Pharmacokinetics of hydralazine and its acid-labile hydrazone metabolites in relation to acetylator phenotype

The pharmacokinetics of hydralazine (H) and its acid-labile hydrazone metabolites were compared in rapid and slow acetylators. Following a 20-mg intravenous infusion, the elimination half-life (t_1/2) and the apparent volume of distribution of H did not differ between the two groups. Plasma clearance estimates approached hepatic blood flow. When a single 100-mg dose of H was given-orally, the area under the plasma concentration-time curve (AUC) and systemic availability () in slow acetylators were, on the average, twice as high as in the rapid acetylators, indicating a difference in the extent of first-pass metabolism of the drug. Furthermore, the observed in the slow individuals exceeded theoretical predictions. Hence saturation of first-pass metabolism of H is suggested, and a nonlinear relationship between AUC and oral dose of H was indeed observed in the three subjects studied with two doses. The half-life of decline of the acidlabile metabolites was similar to the t_1/2 of H. The AUCs for metabolites were 4–12 times larger than for the parentdrug. However, the ratio between the metabolite AUC and drug AUC did not differ irrespective ofroutes of administration or the acetylator status.This study was supported in part by Grant RR 828 from United States Public Health Service and a Research Starter grant from the Pharmaceutical Manufacturers Association Foundation, Inc. (D. D. S.).     

Factors affecting the performance of the styles cell transformation test

The effects of certain factors on the performance of the cell transformation test of Styles were examined by testing the demonstrability of transformation of cells of a subclone of BHK21 C13 in response to treatment with 4-nitroquinoline-1-oxide, N-methyl-N'-nitro-N-nitrosoguanidine, benzo[a]pyrene and 2-acetamidofluorene. An important requirement for success was supplementation of the soft agar medium with a serum which supported microcolony formation by a high proportion of the cells. Increasing the concentration of an unsuitable serum improved the results obtained; this suggests that the serum was inadequate rather than inhibitory. Alteration of the concentration of S-9 fraction used to activate the precarcinogens benzo[a]pyrene and 2-acetamidofluorene had little effect on the induction of transformation by either. A clearer distinction between the transformation frequencies for control and treated cells was usually obtained when 500 microm rather than 200 microm was the minimum diameter set for definition of transformation. It is suggested that, to assess the validity of results obtained with compounds which appear to induce transformation only at highly toxic levels, transformation frequencies for treated cells should be compared with those for control cells seeded at comparable densities.     

Pharmacokinetics and protein binding of cis-dichlorodiammine platinum (II) administered as a one hour or as a twenty hour infusion

Summary The pharmacokinetics of cis-dichlorodiamminoplatinum (II) (cisplatin) have been studied in seven patients, of whom four received the drug as a one hour infusion and three received it as a 20 h infusion. The patients receiving the drug over one hour exhibited biphasic clearance of total platinum with a rapid initial phase (8.7–22.5 min) and a prolonged second phase (30.5–106 h). Free (ultrafilterable) cisplatin was readily detectable in this group and was rapidly cleared (half-life about 22 min). The volume of distribution of the drug was 50.3–65.6 liters and it was 26.6–50% excreted in the urine in 48h. In the patients receiving the 20 h infusion, a more complex plasma elimination curve was seen, with the appearance of a secondary peak. Free drug was not detectable in these patients and they showed less urinary excretion (21.4–25.9% at 48 h) than the one hour group. Cisplatin was bound to several plasma proteins, including albumin, transferrin, and -globulin. The data indicate that cisplatin is retained in the body more extensively after a 20 h infusion than after a one hour infusion.     

Salient factors influencing resident advisor turnover: An exploratory study

Child care workers have been in the forefront of using their expertise in planning and staffing Community Living Arrangements (e.g., small group homes and apartments) for mentally retarded children and adults. Unfortunately, many child care workers who entered the field of Resident Advisorship (e.g., houseparents) with enthusiasm have voluntarily left after a short period of time. This study examines the results of several open-ended interviews with Resident Advisors working in apartment-based Community Living Arrangements for the mildly and moderately retarded. These interviews were conducted to identify those factors they perceived as sources of job satisfaction and dissatisfaction, contributing to employment longevity. Herzberg's formulations regarding the attractiveness of employment are presented as a logical way of interpreting the data.     

Endothelium-derived bradykinin is responsible for the increase in calcium produced by angiotensin-converting enzyme inhibitors in human endothelial cells

Summary The effects of angiotensin-converting enzyme (ACE) inhibitors on intracellular calcium concentration ([Ca²⁺]_i) were examined under resting conditions and after stimulation with bradykinin in cultured human umbilical vein endothelial cells. The ACE inhibitors ramiprilat and enalaprilat (0.3 M) enhanced the increase in [Ca²⁺]_i elicited by bradykinin (3 nM) and also caused an increase in resting [Ca²⁺]_i when given alone. This increase in resting [Ca²⁺]_i was long-lasting and accompanied by an increased formation of nitric oxide, as assessed by a N^G-nitro-l-arginine-sensitive cyclic GMP accumulation in the cells. Both increases in resting [Ca²⁺]_i and nitric oxide production by ACE inhibitors were inhibited by preincubation of the cells with the B₂-receptor antagonist Hoe 140. These data indicate that ACE inhibitors are able to unmask a release of bradykinin from cultured human endothelial cells. This endothelium-derived bradykinin can exert an autocrine function by stimulating endothelial B₂-receptors with a subsequent increase in [Ca²⁺]_i and nitric oxide formation. Send offprint requests to R. Busse at the above address     

Cross-resistance of drug-resistant murine P388 leukemias to toxol in vivo

Summary The antimicrotubule agent taxol (NSC 125973) has shown clinical antitumor activity against several classically refractory tumors. We developed a drug-resistance profile for taxol using ten drug-resistant P388 leukemias to identify potentially useful guides for patient selection for further clinical trials of taxol and possible non-cross-resistant drug combinations with taxol. Multidrug-resistant P388 leukemias exhibited either clear (leukemia resistant to amsacrine) or marginal cross-resistance (leukemias resistant to doxorubicin, actinomycin D, and mitoxantrone) to taxol. Leukemias resistant to vincristine (non-multidrug-resistant leukemia), camptothecin, melphalan, cisplatin, 1--d-arabinofuranosylcytosine, and methotrexate were not cross-resistant to taxol. The data suggest that (1) it may be important to exclude or to monitor with extra care patients who have previously been treated with amsacrine, doxorubicin, actinomycin D, or mitoxantrone and (2) a combination of one of the non-cross-resistant drugs and taxol might exhibit therapeutic synergism.This work was supported by contract NO1-CM-07315 with the Developmental Therapeutics Program, Division of Cancer Treatment, National Cancer Institute     

Thrombospondin as a mediator of cancer cell adhesion in metastasis

Summary Thrombospondin (TSP) is a 450 kDa adhesive glycoprotein. It is present in high concentrations in the platelet -granule and can readily be secreted following platelet activation where local concentrations can be increased by 3–4 orders of magnitude. TSP is also synthesized by a variety of other cells and is incorporated into their extracellular matrix. TSP is a homotrimer with a number of functional domains, at least four of which might serve as receptor recognizing regions. The amino-terminal heparin binding domain interacts with heparin, other glycosaminoglycans and glycolipids and likely recognizes specific cell surface proteoglycans. The central disulfide cross-linked region, 210 kDa non-reduced and 70 kDa reduced, contains a peptide motif CSVTCG which is apparently responsible for binding to glycoprotein IV (CD36) with high affinity. Immediately adjacent to the calcium binding region of TSP, which undergoes considerable molecular relaxation in the absence of calcium, is an RGDA sequence. TSP has been demonstrated to bind to integrins of the _v3 and _IIb3 class. The carboxy-terminal region of TSP also contains at least one binding epitope for a cell receptor. There are 2 well characterized genes for TSP and truncated forms of TSP have been detected which have inhibitory effects on angiogenesis. Finally, TSP can interact with fibrinogen and fibronectin, perhaps on cellular surfaces, which might serve as secondary receptor-like mechanisms for TSP binding and subsequent mediation of cell adhesion.     

Respiratory burst capacity of activated macrophages is resistant to depression by erythrocyte phagocytosis

The present study evaluated whether macrophage activation would reduce the depression in the capacity of macrophages to produce H₂O₂ following EIgG phagocytosis. Macrophage activation was accomplished by exposing inflammatory rat peritoneal macrophages to 10 units of IFN for 72 h. IFN treatment caused a four to fivefold increase in phorbol myristate acetate (PMA)-triggered H₂O₂ production, but Fc receptor phagocytic function was unaltered. IFN-activated macrophages were able to phagocytize a greater number of EIgG before a decrease in PMAtriggered H₂O₂ production was observed and the level of H₂O₂ production did not fall below that of untreated-inflammatory macrophages that had not received an EIgG phagocytic challenge. The depression in Fc receptor phagocytic function was unaltered with macrophage activation. These results indicate that activated macrophages are resistant to the depression of respiratory burst capacity caused by erythrocyte phagocytosis and suggests that IFN treatment may be effective in preventing the impairment of host defense against bacterial infection that is associated with erythrocyte phagocytosis.     

Scopolamine Effects on Visual Information Processing, Attention, and Event-Related Potential Map Latencies

We measured performance and event-related brain potential (ERP) map latencies in 12 subjects during four visual discrimination tasks to compare the timing of scopolamine effects on information processing and attention. "Topographic component recognition" found ERP map latencies at times of best fit with a component model map. This "common topography" criterion minimized topographic differences among conditions to facilitate latency interpretations. Scopolamine slowed N1 latency in all tasks, and P3 and reaction time in some tasks. The drug delayed responses to easy targets more than to hard targets. It also induced a disproportionate N1 delay for unilateral high spatial frequency gratings. Both effects reflect a scopolamine-induced impairment when processing targets that usually capture attention. Scopolamine also impaired accuracy for unilateral high spatial frequency gratings, and for gratings presented at probable locations, confirming and extending previous findings. Scopolamine-induced P1 and N1 delays showed that visual processing was affected. Several results were inconsistent with a serial stage model. We suggest that scopolamine both delays selected processes and impairs a processing mode based on automatic capture of attention, inducing more serial processing.