Age-related decreases in muscarinic cholinergic receptor binding in the human brain measured with positron emission tomography (PET)

Muscarinic cholinergic M1 and M2 receptors in young and aged adult male volunteers were studied using [N-11C-methyl]-benztropine, a specific muscarinic cholinergic receptor ligand, and high resolution positron emission tomography (PET). A regionally specific pattern of decreased binding was observed in aged volunteers. Using two separate methods of data analysis, thalamic, hippocampal and cerebellar regions showed no decreases in the apparent specific binding of [N-11C-methyl]-benztropine while frontal, parietal, temporal and occipital cortices as well as the corpus striatum showed age related changes in binding that declined (in 82 yrs old subject) to about 50% of the value obtained from the youngest volunteer (19 yrs). These data suggest that regions high in muscarinic receptor density, the corpus striatum and the cortical mantle, show a greater rate of decline than those areas that have a relatively low number of muscarinic receptors. Furthermore, this study demonstrates the usefulness of PET and [N-11C-methyl]-benztropine for assessing age related regional changes in muscarinic cholinergic receptor binding in the living human brain.

Graphical analysis of reversible radioligand binding from time-activity measurements applied to [N-11C-methyl]-(-)-cocaine PET studies in human subjects

A graphical method of analysis applicable to ligands that bind reversibly to receptors or enzymes requiring the simultaneous measurement of plasma and tissue radioactivities for multiple times after the injection of a radiolabeled tracer is presented. It is shown that there is a time t after which a plot of integral of t0ROI(t')dt'/ROI(t) versus integral of t0Cp(t')dt'/ROI(t) (where ROI and Cp are functions of time describing the variation of tissue radioactivity and plasma radioactivity, respectively) is linear with a slope that corresponds to the steady-state space of the ligand plus the plasma volume,.Vp. For a two-compartment model, the slope is given by lambda + Vp, where lambda is the partition coefficient and the intercept is -1/[kappa 2(1 + Vp/lambda)]. For a three-compartment model, the slope is lambda(1 + Bmax/Kd) + Vp and the intercept is -[1 + Bmax/Kd)/k2 + [koff(1 + Kd/Bmax)]-1) [1 + Vp/lambda(1 + Bmax/Kd)]-1 (where Bmax represents the concentration of ligand binding sites and Kd the equilibrium dissociation constant of the ligand-binding site complex, koff (k4) the ligand-binding site dissociation constant, and k2 is the transfer constant from tissue to plasma). This graphical method provides the ratio Bmax/Kd from the slope for comparison with in vitro measures of the same parameter. It also provides an easy, rapid method for comparison of the reproducibility of repeated measures in a single subject, for longitudinal or drug intervention protocols, or for comparing experimental results between subjects. Although the linearity of this plot holds when ROI/Cp is constant, it can be shown that, for many systems, linearity is effectively reached some time before this. This analysis has been applied to data from [N-methyl-11C]-(-)-cocaine ([11C]cocaine) studies in normal human volunteers and the results are compared to the standard nonlinear least-squares analysis. The calculated value of Bmax/Kd for the high-affinity binding site for cocaine is 0.62 +/- 0.20, in agreement with literature values.

Secretion of plasminogen activator from bovine parathyroid cells

The characteristics and secretion of plasminogen activator (PA) were examined in fresh and cultured bovine parathyroid cells. Release of PA activity was maximal at low Ca concentrations ([Ca]) and suppressed at physiological [Ca]. PA secretion at high [Ca], like that of PTH, was increased by treatment of cells with chloroquine and/or 3-methyladenine. Secretion from organoids was not affected by hydrocortisone hemisuccinate, but was strongly increased by 1,25-dihydroxyvitamin D3. In cell homogenates, PA specific activity was highest in microsomes, from which less than 50% could be solubilized by Triton X-100. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of microsomes and media followed by zymography on fibrin-agarose gels showed that PA from both sources had an apparent mol wt of 44,000. No inhibitors of PA were detected by reverse zymography. PA activity was inhibited by placental urokinase (uPA) inhibitor and amiloride, which indicated that it was a uPA, but the secreted form required tissue-type PA stimulator (fibrin peptides) or denatured microsomes for full activity. Neither the microsomal nor the secreted forms of PA were active with S-2444, a substrate specific for active uPA. By comparison with the characteristics of human activators, the results suggested that parathyroid cells secrete uPA that is primarily in the precursor form single chain urokinase or scuPA.

In vivo neutrophil delivery in men with alcoholic cirrhosis is normal despite depressed in vitro chemotaxis

Ten patients with far-advanced Laennec's cirrhosis were studied for in vitro polymorphonuclear (PMN) chemotaxis and in vivo PMN delivery into modified skin windows. Random motility was similar for patient and control cells, but the patients' cells' mean chemotaxis to endotoxin-activated homologous serum was only 38% of control. The poor response was due to a serum inhibitor which reduced chemotactic activity of control serum by 75.6% but had no effect on chemotaxis to N-formyl-methionyl-leucyl-phenylalanine. The level of inhibitor activity in each patient did not correlate with the severity of liver dysfunction. In spite of the universal presence of the chemotactic factor inhibitor in all patients' sera, their in vivo PMN delivery into skin chambers was similar to controls. Thus, patients with alcoholic cirrhosis appear able to deliver PMNs normally in response to local tissue injury.

Neutrophil function in healthy elderly subjects

Ten healthy elderly volunteers (mean age: 78.9) underwent a battery of neutrophil function tests. Resting adherence to endothelium, random and directed migration, phagocytosis-induced chemiluminescence, and granule secretory behavior were all indistinguishable from young healthy controls. However, in vivo delivery of neutrophils into skin abrasions was significantly reduced: 8.4 X 10(5), versus 2.7 X 10(6) in the young. In addition, their neutrophils showed a smaller increase in the surface adhesion glycoprotein CD11 and in adherence to endothelium in response to stimulation with FMLP than did cells from young controls. Inversely, baseline CD11 expression was higher in elderly subjects, suggesting that their cells may have an in vivo defect in mediator responsiveness. Serum immunoglobulin and complement concentrations were also compared. The mean IgM level of 106.3 mg/dl in the elderly was significantly below the 154.4 mg/dl in the young. In contrast, concentrations of C3, C4, and total hemolytic complement were significantly higher in the elderly.

Rapid stereoselective hydrolysis of (+)-cocaine in baboon plasma prevents its uptake in the brain: implications for behavioral studies

The naturally occurring enantiomer of cocaine, (-)-cocaine, has been previously labeled with 11C on the N-methyl group and used in conjunction with positron emission tomography to show that cocaine is rapidly taken up in the striata of human and baboon brain. In the present study, the behaviorally inactive (+)-cocaine was similarly labeled, with a view to its use for measuring the nonspecific binding of cocaine. No brain uptake was seen, although transport of cocaine into the brain is not expected to be stereoselective. The explanation for the lack of uptake was determined to be very rapid metabolism of (+)-cocaine in the blood. By 30 s after administration of labeled (+)-cocaine, it was undetectable in plasma. In vitro studies demonstrated that (+)-cocaine is 50% debenzoylated to (+)-ecgonine methyl ester within 5 s of exposure to baboon plasma but not to washed erythrocytes. The hydrolysis of (-)-cocaine is at least 1,000 times slower. Serum butyrylcholinesterase (EC 3.1.1.8) appears to be responsible for this hydrolysis, as evidenced by its inhibition by physostigmine and catalysis by commercially available pseudocholinesterase from horse and human blood.

Positron emission tomography (PET) studies of dopaminergic/cholinergic interactions in the baboon brain

Interactions between the dopaminergic D2 receptor system and the muscarinic cholinergic system in the corpus striatum of adult female baboons (Papio anubis) were examined using positron emission tomography (PET) combined with [18F]N-methylspiroperidol [( 18F]NMSP) (to probe D2 receptor availability) and [N-11C-methyl]benztropine (to probe muscarinic cholinergic receptor availability). Pretreatment with benztropine, a long-lasting anticholinergic drug, bilaterally reduced the incorporation of radioactivity in the corpus striatum but did not alter that observed in the cerebellum or the rate of metabolism of [18F]NMSP in plasma. Pretreatment with unlabelled NMSP, a potent dopaminergic antagonist, reduced the incorporation of [N-11C-methyl]benztropine in all brain regions, with the greatest effect being in the corpus striatum greater than cortex greater than thalamus greater than cerebellum, but did not alter the rate of metabolism of the labelled benztropine in the plasma. These reductions in the incorporation of either [18F]NMSP or [N-11C-methyl]benztropine exceeded the normal variation in tracer incorporation in repeated studies in the same animal. This study demonstrates that PET can be used as a tool for investigating interactions between neurochemically different yet functionally linked neurotransmitters systems in vivo and provides insight into the consequences of multiple pharmacologic administration.

Oral ciprofloxacin for osteomyelitis

Ciprofloxacin is a new, oral, broad spectrum fluoroquinolone antibiotic which has a long serum half-life, a low incidence of significant adverse reactions, and is administered twice daily. Eighteen patients with osteomyelitis were treated with ciprofloxacin, 750 mg orally twice daily. The mean age of the patients was 43 years (range, 21 to 73 years); 12 were men. The duration of treatment ranged from 5 to 52 weeks (mean, 20.0 +/- 15.7 weeks). At follow up (mean, 18 +/- 8.5 months; range, 4 to 34.5 months), 11 patients (61.6%) achieved arrest of infection, 4 (22.2%) had improved with therapy, and 3 (16.6%) failed to improve. Ciprofloxacin was well tolerated. Four case histories are given.

Mapping muscarinic receptors in human and baboon brain using [N-11C-methyl]-benztropine

The muscarinic cholinergic system has been mapped in vivo in human and baboon brain using [N-11C-methyl]-benztropine and high resolution positron emission tomography (PET). [N-11C-methyl]-benztropine uptake was observed in frontal, parietal, occipital, and temporal cortices as well as in subcortical structures including the corpus striatum and thalamus. Uptake continued to increase in baboon and human brain in all areas over an 80 minute experimental period with the exception of the cerebellum where the accumulation of radioactivity began to decrease by 25 minutes postinjection. The ratio of incorporation of [N-11C-methyl]-benztropine between corpus striatum/cerebellum was 1.53 and 1.46 in humans and baboons, respectively, at 60 minutes. Blocking studies in baboons using the muscarinic cholinergic antagonists scopolamine and benztropine and the muscarinic cholinergic agonist pilocarpine combined with blocking studies in humans using benztropine indicate that the binding of this compound is specific for the muscarinic cholinergic system. Pretreatment with the potent dopamine reuptake blocker nomifensine produced no effect on the incorporation of radioactivity in any baboon brain region examined. Analysis of labelled plasma metabolites indicates that in humans, the rate of metabolism of [N-11C-methyl]-benztropine is slow (83.0% unchanged at 30 minutes postinjection) differing quite dramatically from the rate of metabolism observed in baboons (43.4% unchanged at 30 minutes postinjection). These data combined with postmortem studies in humans and primates demonstrate that [N-11C-methyl]-benztropine is a suitable muscarinic cholinergic ligand for use in humans and baboons with PET.

Modulation of endothelial fibronectin synthesis by polymorphonuclear granulocytes

The attachment of polymorphonuclear granulocytes (PMNs) to vascular endothelial cells occurs continually in normal tissues; however, knowledge of the factors that control leukocyte margination is incomplete. In the present study, we used cell cultures of pulmonary artery endothelium to study their interaction with PMNs. Endothelial cells were seeded in Costar 24-well plates following which PMNs were inoculated onto the endothelial monolayers and incubated for 2 to 20 hours. During this period, fibronectin synthesis by endothelial cells was estimated by ELISA. In wells to which PMNs had been added, supernatant fibronectin concentration was increased at all time points during the 20 hour incubation. At 20 hours, supernatants from wells to which PMNs had been added contained approximately 2 1/2 times the control level of fibronectin. Since the amount of fibronectin, as determined by ELISA, adsorbed onto the added PMNs was negligible, these data suggest that PMNs can modulate the synthesis of fibronectin by pulmonary artery cells. Pulse labeling experiments and measurements of endothelial intracellular fibronectin also suggest this possibility. The endothelial response does not appear to be owing to nonspecific physical interaction since similarly sized polystyrene beads did not cause any change in supernatant fibronectin levels while glutaraldehyde-fixed PMNs caused only a 20-25% increase in fibronectin levels.

Inhibitors of cellular proteolysis cause increased secretion from parathyroid cells

The secretion but not the biosynthesis of parathyroid hormone and secretory protein 1 is strongly, negatively regulated by extracellular [Ca2+]. In order to examine the hypothesis that decreased degradation might directly cause increased secretion, we tested the effects of agents that suppress cellular degradation via different mechanisms: 3-methyladenine, chloroquine, and 1-deoxynojirimycin. When secretion was inhibited by high [Ca2+], all agents caused increased secretion, but at low [Ca2+] only deoxynojirimycin was effective. Results derived from the use of two radioimmunoassays for parathyroid hormone suggested that the increased secretion was due to reduced destruction of secretory vesicles by lysosomes, and to reduced proteolysis of their contents by secretory vesicle proteases.

Mechanistic positron emission tomography studies: demonstration of a deuterium isotope effect in the monoamine oxidase-catalyzed binding of [11C]L-deprenyl in living baboon brain

The application of positron emission tomography (PET) to the study of biochemical transformations in the living human and animal body requires the development of highly selective radiotracers whose concentrations in tissue provide a record of a discrete metabolic process. L-N-[11C-methyl]Deprenyl ([11C]L-deprenyl), a suicide inactivator of monoamine oxidase (MAO) type B, has been developed as a radiotracer for mapping MAO B in the living human and animal brain. In this investigation, [11C]L-deprenyl (1) and [11C]L-deprenyl-alpha, alpha-2H2 (2) have been compared in three different baboons by PET measurement of carbon-11 uptake and retention in the brain and the measurement of the amount of unchanged tracer in the arterial plasma over a 90-min time interval. For one baboon, N-[11C-methyl-2H3]L-deprenyl (3) was also studied. Kinetic parameters calculated using a three-compartment model revealed a deuterium isotope effect of 3.8 +/- 1.1. Comparison of the two tracers (1 and 2) in mouse brain demonstrated that deuterium substitution significantly reduced the amount of radioactivity bound to protein. HPLC and GLC analysis of the soluble radioactivity in mouse brain after injection of [11C]L-deprenyl showed the presence of [11C]methamphetamine as a major product along with unidentified labeled products. Sodium dodecyl sulfate-polyacrylamide electrophoresis with carbon-14-labeled L-deprenyl showed that a protein of molecular weight 58,000 was labeled. These results establish that MAO-catalyzed cleavage of the alpha carbon-hydrogen bond on the propargyl group is the rate limiting (or a major rate contributing) step in the retention of carbon-11 in brain and that the in vivo detection of labeled products in brain after the injection of [11C]L-deprenyl provides a record of MAO activity.

Vancomycin concentrations in infected and noninfected human bone

Concentrations of vancomycin in bones of 14 patients undergoing total hip arthroplasty (group 1) and 5 patients with osteomyelitis (group 2) were studied. Group 1 received vancomycin, 15 mg/kg intravenously, 1 h prior to anesthesia. Group 2 received doses adjusted to achieve peak levels in serum of 20 to 30 micrograms/ml and trough levels of less than 12 micrograms/ml; bone specimens were collected during surgical debridement. The specimens were pulverized and eluted into phosphate buffer, and the supernatants were analyzed for vancomycin content by fluorescence polarization immunoassay. In group 1, vancomycin was detectable in all cancellous specimens with a mean concentration of 2.3 +/- 4.0 micrograms/g (range, 0.5 to 16 micrograms/g); 10 of 14 cortical specimens had detectable vancomycin; the mean cortical concentration was 1.1 +/- 0.8 micrograms/g (range, not detectable to 2.6 micrograms/g). In group 2, vancomycin was detectable in only two of five cortical bone specimens (mean concentration, 5.9 +/- 3.5 micrograms/g). Cancellous bone was obtained in one patient; the vancomycin concentration was 3.6 micrograms/g. In most patients the vancomycin levels in bones were higher than the MIC for susceptible staphylococci following single prophylactic doses. In the few infected patients studied, penetration was variable and deserves further study.

Effects of calcium on synthesis and secretion of parathyroid hormone and secretory protein I

Bovine parathyroid organoids were cultured for up to 3 wk in medium containing 1.4 or 1.8 mM calcium. Steady-state secretion of parathyroid hormone and secretory protein I was two- to fourfold greater at 1.4 mM. At the end of culture, organoids were incubated 3.5 h in 1 or 2 mM calcium to examine maximum and minimum acute secretory rates. Relative to organoids cultured at 1.8 mM calcium, culture at 1.4 mM induced a hypersecretory state, i.e., both the maximum and minimum acute secretory rates of organoids previously cultured at 1.4 mM calcium were up to threefold greater than those of organoids previously at 1.8 mM calcium. Proparathyroid hormone synthesis was up to 50% greater in organoids cultured at 1.4 mM calcium, whereas secretory protein I and total protein synthesis were unaltered. The results showed that parathyroid hypersecretion can be induced by chronic hypocalcemic conditions in vitro. We conclude that the secretory adaptation to chronic hypocalcemia in vitro involves alterations in both synthesis and degradation of parathyroid hormone.

Multiply high-level-aminoglycoside-resistant enterococci isolated from patients in a university hospital

Enterococci isolated from different body sites were tested for high-level gentamicin resistance. A total of 259 enterococcal isolates were screened for resistance (MIC, greater than 2,000 micrograms/ml) by a broth-tube method. Thirty-nine (15.1%) were found to exhibit resistance and were confirmed by agar screening (1,000 micrograms/ml) and agar dilution MIC determinations. The majority of isolates also showed high-level resistance to kanamycin and streptomycin. The remaining isolates showed high-level resistance to gentamicin and kanamycin but not streptomycin. Synergy testing of several isolates confirmed the correlation between lack of synergy and high-level resistance. A retrospective clinical review was performed. Most patients had a source of definite or likely infection (79%). Serious infections such as endocarditis or meningitis were not observed during the course of this study. Retrospective clinical data suggest that in cases not involving endocarditis or meningitis, neither infection refractory to therapy nor relapse of infection is a common sequela of infection with gentamicin-resistant enterococci in hospitalized patients.

Effect of ethanol on functions required for the delivery of neutrophils to sites of inflammation

Acute ethanol intoxication inhibits neutrophil delivery to sites of inflammation and, concomitantly, reduces the adhesion of neutrophils to surfaces. The effect of ethanol on several other neutrophil functions required for normal delivery are examined herein. Serum-free neutrophil suspensions showed normal resting adherence to endothelial monolayers in ethanol concentrations up to 1000 mg/dL, but when neutrophils were stimulated by 10(-6)M N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) to induce hyperadherence, ethanol induced a dose-dependent inhibition that was significant at concentrations greater than or equal to 500 mg/dL. Pretreating the endothelium with ethanol had no effect. Similarly, resting surface expression of the adhesive glycoprotein Mac-1 was unaffected by ethanol, but its up-regulation induced by fMLP was inhibited by 25.5% at 250 mg of ethanol/dL and by 52.3% at 1000 mg/dL. Release of both primary and secondary granule contents after activation showed dose-dependent inhibition, whereas resting granule content and spontaneous release were unaffected. Passive neutrophil deformability was significantly enhanced in 500 mg of ethanol/dL. Thus, ethanol affects several neutrophil delivery functions normally activated by inflammatory stimuli.

Serial [18F]N-methylspiroperidol PET studies to measure changes in antipsychotic drug D-2 receptor occupancy in schizophrenic patients

An indirect approach to the relationship among drug dose, plasma level, and the competition between a labeled neuroleptic drug [18F]N-methylspiroperidol (18F-NMS) for binding sites in striatal tissue in normal and schizophrenic subjects is described. The slope of the line plotting the ratio of activity in the striatum (As) to activity in the cerebellum (Ac) versus time up to 5 hr postinjection of 18F-NMS is taken as a marker of site occupancy. An inverse relation between labeled competitor uptake and drug plasma level has been demonstrated for the classes of antipsychotic drug studied. Striatal uptake studies showed a progressive increase in all subjects following drug withdrawal up to 156 hr postwithdrawal. Uptake and clearance of 18F-NMS in cerebellar tissue was not appreciably affected by antipsychotic medication or drug withdrawal.

Increased adherence of human granulocytes to herpes simplex virus type 1 infected endothelial cells

We studied the interaction of human polymorphonuclear leukocytes (PMNs) with umbilical vein endothelial cells infected with herpes simplex virus (HSV) type 1. PMNs labeled with 51Cr were added to endothelial monolayers at varying times after infection and their adherence assessed 1 h later. Granulocyte adherence (GA) to uninfected cells averaged 26.5 +/- 1.9%. Increased adherence began 6 h postinfection and rose to a maximum at 20 to 24 h. HSV-1 glycoproteins seemed to mediate the increase in GA: tunicamycin treatment of infected monolayers for 18 h abolished the increased GA as did incubation of infected cells with F(ab')2 fragments prepared from human antiserum containing HSV-1 antibody.

Alcohol and drugs as co-factors for AIDS

Opiate use in humans is associated with a reduction in the number of circulating T-lymphocytes and in their ability to undergo transformation, probably resulting from opiate binding to T-cell antigens. (See Table 4). Patients also manifest a diffuse hyperglobulinemia, without change in circulating B-cell numbers. In vitro exposure of rodent and human lymphocytes to cannabinoids depresses their transformation, natural killer activity, and interferon production. Similar results occur with in vivo exposure of rodents, but data in man are mixed. Cannabinoids also inhibit primary and secondary antibody responses in rodents. Data regarding the effects of CNS stimulants are too scanty to allow comment. Barbiturate anesthesia in man and animals produces a short-lived depression of lymphocyte transformation, NK activity, and ADCC; no studies of the effects of chronic exposure have been performed. Amyl nitrite has not been proven to possess any immunosuppressive activity.

Opposite effects of 1,25(OH)2D3 on synthesis and release of PTH compared with secretory protein I

Aggregates of bovine parathyroid cells (organoids) were cultured with or without 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and examined for effects on the synthesis, cellular content, and release of parathyroid hormone (PTH) and secretory protein I. Organoids cultured with 120 pM 1,25(OH)2D3 at 1.35 mM calcium contained 27 +/- 2% (mean +/- SE) less and released 26 +/- 7% less PTH and contained 21 +/- 2% more and released 49 +/- 16% more secretory protein I than untreated organoids. After 15-min incubations with radioactive leucine, treated organoids incorporated 25 +/- 2% less radioactivity into precipitable cellular proteins than did untreated organoids, indicating that the overall synthetic rate of proteins was decreased by 1,25(OH)2D3 at 1.35 mM calcium. After separation of cellular proteins by gel electrophoresis, analysis of individual protein bands indicated that the mean treated-control ratio for proparathyroid hormone radioactivity was 0.88 +/- 0.06 (P less than 0.10) while that for secretory protein I was 1.56 +/- 0.17 (P less than 0.01), respectively. Experiments were performed at 1.2, 12, 120, and 1,200 pM 1,25(OH)2D3 and both 1.4 and 1.8 mM calcium. In both cases, increasing levels of 1,25(OH)2D3 progressively decreased PTH synthesis and release and progressively increased that of secretory protein I, significant effects being observed at 1.2 pM 1,25(OH)2D3. We conclude that at physiological calcium levels, 1.2-1,200 pM 1,25(OH)2D3 suppresses the synthesis and secretion of PTH, increases that of secretory protein I, and at similar concentrations decreases the overall protein synthetic rate compared with untreated controls.

Biliary excretion of imipenem-cilastatin in hospitalized patients

Imipenem-cilastatin concentrations in bile were measured in 12 cholecystectomy patients (group 1) and 12 patients with common duct drainage (group 2). Six patients in each group received 0.5 g, and six received 1.0 g intravenously over 30 to 60 min. In group 1, bile was collected a mean of 85 min postinfusion. The mean concentrations of imipenem in bile were 1.3 microgram/ml after the 0.5-g dose and 3.5 micrograms/ml after the 1.0-g dose. The mean concentrations of cilastatin in bile were 9.0 micrograms/ml after the 0.5-g dose and 38.0 micrograms/ml after the 1.0-g dose. In patients with common duct drainage, bile was collected predose and 0 to 2, 2 to 3, 3 to 4, and 4 to 6 h postinfusion. Peak imipenem concentrations in bile were 4.4 micrograms/ml after the 0.5-g dose and 8.6 micrograms/ml after the 1.0-g dose. Peak cilastatin concentrations in bile were 4.6 micrograms/ml for the 0.5-g dose and 10.9 micrograms/ml for the 1.0-g dose. Peak imipenem concentrations in bile occurred a mean of 2.3 h after administration of the drug; cilastatin peak concentrations occurred at a mean of 2.4 h. Less than 0.3% of each drug was recovered in the bile. Our results suggest that imipenem enters bile by simple diffusion and in most patients attains concentrations sufficient to inhibit susceptible organisms. In contrast, cilastatin had a bimodal entry into bile. Some patients had very high concentrations in bile, whereas others had very low or undetectable concentrations, suggesting that cilastatin may be actively secreted into the bile.

Serial PET studies of human cerebral malignancy with [1-11C]putrescine and [1-11C]2-deoxy-D-glucose

Serial PET measurements of [1-11C]putrescine ([11C]PUT) uptake and glucose metabolic rate (GMR) using [1-11C]2-deoxy-D-glucose ([11C]2DG) were made on eight human subjects with a radiological and, in most cases, pathological diagnosis of primary or metastatic brain tumor. Blood-to-brain influx constants (Ki) were calculated for [11C]PUT. Tumor uptake of 11C after [11C]PUT injection was unidirectional peaking at 15 min. The mean +/- s.d. Kis for [11C]PUT for tumor and normal brain tissue were 0.78 +/- 0.045 and 0.024 +/- 0.007 ml cc-1 min-1, respectively (average of ratio, 3.11) whereas the ratio of GMR for tumor and normal brain tissue was 1.2 +/- 0.5. The mean Ki for four active, high grade astrocytomas was 0.098 +/- 0.030 in contrast to 0.027 +/- 0.008 ml cc-1 min-1 for two patients with low grade astrocytoma. Active high grade astrocytomas also showed marked CT contrast enhancement and regional glucose hypermetabolism. In one subject with brain metastases, both [11C]PUT and GMR correlated with a declining clinical picture in repeated studies over a 4-mo period. PET studies with [11C]PUT provide a better signal:noise ratio than GMR measurements, are useful for locating small glycolytically hypometabolic tumors and, when used in longitudinal studies in a single subject, appear to provide an index of degree of malignancy.

Neutrophil dysfunction in the rabbit model of spur cell anemia

In the rabbit model for spur cell anemia, animals fed a 5% cholesterol diet develop marked hypercholesterolemia and hemolytic spur cell anemia after several weeks on the diet. In vitro tests of granulocytes showed a 15% increase in cholesterol: phospholipid ratio, and decreased membrane fluidity measured with a fluorescent probe. Function tests revealed impairment of adherence, phagocytosis, and chemotaxis. Both a plasma factor and an intrinsic cellular defect appeared to contribute to the abnormal adherence. Bactericidal activity was normal. In vivo demargination in response to epinephrine was increased in animals on the diet, but exudation of granulocytes into sterile peritonitis fluid was diminished to 39.4% of control at 8 hours. Therefore, rabbits with experimental spur cell anemia have impaired in vitro and in vivo granulocyte function. The clinical significance of these findings for patients with spur cell anemia and less severe alcoholic liver disease is uncertain.

Turnover of brain monoamine oxidase measured in vivo by positron emission tomography using L-[11C]deprenyl

The distribution of carbon-11-labeled L-deprenyl, an irreversible inhibitor of monoamine oxidase type B (MAO-B), was determined in the baboon brain by positron emission tomography. The irreversible blood-to-brain transfer constant (influx constant, Ki) was measured using a complete metabolite-corrected arterial plasma concentration curve. This influx constant was used as a measure of functional enzyme activity for sequential determinations of MAO-B recovery following a single high dose of unlabeled L-deprenyl. The half-life for turnover of MAO-B was thus determined to be 30 days. Using appropriate irreversible inhibitors, this procedure should be generally useful for determining enzyme turnover rates in any organ in vivo and can be applied to some human studies as well.

Prosthetic joint infections secondary to rapidly growing Mycobacterium fortuitum

Infection is an uncommon but catastrophic complication of joint arthroplasty, usually requiring removal of the implant. In a 30-year-old woman a knee arthroplasty was infected with the rapidly growing mycobacterium Mycobacterium fortuitum. Review of other reports of arthroplasties infected with this organism illustrates the problem, diagnosis, and treatment. M. fortuitum is widely distributed in nature, and although usually of low pathogenicity, it can cause infection in conditions of reduced local tissue resistance, i.e. hypodermic abscesses, implant inflammations, and trauma. Only six cases of M. fortuitum prosthetic joint infection have been previously described. Persistent drainage characterized cases in which the prosthesis was left in place. Although antibiotic treatment temporarily suppressed the signs and symptoms of infection, cure required removal of the prosthesis, as in the present case. Diagnosis of M. fortuitum infection is difficult because acid-fast stains of the organisms are often negative. Routinely bacterial cultures are continued for less than about five days, a period not long enough for growth of M. fortuitum. M. fortuitum infections should be considered in draining prosthetic joints with negative bacterial cultures and in those that have had repeated glucocorticoid intraarticular injections.

Mapping human brain monoamine oxidase A and B with 11C-labeled suicide inactivators and PET

The regional distributions of monoamine oxidase (MAO) types A and B have been identified in human brain in vivo with intravenously injected 11C-labeled suicide enzyme inactivators, clorgyline and L-deprenyl, and positron emission tomography. The rapid brain uptake and retention of radioactivity for both 11C tracers indicated irreversible trapping. The anatomical distribution of 11C paralleled the distribution of MAO A and MAO B in human brain in autopsy material. The corpus striatum, thalamus, and brainstem contained high MAO activity. The magnitudes of uptake of both [11C]clorgyline and L-[11C]deprenyl were markedly reduced in one subject treated with the antidepressant MAO inhibitor phenelzine. A comparison of the brain uptake and retention of the 11C-labeled inactive (D-) and active (L-) enantiomers of deprenyl showed rapid clearance of the inactive enantiomer and retention of the active enantiomer within MAO B-rich brain structures, in agreement with the known stereoselectivity of MAO B for L-deprenyl. Prior treatment with unlabeled L-deprenyl prevented retention of L-[11C]deprenyl. Thus, suicide enzyme inactivators labeled with positron emitters can be used to quantitate the distribution and kinetic characteristics of MAO in human brain structures.

Fluorine-18-N-methylspiroperidol: radiolytic decomposition as a consequence of high specific activity and high dose levels

High specific activity [18F]N-methylspiroperidol(8-[4-(4-[18F]fluorophenyl)-4-oxobutyl]-3-me thyl l-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one, 5-10 mCi/ml, 4-8 Ci/mumol at EOB) in saline solution undergoes significant radiolytic decomposition resulting in a decrease in radiochemical purity of 10-25% during the first hour. The rate of decomposition is affected by the specific activity, total dose to and chemical composition of the solution. That radiolysis is responsible for the observed decomposition was verified by the observation that unlabeled N-methylspiroperidol is decomposed in the presence of [18F]fluoride.

Improved delineation of human dopamine receptors using [18F]-N-methylspiroperidol and PET

The brain uptake of [18F]-N-methylspiroperidol, a butyrophenone neuroleptic with high selectivity for the dopamine receptor, has been measured in three normal human volunteers using positron emission tomography for times up to 12 hr postinjection. These studies demonstrated two unique findings concerning the in vivo distribution of this neuroleptic: (a) it is tightly bound to dopamine D-2 receptors in the caudate-putamen brain regions, and (b) these regions are the only large brain structures which exhibit appreciable long-term retention. In addition, radioactivity clears rapidly from plasma, and the percentage of unchanged [18F]-N-methylspiroperidol in plasma declines rapidly. These results suggest that this compound binds irreversibly to dopamine D-2 receptors, and that there are few if any dopamine D-2 receptors in the human frontal cortex. These studies emphasize not only the importance of characterizing neurotransmitter receptors in living human brain using a ligand labeled with a positron emitting nuclide of sufficiently long half-life to allow monitoring of brain radioactivity distribution for several hours after the injection of radioligand, but also of accurately determining the amount of unchanged tracer in plasma for tracer kinetic modeling.

Ethanol inhibition of granulocyte adherence

Ethanol inhibits granulocyte adherence (GA) in whole blood. To determine the mechanism, GA was measured by the nylon fiber assay. In vitro addition of 300 mg/dl ethanol to whole blood caused a 28.1% decrease of GA compared with the control value (p less than 0.009) but did not affect GA of pure PMNs suspended in plasma or in HBSS. Similarly, GA measured in whole blood from intoxicated rabbits fell 48.8% from preintoxication values, but adherence of isolated postintoxication PMNs suspended in postintoxication plasma was not inhibited. Therefore, inhibition of GA by ethanol requires the presence of other cellular components of whole blood. To determine which cell(s) mediate the inhibition, PMNs were suspended with isolated blood components: platelet-rich and platelet-poor plasma, with and without the addition of mononuclear leukocytes and RBCs. Although the reconstitution of whole blood from its components allowed alcohol-induced inhibition of GA (decrease of 32.9%), none of the incomplete blood component mixtures demonstrated this effect. It was concluded that inhibition of GA by ethanol is mediated by an interaction between the components of whole blood.

Cefoxitin versus clindamycin and gentamicin in the treatment of postcesarean section infections

Cefoxitin, a cefamycin derivative, has demonstrated activity against a broad spectrum of aerobic and anaerobic bacterial pathogens. The efficacy and safety of cefoxitin were compared with that of the combination of clindamycin and gentamicin in the treatment of postcesarean section infection. Ninety-eight patients were evaluated. Cefoxitin cured 36 of 48 patients (75%); clindamycin/gentamicin cured 38 of 50 (76%) (P greater than .05). Febrile degree hours and length of hospital stay did not differ between the two study groups. No patient experienced abscess formation or septic pelvic thrombophlebitis. Both therapies were well tolerated. In the authors' experience, cefoxitin as a single agent was as effective in the treatment of postoperative pelvic infection as the combination of clindamycin and gentamicin.

Formation and secretion of fragments of parathormone. Identification of cleavage sites

Monolayer cultures of bovine parathyroid cells or fresh gland slices were incubated with radioactive amino acids in order to study the formation and metabolism of parathormone (PTH). PTH, secretory protein I, and COOH-terminal fragments of PTH were all released into media within 30 min, most strongly in the first hour after synthesis. Peptides in tissue, cells, and media were separated using reverse-phase high performance liquid chromatography. In eluates of media, six radioactive peaks were prominent. The first four and the sixth were immunoreactive in a COOH-terminal specific PTH radioimmunoassay, but only the sixth was reactive in an NH2-terminal specific assay. Under conditions where recovery of PTH(1-34) was quantitative, gel filtration of media was used to show that no NH2-terminal fragments of PTH were secreted. Sequence analyses of secreted COOH-terminal peptides indicated that the NH2 termini of the first three peaks corresponded to residues 43, 37, and 34 of PTH. The fourth peak contained a mixture of two peptides with NH2 termini at residues 24 and 28 of PTH. The fifth could not be identified; the sixth was PTH. Cleavages at the 23-24 bond of PTH occurred within minutes of the formation of PTH itself, and the other peptides were formed more slowly. Mandatory cleavage of PTH at the 23-24 peptide bond would destroy the biological activity of the hormone on kidney and bone, a situation consistent with the possibility that intracellular PTH metabolism participates in secretory regulation. The results showed that different peptides were generated in parathyroid cells than were previously shown to be produced by cathepsin B or D. The results suggest that the proteolytic pathway which results in the secretion of PTH fragments is nonlysosomal in nature.

Characteristics of bovine parathyroid cell organoids in culture

Adult bovine parathyroid glands were enzymatically dispersed and groups of 2 to 5 million cells were reassociated into multicellular aggregates (organoids) by rotation in roller tubes in serum-free medium. Fifty to seventy percent of the seeded cells were incorporated into each organoid at 3 d of culture, and in a typical experiment where DNA content was assayed before and after culture 49 +/- 3% of the original seeded DNA was present after 19 d of culture. No significant differences in DNA content were observed between experimental groups at any time of culture. The morphology of the cells in organoids was similar to that of cells in fresh tissue as determined by light and electron microscopy. The organoids secreted intact parathyroid hormone (PTH) and COOH-terminal hormone fragments which were similar to those released from monolayer cell cultures. Organoids maintained the ability to modulate PTH secretion in response to extracellular calcium for over 2 wk in culture. Each organoid was cultured separately and secreted PTH such that the mean standard deviation of secretion within groups on a per organoid basis was 16.3% of the mean. Using a perifusion system to study acute regulation over a 2-wk period of culture, PTH secretion was suppressed 58 +/- 4% by 2.5 mM compared to that at 0.25 mM calcium. To examine PTH secretion over a range of calcium concentrations, the perifusion system was used to apply 4-h linear gradients of decreasing calcium to fresh tissue slices and to organoids. The results indicated that the calcium (ionized) concentration at 50% secretory suppression (set-point) were 1.30 +/- 0.11 and 1.20 +/- 0.9 mM for the organoids and slices, respectively. Acute secretory control by calcium decreased after 14 d and was not detectable at 22 d of culture. The results demonstrated that the organoids maintained their differentiated function and tissuelike morphology for extended periods in vitro and therefore represent a suitable model system for studies on the long-term modulation of PTH secretion by vitamin D metabolites, ions, and other agents.

Structural analysis of parathormone fragments elaborated by cells cultured from a hyperplastic human parathyroid gland

Parathyroid cells were obtained by collagenase digestion of 2 g of human parathyroid tissue obtained at surgery from a patient with end stage renal failure and hypercalcemia. Cells were placed into monolayer culture in supplemented Waymouth's MB752/1. Secretion of parathyroid hormone (PTH) from monolayer cultures was inhibited for 3 weeks by 2.5 mM compared to 0.5 mM calcium. The inhibition was 50% on day 3 of culture, and decreased to 19% by day 21. When cultures were incubated with [3H]leucine, radioactive PTH and COOH-terminal PTH fragments were secreted. Sequence analyses were performed on material in radioactive and immunoreactive peaks following gel filtration and high performance liquid chromatography of media. The results indicated that cleavage of PTH or fragments thereof occurred at the 23-24, 27-28, and 33-34 peptide bonds. NH2-terminal fragments of PTH were not detected in media.

Imipenem pharmacokinetics and body fluid concentrations in patients receiving high-dose treatment for serious infections

Serum, urine, tissue, and body fluids were collected from 40 adult patients who were receiving imipenem/cilastatin treatment for serious infections. Thirty-two patients were given 1 g every 6 h (4 g/day), and eight received 500 mg (2 g/day). Mean peak concentrations in serum were 34.9 +/- 4.0 micrograms/ml for the 1-g dose and 26.6 +/- 2.5 micrograms/ml for the 500-mg dose. Trough levels were 3.1 and 1.0 micrograms/ml, respectively. No evidence of drug accumulation was found after comparing peaks measured early in the treatment with those measured late. Peak levels were only marginally increased when infusions were given over 30 versus 60 min. The mean serum half-life was 82.0 +/- 25.3 min, with a range of 50 to 138 min. The apparent volume of distribution was 0.35 +/- 0.13 liter/kg, and the mean total body clearance was 0.183 +/- 0.067 liter/kg per h. Creatinine clearance correlated directly with the plasma elimination rate and inversely with the serum half-life. Moreover, total body clearance fell as the age of the patient rose. The mean urinary recovery was 39.1 +/- 12.8% (range, 15.0 to 59.2%) and did not correlate with creatinine clearance until it was below 15 ml/min. Of 20 specimens of various gastrointestinal secretions, 13 had imipenem concentrations that were low, but above the MIC for most resident flora. Pus, sputum, and bone all had concentrations of the drug sufficient to inhibit the infecting organisms, and these levels reflected generally excellent clinical responses.

Formation of parathormone 8-34 by cathepsin-D digestion of parathormone and its efficacy as a hormone antagonist

It previously has been shown that digestion of bovine parathormone (bPTH) with cathepsin-D results in rapid cleavage of the hormone between Phe34 and Val35 yielding PTH(1-34) and PTH(35-84). Since bPTH also contains a Phe at residue 7 we have conducted additional studies to determine whether cleavage at this position could occur. We have found that following longer incubation periods of hormone and enzyme, 2 additional peptides are generated; PTH(8-34) and PTH(1-7). Time course studies demonstrated that these 2 fragments are formed from the (1-34) peptide generated through the initial cleavage at Phe34-Val35 of PTH. The identification of the bPTH(8-34) was accomplished through amino acid analysis and N-terminal sequencing. bPTH(8-34) behaved as a PTH antagonist in an in vitro mouse calvarial bone resorption assay. Although bPTH(8-34) did not affect the PTH-stimulated cAMP response when added simultaneously with PTH, preincubation of bone cells with this peptide caused desensitization of the PTH-stimulated cAMP response.

Modular automation in PET tracer manufacturing: application of an autosynthesizer to the production of 2-deoxy-2-[18F]fluoro-D-glucose

A compact autosynthesizer was developed and used successfully for the production of 2-deoxy-2-[18F]fluoro-D-glucose [18FDG] from gaseous acetyl hypo[18F]fluorite. The autosynthesizer performs a sequence of general purpose synthesis procedures named Synthesis Unit Operations (SUO's). Each SUO is controlled through execution of a digital control algorithm with a BASIC language subroutine. This automatic synthesis system is based on two industry standard microcomputer architectures, the IBM PC and STD Bus, and it becomes a component of an evolving distributed microprocessor network of task-dedicated subsystems suitable for automated manufacturing of several useful radiotracers. The yield of 18FDG product using the autosynthesizer and remote manually controlled purification procedures is approximately 20% EOB. Radiochemical purity of this product as measured by thin layer chromatography was 96-99%. Chemical purity of the product was measured to be approximately 96%. 2-Deoxy-2-fluoro-D-mannose impurity from this method was determined to be approximately 4%.

A direct comparison of the brain uptake and plasma clearance of N-[11C]methylspiroperidol and [18F]N-methylspiroperidol in baboon using PET

Serial PET studies of N-[11C]methylspiroperidol and [18F]N-methylspiroperidol were carried out in a single baboon with an intervening time period of 2 h between injection of the 11C and the 18F-labeled tracers. The kinetic patterns of uptake and egress of radioactivity in striatum and cerebellum as well as the magnitude of the uptake was very similar with the two tracers. In addition, no significant difference in clearance of total radioactivity from arterial plasma was detected. Analysis of plasma radioactivity for unchanged drug showed no significant differences in the amount of unchanged tracer at different times, although the profile of labeled metabolites was different. These results indicate that the only significant difference between the use of N-[11C]methylspiroperidol and [18F]N-methylspiroperidol for PET studies of brain dopamine receptors relate to the difference in physical half-life of the radionuclide rather than to differences in the profile of metabolically produced labeled compounds.

Structural characterization of adrenal chromogranin A and parathyroid secretory protein-I as homologs

We have isolated and purified adrenal chromogranin A (Ch A) for the purpose of making structural comparisons to parathyroid secretory protein-I (SP-I), because our earlier data indicated these two molecules may be the same protein. An improved purification step, using high-performance liquid chromatography (HPLC), has enabled us to demonstrate that both SP-I and Ch A consists of two species, one of approximately 72,000 Da and one of approximately 66,000 Da. The amino acid composition is the same for all four species. The difference in molecular mass is assumed to be due to carbohydrate content. Cyanogen bromide digestion of each of the four samples, followed by HPLC separation of the generated peptides, resulted in a chromatographic profile that was the same for each digest. Amino acid analysis of the eight peptide fragments obtained from each digest indicates that both species of Ch A and both species of SP-I yielded the same peptide mixtures following this cleavage reaction. One large (approximately 50,000 Da) CNBr peptide was obtained and seven smaller ones, one of which contains cysteine. The large fragment behaved similarly to the intact molecule in a radioimmunoassay. HPLC separation of tryptic digests of Ch A (72,000 Da) and SP-I (72,000 Da) also resulted in elution profiles that were very similar to each other. Amino acid analysis revealed 23 peptides common to each digest. Ch A contained four peptides ranging in size from 4 to 30 residues that were not observed in the SP-I digest. SP-I contained two peptides, each with about 30 residues, that were not found in the Ch A digest. Nothing unusual was noted in any of the uncommon peptides. Thus, both a chemical and an enzymatic digestion of these molecules followed by analysis of the peptides generated, indicates that SP-I and Ch A are nearly identical homologs.

Imipenem/cilastatin in the treatment of osteomyelitis

Thirty-four patients with osteomyelitis were treated for a mean of 32.5 days with 2 to 4 g per day of imipenem/cilastatin. Twenty-six infections involving the lower extremities were associated with accidents and prosthesis implantation, and 19 of 34 patients had more than one organism isolated. Gram-positive and gram-negative organisms were equally represented, but follow-up bone culture samples showed only 11 percent of gram-positive organisms persisted versus 23 percent of gram-negative organisms. Seventy-four percent of patients were cured or improved, and failures were related to resistant organisms and the inability to perform adequate surgical debridement. Adverse drug side effects included nausea, diarrhea, liver enzyme elevations, and neutropenia, but discontinuation of treatment was required in only three patients. Imipenem/cilastatin holds promise as monotherapy in complicated polymicrobial osteomyelitis.

Glucose metabolic rate kinetic model parameter determination in humans: the lumped constants and rate constants for [18F]fluorodeoxyglucose and [11C]deoxyglucose

The rate constants and lumped constants (LCs) for [18F]fluorodeoxyglucose ([18F]FDG) and [11C]deoxyglucose ([11C]DG) were determined in humans for the glucose metabolic rate kinetic model used to measure local cerebral glucose consumption. The mean values (+/- SE) of the LCs for [18F]FDG and [11C]DG are 0.52 +/- 0.028 (n = 9) and 0.56 +/- 0.043 (n = 6), respectively. The mean values (+/- SE) of the rate constants k*1, k*2, k*3, and k*4 for [18F]FDG for gray matter are 0.095 +/- 0.005, 0.125 +/- 0.002, 0.069 +/- 0.002, and 0.0055 +/- 0.0003, respectively. The corresponding values for white matter are 0.065 +/- 0.005, 0.126 +/- 0.003, 0.066 +/- 0.002, and 0.0054 +/- 0.0006, respectively. Using these values and previously published values for the rate constants for [11C]DG, the average whole-brain metabolic rates for glucose in normal subjects measured with [18F]FDG and [11C]DG are 5.66 +/- 0.37 (n = 6) and 4.99 +/- 0.23 (n = 6) mg/100 g/min, respectively. These values are not significantly different (t = 1.56, p greater than 0.10) and agree well with reported values in the literature determined by means of the Kety-Schmidt technique.

Safety and efficacy of high-dose treatment with imipenem-cilastatin in seriously ill patients

Imipenem-cilastatin was given in doses of 1 g intravenously every 6 h to 31 patients. Twenty-five patients, with 27 infections, were clinically evaluable and received 20 to 210 g of imipenem for a duration of 5 to 56 days (average 16.3 days). Infections included seven cases of osteomyelitis, seven of bacteremia, five of cellulitis, two of pneumonia, three of pelvic cellulitis, two of intraabdominal abscess, and one each of empyema, mediastinitis, and endometritis. Fifty-five percent of the infections were caused by gram-negative bacilli, 33% were due to gram-positive organisms, and 10% were caused by anaerobes. Twenty-two patients (81%) were cured, three improved, one relapsed, and one became superinfected with a resistant organism. In 5 of 11 cases with Pseudomonas aeruginosa, the imipenem MIC for organisms isolated by the end of treatment was higher than it was initially, raising concern that imipenem should not be used alone to treat Pseudomonas aeruginosa infections. Twenty-one patients had no adverse reaction; of the remaining 10 patients, 4 had nausea, 1 had urticaria, and 6 had mild abnormalities in hepatic function; three episodes of diarrhea included two with Clostridium difficile toxin in stool and one with pseudomembranous colitis, as determined by sigmoidoscopy. Levels of creatinine, hemoglobin, leukocytes, platelets, prothrombin, and urine components were unchanged. Imipenem-cilastatin is a clinically effective antibiotic with freedom from nephrotoxicity and hematological abnormalities in the large doses used in this study.

Strongyloides stercoralis hyperinfection masquerading as cerebral vasculitis

Strongyloides stercoralis hyperinfection is a unique opportunistic infection in which the nematode disseminates widely to cause a multisystem illness. We treated a patient with systemic lupus erythematosus in whom ileus and fever developed and who later lapsed into coma. A xenon Xe 133 cerebral blood flow study showed a global reduction in flow, compatible with CNS vasculitis. The patient's condition failed to improve with high-dose steroid therapy, but he recovered rapidly after Strongyloides larvae were found in stool and sputum and treatment with thiabendazole was begun. We believe that hyperinfection explained the patient's symptoms and should be considered as a cause of diminished cerebral perfusion and mentation in immunosuppressed patients.

Multiple-dose pharmacokinetics of imipenem-cilastatin

We characterized the pharmacokinetic profile of imipenem-cilastatin administered intravenously to six normal volunteers in a dose of 1,000 mg of each drug every 6 h for 40 doses. The plasma concentrations of imipenem and cilastatin 1 h after the end of a 30-min infusion were 18.7 (+/- 2.1) and 19.1 (+/- 4.6), 20.0 (+/- 3.2) and 17.8 (+/- 4.8), and 23.4 (+/- 2.3) and 19.1 (+/- 3.5) micrograms/ml in the 1st, 17th, and 37th dosing intervals, respectively. The central compartment volumes of distribution for imipenem and cilastatin were 0.16 (+/- 0.05) and 0.14 (+/- 0.03) liter/kg, respectively. Elimination half-lives were short: 0.93 (+/- 0.09) h for imipenem and 0.84 (+/- 0.11) h for cilastatin. Plasma clearances were 12.1 (+/- 0.06) liters/h per 1.73 m2 for imipenem and 12.4 (+/- 1.1) liters/h per 1.73 m2 for cilastatin. Renal clearance accounted for 54% of the plasma clearance of imipenem and 69% of the plasma clearance of cilastatin. The concentrations of imipenem in plasma and urine remained above the MICs of the vast majority of pathogens throughout the dosing interval.

Mapping brain neuroleptic receptors in the live baboon

An experimental strategy for external detection of specific neuroleptic receptors in living brain using positron emission transaxial tomography (PETT) and [11C]spiroperidol was applied to the mapping of brain neuroleptic receptors in the live baboon. A double injection of [11C]spiroperidol with an intervening time interval for carbon-11 decay and an intervening dose of (+)-butaclamol to block specific neuroleptic receptors produced two sets of PETT scans which were subtracted to produce a three-dimensional map of relative regional binding of neuroleptic receptors in the baboon brain. Sixty-five percent of the total radioactivity in the striatum was bound to neuroleptic receptors at 65 min after injection.

Effects of isoproterenol and cycloheximide on parathyroid secretion

Tissue slices or dispersed cells of bovine parathyroid gland were incubated with [3H]leucine to label the intracellular proteins and then tested for their secretory response to isoproterenol and cycloheximide at different calcium concentrations. Secretion of the newly synthesized as well as the older PTH and SP-I was stimulated by isoproterenol at all calcium levels tested, even when it was maximally enhanced by low calcium. Cycloheximide interfered with neither the secretory process nor the secretory response to different stimuli, but decreased the amount of PTH and SP-I secreted. We conclude that the inhibitor decreased the secretion by reducing the supply of PTH and SP-I. Calculations derived from the data reveal that, under most secretory conditions, newly synthesized PTH contributed a major portion of the total hormone secretion in bovine parathyroid cells.

Cleavage of parathyroid hormone to the 1-34 and 35-84 fragments by cathepsin D-like activity in bovine parathyroid gland extracts

We have obtained a crude enzyme preparation from bovine parathyroid gland homogenates which when incubated with PTH, cleaves the hormone into two major fragments. Isolation and chemical analysis has led to the identification of these peptides, the 1-34 fragment and the 35-84 fragment. Digestion of PTH was totally inhibited by the inclusion of the cathepsin D inhibitor, pepstatin, in the enzyme digest. A comparison of the digest obtained using the crude enzyme fraction vs. digestion of PTH by purified bovine cathepsin D led to the findings that the same peptide products were formed in each case. The natural 1-34 hormone fragment derived from the procedure has been determined to be fully biologically active in a bone resorption system.