Process of care events in transplantation: effects on the cost of hospitalization.

Deviations in the processes of healthcare delivery that affect patient outcomes are recognized to have an impact on the cost of hospitalization. Whether deviations that do not affect patient outcome affects cost has not been studied. We have analyzed process of care (POC) events that were reported in a large transplantation service (n = 3,012) in 2005, delineating whether or not there was a health consequence of the event and assessing the impact on hospital resource utilization. Propensity score matching was used to adjust for patient differences. The rate of POC events varied by transplanted organ: from 10.8 per 1000 patient days (kidney) to 17.3 (liver). The probability of a POC event increased with severity of illness. The majority (81.5%) of the POC events had no apparent effect on patients' health (63.6% no effect and 17.9% unknown). POC events were associated with longer length of stay (LOS) and higher costs independent of whether there was a patient health impact. Multiple events during the same hospitalization were associated with the highest impact on LOS and cost. POC events in transplantation occur frequently, more often in sicker patients and, although the majority of POC events do not harm the patient, their effect on resource utilization is significant.

Basolateral membrane H/OH/HCO3 transport in the rat cortical thick ascending limb. Evidence for an electrogenic Na/HCO3 cotransporter in parallel with a Na/H antiporter.

Mechanisms involved in basolateral H/OH/HCO3 transport in the in vitro microperfused rat cortical thick ascending limb were examined by the microfluorometric determination of cell pH using (2',7')-bis-(carboxyethyl)-(5,6)-carboxyfluorescein. The mean cell pH in this segment perfused with 147 mM sodium and 25 mM HCO3 at pH 7.4 was 7.13 +/- 0.02 (n = 30). Lowering bath HCO3 from 25 to 5 mM (constant PCO2 of 40 mmHg) acidified the cells by 0.31 +/- 0.02 pH units at a rate of 0.56 +/- 0.08 pH units/min. Removal of bath sodium acidified the cells by 0.28 +/- 0.03 pH units at a rate of 0.33 +/- 0.04 pH units/min. The cell acidification was stilbene inhibitable and independent of chloride. There was no effect of bath sodium removal on cell pH in the absence of CO2/HCO3. Depolarization of the basolateral membrane (step increase in bath potassium) independent of the presence of chloride. Cell acidification induced by bath sodium removal persisted when the basolateral membrane was voltage clamped by high potassium/valinomycin. Although these results are consistent with a Na/(HCO3)n greater than 1 cotransporter, a Na/H antiporter was also suggested: 1 mM bath amiloride inhibited the cell pH defense against an acid load (rapid ammonia washout), both in the presence and absence of CO2/HCO3, and inhibited the cell acidification induced by bath sodium reduction from 50 to 0 mM. In conclusion, an electrogenic Na/(HCO3)n greater than 1 cotransporter in parallel with a Na/H antiporter exist on the basolateral membrane of the rat cortical thick ascending limb.

Mechanisms of adaptation to chronic respiratory acidosis in the rabbit proximal tubule.

The hyperbicarbonatemia of chronic respiratory acidosis is maintained by enhanced bicarbonate reabsorption in the proximal tubule. To investigate the cellular mechanisms involved in this adaptation, cell and luminal pH were measured microfluorometrically using (2",7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein in isolated, microperfused S2 proximal convoluted tubules from control and acidotic rabbits. Chronic respiratory acidosis was induced by exposure to 10% CO2 for 52-56 h. Tubules from acidotic rabbits had a significantly lower luminal pH after 1-mm perfused length (7.03 +/- 0.09 vs. 7.26 +/- 0.06 in controls, perfusion rate = 10 nl/min). Chronic respiratory acidosis increased the initial rate of cell acidification (dpHi/dt) in response to luminal sodium removal by 63% and in response to lowering luminal pH (7.4-6.8) by 69%. Chronic respiratory acidosis also increased dpHi/dt in response to peritubular sodium removal by 63% and in response to lowering peritubular pH by 73%. In conclusion, chronic respiratory acidosis induces a parallel increase in the rates of the luminal Na/H antiporter and the basolateral Na/(HCO3)3 cotransporter. Therefore, the enhanced proximal tubule reabsorption of bicarbonate in chronic respiratory acidosis may be, at least in part, mediated by a parallel adaptation of these transporters.

Na/H antiporter mRNA expression in single nephron segments of rat kidney cortex.

Renal cortical tubules consist of polarized epithelial cells where Na/H antiport activity has been demonstrated on the apical and/or basolateral membrane. Apical Na/H antiport activity plays an important role in transcellular bicarbonate (HCO3-) reabsorption, whereas basolateral Na/H antiport activity could be involved in transcellular HCO3- secretion as well as cell volume and pH control. To determine whether this heterogeneity in both localization and function is due to the existence of more than one Na/H antiporter, we studied the tissue distribution of Na/H antiporter mRNA by use of reverse transcription (RT) and polymerase chain reaction (PCR) in isolated nephron segments from rat renal cortex. The primers used were directed against the rat renal cortical Na/H antiporter cDNA which is homologous to the human growth factor-activatable Na/H antiporter. RT/PCR of beta-actin mRNA were performed as positive controls. Na/H antiporter mRNA expression in the proximal tubule was not detectable in S1 and S2 segments from superficial and most midcortical nephrons, which exhibit exclusively luminal Na/H antiport activity. It was expressed in S1 and S2 segments from juxtamedullary nephrons which have also basolateral Na/H antiport activity. Beta-actin mRNA was expressed uniformly in all segments of the proximal tubule. Na/H antiporter mRNA was also expressed in cortical thick ascending limb and cortical collecting duct, segments with basolateral Na/H antiport activity as well as in the glomeruli. In conclusion, at least two different Na/H antiporters exist in the renal cortex, i.e., the proximal tubule. The close correlation between functional localization of basolateral Na/H antiport activity and mRNA expression suggests that the rat kidney Na/H antiporter DNA homologous to the human growth factor activatable Na/H antiporter encodes a basolateral exchanger. The observed expression in a minority of midcortical proximal tubules could reflect a certain heterogeneity in these nephron segments.

Chronic metabolic acidosis increases the serum concentration of 1,25-dihydroxyvitamin D in humans by stimulating its production rate. Critical role of acidosis-induced renal hypophosphatemia.

Chronic metabolic acidosis results in metabolic bone disease, calcium nephrolithiasis, and growth retardation. The pathogenesis of each of these sequelae is poorly understood in humans. We therefore investigated the effects of chronic extrarenal metabolic acidosis on the regulation of 1,25-(OH)2D, parathyroid hormone, calcium, and phosphate metabolism in normal humans. Chronic extrarenal metabolic acidosis was induced by administering two different doses of NH4Cl [2.1 (low dose) and 4.2 (high dose) mmol/kg body wt per d, respectively] to four male volunteers each during metabolic balance conditions. Plasma [HCO3-] decreased by 4.5 +/- 0.4 mmol/liter in the low dose and by 9.1 +/- 0.3 mmol/liter (P < 0.001) in the high dose group. Metabolic acidosis induced renal hypophosphatemia, which strongly correlated with the severity of acidosis (Plasma [PO4] on plasma [HCO3-]; r = 0.721, P < 0.001). Both metabolic clearance and production rates of 1,25-(OH)2D increased in both groups. In the high dose group, the percentage increase in production rate was much greater than the percentage increase in metabolic clearance rate, resulting in a significantly increased serum 1,25-(OH)2D concentration. A strong inverse correlation was observed for serum 1,25-(OH)2D concentration on both plasma [PO4] (r = -0.711, P < 0.001) and plasma [HCO3-] (r = -0.725, P < 0.001). Plasma ionized calcium concentration did not change in either group whereas intact serum parathyroid hormone concentration decreased significantly in the high dose group. In conclusion, metabolic acidosis results in graded increases in serum 1,25-(OH)2D concentration by stimulating its production rate in humans. The increased production rate is explained by acidosis-induced hypophosphatemia/cellular phosphate depletion resulting at least in part from decreased renal tubular phosphate reabsorption. The decreased serum intact parathyroid hormone levels in more severe acidosis may be the consequence of hypophosphatemia and/or increased serum 1,25-(OH)2D concentrations.

Regulation of cell pH by ambient bicarbonate, carbon dioxide tension, and pH in the rabbit proximal convoluted tubule.

UNLABELLED: To study the regulation of cell pH by ambient pH, carbon dioxide tension (PCO2), and bicarbonate (HCO3), cell pH was measured in the isolated, in vitro microperfused rabbit proximal convoluted tubule using the fluorescent dye (2',7')-bis-(carboxyethyl)-(5,6)-carboxyfluorescein. For the same changes in external pH, changes in [HCO3] and PCO2 affected cell pH similarly ([HCO3]: pHi/pHe = 0.67, PCO2: pHi/pHe = 0.64, NS). Isohydric changes in extracellular [HCO3] and PCO2 did not change cell pH significantly. Changes in peritubular [HCO3] elicited larger changes in cell pH than changes in luminal [HCO3], which were enhanced by peritubular 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS). The cell pH defense against acute increases and decreases in PCO2 was inhibited by sodium, but not by chloride removal. Peritubular SITS inhibited the cell pH defense against increases and decreases of PCO2, whereas luminal amiloride inhibited cell pH defense against increases in PCO2. CONCLUSIONS: (a) Steady-state cell pH changes in response to changes in extracellular [HCO3] and PCO2 are quantitatively similar for a given change in extracellular pH; (b) the rate of the basolateral Na/(HCO3)3 cotransporter is a more important determinant of cell pH than the rate of the apical membrane mechanism(s); (c) cell pH defense against acute changes in PCO2 depends on the basolateral Na/(HCO3)3 cotransporter (acid and alkaline loads) and the luminal Na/H antiporter (acid loads).

Expression of rat renal Na/H antiporter mRNA levels in response to respiratory and metabolic acidosis.

The mammalian proximal tubule is an important mediator of the renal adaptive response to systemic acidosis. In chronic metabolic and respiratory acidosis the bicarbonate reabsorptive (or proton secretory) capacity is increased. This increase is mediated, at least in part, by an increase in Vmax of the luminal Na/H antiporter. To determine whether this adaptation involves increased mRNA expression, Na/H antiporter mRNA levels were measured by Northern analysis in renal cortex of rats with metabolic (6 mmol/kg body wt NH4Cl for 2 or 5 d) and respiratory (10% CO2/air balanced for 2 or 5 d) acidosis and of normal, pair-fed rats. Na/H antiporter mRNA levels were unchanged after 2 d of both metabolic and respiratory acidosis. After 5 d, however, Na/H antiporter mRNA expression was increased 1.76 +/- 0.12-fold in response to metabolic acidosis (P less than 0.005, n = 8), but was not different from normal in response to respiratory acidosis: 1.1 +/- 0.2 (NS, n = 8). Thus, the renal adaptive response to metabolic acidosis involves increased cortical Na/H antiporter mRNA levels. In contrast, the enhanced proximal tubule Na/H antiporter activity and bicarbonate reabsorption in respiratory acidosis seem to involve mechanisms other than increased Na/H antiporter gene expression.

Chronic metabolic acidosis decreases albumin synthesis and induces negative nitrogen balance in humans.

Chronic metabolic acidosis has been previously shown to stimulate protein degradation. To evaluate the effects of chronic metabolic acidosis on nitrogen balance and protein synthesis we measured albumin synthesis rates and urinary nitrogen excretion in eight male subjects on a constant metabolic diet before and during two different degrees of chronic metabolic acidosis (NH4Cl 2.1 mmol/kg body weight, low dose group, and 4.2 mmol/kg body weight, high dose group, orally for 7 d). Albumin synthesis rates were measured by intravenous injection of [2H5ring]phenylalanine (43 mg/kg body weight, 7.5 atom percent and 15 atom percent, respectively) after an overnight fast. In the low dose group, fractional synthesis rates of albumin decreased from 9.9 +/- 1.0% per day in the control period to 8.4 +/- 0.7 (n.s.) in the acidosis period, and from 8.3 +/- 1.3% per day to 6.3 +/- 1.1 (P < 0.001) in the high dose group. Urinary nitrogen excretion increased significantly in the acidosis period (sigma delta 634 mmol in the low dose group, 2,554 mmol in the high dose group). Plasma concentrations of insulin-like growth factor-I, free thyroxine and tri-iodothyronine were significantly lower during acidosis. In conclusion, chronic metabolic acidosis causes negative nitrogen balance and decreases albumin synthesis in humans. The effect on albumin synthesis may be mediated, at least in part, by a suppression of insulin-like growth factor-I, free thyroxine and tri-iodothyronine.

Basolateral membrane Na/base cotransport is dependent on CO2/HCO3 in the proximal convoluted tubule.

The mechanism of basolateral membrane base transport was examined in the in vitro microperfused rabbit proximal convoluted tubule (PCT) in the absence and presence of ambient CO2/HCO3- by means of the microfluorometric measurement of cell pH. The buffer capacity of the cells measured using rapid NH3 washout was 42.8 +/- 5.6 mmol.liter-1.pH unit-1 in the absence and 84.6 +/- 7.3 mmol.liter-1.pH unit-1 in the presence of CO2/HCO3-. In the presence of CO2/HCO3-, lowering peritubular pH from 7.4 to 6.8 acidified the cell by 0.30 pH units and lowering peritubular Na from 147 to 0 mM acidified the cell by 0.25 pH units. Both effects were inhibited by peritubular 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS). In the absence of exogenous CO2/HCO3-, lowering peritubular pH from 7.4 to 6.8 acidified the cell by 0.25 pH units and lowering peritubular Na from 147 to 0 mM decreased cell pH by 0.20 pH units. Lowering bath pH from 7.4 to 6.8 induced a proton flux of 643 +/- 51 pmol.mm-1.min-1 in the presence of exogenous CO2/HCO3- and 223 +/- 27 pmol.mm-1.min-1 in its absence. Lowering bath Na from 147 to 0 mM induced proton fluxes of 596 +/- 77 pmol.mm-1.min-1 in its absence. The cell acidification induced by lowering bath pH or bath Na in the absence of CO2/HCO3- was inhibited by peritubular SITS or by acetazolamide, whereas peritubular amiloride had no effect. In the absence of exogenous CO2/HCO3-, cyanide blocked the cell acidification induced by bath Na removal, but was without effect in the presence of exogenous CO2/HCO3-. We reached the following conclusions. (a) The basolateral Na/base n greater than 1 cotransporter in the rabbit PCT has an absolute requirement for CO2/HCO3-. (b) In spite of this CO2 dependence, in the absence of exogenous CO2/HCO3-, metabolically produced CO2/HCO3- is sufficient to keep the transporter running at 30% of its control rate in the presence of ambient CO2/HCO3-. (c) There is no apparent amiloride-sensitive Na/H antiporter on the basolateral membrane of the rabbit PCT.

Kinetics and dynamics of orally administered 18 beta-glycyrrhetinic acid in humans.

18 beta-Glycyrrhetinic acid (GRA) represents a major metabolite of glycyrrhizic acid (glycyrrhizin), an important constituent of licorice and licorice root, and is a potent inhibitor of 11 beta-hydroxysteroid dehydrogenase (11 beta OHSD). Different oral doses of GRA (500, 1000, or 1500 mg) were administered to healthy volunteers in order to study its kinetics and dynamics. In agreement with the lipophilic nature of GRA, with a biphasic decay of the plasma concentration-time curve at doses greater than 500 mg. The mean (+/-SEM) half-life of the second elimination phase was 11.5 +/- 1.2 h after 1000 mg GRA and 38.7 +/- 10.5 h after 1500 mg GRA (P < 0.05). The peak plasma concentration and the area under the plasma concentration-time curve (AUC) increased with increasing GRA doses. Urinary elimination of GRA and GRA glucuronides over 24 h was less than 1% of the dose administered. The dynamics of GRA were assessed by measuring the activity of the 11 beta OHSD in vivo, as reflected by the cortisol and cortisone concentrations in plasma. With increasing doses of GRA, the cortisone concentration declined, and the cortisol/cortisone ratio increased. Both peak plasma concentration and AUCs of GRA correlated with changes in the AUC values of cortisone. Based on the single dose kinetics, the kinetic/dynamic analysis of the data revealed that after multiple doses of 1.5. g GRA/day, the 11 beta OHSD might be constantly inhibited, whereas at daily doses of 500 mg or less, such an inhibition might occur only transiently.

A fatality during haloperidol treatment: mechanism of sudden death.

The authors report a case of unexpected sudden death in a woman receiving relatively high dose of haloperidol. They postulate that drug-induced laryngeal spasm leading to cardiac arrest via vagal reflexes may represent the mechanism of neuroleptic sudden death in some cases.

Copper pumping ATPases: common concepts in bacteria and man.

Recently, four genes encoding putative copper pumping ATPases have been cloned from widely different sources: two genes from Enterococcus hirae that are involved in copper metabolism and two human genes that are defective in the copper-related Wilson and Menkes disease. The predicted gene products are P-type ATPases. They exhibit extensive sequence similarity and appear to be members of a new class of ATP driven copper pumps involved in the regulation of cellular copper.

Glomerulopathy associated with predominant fibronectin deposits: exclusion of the genes for fibronectin, villin and desmin as causative genes.

Glomerulopathy with predominant fibronectin deposits (GFD) is a newly recognized autosomal dominant renal disease that leads to albuminuria, microscopic hematuria, hypertension, renal tubular acidosis type IV, and end-stage renal disease in the second to fourth decade of life. Light microscopy documents extensive deposits in the subendothelial space, which on electron microscopy consist of non-oriented 12 x 125 nm fibers. Deposits are strongly immunoreactive for antibodies to fibronectin. We examined the hypothesis that a genetic defect in the gene for fibronectin is responsible for the disease. In a 197 member pedigree, 13 relatives developed end-stage renal failure from the disease. In 99 individuals haplotype analysis was performed using 6 microsatellite markers spanning a > 56 cM interval in chromosome region 2q34, where fibronectin, villin, and desmin map in close proximity. Haplotype analysis resulted in exclusion of the whole range of 78 cM covered by the markers examined. This result excludes fibronectin, villin, and desmin from being the causative genes for GFD in this large kindred.

Ventilatory support during magnetic resonance imaging.

Ventilatory support during magnetic resonance imaging is difficult because metallic objects on ventilatory support devices can interfere with the imaging field and/or become magnetized and move inside the patient or become flying projectiles. We report the successful MRI examination of an intubated respirator-dependent pediatric patient. Ventilatory support was carried out with a plastic ambu bag, exhalation valve circuit, and tubing.

Characteristics and prognosis of myocardial infarction in patients with normal coronary arteries.

STUDY OBJECTIVES: Myocardial infarction with angiographically normal coronary arteries (MINC) is a life-threatening event with many open questions for physicians and patients. There are little data concerning the prognosis for patients with MINC. DESIGN: Retrospective follow-up study. SETTING: Tertiary referral center. PATIENTS: Patients with MINC were investigated and compared to age- and sex-matched control subjects with myocardial infarction due to coronary artery disease (CAD). The patients were examined clinically using stress exercise and hyperventilation tests. Migraine and Raynaud's symptoms were determined by means of a standardized questionnaire. Serum lipoproteins; the seroprevalence of cytomegalovirus, Helicobacter pylori, and Chlamydia pneumoniae infections; and the most frequent causes of thrombophilia were assessed. MEASUREMENTS AND RESULTS: From > 4,300 angiographies that were performed between 1989 and 1996, 21 patients with MINC were identified. The mean +/- SD patient age at the time of myocardial infarction was 42 +/- 7.5 years. When compared to control subjects (n = 21), patients with MINC had fewer risk factors for CAD. In contrast, MINC patients had more frequent febrile reactions prior to myocardial infarction (six patients vs zero patients; p < 0.05), and the migraine score was significantly higher (7.1 +/- 6.3 vs 2.2 +/- 4.1; p < 0.01). The seroprevalence of antibodies against cytomegalovirus, C pneumoniae, and H pylori tended to be higher in patients with MINC and CAD as compared to matched healthy control subjects. Three patients with MINC vs none with CAD had coagulopathy. During follow-up (53 +/- 37 months), no major cardiac event occurred in the MINC group; no patients with MINC vs nine with CAD (p = 0.0001) underwent repeated angiography. CONCLUSION: High migraine score and prior febrile infection together with a lower cardiovascular risk profile are compatible with an inflammatory and a vasomotor component in the pathophysiology of the acute coronary event in MINC patients. The prognosis for these patients is excellent.

Quantification and predictors of plasma volume expansion from mannitol treatment.

OBJECTIVE: To determine the effects of acute hypertonic mannitol infusion on intravascular volume expansion and to identify potential predictors of hypervolemia. DESIGN: Measurements of plasma volume and volume regulatory hormones were performed in healthy volunteers before and over 90 min after acute infusion of 20% mannitol solution in a therapeutic dose of 0.5 g/kg body weight, equalling an average infusion volume of 180 ml. SETTING: Clinical research unit in an 800-bed teaching hospital in the eastern part of Switzerland. PARTICIPANTS: Eight normal male volunteers. MEASUREMENTS AND RESULTS: Baseline plasma volume was determined by the indocyanine green dye dilution technique. Serial plasma protein measurements were performed after mannitol infusion to calculate intravascular volume changes. Mannitol administration resulted in a plasma expansion that persisted for more than 90 min and peaked at 112% of the baseline plasma volume 15 min after infusion. Concomitantly, an increase in systolic blood pressure and a fall in plasma sodium concentration occurred. Pharmacokinetic analyses of mannitol distribution and elimination revealed a close relation between plasma volume expansion and mannitol serum concentrations. While renin activity and aldosterone concentrations were suppressed proportionally to the intravascular volume increase, antidiuretic hormone was increased despite notable volume expansion and hyponatremia. Similarly, a rise in atrial natriuretic peptide was detected. CONCLUSIONS: Therapeutic doses of hypertonic mannitol cause substantial plasma volume expansion, resulting in increased blood pressure. Plasma volume expansion is related to mannitol serum concentrations and mannitol clearance determines the time required to restore normovolemia. ADH and ANP are potentially aggravating factors of mannitol-induced hyponatremia.

Growth hormone corrects acidosis-induced renal nitrogen wasting and renal phosphate depletion and attenuates renal magnesium wasting in humans.

We have shown previously that chronic hyperchloremic metabolic acidosis (CMA) induces severe negative nitrogen balance and renal phosphate depletion and decreases serum insulin-like growth factor-1 (IGF-1) in association with growth hormone (GH) insensitivity in humans. The present study investigated whether acidosis-induced renal nitrogen wasting and renal phosphate depletion are mediated by GH insensitivity/low IGF-1 and thereby responsive to GH treatment. The effects of GH on acidosis-induced changes in divalent cation metabolism and acidosis-induced hypothyroidism were also investigated. CMA (delta[HCO3], -10.5 mmol/L) was induced in six healthy male subjects ingesting 4.2 mmol NH4Cl/kg body weight [BW]/d for 7 days. Recombinant human GH (0.1 U/kg BW/12 h subcutaneously) was administered for 7 days while acid feeding was continued. GH increased serum IGF-1 from 22.1 +/- 1.4 to 87 +/- 8.4 nmol/L (control level, 36.4 +/- 2.2). GH decreased urinary nitrogen excretion, resulting in a cumulative nitrogen retention of 2,404 mmol, thereby correcting the acidosis-induced cumulative increase in nitrogen excretion (2,506 mmol) despite continued acid feeding. GH attenuated the acidosis-induced hyperphosphaturia (cumulative phosphate retention, 91 mmol) and corrected the hypophosphatemia. GH did not affect acidosis-induced ionized hypercalcemia, but further exacerbated acidosis-induced hypercalciuria (cumulative loss, 27.3 mmol). GH significantly further increased serum 1,25-dihydroxyvitamin D (1,25(OH)2D) and further decreased intact PTH (from 10 +/- 1 to 6 +/- 1 pg/mL). Acidosis also induced hypomagnesemia and hypermagnesuria (cumulative loss, 9.4 mmol, ie, renal magnesium wasting), a novel finding, which was significantly attenuated by GH (cumulative retention, 5.0 mmol). In conclusion, GH corrected acidosis-induced renal nitrogen wasting, which may be caused, at least in part, by decreased IGF-1 levels. GH further increased serum 1,25(OH)2D and the systemic calcium load, which account for the suppression of parathyroid hormone (PTH) despite renal PO4 retention and correction of hypophosphatemia. GH attenuated acidosis-induced renal magnesium wasting.

Analysis and pharmacokinetics of glycyrrhizic acid and glycyrrhetinic acid in humans and experimental animals.

Glycyrrhizic acid (GZA) and glycyrrhetinic acid (GRA) can be determined rapidly and precisely by high-performance liquid chromatography (HPLC) in biological fluids and tissues from experimental animals and humans. From plasma and tissues, GZA and GRA are extracted by organic solvents and the extracts can directly be used for HPLC. From bile or urine, extraction and determination of GZA and GRA are more difficult due to interfering endogenous compounds and conjugation of GRA with glucuronides or sulfates. Extraction of GZA and GRA from urine or bile can be performed by ion-pairing followed by extraction with organic solvents or by solid phase extraction. GRA conjugates can be determined by chromatographic separation or by pretreatment with beta-glucuronidase. The pharmacokinetics of GRA and GZA can be described by a biphasic elimination from the central compartment with a dose-dependent second elimination phase. Depending on the dose, the second elimination phase in humans has a half-life of 3.5 hours for GZA and between 10-30 hours for GRA. The major part of both GRA or GZA is eliminated by the bile. While GZA can be eliminated unmetabolized and undergoes enterohepatic cycling, GRA is conjugated to GRA glucuronide or sulfate prior to biliary excretion. Orally administered GZA is almost completely hydrolyzed by intestinal bacteria and reaches the systemic circulation as GRA.

Failure to demonstrate a vasoconstrictive effect of vasopressin on the internal carotid and middle cerebral arteries: a transcranial ultrasound Doppler study.

Vasopressin (AVP) was infused into four healthy human volunteers to explore by Doppler ultrasound the vasoconstrictive action of AVP on the internal carotid (ICA) and the medial cerebral artery (MCA, transcranial Doppler technique). Although AVP levels rose to 74.2 pg/ml (+/- 13 pg, SEM) no significant changes of flow velocity were observed in the ICA as well as the MCA. There was no effect on the pulsatility index of the MCA velocity profile indicating that peripheral vascular resistance remained unchanged during AVP infusion. These results do not support an effect of AVP at high physiological levels on the vascular diameters of the ICA, MCA and cerebral arteriolar system in humans.

Metabolic and endocrine effects of metabolic acidosis in humans.

Metabolic acidosis is an important acid-base disturbance in humans. It is characterised by a primary decrease in body bicarbonate stores and is known to induce multiple endocrine and metabolic alterations. Metabolic acidosis induces nitrogen wasting and, in humans, depresses protein metabolism. The acidosis-induced alterations in various endocrine systems include decreases in IGF-1 levels due to peripheral growth hormone insensitivity, a mild form of primary hypothyroidism and hyperglucocorticoidism. Metabolic acidosis induces a negative calcium balance (resorption from bone) with hypercalciuria and a propensity to develop kidney stones. Metabolic acidosis also results in hypophosphataemia due to renal phosphate wasting. Negative calcium balance and phosphate depletion combine to induce a metabolic bone disease that exhibits features of both osteoporosis and osteomalacia. In humans at least, 1,25-(OH)2 vitamin D levels increase, probably through phosphate depletion-induced stimulation of 1-alpha hydroxylase. The production rate of 1,25-(OH)2 vitamin D is thus stimulated, and parathyroid hormone decreases secondarily. There is experimental evidence to support the notion that even mild degrees of acidosis, such as that occurring by ingestion of a high animal protein diet, induces some of these metabolic and endocrine effects. The possible role of diet-induced acid loads in nephrolithiasis, age-related loss of lean body mass and osteoporosis is discussed.