Serotonin-induced increase in cAMP in ganglia isolated from the myenteric plexus of the guinea pig small intestine: Mediation by a novel 5-HT receptor

Serotonin (5-HT) is a mediator (through 5-HT_1P receptors) of slow EPSPs in myenteric ganglia of the small intestine. The effect of 5-HT can be mimicked by elevating cAMP; therefore, we tested the hypothesis that the slow EPSP-like response to 5-HT is cAMP-mediated. Guinea pig gut was enzymatically dissociated; myenteric ganglia remained intact and were collected by filtration. Neurons in the isolated ganglia retained their ability to manifest the slow EPSP-like response to 5-HT. Exposure to 5-HT raised the ganglionic level of cAMP (ED₅₀ 0.3 μM). This effect was not antagonized by the 5-HT_1P antagonist, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide (100.0 μM), or mimicked by the 5-HT_1P agonist, 5-hydroxyindalpine (10.0 μM). Increases in cAMP were also evoked by the 5-HT₁ agonist, 5-carboxyamidotryptamine (10.0 μM), the 5-HT₂ agonist, (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI; 1.0–10.0 μM), and by the 5-HT₄ agonists, renzapride (1.0–10.0 μM) and 5-methoxytryptamine (1.0–10.0 μM); however, neither the 5-HT₁/5-HT₂ antagonists, spiperone, methysergide, and methiothepin, nor the 5-HT₄ antagonist, tropisetron (ICS 205–930; 10.0 μM), were able to inhibit the rise in cAMP evoked by these compounds or by 5-HT (0.1–10.0 μM). The 5-HT-evoked elevation of cAMP was antagonized by ketanserin (10.0 μM), which also blocked the effects of 5-methoxytryptamine and DOI, but not those of renzapride. The effective concentration of DOI, however, was higher than that needed for activation of 5-HT₂ receptors, and Northern analysis using a cDNA probe encoding the rat 5-HT₂ receptor failed to reveal the presence of 5-HT₂ mRNA in myenteric ganglia, although it hybridizes with mRNA of the right size in the guinea pig brain. Compounds that failed to change levels of cAMP or to antagonize the action of 5-HT included 8-hydroxy-di-n-propylamino tetralin, R58639, R88226, and sumatriptan. It is concluded that the receptor responsible for the 5-HT-induced rise in cAMP in ganglia isolated from the guinea pig myenteric plexus is not a known subtype of 5-HT receptor. Since the pharmacology of this novel receptor is different from that of the slow EPSP-like response to 5-HT, the receptor probably does not mediate the slow EPSP. © 1993 Wiley-Liss, Inc.     

Insights into Mechanisms of Cisplatin Resistance and Potential for Its Clinical Reversal

Cisplatin in combination with other cytotoxic agents is the backbone for a potential cure of testicular germ cell neoplasms and is a critical factor in the substantial activity observed in the treatment of small cell lung cancer, bladder cancer, and ovarian germ cell tumors. Resistance to cisplatin at the onset of treatment or at relapse limits its curative potential, however. Laboratory studies using both cells selected for cisplatin resistance by exposure to sublethal concentrations and biopsy specimens from patients' tumors provide insights for the potential mechanisms of resistance. The mechanisms identified in vitro include a complex and wide array of related and unrelated pathways such as alterations in cellular drug transport, enhanced DNA repair dependent and independent of signal transduction pathways, and enhanced intracellular detoxification such as glutathione and metallothionein systems. Studies of these mechanisms have identified a number of agents with known potential for administration to humans and that reverse cisplatin resistance in vitro; for example, reversal of cellular accumulation defects by dipyridamole; inhibition of DNA repair by hydroxyurea, pentoxifylline, and novobiocin; inhibition of the glutathione system by ethacrynic acid and buthionine sulfoximine; and inhibition of signal transduction pathways by cyclosporine, tamoxifen, and calcium channel-blocking agents. Current phase I clinical trials are focusing on the most effective doses and schedules to administer these agents in combination with cisplatin. Initial uncontrolled trials in limited numbers of patients suggest that the addition of modulators of cisplatin has the potential to reverse resistance in patients previously failing therapy. Another promising avenue for circumventing cisplatin resistance is the development of noncross-resistant platinum analogs.     

The Perceived Influence of Clinical Pharmacy Services on Physician Prescribing Behavior: A Matched-Pair Comparison of Pharmacists and Physicians

In contrast with cross-sectional designs used in previous studies, this exploratory study compared survey data from 127 matched pairs of clinical pharmacists and physicians working together. Physicians' perceptions of the importance of clinical pharmacy activities for patient care and the competence of pharmacists performing the activities were examined for their influence on prescribing behavior in an institutional setting. Data from a national survey showed that physicians rated pharmacists higher regarding recommendations based on drug use evaluations (p = 0.004) and competency to provide all clinical pharmacy services. Scores for pharmacokinetics ratings were similar between pharmacists and physicians (p = 0.168). Pharmacists rated the importance of recommendations based on cost-effectiveness higher than physicians (p = 0.012). Overall, physicians' perceptions of activity importance for patient care and pharmacist competency appear to dictate pharmacists' influence on physician prescribing behavior (R = 0.723).     

Pharmaceutical Marketing: Implications for Medical Residency Training

An educational intervention was developed to improve family practice residents' ability to obtain useful information from pharmaceutical representatives. The curriculum is based on the traditional one-on-one drug detail. The objectives are to develop residents' skills in controlling the interview, promote skills for critically analyzing drug-promotional material, and discuss ethical issues. The contents include an assessment tool, suggested readings, and interview questions with rationale. After 5 years, residents' confidence in all areas of the curriculum improved significantly.     

Age-related Changes in Bovine α-crystallin and High-molecular-weight Protein

The high-molecular-weight (HMW) protein from the lens is composed mostly of α-crystallin in a highly aggregated state. Bovine HMW protein was carefully separated from α-crystallin by size-exclusion chromatography. α-Crystallin has chaperone-like ability whereby it stabilizes other proteins under conditions of stress (e.g. heat). Comparison of bovine HMW protein and α-crystallin shows that the HMW protein has a markedly reduced chaperone ability compared to α-crystallin. However, in contrast to the results of other workers, we observe no alteration with age in the ability of α-crystallin to act as a chaperone. Using electrospray ionisation mass spectrometry, changes in the phosphorylation of the α-crystallin subunits with age have been quantified. Phosphorylation of α-crystallin occurs early in life but does not alter in proportion after about three years of age. In addition, phosphorylation of the A subunit of α-crystallin has little effect on its chaperone ability. As is found in the artificially prepared HMW complex of α- and γ-crystallin, NMR spectroscopy shows that in the naturally occurring HMW protein, the short C-terminal extension of the α_Bsubunit has lost its flexibility whereas the α_Asubunit extension is still flexible. Post-translational modifications therefore seem to have little effect on the chaperone action of α-crystallin, but alterations in the quaternary structure of α-crystallin via incorporation into the HMW aggregate, lead to major changes in the chaperone ability of the protein. The results are consistent with the notion that one of the contributing factors to cataract formation in the lens is the depletion of α-crystallin with age as it is converted into the HMW protein.     

Monitoring Anti-HPA-1a Platelet Antibody Levels during Pregnancy Using the MAIPA Test

Anti-HPA-1a platelet antibody levels in pregnant women with a history of fetomaternal alloimmune thrombocytopenia (FMAIT) were monitored longitudinally using the monoclonal antibody immobilisation of platelet antigens (MAIPA) assay, in order to examine any variation in optical density (OD) readings obtained over the course of pregnancy and after delivery. Seven women were selected; 4 were studied retrospectively and 3 prospectively (the latter being treated with intravenous gammaglobulin; IVGG). Levels of anti-HPA-1a were measured at various intervals after delivery of the first affected infant, to post delivery of the following affected infant. A decrease in MAIPA OD was demonstrated in all patients during the course of these pregnancies. This assay is a useful tool for monitoring anti-HPA-1a in women with a history of infants affected with FMAIT. A maternal antibody 'resting' level prior to, or early in the first trimester, must be established for comparison.