosolic [Ca2+] within 5 minutes compared to controls in the absence of glucose. A maximal increase in cytosolic [Ca2+] was obtained with 5 mM glucose. The magnitude of the response was markedly dependent upon the concentration of extracellular Ca2+, and the rise in cytosolic [Ca2+] was inhibited by verapamil. Cytosolic [Ca2+] was greatly increased by depolarization of the cells with KCl (50 mM), whereas carbamylcholine had no apparent effect. Glucose and KCl were also effective in stimulating insulin release from HIT cells, although carbamylcholine was again ineffective. The secretory response to glucose was also found to be directly related to the concentration of extracellular [Ca2+]. Glucose and KCl, but not carbamylcholine, were found to slightly enhance the production of [3H]-inositol trisphosphate in HIT cells pre-labelled with myo-[3H]-inositol, indicating a modest stimulation of inositol lipid hydrolysis.

Lactate alters plasma membrane potential, increases the concentration of cytosolic Ca2+ and stimulates the secretion of insulin by the hamster beta-cell line HIT-T15

We have studied the effect of lactate on a number of intracellular events which may be important in controlling the secretion of insulin by the hamster beta-cell line HIT-T15. Using the fluorescent dye Oxonol V, as well as intracellular recording techniques to measure changes in membrane potential, we found that lactate, glucose, K+ and tolbutamide caused depolarization of HIT cells, while valinomycin resulted in hyperpolarization. Consistent with these findings was the observation that 10 mM lactate caused an increase of 69.0 +/- 18.4% (S.E.M., n = 6) in the level of free cytosolic Ca2+ within HIT cells (assessed by fluorescence of quin 2). This was probably due to influx of Ca2+ through voltage-sensitive calcium channels, since it was dependent upon the concentration of extracellular Ca2+ and inhibited by verapamil. Lactate also caused cytosolic acidification in HIT cells and increased the secretion of insulin. These findings are consistent with the view that the electrogenic efflux of lactate could be a determinant in the activation of HIT cells by lactate and possibly by glucose.

Effects of nutrient and non-nutrient stimuli on cytosolic pH in cultured insulinoma (HIT-T15) cells

Intracellular pH (pHi) was measured in the insulin-secreting HIT-T15 cell line using the pH-sensitive fluorescent dye, 2',7'-bis(carboxyethyl)-5'(6')-carboxyfluorescein (BCECF). It was observed that the addition of a weak acid (e.g., acetate or propionate) caused a rapid decrease in pHi, followed by a slower recovery to the resting pH value. Conversely the addition of N4Cl caused an increase in pHi followed by recovery. The addition of amiloride caused a fall in pHi; however, in this case no recovery to basal pH levels was observed. Subsequent addition of a weak acid caused a further fall in pHi with no recovery. The addition of glucose caused a transient acidification followed by alkalinization. When glucose was added to cells which had been pretreated with amiloride, the initial acidification was not followed by recovery or alkalinization. Addition of glyceraldehyde, alpha-ketoisocaproate, lactate or pyruvate to HIT cells also resulted in intracellular acidification followed by recovery. Similarly, depolarisation of HIT cells by treatment with high K+ or with Ba2+ was associated with a pronounced fall in pHi, followed by a gradual recovery. Insulin secretion from HIT cells was stimulated by glucose, glyceraldehyde, alpha-ketoisocaproate, lactate, pyruvate and KCl, whilst amiloride and weak acids exerted only modest effects in the absence of glucose, but amiloride in particular markedly potentiated glucose-induced insulin release. Thus, HIT cells appear to have an amiloride-sensitive mechanism for the extrusion of protons, probably Na+-H+ exchange. Whilst intracellular acidification appears to potentiate secretory responses to nutrient stimuli, it seems unlikely that the activation of HIT cells by these nutrients occurs as a result of intracellular acidification. The mechanisms by which various nutrient and non-nutrient stimuli might exert distinct effects on pHi are discussed.

Placental growth in rats exposed to carbon monoxide at selected stages of pregnancy

Maternal hypoxemia has been associated with fetal-growth retardation and placental hypertrophy. Here, rats were exposed to carbon monoxide (CO), 100 ppm, at different stages of gestation to determine when during pregnancy placental hypertrophy can be elicited, whether hypertrophy is sustained when the stimulus is removed, and whether placental hypertrophy correlates with maintenance of normal fetal growth. Groups of rats (11-17 per group) were exposed to CO, throughout gestation, or over days 1-16, 4-12, 10-22 and 18-22, to cover significant periods of placental growth. Maternal carboxyhemoglobin levels were estimated to be in the order of 10-14%, but there was no effect on fetal survival. Fetal weights were significantly reduced by 8 and 6% in groups treated over days 1-22 and 10-22 of pregnancy, but not in those where treatment ceased before term, and surprisingly not in the group treated over days 18-22, the stage of maximal fetal growth. Placental weights were significantly increased by 11-13% in all groups in which carbon monoxide exposure was continued to term, but were unaffected in cases where treatment ceased before term. These results show that near term the placenta, when it is thought to normally reach the limit of its functional capacity, can hypertrophy in response to CO, and suggest that this response benefits the fetus presumably by improving oxygen transport.

A rapid method for the reconstitution of Na+-dependent neutral amino acid transport from bovine renal brush-border membranes

1. A simple and rapid method for the reconstitution of Na+-dependent neutral amino acid transport activity from bovine renal brush border membranes is described. 2. The neutral detergent decanoyl-N-methylglucamide ('MEGA-10') was employed to solubilize the membrane protein. This obviated the necessity for a prolonged dialysis step. 3. The properties of amino acid transport in these vesicles were similar to those observed in native membranes. 4. This should be a useful procedure in the eventual identification and isolation of amino acid transport proteins.

Evidence for a single common Na+-dependent transport system for alanine, glutamine, leucine and phenylalanine in brush-border membrane vesicles from bovine kidney

The characteristics of the Na+-dependent transport of alanine, glutamine, leucine and phenylalanine were studied in bovine renal brush-border membrane vesicles. Inhibition of the transport of any one of these amino acids by any other was mutually competitive. The Ki value for the inhibition of alanine transport by leucine was similar to the Km for leucine transport; similar interrelationships existed for the other amino acids. Each amino acid was shown to exchange with each of the other amino acids across the membrane. From these and other results it is concluded that the Na+-dependent transport of these four amino acids is catalysed by a single common transport system.