Matrix metalloproteinases regulate ECM accumulation but not larval heart growth in Drosophila melanogaster

The Drosophila heart provides a simple model to examine the remodelling of muscle insertions with growth, extracellular matrix (ECM) turnover, and fibrosis. Between hatching and pupation, the Drosophila heart increases in length five-fold. If major cardiac ECM components are secreted remotely, how is ECM "self assembly" regulated? We explored whether ECM proteases were required to maintain the morphology of a growing heart while the cardiac ECM expanded. An increase in expression of Drosophila's single tissue inhibitor of metalloproteinase (TIMP), or reduced function of metalloproteinase MMP2, resulted in fibrosis and ectopic deposition of two ECM Collagens; type-IV and fibrillar Pericardin. Significant accumulations of Collagen-IV (Viking) developed on the pericardium and in the lumen of the heart. Congenital defects in Pericardin deposition misdirected further assembly in the larva. Reduced metalloproteinase activity during growth also increased Pericardin fibre accumulation in ECM suspending the heart. Although MMP2 expression was required to remodel and position cardiomyocyte cell junctions, reduced MMP function did not impair expansion of the heart. A previous study revealed that MMP2 negatively regulates the size of the luminal cell surface in the embryonic heart. Cardiomyocytes align at the midline, but do not adhere to enclose a heart lumen in MMP2 mutant embryos. Nevertheless, these embryos hatch and produce viable larvae with bifurcated hearts, indicating a secondary pathway to lumen formation between ipsilateral cardiomyocytes. MMP-mediated remodelling of the ECM is required for organogenesis, and to prevent assembly of excess or ectopic ECM protein during growth. MMPs are not essential for normal growth of the Drosophila heart.

Functional outcomes after supracricoid laryngectomy

OBJECTIVES

Local control and 5-year survival rates are similar for patients undergoing total laryngectomy and supracricoid laryngectomy for the treatment of advanced-stage laryngeal carcinoma. However, comprehensive studies of functional outcomes after supracricoid laryngectomy are lacking.

STUDY DESIGN

Cohort study.

METHODS

This investigation provides objective voice laboratory data, skilled listener impressions of voice samples, swallowing evaluations, and patient self-perceptions of speech ability obtained from 10 supracricoid laryngectomees.

RESULTS

Results demonstrated variable acoustic and speech aerodynamic disturbances, hoarse-breathy vocal quality, and speech dysfluency. Patients' self-perceptions of voice revealed severe dysphonia that induced certain emotional, physical, and functional setbacks. However, blinded judges rated these individuals as possessing intelligible speech and communication skills. All patients demonstrated premature spillage of the bolus and varying degrees of laryngeal penetration, aspiration, and retention during swallowing studies. However, each patient used a compensatory strategy to protect the airway. Voice and swallowing abilities appeared to depend on the mobility of the arytenoid cartilages, base of tongue action, and residual supraglottic tissue for the creation of a competent neoglottal sphincter complex that vibrated during phonation efforts and protected the airway during deglutition.

CONCLUSIONS

Supracricoid laryngectomy avoids the potential complications, limitations, and emotional problems associated with a permanent tracheostoma. All patients demonstrated intelligible voice and effective swallowing function postoperatively, supporting supracricoid laryngectomy as a suitable alternative surgical approach to the total laryngectomy in select patients.

Prognostic factors in major salivary gland cancer

OBJECTIVE

To identify features of major salivary gland cancers that are prognostic for disease-free survival.

STUDY DESIGN

A retrospective study of 78 patients with major salivary gland cancer (64 parotid and 14 submandibular gland) who underwent surgery for definitive treatment from 1976 to 1996. A select group of patients also received adjuvant radiation (56%) and/or chemotherapy (13%).

METHOD

Clinical and pathological risk factors were obtained from patients' charts and pathology reports. Age, gender, tumor site, T-stage, facial paralysis, histologic neck involvement, perineural invasion, and cancer grade were analyzed with respect to disease-free survival. The role of adjuvant treatment in terms of clinical outcome was also investigated.

RESULTS

In our series, the 5-year disease-free survival was 65%. Examining clinical and histologic features one at a time, we found poorer prognosis was associated with submandibular tumors compared with parotid (P =.02), higher T-stage (P =.001), positive cervical nodes (P <.001), perineural invasion (P =.002), and high-grade or adenoid cystic tumors (P =.002). A multivariable analysis indicated that positive lymph nodes (P =.07) and perineural invasion (P =.03) were important histologic predictors of shorter disease-free survival. Receipt of both adjuvant radiation and cisplatin-based chemotherapy (P =.05) was an independent predictor of longer disease-free survival.

CONCLUSION

Our study indicated that the presence of positive lymph nodes and perineural invasion is important independent predictors of disease-free survival. Our limited data also suggest that adjuvant chemotherapy and radiation therapy may improve disease-free survival.

Growth and development in term infants fed long-chain polyunsaturated fatty acids: a double-masked, randomized, parallel, prospective, multivariate study

OBJECTIVE

To evaluate the effects of dietary intake of the long-chain polyunsaturated fatty acids, arachidonic acid (AA), and docosahexaenoic acid (DHA) on multiple indices of infant growth and development.

DESIGN

A double-masked, randomized, parallel trial was conducted with term infants fed formulas with or without AA+DHA for 1 year (N = 239). Reference groups of breastfed infants (N = 165) weaned to formulas with and without AA+DHA were also studied. Infants in the formula groups were randomized at </=9 days of age to a control formula with no AA or DHA (n = 77) or 1 of 2 otherwise identical formulas containing AA+DHA (AA, 0.46% and DHA, 0.14% of total fatty acids) from either egg-derived triglyceride (egg-DTG [n=80]) or fish oil and fungal oil (fish/fungal [n = 82]) at levels similar to the average in breast milk samples as measured in the reference group. All formulas contained 50% of energy from fat with the essential dietary fatty acids, linoleic acid (20% fatty acids) and alpha-linolenic acid (2% fatty acids). The main study outcomes were AA and DHA levels in plasma and red blood cells, and multiple measures of infant development at multiple ages from birth to 14 months: growth, visual acuity, information processing, general development, language, and temperament.

RESULTS

AA and DHA levels in plasma and red cells were higher in AA+DHA-supplemented groups than in the control formula group and comparable to those in reference groups. No developmental test results distinguished these groups. Expected differences in family demographics associated with breastfeeding were found, but no advantages to breastfeeding on any of the developmental outcome demonstrated.

CONCLUSIONS

These findings do not support adding AA+DHA to formulas containing 10% energy as linoleic acid and 1% energy as alpha-linolenic acid to enhance growth, visual acuity, information processing, general development, language, or temperament in healthy, term infants during the first 14 months after birth.infant development, breast feeding, infant formula, long-chain polyunsaturated fatty acids, docosahexaenoic acid.

Repellent signaling by Slit requires the leucine-rich repeats

Slit is a repellent axon guidance cue produced by the midline glia in Drosophila that is required to regulate the formation of contralateral projections and the lateral position of longitudinal tracts. Four sequence motifs comprise the structure of Slit: a leucine-rich repeat (LRR), epidermal growth factor-like (EGF) repeats, a laminin-like globular (G)-domain, and a cysteine domain. Here we demonstrate that the LRR is required for repellent signaling and in vitro binding to Robo. Repellent signaling by slit is reduced by point mutations that encode single amino acid changes in the LRR domain. By contrast to the EGF or G-domains, the LRR domain is required in transgenes to affect axon guidance. Finally, we show that the midline repellent receptor, Robo, binds Slit proteins with internal deletions that also retain repellent activity. However, Robo does not bind Slit protein missing the LRR. Taken together, our data demonstrate that Robo binding and repellent signaling by Slit require the LRR region.

One stage carotid artery resection: reconstruction in radiated head and neck carcinoma

PURPOSE

Management of the carotid artery involved with metastatic squamous cell carcinoma continues to be a topic of much discussion. Early reports, for the most part, focused on the sequel of ligation and the development of various tests to predict patient tolerance for the procedure. More recent alternatives have described resection reconstruction in multistage procedures. By using immediate reconstruction with autogenous arterial grafting, carotid artery resection can be accomplished in patients with radiation failure in a single stage. This technique can be used without the addition of myocutaneous flaps, controlled fistulas, or intracranial surgery advocated for usage with alternative techniques.

PATIENTS AND METHODS

Immediate reconstruction after resection of the carotid artery with superficial femoral arterial graft is described.

RESULTS

In a series of 18 high-risk patients with radiation failure, the artery was successfully resected and reconstructed in 1 stage without any neurologic or vascular complications. The technique has been associated with prolonged survival in selected patients.

CONCLUSION

Carotid artery resection and immediate reconstruction can be performed in high-risk radiation failure patients with acceptable complications, and is associated with prolonged survival in selected cases.

Short-term glucosamine infusion does not affect insulin sensitivity in humans

Overactivity of the hexosamine biosynthetic pathway may underlie hyperglycemia-associated insulin resistance, but to date human studies are lacking. Hexosamine pathway activation can be mimicked by glucosamine (GlcN). In the present placebo-controlled study we determined whether GlcN infusion affects insulin resistance in vivo. In 18 healthy subjects, we applied the double forearm balance technique (infused arm vs. control arm) combined with the euglycemic hyperinsulinemic clamp (60 mU/m(2).min insulin) for at least 300 min. During the clamp, subjects received infusions in the brachial artery of 4 micromol/dL.min GlcN from 90-240 min (n = 6) or from 0-300 min (n = 6) or saline (placebo; n = 6). We studied the effects of GlcN on forearm glucose uptake (FGU; infused arm vs. control arm, and vs. placebo experiments) and on whole body glucose uptake. GlcN infusion raised the plasma GlcN concentration in the infusion arms to 0.42 +/- 0.14 and 0.81 +/- 0.46 mmol/L; plasma GlcN remained very low (< 0.07 mmol/L) in the control arms and in the placebo group. GlcN infusion did not change forearm blood flow. During insulin, FGU increased more than 10-fold. At all time points, FGU was similar in the GlcN-infused arm compared with the control arm and was not different from FGU in the placebo experiments. Similar results were obtained for forearm arteriovenous glucose differences or extraction and for whole body glucose uptake. Thus, despite relevant GlcN concentrations for 5 h in the infused forearm, GlcN had no effect on insulin-induced glucose uptake. These results do not support involvement of the hexosamine pathway in the regulation of insulin sensitivity in humans, at least not in the short-term setting.

The midline glia of Drosophila: a molecular genetic model for the developmental functions of glia

The Midline Glia of Drosophila are required for nervous system morphogenesis and midline axon guidance during embryogenesis. In origin, gene expression and function, this lineage is analogous to the floorplate of the vertebrate neural tube. The expression or function of over 50 genes, summarised here, has been linked to the Midline Glia. Like the floorplate, the cells which generate the Midline Glia lineage, the mesectoderm, are determined by the interaction of ectoderm and mesoderm during gastrulation. Determination and differentiation of the Midline Glia involves the Drosophila EGF, Notch and segment polarity signaling pathways, as well as twelve identified transcription factors. The Midline Glia lineage has two phases of cell proliferation and of programmed cell death. During embryogenesis, the EGF receptor pathway signaling and Wrapper protein both function to suppress apoptosis only in those MG which are appropriately positioned to separate and ensheath midline axonal commissures. Apoptosis during metamorphosis is regulated by the insect steroid, Ecdysone. The Midline Glia participate in both the attraction of axonal growth cones towards the midline, as well as repulsion of growth cones from the midline. Midline axon guidance requires the Drosophila orthologs of vertebrate genes expressed in the floorplate, which perform the same function. Genetic and molecular evidence of the interaction of attractive (Netrin) and repellent (Slit) signaling is reviewed and summarised in a model. The Midline Glia participate also in the generation of extracellular matrix and in trophic interactions with axons. Genetic evidence for these functions is reviewed.

Genetic analysis of vein function in the Drosophila embryonic nervous system

The Drosophila epidermal growth factor receptor (EGFR) may be activated by two ligands expressed in the embryonic nervous system, Spitz and Vein. Previous studies have established Spitz as an essential activator of EGFR signaling in nervous system development. Here, we report the pattern of expression of vein mRNA in the nervous system and characterize the contribution of vein to cell lineage and axonogenesis. The number of midline glia (MG) precursors is reduced in vein mutants before the onset of embryonic apoptosis. In contrast to spitz, mis-expression of vein does not suppress apoptosis in the MG. These data indicate that early midline EGFR signaling, requiring vein and spitz, establishes MG precursor number, whereas later EGFR signals, requiring spitz, suppress apoptosis in the MG. vein mutants show early irregularities during axon tract establishment, which resolve later to variable defasciculation and thinner intersegmental axon tracts. vein and spitz phenotypes act additively in the regulation of MG cell number, but show synergism in a midline neuronal cell number phenotype and in axon tract architecture. vein appears to act downstream of spitz to briefly amplify local EGFR activation.

Early and chronic stress and their relation to breast cancer

BACKGROUND

The study examined the role of parental death and chronic depression with severe episodes in affecting risk of breast cancer. This avenue of research is in accord with oncology findings, which suggests that causative factors of breast cancer occur and develop over a period of 20 years or longer.

METHODS

Participants consisted of 1213 women in the Baltimore Epidemiologic Catchment Area study surveyed in 1980 and followed through 1994-1995. They were assessed for depressive and anxious disorders, paternal death in childhood and relatively recent adverse life events prior to cancer hospitalization.

RESULTS

In the course of the study, 29 women were hospitalized for breast cancer and 10 died of breast cancer. The psychosocial variables that predicted increased risk of breast cancer were maternal death in childhood (OR = 2.56, P < 0.001) and chronic depression with severe episodes (OR = 14.0, P < 0.001). Neither relatively recent life events nor other depressive and anxiety disorders were associated with increased risk. Maternal death and chronic depression with severe episodes were reported to have occurred at least 20 years prior to breast cancer hospitalization.

CONCLUSIONS

Maternal death and chronic and severe depression occurred at least 20 years prior to breast cancer hospitalization and could have been involved in the causation or facilitation of cancer development. The authors suggest that meta-analysis of other prospective studies are needed to create larger groups of individuals with these stresses to confidently establish these variables as risk factors.

Assessment of carotid artery invasion in patients with head and neck cancer

PURPOSE

Define radiological and histological features in which patients with head and neck cancer would benefit from a carotid artery resection. Resection of the carotid artery has been advocated for local control of advanced squamous cell carcinoma of the head and neck. To provide appropriate preoperative counseling and optimize the utilization of resources, the criteria for patient selection has to be defined.

METHODS

Thirty-four patients underwent carotid artery resection based on the clinical impression of tumor fixation. Eighteen and 28 patients were evaluated using computed tomography (CT) and histological analysis, respectively. The distance between the tumor cells and external elastic lamina was measured. CT scans were examined to determine the circumference of tumor attachment around the carotid artery.

RESULTS

Clinical assessment predicted tumor within 1.8 mm of the carotid artery in 68% of cases. The overall survival for patients with tumor greater than 1.8 mm (N = 9) was better than that of patients with less (N = 19) than 1.8 mm (33.3% vs. 5.3%; median 24 versus 9 mo, P = .0899). Three of six patients (50%) with less than 180 degrees circumference tumor attachment had tumor within 1.8 mm from the external elastic lamina. Eight of twelve patients (67%) with tumors encompassing more than 180 degrees of the artery wall had tumor within 1.8 mm from the external elastic lamina. The overall survival rates for patients with tumor attachment greater and less than 180 degrees were 8.3% and 33%, respectively.

DISCUSSION

Tumor invasion into the carotid artery was the strongest predictor of outcome. Clinical assessment was as predictive as CT for tumor invasion. If tumor involvement of the carotid artery is less than 180 degrees, peeling the tumor is an alternative to carotid artery resection.

Rhomboid function in the midline of the Drosophila CNS

Rhomboid (Rho), a cell surface, seven-transmembrane domain protein, participates in Spitz-dependent activation of the Drosophila EGF receptor (EGFR). By contrast to transient expression in other embryonic tissues, rho is expressed continuously in the embryonic and larval Midline Glia (MG) lineage and is required upstream of, or in parallel with, S, Spi, and EGFR to establish MG cell number. EGFR signaling is necessary for the expression of rho in the MG and sufficient to stimulate rho expression in additional MG progenitors. rho expression is required continuously from embryonic stage 9-17 to suppress apoptosis in the MG. Although rho misexpression can increase MG number through a non-cell autonomous mechanism, the pattern of normal rho expression suggests that it functions by enhancing autocrine or paracrine signaling among MG cells.

Growth of newborn, term infants fed soy formulas for 1 year

Few studies have measured long-term growth in infants fed soy protein-based formulas. The effect of nucleotide (NT) supplementation of soy protein-based infant formulas on growth is unknown. Growth was therefore evaluated in healthy term infants fed a soy protein-based formula (SOY; n = 73), SOY with added NT (72 mg added NT/L) at human milk (HM) levels (SOYN, n = 73), or mixed feeding (MF, n = 67) in a randomized, masked, parallel 1-year feeding study. The MF group (a nonrandomized reference group) was fed HM exclusively from birth to 2 months of age followed by HM and/or a standard milk-based formula (Similac with Iron with no supplemental NTs) to 1 year of age. Results indicated that growth (weight, length, and head circumference) was normal and comparable among the three groups. All three groups had similar plasma albumin (at 2 months of age) and hemoglobin levels (at 12 months of age). Thus, this study demonstrated similar growth in the first year of life among infants fed MF feeding or soy formula with or without supplemental NTs.

Failure of cricopharyngeal myotomy to improve dysphagia following head and neck cancer surgery

OBJECTIVE

To determine whether cricopharyngeal myotomy can improve dysphagia associated with head and neck cancer surgery.

DESIGN

Prospective, randomized, multicenter trial.

SETTING

Twelve clinical sites across the United States.

PATIENTS

Between 1989 and 1994, 125 patients undergoing combined modality therapy for head and neck cancer, including resection of the tongue base or supraglottic larynx, were prospectively entered into the trial.

INTERVENTION

Cricopharyngeal myotomy on a randomized basis.

MAIN OUTCOME MEASURES

Videofluoroscopic examination to determine oropharyngeal swallowing efficiency, which is defined as the ratio of percentage of the bolus swallowed to total swallowing time using 3 different bolus consistencies.

RESULTS

No significant difference in oropharyngeal swallowing efficiency between myotomy vs no myotomy was seen at 6 months of follow-up regardless of bolus consistency.

CONCLUSIONS

In this prospective test of cricopharyngeal myotomy, the procedure fails to significantly improve dysphagia associated with head and neck cancer surgery. The efficacy of this surgical procedure in other disease entities should also be rigorously explored.

Axon repulsion from the midline of the Drosophila CNS requires slit function

Guidance of axons towards or away from the midline of the central nervous system during Drosophila embryogenesis reflects a balance of attractive and repulsive cues originating from the midline. Here we demonstrate that Slit, a protein secreted by the midline glial cells provides a repulsive cue for the growth cones of axons and muscle cells. Embryos lacking slit function show a medial collapse of lateral axon tracts and ectopic midline crossing of ventral muscles. Transgene expression of slit in the midline restores axon patterning. Ectopic expression of slit inhibits formation of axon tracts at locations of high Slit production and misdirects axon tracts towards the midline. slit interacts genetically with roundabout, which encodes a putative receptor for growth cone repulsion.

Prognostic significance of p53 gene mutations in laryngeal cancer

OBJECTIVE/HYPOTHESIS

We examined whether p53 gene mutations were predictive of clinical behavior in laryngeal cancer.

STUDY DESIGN

Retrospective study of 45 patients with laryngeal cancer from 1985 to 1997.

METHODS

DNA was extracted from tumor tissue and subject to polymerase chain reaction single-strand conformational polymorphism (PCR-SSCP) as well as DNA sequencing. The clinical outcome was correlated to the presence or absence of a p53 mutation.

RESULTS

The p53 gene was analyzed by direct DNA sequencing and was found to be mutated in 33% (15/45) of patients. The presence of a p53 mutation was associated with a significant improvement in overall survival (80% vs. 43%, P < .03) and a trend toward improved disease-free survival (87% vs. 60%, P = .08). When other prognostic factors were adjusted, multivariate analysis revealed a trend toward improvement in overall survival as well as disease-free survival.

CONCLUSION

Depending on the location of a p53 mutation, the suppressive functions or clinical outcome may or may not be affected. Fifty-three percent of mutations were detected in nonconserved regions as opposed to 17% as reported in colon cancer. In colon cancer, mutations in conserved regions of the p53 gene predicted a poorer survival, whereas nonconserved gene mutations were not predictive. In our group of patients. p53 mutations predicted a better prognosis, which may be due to a large proportion of mutations that lie within nonconserved areas. The predictive power of p53 gene mutations may depend on functional loss and inactivation of highly conserved areas and must be tested in a prospective trial.

Videostroboscopy of the pharyngoesophageal segment in total laryngectomees

OBJECTIVES

The reconstructed pharyngoesophageal segment (PES) serves as the neoglottis following total laryngectomy, as it provides the source of vibration for production of tracheoesophageal puncture (TEP) voice. To date, little information exists regarding the vibratory characteristics of the PES. The purpose of this investigation was to study the anatomy and physiology of the PES using videostroboscopy.

STUDY DESIGN

Prospective study investigating the anatomy and physiology of the PES in 34 laryngectomees who used TEP speech as their primary form of communication.

MATERIALS AND METHODS

Videostroboscopy and voice recordings were graded by three trained, blinded judges using a seven-point scale.

RESULTS

The patients demonstrated differences that allowed for separation of patients into two main groups: "poor" and "effective" TEP speakers. The voice quality differences were explained by anatomic and physiologic characteristics of the PES. Redundant, thick, and dyssynchronous PES features were observed in patients with poor TEP speech skills; the effective speakers exhibited less redundant, thinner mucosa and more synchronous vibratory patterns. Moreover, the latter subgroup consistently demonstrated a greater degree of volitional PES control and less spasmodic activity than their poorly speaking counterparts. Length of the PES opening (measured in the horizontal plane) as well as amount and consistency of secretions did not appear to influence TEP speech or voice proficiency.

CONCLUSION

Videostroboscopy in laryngectomees is a noninvasive, inexpensive, easily performed procedure that may contribute valuable information regarding the anatomy and physiology of the PES, especially in patients who experience difficulties achieving satisfactory TEP voice and speech production.

Carotid resection and replacement with autogenous arterial graft during operation for neck malignancy

Carotid artery resection as part of the management of advanced head and neck cancers remains controversial. Since 1991, 30 patients have undergone resection of the carotid artery with immediate reconstruction using superficial femoral artery as replacement conduit. There was one stroke/death. Forty-three percent developed neck wound problems but no grafts failed or hemorrhaged. Mean follow-up was 20 months (3-76) and mean life expectancy was 16 months from the time of surgery. Fifty-eight percent were free of local recurrence at the time of death. There was a 35% disease-free survival rate at 2 years. These results compare favorably with alternative therapy including carotid ligation or shaving tumor from the carotid artery. Given the importance of cerebral perfusion and local tumor control we offer superficial femoral artery as a durable conduit for immediate extracranial carotid reconstruction in the often hostile environment associated with cancer resection in the neck.

The expression of MDP-1, a component of Drosophila embryonic basement membranes, is modulated by apoptotic cell death

Using a novel monoclonal antibody we have studied the expression of a large proteoglycan-type molecule in Drosophila embryos. This molecule is secreted exclusively by migratory, embryonic hemocytes/macrophages and was therefore named MDP-1 for Macrophage-Derived Proteoglycan-1. Expression of MDP-1 begins late during hemocyte differentiation, after these cells have left their birthplace in the head mesoderm. At this time, macrophages are engaged in extracellular matrix deposition and the phagocytosis of cell debris generated by apoptotic events in various parts of the embryo, in particular from the developing central nervous system. Embryos deficient for programmed cell death display a greatly reduced amount of MDP-1 deposition in tissues that normally undergo morphogenetic cell death. This suggests a regulatory role for apoptosis in the terminal differentiation of Drosophila hemocytes. MDP-1 is initially deposited around the developing central nervous system and is later found in basement membrane structures surrounding various other organs, such as the gut, Malpighian tubules and part of the tracheal system. The temporal and localized deposition of MDP-1 suggests that it may play a role in delineating the central nervous system structure during axonogenesis and may participate in the formation of a functional 'blood-brain barrier' in Drosophila.

Origin and differentiation of supernumerary midline glia in Drosophila embryos deficient for apoptosis

Drosophila embryos deficient for programmed cell death produce 9 midline glia (MG) in addition to the wild-type complement of 3.2 MG/segment. More than 3 of the supernumerary MG derive from the MGP (MG posterior) lineage and the remainder from the MGA/MGM (MG anterior and middle) lineage. There is one unidentified additional neuron in the mesectoderm of embryos deficient for apoptosis. The supernumerary MG are not diverted from other lineages nor do they arise from an altered pattern of mitosis. Instead, these MG appear to arise from a normally existing pool of 12 precursor cells, larger than anticipated by earlier studies. During normal development, MG survival is dependent upon signaling to the Drosophila EGF receptor. The persistence of supernumerary MG in embryos deficient for apoptosis does not alter the spatial pattern of Drosophila EGF receptor signaling. The number and position of MG which express genes dependent upon EGF receptor function, such as pointed or argos, are indistinguishable from wild type. Genes of the spitz group are required for Drosophila EGF receptor function. Surviving MG in spitz group/H99 double mutants continue to express genes characteristic of the MG, but the cells fail to differentiate into ensheathing glia and are displaced from the nerve cord.

Argos and Spitz group genes function to regulate midline glial cell number in Drosophila embryos

The midline glia of the Drosophila embryonic nerve cord undergo a reduction in cell number after facilitating commissural tract morphogenesis. The numbers of midline glia entering apoptosis at this stage can be increased by a loss or reduction of function in genes of the spitz group or Drosophila EGF receptor (DER) pathway. Argos, a secreted molecule with an atypical EGF motif, is postulated to function as a DER antagonist. In this work, we assess the role of argos in the determination of midline glia cell number. Although all midline glia express DER, argos expression is restricted to the midline glia which do not enter apoptosis. Fewer midline glia enter apoptosis in embryos lacking argos function. Ectopic expression of argos is sufficient to remove all DER-expressing midline glia from the nerve cord, even those that already express argos. DER expression is not terminated in the midline glia after spitz group signaling triggers changes in gene expression. It is therefore likely that an attenuation of DER signaling by Argos is integrated with the augmentation of DER signaling by Spitz throughout the period of reduction of midline glia number. We suggest that signaling by Spitz but not Argos is restricted to adhesive junctions. In this manner, midline glia not forming signaling junctions remain sensitive to juxtacrine Argos signaling, while an autocrine Argos signal is excluded by the adhesive junction.

Selenate fortification of infant formulas improves the selenium status of preterm infants

The purpose of this study was to determine whether selenate fortification of infant formula would improve the selenium status of relatively well, growing, preterm infants during the first 12 wk of enteral feeding. A high-selenium group (n = 7, mean body weight = 1312 g) received selenate-fortified preterm and full-term infant formulas containing 0.36 and 0.22 mumol Se/L, respectively, and a low-selenium group (n = 10, mean body weight = 1262 g) received non-selenium-fortified preterm and full-term infant formulas containing 0.12 and 0.11 mumol Se/L, respectively. There were no significant differences in growth between the two groups throughout the study. The high-selenium group had significantly greater mean selenium intakes than did the low-selenium group from weeks 2 to 12. Plasma selenium concentrations decreased over the study period in the low-selenium group. Plasma selenium-dependent glutathione peroxidase activity was greater in the high-selenium group at week 12 only. Red blood cell selenium concentrations decreased over time in both groups and were significantly greater in the high-selenium group at weeks 4, 8, and 12. Plasma selenium concentrations were significantly correlated with plasma glutathione peroxidase activity for all infants on study day 1 and at weeks 4 and 12. Selenium intake of all infants was significantly correlated with plasma glutathione peroxidase activity at 12 wk. Selenate fortification of infant formulas can improve the selenium status of preterm infants. Current selenium contents of infant formulas and recommendations for dietary intakes of selenium for some preterm infants may be inadequate.

Mutations in the gene stand still disrupt germ cell differentiation in Drosophila ovaries

During oogenesis in Drosophila, germ cells appear in sequential clusters of 16 interconnected cells. The events surrounding the differentiation of these cells are not fully understood. Here we present genetic and morphological analysis of mutations in the gene stand still (stil). Through complementation analyses we have refined the location of this gene to cyological region 49B-C. Our analyses of ovaries from ethylmethane sulfonate (EMS)-induced mutant alleles of this gene suggest that mutations in the stil gene produce a wide range of phenotypic abnormalities, from the absence of germ cells in the most severe alleles, to egg chambers with cytoskeletal defects in the less severe alleles. Our results suggest a role for this gene in specifying or maintaining a cytoskeletal component, with consequences during oogenesis and possibly during germ line sex determination.

Outcome of pyriform sinus cancer: a retrospective institutional review

Pyriform sinus cancer remains one of the most lethal of human diseases. Regardless of approach attempted significant enhancement of survival has not been realized. In this study a retrospective single institutional review of all patients diagnosed with pyriform sinus cancer during the 1980s was conducted. The results in 93 patients show an overall determinant 5-year survival of 14.3%. Of patients undergoing surgery, median determinant survival was 37 months and 5-year survival was 34.6%. In resectable patients treated with radiation with or without chemotherapy, median determinant survival was 13 months with 5-year survival of 7.1% (P < .01). Surgical salvage was attempted in 8 patients without success. In conclusion, due to the apparent survival advantage for surgical patients, the low rate of surgical salvage, and the relatively low rate of organ preservation in prospective trials, pyriform sinus cancer is a poor site for organ preservation. Surgery followed by radiation therapy should remain the standard of care for pyriform sinus cancer.

Sinus disease in the bone marrow transplant population: incidence, risk factors, and complications

BACKGROUND

Fever associated with sinus disease in the immunocompromised bone marrow transplant recipient requires prompt evaluation and therapy. Very little is known about the incidence, risk factors, and sequelae of nonsurgically treated sinus disease in this population.

METHODS

A retrospective review of 107 consecutive allogeneic and autologous bone marrow transplant recipients from August 1987 to July 1989 was performed to determine (1) the overall incidence of sinus disease; (2) factors that influence the development of sinus disease; and (3) the sequelae of sinus disease treated nonsurgically.

RESULTS

Overall 33 (31%) of 107 bone marrow transplant recipients had sinus disease defined as a radiographic abnormality with clinical symptoms. Eleven (10%) of 107 recipients had preexisting sinus disease. Sinus disease developed in 22 (21%) of 107 recipients after bone marrow transplantation. Sinus abnormalities were significantly higher among allografted bone marrow transplant recipients than among autografted recipients (p = 0.027). The diagnosis, stage of disease, cytoreductive regimen, or graft-vs.-host disease were not different between recipients in whom sinus disease did and did not develop. There were no deaths as a result of sinus complications.

CONCLUSIONS

Sinus disease developed in 21% of the studied population after bone marrow transplantation. Allogeneic recipients had a higher incidence of sinus disease than autologous recipients. There were no deaths attributed to sinus complications. All sinus disease in this bone marrow transplant population was treated medically. No patient required surgical intervention either before or after bone marrow transplantation.

Measured context-sensitive half-times of remifentanil and alfentanil

BACKGROUND

The context-sensitive half-time, rather than the terminal elimination half-life, has been proposed as a more clinically relevant measure of decreasing drug concentration after a constant infusion of a given duration. The context-sensitive half-time is derived from computer modelling using known pharmacokinetic parameters. The modelled context-sensitive half-time for a 3-h infusion of alfentanil is 50-55 min and is 3 min for remifentanil. The terminal elimination half-life is 111 min for alfentanil and 12-30 min for remifentanil. It has not been tested whether the modelled context-sensitive half-time reflects the true time for a 50% decrease in drug concentration or drug effect.

METHODS

Thirty volunteers received a 3-h infusion of remifentanil or alfentanil at equieffective concentrations. Depression of minute ventilation to 7.5% ETCO2 was used as a measure of drug effect. Minute ventilation response was measured, and blood samples for drug concentration were taken during and after drug infusion. The recovery of minute ventilation (drug effect) and decrease in blood drug concentration was plotted, and the time for a 50% change was determined.

RESULTS

The measured pharmacokinetic context-sensitive half-time for remifentanil after a 3-h infusion was 3.2 +/- 0.9 min, and its pharmacodynamic offset was 5.4 +/- 1.8 min. Alfentanil's measured pharmacokinetic context-sensitive half-time was 47.3 +/- 12 min, and its pharmacodynamic offset was 54.0 +/- 48 min. The terminal elimination half-life modelled from the volunteers was 11.8 +/- 5.1 min for remifentanil and 76.5 +/- 12.6 min for alfentanil.

CONCLUSIONS

The measured context-sensitive half-times were in close agreement with the context-sensitive half-times previously modelled for these drugs. The results of this study confirm the value of the context-sensitive half-time in describing drug offset compared to the terminal elimination half-life.

Ameloblastic carcinoma of the maxilla

Ameloblastic carcinoma is an unusual tumour. There have been a total of 34 cases of ameloblastic carcinoma in the English literature to date. Of these only 11 cases have occurred in the maxilla. The authors report the 12th such case. The histological classification for odontogenic carcinoma has been debated for many years and recently revised, thus differentiating between malignant ameloblastoma and ameloblastic carcinoma. The authors review the current literature regarding diagnosis and treatment of this unusual lesion, and support the use of the term malignant ameloblastoma for the tumours that metastasize in spite of their benign histological appearance, whereas, the ameloblastic carcinoma is referred to as the primary tumour with malignant transformation, regardless of its metastatic potential.

Macrophages and glia participate in the removal of apoptotic neurons from the Drosophila embryonic nervous system

Cell death in the Drosophila embryonic central nervous system (CNS) proceeds by apoptosis, which is revealed ultrastructurally by nuclear condensation, shrinkage of cytoplasmic volume, and preservation of intracellular organelles. Apoptotic cells do not accumulate in the CNS but are continuously removed and engulfed by phagocytic haemocytes. To determine whether embryonic glia can function as phagocytes, we studied serial electronic microscopic sections of the Drosophila CNS. Apoptotic cells in the nervous system are engulfed by a variety of glia including midline glia, interface (or longitudinal tract) glia, and nerve root glia. However, the majority of apoptotic cells in the CNS are engulfed by subperineurial glia in a fashion similar to the microglia of the vertebrate CNS. A close proximity between macrophages and subperineurial glia suggests that glia may transfer apoptotic profiles to the macrophages. Embryos affected by the maternal-effect mutation Bicaudal-D have no macrophages. In the absence of macrophages, most apoptotic cells are retained at the outer surfaces of the CNS, and subperineurial glia contain an abundance of apoptotic cells. Some apoptotic cells are expelled from the CNS, which suggests that the removal of apoptotic cells can occur in the absence of macrophages. The number of subperineurial glia is unaffected by changes in the rate of neuronal apoptosis.

Identification of Genes Predisposing to Clinically Severe Obesity: An Approach

BACKGROUND: Familial correlations, twin studies and adoption studies have all indicated that human obesity has a substantial genetic component. To date, obesity genes have only been identified using mouse models. METHODS: In an attempt to identify human obesity genes large numbers of multigenerational families, in whom extreme obesity segregates, are currently being collected. RESULTS AND CONCLUSIONS: Relative risk estimates and models of genetic heterogeneity indicate that at least 500 affected sibling pairs will need to be collected to identify major genes.

Bipedicle delayed flap closure of persistent radiated tracheocutaneous fistulas

Increasing numbers of patients have had tracheostomies for prolonged periods of time and when subsequently decannulated have developed persistent tracheocutaneous fistula. A substantial percentage of these patients have undergone successful combined modality therapy excluding surgery for advanced head and neck cancer with resulting healing deficits of the remaining tissues. Although these patients may be deemed suitable for decannulation at this particular point, the potential still exists that access to the trachea will be required sometime in the future. This situation requires a method of closure that is reasonably reliable and yet, at the same time, relatively easily reversible. The surgical technique presented appears to meet these demands. After primary inversion of the edges of the tracheocutaneous fistula, a bipedicle flap is developed and positioned over the tracheostomy site. The inferior edge of the flap is left open for temporary air escape to decompress the suture line. This line subsequently heals by secondary intention over the succeeding weeks. Although there has not been, to date, the need to reverse the closure, the relative thinness of the tissue as opposed to alternative techniques suggests that it should not be difficult.

Compartment model to describe peripheral arterial-venous drug concentration gradients with drug elimination from the venous sampling compartment

The central compartment of an n-compartment mammillary model was concatenated with a gradient compartment (i.e., venous sampling compartment) and with a conventional effect compartment to model arterial-venous drug concentration gradients and the arterial drug concentration vs effect relationship, respectively. To model drug metabolism during transit between the peripheral arterial and peripheral venous circulations, the gradient compartment included a first-order elimination path. Simulations of the model were employed to demonstrate the impact of sampling site (e.g., arterial vs peripheral venous) on analyses of the concentration vs effect relationship.

Fortification of human milk: evaluation of a novel fortification scheme and of a new fortifier

Human milk fed to very-low-birth-weight infants must be fortified with protein, minerals, and vitamins. We tested a new fortification regimen in which the amount of fortifier was adjusted on the basis of frequent determinations of serum urea nitrogen (SUN). A newly formulated fortifier based on bovine milk proteins was employed either in the new fashion (regimen ADJ) or in the conventional fixed proportion (regimen FIX). Using the fixed proportion, the study also compared the new fortifier with a fortifier based on human milk protein (regimen HMP). Twelve infants were studied with each of the three regimens; nearly all completed 3 weeks of study. Protein intake was generally higher in ADJ than FIX; the difference was significant (p < 0.01) during week 2. Weight gain was somewhat (but not significantly) greater in regimen ADJ (32.3 g/d or 18.8 g/kg/d) than in regimen FIX (30.0 g/d or 18.3 g/kg/d). SUN was higher in ADJ than in FIX, and several other serum chemical values (calcium, phosphorus, potassium) tended to be higher, probably reflecting higher intakes of these nutrients with ADJ than with FIX. Plasma concentrations of several amino acids were higher in ADJ than FIX, but none, including threonine, were outside the physiological range. In comparing regimen FIX to regimen HMP, infants on FIX received similar intakes of protein and showed slightly but not significantly more rapid weight gain. Concentrations of SUN were lower with FIX, but other serum chemical values, including amino acids, were generally similar to HMP. We conclude that use of the new adjustable fortification regimen is feasible and safe and that it should be studied further. It produced the expected increases in nutrient intakes and growth. The new bovine milk-based fortifier appears to be equivalent to the human milk-based fortifier.

Apoptosis of the midline glia during Drosophila embryogenesis: a correlation with axon contact

We have examined cell death within lineages in the midline of Drosophila embryos. Approximately 50% of cells within the anterior, middle and posterior midline glial (MGA, MGM and MGP) lineages died by apoptosis after separation of the commissural axon tracts. Glial apoptosis is blocked in embryos deficient for reaper, where greater than wild-type numbers of midline glia (MG) are present after stage 12. Quantitative studies revealed that MG death followed a consistent temporal pattern during embryogenesis. Apoptotic MG were expelled from the central nervous system and were subsequently engulfed by phagocytic haemocytes. MGA and MGM survival was apparently dependent upon proper axonal contact. In embryos mutant for the commissureless gene, a decrease in axon-glia contact correlated with a decrease in MGA and MGM survival and accelerated the time course of MG death. In embryos mutant for the slit gene, MGA and MGM maintained contact with longitudinally and contralaterally projecting axons and MG survival was comparable to that in wild-type embryos. The initial number of MG within individual ventral nerve cord segments was increased by ectopic expression of the rhomboid gene, without changing axon number. Extra MGA and MGM were eliminated from the ventral nerve cord by apoptosis to restore wild-type numbers of midline glia. Ectopic rhomboid expression also shifted MGA and MGM cell death to an earlier stage of embryogenesis. One possible explanation is that axon-glia contact or communication promotes survival of the MG and that MG death may result from a competition for available axon contact.

Lectin histochemistry of the Drosophila embryo

A selection of lectins was used to characterise changes in the distribution of glycoconjugates during the embryonic development of Drosophila melanogaster. The blastoderm of pre-gastrulation embryos bound low levels of the lectins LPA, UEA-I and PNA. The germ line progenitors (pole cells) bound ConA, PNA and LPA. The yolk granules, the trachea, and the gut bound GSA-I. All lectins had detectable labeling of the ectoderm. The somata of the nervous system bound ConA and LPA. Electron microscopic analysis of PNA labeling of the nervous system revealed exclusive binding to the axon tracts and ensheathing glia. Hyaluronate lyase digestion of oligosaccharides revealed gut and nervous system binding with WGA and UEA-I. This study revealed useful biochemical probes of gut, epidermal and nervous system development that identify the distribution of likely ligands for as yet uncharacterised endogenous lectins.

Aging increases pharmacodynamic sensitivity to the hypnotic effects of midazolam

The effect of aging on the pharmacodynamics of midazolam was investigated in a double-blinded study involving 39 consenting patients ranging in age from 39 to 77 yr. Midazolam was infused intravenously (i.v.) using a pharmacokinetic model-driven drug infusion device to achieve a plasma midazolam concentration that was held constant for the 10-min duration of the study. Blood samples were obtained from the radial artery at 5 and 10 min for subsequent measurement of the plasma midazolam concentrations. With the 10-min sample, the patients were also assessed for the presence or absence of responsiveness to verbal command. To ensure that the pharmacodynamic end-point was assessed under the condition of a relative steady-state effect-site midazolam concentration, only those patients (n = 33) in whom the plasma midazolam concentration at 10 min was within 30% of the measured concentration at 5 min were included in the subsequent data analyses. Logistic regression was used to fit the verbal command response/no response data to a mathematical model that included patient age and the plasma midazolam concentration measured at 10 min. Cp50, the steady-state plasma midazolam concentration at which 50% of patients would be expected not to respond to a specific stimulus (e.g., verbal command), was calculated as a function of age from the parameterized logistic model. The midazolam Cp50 for response to verbal command decreased significantly (P = 0.034) with increasing patient age, demonstrating that aging increases pharmacodynamic sensitivity to the hypnotic effects of midazolam independent of pharmacokinetic factors.

Effects of human milk or formula feeding on the growth, behavior, and protein status of preterm infants discharged from the newborn intensive care unit

The growth, behavior, and protein status of 59 healthy preterm (mean gestational age 30 wk) infants fed either human milk or one of three infant formulas were studied post-discharge from the hospital. Formula-fed infants received either a standard term formula, a standard preterm formula, or an experimental preterm formula from discharge to 8 wk of age. From 8 to 16 wk, all formula-fed infants received the standard term formula. At 2, 8, and 16 wk, anthropometric, dietary intake, blood biochemistry, amino acid, and Brazelton Neonatal Behavioral Assessment measurements were evaluated. Weights, lengths, and head circumferences were similar for all feeding groups at discharge. After discharge all formula-fed infants were heavier than human milk-fed infants. Length and head circumference values and plasma urea nitrogen and retinol-binding protein concentrations were not different among dietary groups. Formula-fed infants had higher plasma concentrations of numerous amino acids compared with those of human milk-fed infants during the first 8 wk but not at 16 wk. There were no differences among the feeding groups in the Brazelton assessment. This study found little effect on the growth or behavioral or protein status of preterm infants discharged from the hospital who were fed either human milk or formulas designed for term or preterm infants.

Surgical reporting instrument designed to improve outcome data in head and neck cancer trials

Precise reporting of surgical staging and operative data in multi-institutional protocol studies could provide a number of benefits: 1) fewer cases would be discarded because of inadequate data, 2) staff review time would be reduced, 3) there would be assurance that participating surgeons were performing similar operations on similar tumors, 4) the resulting precision in stratification should improve the likelihood of achieving accurate comparison of the treatment options under study, and 5) by comparing the surgical parameters with local-regional control of disease, the specific factors that have a statistically significant correlation with outcome could be identified. This paper presents a computer-based, anatomically oriented reporting instrument that should improve the reliability of surgical data available to multi-institutional protocols.

Carotid artery reconstruction using superficial femoral arterial grafts

The indications, consequences, and value of resection of the carotid artery as part of an extended neck dissection has been discussed for many years. Many of the earlier reports have focused on the sequelae of carotid artery ligation and tests to predict patient tolerance for the procedure. Efforts to reconstruct the carotid artery have been limited primarily to vein grafts. The authors report on 11 cases of reconstruction of the carotid artery using the patient's superficial femoral artery. The femoral artery itself is reconstructed using a Gore-Tex graft. Free autografts of the superficial femoral artery in the carotid location have been found to be an excellent size match, mechanically stronger than a vein graft, and tolerant of bacterial contamination. Arteriography in 1 case with 14 months' follow-up demonstrates long-term patency.

Mesectodermal cell fate analysis in Drosophila midline mutants

We have used enhancer traps and antibodies as markers of cell identity to assess the relative contribution of individual mesectodermal cell (MEC) lineages to CNS midline morphogenesis in four mutations that disrupt commissure formation in Drosophila. The absence of commissures, leading to longitudinal tract collapse, was seen in embryos mutant for the genes single-minded and slit. MEC lineages did not survive in single-minded mutant embryos, in contrast to the survival of all MEC lineages in slit mutant embryos. The midline glial cells were displaced and appeared ultrastructurally normal in slit mutant embryos, yet the presence of the MG was not sufficient to generate commissures. Commissure formation requires correct MEC cytoarchitecture, dependent upon slit activity. In fused commissure mutants (rhomboid and Star) neuron number was reduced in the ventral unpaired median neuron (VUM) lineage and the median neuroblast lineage before commissure formation (stage 12). Subsequent to these neuronal defects, the midline glia died by apoptosis (stage 13). Commissure fusion and glial apoptosis may be triggered by the earlier perturbations in MEC neuronal lineages. These studies establish when the respective activities of each gene are required for the development of each MEC lineage.

Chemotherapy as predictor of compliance

Patient compliance with the increasingly complex adjuvant therapy protocols has always been of concern, particularly in the head and neck cancer population. The Head and Neck Intergroup recently concluded a phase III prospective randomized trial testing the addition of three courses of cisplatinum containing combination chemotherapy to standard treatment defined as surgery and postoperative radiotherapy for advanced stage III and IV squamous cell carcinoma. The chemotherapy was administered following the surgery prior to the postoperative radiotherapy. Variation from protocol is ranked retrospectively as minor acceptable, major acceptable, and major unacceptable. The incidence of major unacceptable variation from the protocol for radiotherapy immediately following the surgery was 15% vs. 19% in the population that completed all three courses of the chemotherapy (P < 0.10). However, for those patients that completed less than the three courses of chemotherapy, the incidence of major unacceptable variation in radiotherapy was 33% (P < 0.001). This observation was controlled for site, stage, performance status, age, sex, surgical margins and experience of participating institution. We conclude that compliance with a multicourse adjuvant chemotherapy regimen is predictive of subsequent compliance to radiotherapy in the head and neck cancer population.

Is a surgical resection leaving positive margins of benefit to the patient with locally advanced squamous cell carcinoma of the head and neck: a comparative study using the intergroup study 0034 and the Radiation Therapy Oncology Group head and neck database

PURPOSE

The purpose of this study was to determine whether or not for patients with squamous cell carcinomas of the head and neck, a surgical resection leaving positive margins followed by postoperative adjuvant therapy improves the outcome compared to a matched group of patients treated with definitive radiotherapy alone.

METHODS AND MATERIALS

From January 1985 through January 1990 a consortium of national cooperative groups (Radiation Therapy Oncology Group, Cancer and Leukemia Group B, Eastern Cooperative Oncology Group, Northern California Oncology Group, Southeast Group, and Southwest Oncology Group) conducted a phase III clinical trial testing the efficacy of adjuvant chemotherapy for patients with resectable, squamous cell carcinomas of the head and neck. One hundred and nine patients were excluded from this study due to positive surgical margins. These patients have been followed prospectively with regards to local/regional tumor control, development of distant metastases, and survival. The postoperative treatment of these patients was not specified by the protocol but the majority of patients received postoperative radiotherapy +/- chemotherapy. These patients were compared with a matched group of patients from the Radiation Therapy Oncology Group head and neck database of patients treated with definitive radiotherapy alone using a standard fractionation schema. Matching parameters included primary tumor site, T-stage, N-stage, Karnofsky performance status, and age.

RESULTS

Actuarial curves are presented for local/regional control and survival. At 4 years the local/regional control rate is 44% for the positive margin patients compared to 24% for the patients from the data base (p = 0.007). However, there is no significant difference between the survival curves (p = 0.76) with respective median survivals being 18.1 months vs. 17.9 months and 4-year survivals being 29% vs. 25%.

CONCLUSION

While an incomplete excision followed by postoperative therapy does not seem to improve survival compared to treatment with radiotherapy alone, it appears to yield significantly better local/regional control. This would argue for its applicability in selected palliative settings. A follow-up, Phase III trial for patients with advanced tumors may be warranted to test traditional resectability criteria.

Algorithm to control "effect compartment" drug concentrations in pharmacokinetic model-driven drug delivery

In most computer-controlled pharmacokinetic model-driven drug infusion pumps, simulation of a linear compartmental pharmacokinetic model is used to compute the rate of intravenous drug infusion required to achieve setpoint central compartment (plasma) drug concentrations. For many drugs, it has been suggested that it is the drug concentration in a hypothetical "effect" compartment, rather than in the plasma, that should be manipulated to achieve maximum control over pharmacologic action. Controlling the effect compartment drug concentration is algorithmically more difficult than controlling the central compartment drug concentration because of the time delay between administration of drug into the central compartment and its subsequent appearance in the effect compartment. Presented in this paper is a model-based dosing algorithm for use in pharmacokinetic model-driven drug infusion devices that target the theoretical effect compartment drug concentration.

Evaluation of the effect of alfentanil on the minimum alveolar concentration of halothane in horses

The effect of 3 plasma concentrations of alfentanil on the minimum alveolar concentration (MAC) of halothane in horses was evaluated. Five healthy geldings were anesthetized on 3 occasions, using halothane in oxygen administered through a mask. After induction of anesthesia, horses were instrumented for measurement of blood pressure, airway pressure, and end-tidal halothane concentrations. Blood samples, for measurement of pH and blood gas tensions, were taken from the facial artery. Positive pressure ventilation was begun, maintaining PaCO2 at 49.1 +/- 3.3 mm of Hg and airway pressure at 20 +/- 2 cm of H2O. The MAC was determined in triplicate, using a supramaximal electrical stimulus of the oral mucous membranes. Alfentanil infusion was then begun, using a computer-driven infusion pump to achieve and maintain 1 of 3 plasma concentrations of alfentanil. Starting at 30 minutes after the beginning of the infusion, MAC was redetermined in duplicate. Mean +/- SD measured plasma alfentanil concentration during the infusions were 94.8 +/- 29.0, 170.7 +/- 29.2 and 390.9 +/- 107.4 ng/ml. Significant changes in MAC were not observed for any concentration of alfentanil. Blood pressure was increased by infusion of alfentanil and was dose-related, but heart rate did not change. Pharmacokinetic variables of alfentanil were determined after its infusion and were not significantly different among the 3 doses.