Inhibition and metabolite complexation of rat hepatic microsomal cytochrome P450 by tricyclic antidepressants.

Administration of imipramine (IMIP) and other tricyclic antidepressants to humans and experimental animals has been associated with inhibition of hepatic cytochrome P450 (P450)-mediated drug oxidation. This study investigated the capacity of several structurally related tricyclic antidepressants to inhibit microsomal P450 activity in vitro. It was found that IMIP, desipramine (DES), amitriptyline (AMIT) and nortriptyline (NOR) were poor inhibitors of P450 activity unless they were preincubated with microsomes and NADPH prior to transfer to flasks containing substrate. Thus, subsequent experiments characterized the time-dependent intensification of inhibition produced by the drugs. Preincubation of the N-methylaminoalkyl agents DES and NOR (200 microM) with NADPH-supplemented microsomes for 30 min led to an approximate 30% decrease in spectrally apparent P450 content; the N,N-dimethylaminoalkyl drugs IMIP and AMIT did not significantly decrease apparent P450 content. Analysis of optical difference spectra of microsomes during NADPH-mediated metabolism of these drugs revealed a prominent increase in absorbance at 454 nm with DES and NOR but not IMIP or AMIT. Monospecific antibodies to the male-specific P450 2C11 and, to a lesser extent, P450 3A2 were effective in preventing the formation of the DES metabolite 454 nm-Soret peak. In addition, the 454 nm absorbance was not produced by the incubation of DES with NADPH-fortified hepatic microsomes from adult female or immature male rats. Studies with the steroid substrate testosterone, which undergoes P450-specific positional hydroxylation, indicated that P450 2C11-mediated 2 alpha- and 16 alpha-hydroxylation were most susceptible to the time-dependent intensification of inhibition produced by DES (8.5 and 7.0 min preincubation required for loss of 50% activity, respectively) and NOR (4.0 and 4.0 min for loss of 50% of both activities). The 6 beta- (P450 3A2) and 7 alpha-hydroxylase (P450 2A1) pathways were somewhat less susceptible to inhibition than 2 alpha- and 16 alpha-hydroxylation. These findings suggest that DES and NOR form a metabolite intermediate (MI)-complex, characterized by a Soret region absorbance maximum near 454 nm in the optical difference spectrum, with microsomal P450 in male rat liver in vitro. Studies with the steroid substrate testosterone as well as immunoinhibition experiments are consistent with the proposition that this MI complex forms principally with the male-specific enzymes P450 2C11 and 3A2. Although a human orthologue of P450 2C11 has not yet been identified, P450s of the 3A subfamily are quantitatively important enzymes in human liver. MI complexation of such enzymes could be a feasible underlying mechanism for certain clinically important drug interactions involving tricyclic antidepressants.     

Biological and physical properties of autogenous vascularized fibular grafts in dogs

The biological and biomechanical properties of normal fibulae, fibulae that had had a sham operation, and both vascularized and non-vascularized autogenous grafts were studied in dogs at three months after the operation. The study was designed to quantify and correlate changes in these properties in orthotopic, stably fixed, weight-bearing grafts and to provide a baseline for additional studies of allografts. The grafts were eight centimeters long and internally fixed. The mechanical properties of the grafts were studied by torsional testing. Metabolic turnover of the grafts was evaluated by preoperative labeling of the dogs with 3H-tetracycline for resorption of bone mineral and with 3H-proline for turnover of collagen. Cortical bone area and porosity were measured. Postoperative formation of bone was evaluated by sequential labeling with fluorochrome. The vascularized grafts resembled the fibulae that had had a sham operation and those that had not had an operation with regard to the total number of osteons and the remodeling process, as measured both morphometrically and metabolically. The vascularized grafts were stronger and stiffer than the non-vascularized grafts and were not different from the bones that had had a sham operation. In contrast, the non-vascularized grafts were smaller, weaker, less stiff, and more porotic, had fewer osteons, and demonstrated increased turnover and resorption compared with the vascularized grafts, the bones that had had a sham operation, and the bones that had not been operated on.     

The Transfer of Polystyrene Microspheres from the Gastrointestinal Tract to the Circulation after Oral Administration in the Rat

Factors relating to the transfer of latex microspheres of 0·87 μm mean diameter from the gastrointestinal tract (GIT) to the circulation have been investigated. The rapidity of appearance and the number of particles increased when the volume of water used as a suspending vehicle was increased. This was probably due to barrier cell integrity being compromised so that the movement of particles across the enterocytes would be enhanced. Particles were swept into these channels by the waterflow. The tonicity of the fluid was important as isotonic and hypertonic saline were not as affective as water in transferring particles. Particles were transferred from GIT segments adjacent to the stomach which may in part explain the rapid appearance of particles in the circulation. Particle uptake was blocked by cytochalasin B which suggests an active component may also be involved.     

Juvenile Rheumatoid Arthritis: Benefits from Massage Theraphy

Studied children with mild to moderate juvenile rheumatoid arthritiswho were massaged by their parents 15 minutes a day for 30 days(and a control group engaged in relaxation therapy). The children'sanxiety and stress hormone (cortisol) levels were immediatelydecreased by the massage, and over the 30-day period their paindecreased on self-reports, parent reports, and their physician'sassessment of pain (both the incidence and severity) and pain-limitingactivities     

Evidence for opioid modulation and generation of prostaglandins in sulphur dioxide (SO)2-induced bronchoconstriction.

BACKGROUND: Inhalation of sulphur dioxide (SO2) provokes bronchoconstriction in asthmatic subjects. Cholinergic mechanisms contribute, but other mechanisms remain undefined. The effect of morphine, an opioid agonist, on the cholinergic component of SO2-induced bronchoconstriction was investigated, and the effect of indomethacin, a cyclooxygenase inhibitor, on SO2-induced bronchoconstriction and tachyphylaxis was studied. METHODS: In the first study 16 asthmatic subjects inhaled either ipratropium bromide or placebo 60 minutes before an SO2 challenge on days 1 and 2. On day 3 an SO2 challenge was performed immediately after intravenous morphine. In the second study 15 asthmatic subjects took either placebo or indomethacin for three days before each study day when two SO2 challenges were performed 30 minutes apart. The response was measured as the cumulative dose causing a 35% fall in specific airways conductance (sGaw; PDsGaw35). RESULTS: Ipratropium bromide significantly inhibited SO2 responsiveness, reducing PDsGaw35 by 0.89 (95% CI 0.46 to 1.31) doubling doses. This effect persisted after correction for bronchodilatation induced by ipratropium bromide. The effect of ipratropium bromide and morphine on SO2 responsiveness also correlated (r2 = 0.71). In the second study SO2 tachyphylaxis developed with PDsGaw35 on repeated testing, being reduced by 0.62 (95% CI 0.17 to 1.07) doubling doses. Indomethacin attenuated baseline SO2 responsiveness, increasing PDsGaw35 by 0.5 (95% CI 0.06 to 0.93) doubling doses. CONCLUSIONS: These results suggest that opioids modulate the cholinergic component of SO2 responsiveness and that cyclooxygenase products contribute to the immediate response to SO2.