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Biomedical subjects

D A Noe

Publications and source records attributed to D A Noe.

At least 19 recordsLinked to original sources
PubMed2001

Multiple functional interactions between components of the Lsm2-Lsm8 complex, U6 snRNA, and the yeast La protein.

The U6 small nuclear ribonucleoprotein is a critical component of the eukaryotic spliceosome. The first protein that binds the U6 snRNA is the La protein, an abundant phosphoprotein that binds the 3' end of many nascent small RNAs. A complex of seven Sm-like proteins, Lsm2-Lsm8, also binds the 3' end of U6 snRNA. A mutation within the Sm motif of Lsm8p causes Saccharomyces cerevisiae cells to require the La protein Lhp1p to stabilize nascent U6 snRNA. Here we describe functional interactions between Lhp1p, the Lsm proteins, and U6 snRNA. LSM2 and LSM4, but not other LSM genes, act as allele-specific, low-copy suppressors of mutations in Lsm8p. Overexpression of LSM2 in the lsm8 mutant strain increases the levels of both Lsm8p and U6 snRNPs. In the presence of extra U6 snRNA genes, LSM8 becomes dispensable for growth, suggesting that the only essential function of LSM8 is in U6 RNA biogenesis or function. Furthermore, deletions of LSM5, LSM6, or LSM7 cause LHP1 to become required for growth. Our experiments are consistent with a model in which Lsm2p and Lsm4p contact Lsm8p in the Lsm2-Lsm8 ring and suggest that Lhp1p acts redundantly with the entire Lsm2-Lsm8 complex to stabilize nascent U6 snRNA.

Alleles↗
PubMed2001

Phosphorylation of the Saccharomyces cerevisiae La protein does not appear to be required for its functions in tRNA maturation and nascent RNA stabilization.

An abundant nuclear phosphoprotein, the La autoantigen, is the first protein to bind all newly synthesized RNA polymerase III transcripts. Binding by the La protein to the 3' ends of these RNAs stabilizes the nascent transcripts from exonucleolytic degradation. In the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, the La protein is required for the normal pathway of tRNA maturation. Experiments in which the human protein was expressed in S. pombe have suggested that phosphorylation of the La protein regulates tRNA maturation. To dissect the role of phosphorylation in La protein function, we used mass spectrometry to identify three sites of serine phosphorylation in the S. cerevisiae La protein Lhp1p. Mutant versions of Lhp1p, in which each of the serines was mutated to alanine, were expressed in yeast cells lacking Lhp1p. Using two-dimensional gel electrophoresis, we determined that we had identified and mutated all major sites of phosphorylation in Lhp1p. Lhp1p lacking all three phosphorylation sites was functional in several yeast strains that require Lhp1p for growth. Northern blotting revealed no effects of Lhp1p phosphorylation status on either pre-tRNA maturation or stabilization of nascent RNAs. Both wild-type and mutant Lhp1 proteins localized to both nucleoplasm and nucleoli, demonstrating that phosphorylation does not affect subcellular location. Thus, although La proteins from yeast to humans are phosphoproteins, phosphorylation does not appear to be required for any of the identified functions of the S. cerevisiae protein.

Amino Acid Sequence↗
PubMed1998

The partitioning of phosphoramide mustard and its aziridinium ions among alkylation and P-N bond hydrolysis reactions.

NMR (1H and 31P) and HPLC techniques were used to study the partitioning of phosphoramide mustard (PM) and its aziridinium ions among alkylation and P-N bond hydrolysis reactions as a function of the concentration and strength of added nucleophiles at 37 degrees C and pH 7.4. With water as the nucleophile, bisalkylation accounted for only 10-13% of the product distribution given by PM. The remainder of the products resulted from P-N bond hydrolysis reactions. With 50 mM thiosulfate or 55-110 mM glutathione (GSH), bisalkylation by a strong nucleophile increased to 55-76%. The rest of the PM was lost to either HOH alkylation or P-N bond hydrolysis reactions. Strong experimental and theoretical evidence was obtained to support the hypothesis that the P-N bond scission observed at neutral pH does not occur in the parent PM to produce nornitrogen mustard; rather it is an aziridinium ion derived from PM which undergoes P-N bond hydrolysis to give chloroethylaziridine. In every buffer studied (bis-Tris, lutidine, triethanolamine, and Tris), the decomposition of PM (with and without GSH) gave rise to 31P NMR signals which could not be attributed to products of HOH or GSH alkylation or P-N bond hydrolysis. The intensities of these unidentified signals were dependent on the concentration of buffer.

Alkylation↗
PubMed1997

Quadriceps femoris function during knee extension following total knee arthroplasty.

Electromyographic signals (EMG) from surface electrodes over the vastus medialis, rectus femoris and vastus lateralis were monitored during isometric knee extension for 10 TKA patients and 6 control subjects. No significant side-to-side differences in normalized EMG signals from any of the monitored muscles were found when the left and right legs of the control group were compared or when the operative and the non-operative legs of the patient group were compared. However, both the operative and the non-operative legs in the patient group differed significantly (p < 0.01) in normalized EMG from the control group. This study has shown that a muscle imbalance, possibly leading to patellar tracking problems, does not routinely exist following TKA through a medial parapatellar incision.

Adult↗
PubMed1997

Phase I and pharmacological study of CI-980, a novel synthetic antimicrotubule agent.

CI-980 (NSC 613862) is one of a novel class of 1,2-dihydropyrido[3, 4-b]pyrazines that inhibits tubulin polymerization, presumably by binding to the colchicine binding site of tubulin. In a Phase I and pharmacological study, 16 patients with advanced solid neoplasms were treated with CI-980 on a continuous 72-h infusion schedule at doses ranging from 3.0-5.4 mg/m2/day every 3 weeks. High rates of central nervous system (CNS) toxicity and neutropenia occurred in both minimally and heavily pretreated patients who were treated with CI-980 doses above 3.75 mg/m2/day, which is the maximum tolerated dose and the recommended dose for additional evaluations. CNS effects, characterized by neurocortical, mood, and cerebellar manifestations, were generally observed toward the end of the infusion and immediately posttreatment and usually resolved within 48 h after the completion of treatment. Toxicity was mild to modest at the 3.75 mg/m2/day dose level. Neither clinical nor pharmacological risk factors that may predispose patients to the development of CNS effects were evident. Although no objective antineoplastic activity was observed in this Phase I study, CI-980 steady-state plasma concentrations achieved at the recommended dose of 3.75 mg/m2/day (mean +/- SE, 5.74 +/- 0.54 nM) approached and exceeded concentrations that have been associated with significant activity in preclinical studies, indicating that additional disease-directed evaluations of CI-980 may be warranted.

Adult↗
PubMed1996

Pharmacokinetic, oral bioavailability, and safety study of fluorouracil in patients treated with 776C85, an inactivator of dihydropyrimidine dehydrogenase.

PURPOSE: To study the absolute bioavailability and pharmacokinetics of an oral solution of fluorouracil (5-FU) in patients treated with 776C85, an oral inactivator of dihydropyrimidine dehydrogenase (DPD), and to evaluate the feasibility of administering oral 5-FU and 776C85 on a multiple-daily dosing schedule. PATIENTS AND METHODS: Twelve patients with refractory solid tumors were enrolled onto this three-period study. In periods 1 and 2, patients were randomly assigned to treatment with 5-FU 10 mg/m2 on day 2 given by either the oral or intravenous (IV) route with oral 776C85 3.7 mg/m2/d on days 1 and 2. In period 3, patients received escalating doses of 5-FU (10 to 25 mg/ m2/d) orally for 5 days (days 2 to 6) with 776C85 3.7 mg/m2/d orally (days 1 to 7) every 4 weeks. Pharmaco-kinetic studies were performed in periods 1 and 2, and after the fifth oral dose of 5-FU in period 3. RESULTS: Twelve patients completed the bioavailability and pharmacokinetic studies. Following oral 5-FU 10 mg/m2, the bioavailability was 122% +/- 40% (mean +/- SD), the terminal half-life (t1/2 beta) was 4.5 +/- 1.6 hours, the apparent volume of distribution (V beta) was 21.4 +/- 5.9 L/ m2, and the systemic clearance (Clsys) was 57.6 +/- 16.4 mL/min/m2. A correlation was observed between oral 5-FU systemic clearance and calculated creatinine clearance (r = .74; P = .009). Multiple-daily dosing did not appear to affect the pharmacokinetics of oral 5-FU. Neutropenia was the principal toxicity of oral 5-FU and 776C85, precluding escalation of oral 5-FU to doses greater than 25 mg/m2/d for 5 days every 4 weeks with 776C85. CONCLUSION: The oral DPD inactivator 776C85 enables oral administration of 5-FU and may alter conventional 5-FU administration practices.

Absorption↗
PubMed1996

Phase I and pharmacologic study of sequences of paclitaxel and cyclophosphamide supported by granulocyte colony-stimulating factor in women with previously treated metastatic breast cancer.

PURPOSE: Pacltaxel is active in metastatic breast cancer, but limited information is available on combinations of this agent with other cytotoxic agents. Study aims were to determine the maximum-tolerated doses (MTDs) of paclitaxel (24-hour infusion) and cyclophosphamide (1-hour infusion) administered every 21 days with granulocyte colony-stimulating factor (G-CSF, filgrastim) to determine the effect of drug sequence on toxicity and pharmacology and to evaluate the activity of this combination in women with anthracycline-resistant disease. PATIENTS AND METHODS: Thirty-seven women with metastatic breast cancer were treated. Starting doses were paclitaxel 135 mg/m2 and cyclophosphamide 750 mg/m2, with filgrastim 5 microG/kg/d subcutaneously beginning 24 hours after chemotherapy. Four patients were treated at each dose level. The sequence of drug administration was alternated between sequential patients, and with subsequent courses of therapy in each patient, to enable evaluation of effects of drug sequence on toxicity and pharmacology. Patients were treated every 21 days and disease status was reevaluated every two courses. RESULTS: Paclitaxel 200 mg/m2 and cyclophosphamide 1,250 mg/m2 is the MTD for this combination on this schedule. The hematopoietic toxicity of therapy was sequence-dependent. Paired analysis of toxicity data indicated more severe toxicity in courses in which paclitaxel was administered first. Sequence-dependent pharmacologic effects did not account for this phenomenon. Responses were noted in 29% of patients with anthracycline-resistant disease. CONCLUSION: Paclitaxel 200 mg/m2 and cyclophosphamide 1,250 mg/m2 with filgrastim administered every 21 days are the doses recommended for further study.

Adult↗
PubMed1995

Nonlinear pharmacokinetics of cyclophosphamide in patients with metastatic breast cancer receiving high-dose chemotherapy followed by autologous bone marrow transplantation.

The pharmacokinetics of cyclophosphamide has been evaluated in 15 patients with metastatic breast cancer undergoing high-dose chemotherapy with alkylating agents followed by autologous bone marrow transplantation. Each patient received two courses of chemotherapy: 4 g/m2 of cyclophosphamide by 90-min infusion prior to peripheral blood progenitor cell collection (the first course) and 6 g/m2 of cyclophosphamide with 800 mg/m2 of thiotepa by 96-h constant infusion before marrow and stem cell reinjection (the second course). In the first course, plasma cyclophosphamide concentration-time data of 9 of 15 patients were fit by a one-compartment model with Michaelis-Menten saturable elimination in parallel with first-order renal elimination. The mean (SD) Vmax and Km values were 1.47 (0.89) microM/min and 575 (347) microM, respectively. The first course data of the remaining six patients were fit using first-order elimination only. In the second drug course, plasma cyclophosphamide disposition curves of 13 of 15 patients demonstrated a decline in concentration following attainment of an initial steady state. The plasma cyclophosphamide disposition data of these patients were fit by a one-compartment pharmacokinetic model, in which the decline of plasma cyclophosphamide concentration after reaching the initial steady state was modeled as being due to an increase in the clearance rate of cyclophosphamide. The mean (SD) initial and final clearance rates were 51 (16) ml/min and 106 (48) ml/min, respectively. Michaelis-Menten elimination was not apparent in the second course because the plasma concentration of cyclophosphamide was much lower. The mean renal clearance rate was 17 ml/min in the first course and 16 ml/min in the second course. Urinary excretion of cyclophosphamide accounted for 17% and 23% of the total dose administered in the first and the second course, respectively. No change in cyclophosphamide clearance rate was apparent in a patient who was taking phenytoin, but a change was present in a patient who was taking phenobarbital. A drug interaction between cyclophosphamide and thiotepa may explain the smaller initial clearance rate for cyclophosphamide during the second drug course.

Adult↗
PubMed1995

Phase I and pharmacologic studies of pyrazoloacridine, a novel DNA intercalating agent, on single-dosing and multiple-dosing schedules.

PURPOSE: To determine the maximum-tolerated doses (MTDs), principal toxicities, and pharmacologic behavior of pyrazoloacridine (PZA), a novel DNA intercalator with a unique mechanism of action, on single- and multiple-dosing schedules. PATIENTS AND METHODS: PZA was administered on a single-dosing schedule as a 1- to 3-hour infusion and on a multiple-dosing schedule as a 1-hour infusion daily for 5 days to cancer patients at doses ranging from 400 to 935 mg/m2 and 40 to 180 mg/m2/d every 3 weeks, respectively. RESULTS: On the single-dosing 1-hour schedule, CNS toxicity, characterized by neuropsychiatric and neuromotor effects, prompted prolongation of the infusion duration to 3 hours and led to a study of PZA on a multiple-dosing schedule. Both measures resulted in lower incidence of CNS toxicity. Neutropenia was the principal toxicity and precluded dose escalation to levels greater than 750 mg/m2 on the single-dosing (3-hour) schedule and 150 mg/m2/d x 5 (total dose, 750 mg/m2) on the multiple-dosing schedule. Thrombocytopenia, anemia, and nonhematologic effects occurred less frequently. Responses were observed in several patients with platinum- and taxane-refractory ovarian carcinoma; antitumor activity was also noted in patients with cervical and colorectal carcinomas. Significant intraindividual variability characterized by the presence of multiple drug peaks and troughs was observed in the pharmacologic studies. The maximal PZA concentrations achieved in both studies exceeded drug concentrations associated with significant cytotoxicity in preclinical studies and correlated with the occurrence of CNS toxicity. CONCLUSION: Neutropenia is the dose-limiting toxicity on both schedules and 750 mg/m2 and 150 mg/m2/d are the recommended starting doses of PZA on single- and multiple-dosing schedules, respectively, for minimally pretreated patients in phase II studies; slightly lower doses are recommended for more heavily pretreated subjects. The favorable toxicity profile of PZA and its antitumor activity in several refractory tumors warrant broad phase II evaluations of this agent.

Acridines↗
PubMed1994

Pharmacokinetic, bioavailability, and feasibility study of oral vinorelbine in patients with solid tumors.

PURPOSE: The feasibility of administering vinorelbine (Navelbine, Burroughs Wellcome Co, Research Triangle Park, NC), a semisynthetic vinca alkaloid with broad activity, as a liquid-filled gelatin capsule was evaluated in a bioavailability (F) and pharmacokinetic study. PATIENTS AND METHODS: Each of 17 cancer patients had pharmacokinetic studies performed after receiving vinorelbine 30 mg/m2 intravenously (IV), which is the maximum-tolerated dose (MTD) for weekly IV administration, and twice after receiving the oral formulation at a nominal dose of 100 mg/m2. Subsequently, these patients and 10 other subjects received the oral formulation at a dose of 100 mg/m2/wk to evaluate the feasibility of chronic oral administration. RESULTS: Plasma drug disposition was well described by a triphasic model. Mean central volume of distribution and steady-state volume of distribution (Vss) were large (0.66 +/- 0.46 L/kg and 20.02 +/- 8.55 L/kg, respectively); the mean harmonic terminal half-life (t1/2) was long (18 hours); and the high mean clearance (CI) rate (0.80 +/- 0.68 L/h/kg) approached hepatic blood flow. F was low (0.27 +/- 12), and absorption was rapid (mean time of maximum plasma concentration [Tmax], 0.91 +/- 0.22 hours). Absorption parameters after the first and second oral doses were similar, with mean F values of 0.27 +/- 0.14 and 0.25 +/- 0.11, respectively. Coefficients of variability (CVs) for F, maximum plasma concentration (Cmax), and Tmax were 32%, 42%, and 78%, respectively, indicating moderate intraindividual variability. The pharmacologic profile of this oral formulation indicates that there is a large first-pass effect. Neutropenia was the principal toxicity of oral vinorelbine. Grade 3 or 4 neutropenia occurred in 63% of patients, but only 11% developed neutropenia and infection. Nausea, vomiting, and diarrhea were also common with oral administration, but these effects were rarely severe and could be ameliorated by using a divided-dose schedule and/or prophylactic antiemetic and antidiarrheal agents. The mean nominal oral dose was 82 mg/m2, and the mean percentage of intended dose that was received was 92%. Although dose escalations were permitted for negligible toxicity, doses were not escalated to greater than 100 mg/m2/wk in any patient. Vinorelbine given as a liquid-filled gelatin capsule at 100 mg/m2 provided equivalent pharmacologic exposure as 30 mg/m2 IV. CONCLUSION: The oral administration of vinorelbine, specifically as a liquid-filled, soft gelatin capsule, is a feasible route of administration. Weekly oral dosing at 100 mg/m2 induces a consistent degree of myelosuppression, but the high frequency of grade 3 or 4 neutropenia, albeit brief and uncomplicated, warrants the recommendation of a slightly lower starting dose, ie, 80 mg/m2/d, for subsequent phase II evaluations, especially in heavily pretreated patients.

Absorption↗
PubMed1993

Phase I and pharmacological study of the pulmonary cytotoxin 4-ipomeanol on a single dose schedule in lung cancer patients: hepatotoxicity is dose limiting in humans.

4-Ipomeanol (IPO), a naturally occurring pulmonary toxin, is the first cytotoxic agent to undergo clinical development based on a biochemical-biological rationale as an antineoplastic agent targeted specifically against lung cancer. This rationale is based on preclinical observations that metabolic activation and intracellular binding of IPO, as well as cytotoxicity, occurred selectively in tissues and cancers derived from tissues that are rich in specific P450 mixed function oxidase enzymes. Although tissues capable of activating IPO to cytotoxic intermediates in vitro include liver, lung, and kidney, IPO has been demonstrated in rodents and dogs to undergo in situ activation, bind covalently, and induce cytotoxicity preferentially in lung tissue at doses not similarly affecting liver or kidneys. Although the drug was devoid of antitumor activity in the conventional murine preclinical screening models, cytotoxic activity was observed in human lung cancers in vitro and in human lung cancer xenografts in vivo, adding to the rationale for clinical development. Somewhat unexpectantly, hepatocellular toxicity was the dose-limiting principal toxicity of IPO administered as a 30-min infusion every 3 weeks to patients with lung cancer. In this study, 55 patients received 254 courses at doses almost spanning 3 orders of magnitude, 6.5 to 1612 mg/m2. Transient and isolated elevations in hepatocellular enzymes, predominantly alanine aminotransferase, occurred in the majority of courses of IPO at 1032 mg/m2, which is the recommended IPO dose for subsequent phase II trials. At higher doses, hepatocellular toxicity was more severe and was often associated with right upper quadrant pain and severe malaise. Toxic effects were also noted in other tissues capable of activating IPO, including possible nephrotoxicity in a patient treated with one course of IPO at 154 mg/m2 and severe, reversible pulmonary toxicity in another patient who received nine courses of IPO at doses ranging from 202 to 826 mg/m2. Although individual plasma drug disposition curves were well described by a two-compartment first order elimination model, The relationship between IPO dose and area under the disposition curve was curvilinear, suggesting saturable elimination kinetics. At the maximum tolerated dose, the mean half-lives (lambda 1 and lambda 2) were 6.7 and 114.5 min, respectively. Renal excretion of parent compound accounted for less than 2% of the administered dose of IPO. An unidentified metabolite was detected in the plasma of patients treated at higher doses. No objective antitumor responses were observed; however, stable disease persisted for at least eight courses in 27% of patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1993

Sequence-dependent cytotoxic effects due to combinations of cisplatin and the antimicrotubule agents taxol and vincristine.

The antineoplastic activity that taxol has demonstrated in advanced ovarian cancer and other neoplasms in which the platinum analogues are among the most active agents has been the impetus for the development of taxol/platinum combination regimens. Since both classes of agents are known to induce cell-cycle-dependent effects and to delay cell-cycle traverse in specific phases of the cycle, an evaluation of drug sequence dependence was incorporated into initial clinical studies of the drug combination. To complement clinical studies, sequence-dependent interactions were assessed in vitro using L1210 leukemia. Cytotoxicity resulting from the combination of taxol and cisplatin was significantly increased over that achieved with cisplatin alone only when cisplatin was administered after taxol. This sequence was significantly superior to both the reverse sequence and to simultaneous drug treatment. Results achieved with sequence iterations of vincristine and cisplatin were nearly identical. In addition, alkaline-elution studies, using the optimal sequence of cisplatin and either taxol or vincristine, demonstrated that these antimicrotubule agents do not increase the formation of cisplatin-induced DNA interstrand and DNA-protein crosslinking over that produced by cisplatin alone. Although the mechanisms for the sequence-dependent cytotoxic interactions between cisplatin and the antimicrotubule agents have not been determined, it is likely that antagonistic interactions occur with the suboptimal sequences, probably because of cell-cycle-dependent phenomena.

Animals↗
PubMed1993

Role of the calcaneal heel pad and polymeric shock absorbers in attenuation of heel strike impact.

The capacity of the calcaneal heel pad, with and without augmentation by a polymeric shock absorbing material (Sorbothane 0050), to attenuate heel strike impulses has been studied using five fresh human cadaveric lower leg specimens. The specimens, instrumented with an accelerometer, were suspended and impacted with a hammer; a steel rod was similarly suspended and impacted. The calcaneal heel pad attenuated the peak accelerations by 80%. Attenuations of up to 93% were achieved by the shock absorbing material when tested against the steel rod; however, when tested in series with the calcaneal heel pad, the reduction in peak acceleration due to the shock absorbing material dropped to 18%. Any evaluation of the effectiveness of shock absorbing shoe materials must take into account their mechanical interaction with the body.

Biomechanical Phenomena↗
PubMed1992

Isokinetic lifting strength and occupational injury. A prospective study.

One hundred seventy-one nurses had their back strength evaluated on an isokinetic lifting device and filled out an epidemiologic questionnaire. They were then followed prospectively for 2 years to determine the incidence of job-related low-back injuries. The data were analyzed to determine if the injury incidence correlated with any of the strength or epidemiologic variables collected during the original evaluation. Average peak force measured during the isokinetic lift was 63.8 kg + 13.6 kg at a lift speed of 30.5 cm/sec and 59.1 kg + 14.9 kg at a lift speed of 45.7 cm/sec. Sixteen nurses reported an occurrence of job-related low-back pain or injury during the 2-year prospective period. Discriminate statistical techniques showed that none of the strength or epidemiologic variables correlated with the incidence of pain or injury or explained significant amounts of variance when the variables were regressed on strength or work calculated from the lift force/lift height data. It was concluded that in this high risk population, in which loads are heavy and lifting postures are variable, the use of low-back strength or prior history of pain or injury are poor predictors as to subsequent low-back pain or injury.

Adult↗
PubMed1992

Myoelectric activity and sequencing of selected trunk muscles during isokinetic lifting.

Trained weight lifters lift heavy loads without a concomitant degree of acute low-back injuries. To study the process by which large loads are lifted with minimal injury, integrated electromyographic signals were recorded from four large muscle groups: gluteus maximus, quadriceps, latissimus dorsi, and erector spinae in 4 weight lifters and 11 asymptomatic control subjects. These signals were recorded during a floor-to-knuckle-height isokinetic lift (dead lift) at 30.5 and 45.7 cm/sec. The signals were normalized for the height of the lift and the maximal isokinetic integrated electromyographic activity. The weight lifters achieved maximal force at 50% of maximal lift height, whereas the control subjects achieved it at 67%. Although not statistically significant, the weight lifters used the gluteus maximus more during the early stages of the lift, perhaps contributing to earlier development of force. This process would stabilize the pelvis and permit the erector spinae to extend the trunk more efficiently. The weight lifter then completed the lift with prolonged and increasing activity in the quadriceps. This technique may minimize the required force in the erector spinae and the forces on the low-back structures. Clinical implications include more effective strength training of lifting muscle groups other than spinal extensors and the teaching of lifting strategies employed by weight lifters in low-back rehabilitation and work-hardening programs.

Back↗
PubMed1991

A pharmacokinetic-pharmacodynamic model of heart rate during cocaine administration in humans.

We developed a pharmacokinetic-pharmacodynamic model of the heart rate response to cocaine consisting of the sum of the baseline heart rate, a chronotropic drug effect, and a conditioned heart rate response. The conditioned response was modeled as having a monoexponential decline. Cocaine's chronotropic effect was modeled as obeying a maximum (Emax) drug-effect relationship without tachyphylaxis. The model was tested by fitting the kinetic and heart rate data from an earlier study. The data from five subjects in that study were well fit by the model: mean Emax, 64 beats/min, and mean drug concentration producing 50% of Emax, 838 ng cocaine/ml. The data from the other three subjects in that study were fit well, employing a linear rather than an Emax drug effect relationship: mean effect coefficient, 0.035 beats/min/ng cocaine/ml. The findings emphasize the importance of conditioning in the responses to psychoactive drugs.

Cocaine↗