Platelet-activating factor-induced ischemic bowel necrosis: the effect of platelet-activating factor acetylhydrolase

In the present investigation, the rat model of necrotizing enterocolitis (NEC) was further developed by injection of platelet-activating factor (PAF) in the descending aorta. The role of the plasma PAF-acetylhydrolase (PAF-AH) was examined in the prevention of this disease. PAF (0.35 micrograms) caused ischemic intestinal necrosis when administered intraaortically. The effects of PAF injection on the small intestine were examined histologically in samples of the duodenum, jejunum, and ileum. The administration of PAF resulted in extensive hemorrhagic damage in all regions of the small bowel and a marked hemoconcentration. Pretreatment of the rats with dexamethasone or medroxyprogesterone significantly increased plasma PAF-AH activity. Dexamethasone and medroxyprogesterone prevented the gross and histologic features of NEC as well as the hemoconcentration. In contrast, lower amounts of PAF were sufficient to cause bowel necrosis and hemoconcentration when decreased activities of plasma PAF-AH were induced by 17 alpha-ethynylestradiol or 4-aminopyrazolopyrimidine administration. We have recently reported that PAF-AH is present in human milk. The beneficial effect of breast feeding in preventing the development of NEC in the newborn is discussed and a mechanism proposed to explain this finding. It is suggested that PAF may play an important role in the pathogenesis of NEC and that the increased plasma activity of PAF-AH caused by dexamethasone and the presence of this enzyme, of milk origin, in the lumen of the small bowel may prove to be beneficial in the prevention of this disease.

Hormonal regulation of platelet-activating factor-acetyltransferase activity in rat tissues

Platelet-activating factor (PAF) plays a very important role in a number of physiological or pathological conditions. Recently, we and others have suggested that the PAF concentration in various tissues may be regulated by the enzyme that inactivates PAF, PAF acetylhydrolase (PAF-AH). Furthermore, it has been shown that the plasma isozyme of PAF-AH is regulated by various steroid hormone. Lyso-PAF:acetyl-CoA acetyltransferase (PAF-AT) is a key enzyme in PAF biosynthesis by the remodeling pathway. In the present study, the hormonal effects on the tissue levels of PAF-AT activity were investigated in various organs of the rat. The microsomal fraction was prepared from the spleen, lung, uterus, and liver of female rats which had been pretreated with dexamethasone, 17 alpha-ethynylestradiol, medroxyprogesterone-acetate, or vehicle and the PAF-AT activity was assayed. The rats treated with dexamethasone demonstrated significantly lower PAF-AT specific activity in the liver (P < 0.001) and spleen (P < 0.01), compared to the control group. A dose-dependent decrease of PAF-AT specific activity was demonstrated following dexamethasone treatment. Medroxyprogesterone injection also caused a significant decrease of PAF-AT activity in the liver (P < 0.01). No change of PAF-AT activity in any tissue was observed in the 17 alpha-ethynylestradiol-injected animals. Plasma PAF-AH activity was increased significantly by the administration of dexamethasone (P < 0.001) or medroxyprogesterone (P < 0.001), and decreased by 17 alpha-ethynylestradiol (P < 0.001), as previously described. The observation that dexamethasone or medroxyprogesterone treatment decreases the activity of PAF-AT and increases the plasma PAF-AH activity provides a mechanism for the tight control of PAF in tissues.

Model for the statewide delivery of programming services

Elements of a model for delivering behavioral programming services to individuals with mental retardation in residential, training, and educational settings were described. The model includes (a) identification of levels of behavioral competence among staff members, (b) an intervention approval process, (c) regional behavioral programming committees, (d) a doctoral advisory committee, (e) client advocacy committees, (f) a monitoring system, (g) a regulatory manual, and (h) leadership from a state agency office.

Platelet-activating factor in surfactant preparations

Surfactant administration is used for treatment of neonatal respiratory distress syndrome. We studied whether currently used surfactant preparations contain platelet-activating factor (PAF), a potent lipid mediator produced by fetal lungs. Three surfactant preparations from animal sources contained between 36 and 218 pmol of PAF per mL, whereas PAF was undetectable in an artificial surfactant. Based on current recommendations, about 144-654 pmol PAF would be administered per dose of natural surfactant, sufficient to exert possible physiological effects on the lung. The action of PAF may be exacerbated by low activity of PAF-acetylhydrolase, which inactivates PAF, in tracheal fluid from infants with respiratory distress syndrome.

Dopamine regulates D2 receptor gene expression in normal but not in tumorous rat pituitary cells

Abnormalities of dopamine D2 receptors may be implicated in the development of some pituitary tumours. Previously we have identified dopamine D2 receptor gene expression both in normal rat pituitaries and in dopamine resistant GH3 rat pituitary tumour cells. In this study we have examined the effect of dopamine on D2 receptor gene expression in these cells using a probe specific for both D2 receptor isoforms. Normal rat pituitary cells were maximally stimulated by 100 nM dopamine at which concentration D2 receptor mRNA concentrations were 400% greater than that measured in controls. No increase in D2 receptor gene expression was observed in GH3 pituitary tumour cells.

Secretion of platelet-activating factor acetylhydrolase following phorbol ester-stimulated differentiation of HL-60 cells

Platelet-activating factor (PAF) plays an important role in a number of biological processes ranging from inflammation to reproductive biology. We have reported that the enzyme that inactivates this potent autacoid, PAF-acetylhydrolase (PAF-AH), is decreased in maternal plasma during the latter stages of pregnancy. This enzyme is associated with the plasma lipoprotein fraction and therefore its tissue origin was thought to be the liver. Prescott and colleagues (J. Biol. Chem. 265, 17381, 1990) have reported that both a rat liver cell line (HepG2 cells) and human peripheral macrophages secrete PAF-AH of the plasma type. We have shown previously that the injection of rats with dexamethasone or medroxyprogesterone causes an increase and estrogen a decrease in the plasma PAF-AH activity. To clarify the mechanism of hormonal regulation of PAF-AH production, we employed a monocyte-macrophage model system to investigate the secretion of PAF-AH during differentiation. In the present study, we have demonstrated that a myelocytic leukemic cell line (HL-60) produces and secretes PAF-AH into a defined medium when the cells are differentiated into macrophages following stimulation by 12-O-tetradecanoylphorbol-13-acetate (TPA). The medium obtained from unstimulated HL-60 cells did not contain detectable amounts of PAF-AH activity. Stimulation with TPA caused a dose- and time-dependent increase in PAF-AH activity in the media. No increase in cell number was observed in the HL-60 cells during the culture period after the cells were treated with TPA. Cell lysis was excluded by the demonstration that the TPA-induced adherent cells excluded trypan blue and did not release lactate dehydrogenase activity into the medium. The increase in PAF-AH activity was inhibited by actinomycin D and cycloheximide. Dexamethasone and medroxyprogesterone markedly increased the secretion of PAF-AH by these cells, while estrogen was without effect. Bacterial endotoxin (lipopolysaccharide, LPS) inhibited the production of PAF-AH by these cells in a dose-dependent manner. The stimulation of PAF-AH secretion during differentiation of HL-60 cells and its modulation by LPS and steroid hormones may provide a useful model system for studying PAF metabolism during the inflammatory response and pregnancy.

[Analysis of platelet-activating factor and its effect on the lung]

One of the lipid mediators, platelet-activating factor (PAF), is reported to be involved in a variety of biological phenomena including not only harmful reactions such as allergy or inflammation, but also physiological phenomena like nerve cell differentiation, sperm mobilization, ovulation, implantation, parturition etc. We reviewed the methods of detecting PAF in biological fluids and the effects of PAF on fetal lung maturation and pulmonary diseases. Fetal lung has a capacity to produce PAF and this autacoid is involved in glycogen breakdown to furnish both glycerol backbone, such as dihydroxyacetone phosphate and glycerol-3-phosphate, and the fatty acids utilized to synthesize pulmonary surfactant. PAF also enhances secretion of pulmonary surfactant. However, PAF causes eosinophil recruitment to the lung, activation of eosinophil and neutrophil, bronchoconstriction, and lung edema, and increases bronchial hyperreactivity. All are characteristics of the pathophysiology of bronchial asthma. We examined PAF acetylhydrolase activity in plasma from patients with bronchial asthma, and found the activity was significantly lower in severe cases than that in mild or moderate cases. Ketotifen had no effect on this enzymatic activity. Evaluating PAF acetylhydrolase activity may help determine the severity of bronchial asthma. PAF is also involved in chronic lung disorders of newborns, such as bronchopulmonary dysplasia. We treated a 3-month-old child with frequent pulmonary problems who was made a diagnosis of bronchopulmonary dysplasia during neonatal period. After administration of Ketotifen for one and a half months, his clinical symptoms improved dramatically.

Platelet-activating factor-acetylhydrolase activity in normotensive and hypertensive pregnancies

OBJECTIVE

The purpose of our study was to evaluate the hypothesis that pregnancy is associated with decreased platelet-activating factor-acetylhydrolase activity in women with normotension, but not in women with hypertension.

STUDY DESIGN

We evaluated plasma platelet-activating factor-acetylhydrolase activity in normal nonpregnant women (n = 10), normal pregnant women (n = 24), pregnant women with pregnancy-induced hypertension-preeclampsia (n = 7), and a group of men with normotension (n = 10).

RESULTS

Platelet-activating factor-acetylhydrolase activity was lower at 32 weeks of gestation during normal pregnancies compared with nonpregnant controls (p < 0.001); however, in women with pregnancy-induced hypertension-preeclampsia, platelet-activating factor-acetylhydrolase activity was not decreased. Platelet-activating factor-acetylhydrolase activity in men was higher than in all women (p < 0.01).

CONCLUSION

Pregnant women with normotension may be refractory to pressor agents such as angiotensin II in part because of the decrease in plasma platelet-activating factor-acetylhydrolase activity, which results in an increase in platelet-activating factor. In contrast, enzyme activity is not decreased in pregnant women with hypertension, who have increased sensitivity to various pressor agents.

c-myc hypermutation in Burkitt's lymphoma

Translocation between the c-myc protooncogene and one of the three immunoglobulin loci is a cytogenetic hallmark of the B cell tumor, Burkitt's lymphoma. The resulting deregulation of c-myc expression is a critical step in tumorigenesis. The translocation breakpoint may lie within c-myc proper, in which case deregulation is due, in part, to dissociation of key 5' regulatory sequences from the protein-coding portions of the gene. Alternatively, the breakpoint may flank c-myc, leaving the gene grossly intact. In these latter cases, mutation, which may be extensive, is usually seen within c-myc, specifically at or near the same key regulatory sequences. The precise contribution of these mutations to c-myc deregulation is gradually being clarified. The mechanisms underlying c-myc mutations are not known. Hypermutation in c-myc may reflect the influence of the juxtaposed immunoglobulin gene, which is subject to hypermutation during an intermediate stage of normal B lymphoid development. This relationship, however, has not been firmly established.

Metabolic conversion of platelet-activating factor into ethanolamine plasmalogen in an amnion-derived cell line

Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF) labeled with 3H in the alkyl side chain was taken up rapidly by amnion-derived WISH cells in culture. The radioactivity was found in a number of cellular metabolites, principally 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (alkyl-acyl-GPC) which was labeled at a rapid rate. No intracellular accumulation of lyso-PAF was detected. At longer time periods, a substantial proportion of the radioactivity was found in association with the phosphatidylethanolamine fraction extracted from the cells. This fraction contained a high proportion of the corresponding 1',2'-alkenyl derivative (plasmalogen), as judged by the formation of long-chain fatty aldehyde after exposure to acid. The magnitude of the conversion of PAF into ethanolamine plasmalogen is suggestive of a correlation between plasmalogen content and exposure to PAF in some tissues. The exact sequence of reactions leading from alkyl-acyl-GPC to the ethanolamine derivatives is yet to be established.

Preparation and characterization of an antibody specific to the rat dopamine D2 receptor

Antibodies specific to the dopamine D2 receptor have been raised in rabbits using synthetic peptides. The resulting antiserum was sensitive to picogram quantities of peptide as measured by enzyme-linked immunoassay and was shown to have a 33% cross-reactivity with partially purified D2 receptor protein. No detectable cross-reactivity with similarly prepared fungal membranes was observed. D2 receptor preparations from normal rat pituitary cells were used in Western blot analysis. Bands of M(r) = 95,000 and 34,000 were detected in these preparations with a third faint band at 120,000. These correspond to the pituitary D2 receptor.

A shuttle vector system for the investigation of immunoglobulin gene hypermutation: absence of enhanced mutability in intermediate B cell lines

Somatic hypermutation focused to the rearranged V(D)J segment of the immunoglobulin (Ig) loci contributes substantially to antibody gene diversification. However, neither the precise B cell subset subject to hypermutation nor the molecular mechanism(s) involved is known. One model proposes that Ig segments may be uniquely susceptible to DNA nicking and subsequent error-prone repair during a specific B cell developmental stage. We describe an SV40-based shuttle vector system for testing such a model. Plasmids containing two distinct Ig segments juxtaposed to the supF marker gene have been passaged through cell lines representing intermediate stages of B cell development, rescued and screened for marker gene mutations. To date we have not demonstrated enhanced supF mutation in any cell line examined, irrespective of the adjacent Ig segment. Thus, these cell lines exhibit normal DNA repair mechanisms and no evidence of increased endonuclease activity on the Ig segments tested. The feasibility of this system will allow similar experiments using other Ig target sequences exposed to a broader range of B cells.

The presence of platelet-activating factor binding sites in human myometrium and their role in uterine contraction

It has recently been suggested that platelet-activating factor is involved in a number of processes associated with reproductive biology. We have demonstrated a critical role for this autacoid in the initiation and maintenance of parturition both in animals and man. In the present investigation, it has been demonstrated that platelet-activating factor affects contraction in strips of human myometrium at concentrations as low as 10(-10) mol/L. A platelet-activating factor receptor has been identified and characterized in human myometrium. Platelet-activating factor acts to cause an increase in intracellular Ca2+ concentration of isolated myometrial smooth muscle cells in culture and an increase in the phosphorylation of the 20 kd light chain of myosin in a concentration-dependent fashion. The presence of platelet-activating factor receptors in human myometrium, the observed increase in Ca2+ concentration and phosphorylation of myosin light chain in the presence of platelet-activating factor provide further support for the importance of this autacoid in the initiation of parturition.

Effect of a cigarette smoke extract on the metabolism of the proinflammatory autacoid, platelet-activating factor

Cigarette smoking is associated with an increased incidence of a number of diseases. Minimal information is available at the molecular level concerning the mechanism of action of cigarette smoke. Platelet-activating factor (PAF) is one of the most potent proinflammatory agents described. PAF concentration may be regulated by the degradation of PAF as catalyzed by the plasma enzyme, PAF acetylhydrolase (PAF-AH). This enzyme is associated with the lipoprotein fraction. The exposure of low density lipoprotein to a cigarette smoke extract (CSE) has been shown to alter the charge of low density lipoprotein and its uptake by macrophages. The activity of PAF-AH in the lipoprotein fraction has been assayed after exposure to CSE. The activity of PAF-AH was inhibited by the CSE in a dose-dependent manner. The inhibition of PAF-AH by the CSE was not altered by superoxide dismutase or catalase addition. Sulfhydryl compounds prevented and reversed the inhibition of PAF-AH caused by CSE. The inhibitor present in CSE was not nicotine, its major metabolic product, (-)-cotinine, or several compounds known to be present in the extract. The charge alteration reaction(s) and PAF-AH inhibition appear to be localized at different sites of the lipoprotein molecule. The observed inhibition may account for the increase in the plasma PAF concentration that is known to occur in smokers. The increase of PAF may contribute to the increased incidence of cardiovascular and lung diseases known to be present in smokers.

Relation between ruminating and quantity of food consumed

Data were summarized from 1,841 sessions involving 10 subjects who participated in a number of experiments over a 10-year research program concerning dietary influences on ruminating. Results showed the relation between the quantity of food consumed at meals and rates of postmeal ruminating. Some important features of this relation were discussed.

The hormonal regulation of platelet-activating factor-acetylhydrolase in the rat

Platelet-activating factor-acetylhydrolase (PAF-AH), the enzyme that inactivates PAF, is decreased in the plasma of both rabbits and humans during the latter stages of pregnancy. The activity of the enzyme was decreased in rats by the administration of 1,3,5(10)-estratrien-17 alpha-ethynyl-3,17 beta-diol (17 alpha-ethynylestradiol) and increased by dexamethasone treatment. In the present study, we have further defined the hormonal regulation of PAF-AH levels in plasma of adult and juvenile rats. Estrone (E1), 17 beta-estradiol (E2), estriol (E3), and various progestins [4-pregnen-6 alpha-methyl-17 alpha-ol-3,20-dione (medroxyprogesterone), 4-estren-17 alpha-ethynyl-17 beta-ol-3-one (norethindrone), and 5(10)-estren-17 alpha-ethynyl-17 beta-ol-3-one (norethynodrel)] were administered to adult rats, and the plasma PAF-AH activities were assayed. E1, E2, and E3 administration to adult female rats lowered the plasma PAF-AH activity, E3 being the most effective. After administration of these estrogens the activity returned to the preinjection level within 4 days. The administration of medroxyprogesterone resulted in a 2-fold increase in plasma PAF-AH activity in adult female rats, and the activity remained elevated for up to 30 days. When adult male rats were treated with similar doses only a 20% increase was observed and the PAF-AH activity returned to control values by day 10. In contrast, norethindrone and norethynodrel administration resulted in a reduction of the enzyme activity in adult female rats. The plasma PAF-AH activity in juvenile male and female rats (3 weeks of age, 45-60 g body wt) was two times higher than that in adult rats of both sexes and spontaneously decreased up to the time of puberty. When juvenile male or female rats were injected with either 17 alpha-ethynylestradiol or medroxyprogesterone, a minimal change in PAF-AH activity was observed. In contrast, when dexamethasone was administered to juvenile male and female rats the plasma PAF-AH activity increased in a manner similar to adult animals. It is suggested that estrogens cause a decrease and medroxyprogesterone an increase in plasma PAF-AH activity. It is suggested that the different responsiveness to medroxyprogesterone between adult female and male rats and juvenile animals may depend on the concentration of the hormone receptor in the tissue responsible for the synthesis of PAF-AH. The decrease in PAF-AH activity after the administration of norethindrone and norethynodrel may be due to the known estrogenic activity of these steroids.

The hormonal regulation of platelet-activating factor acetylhydrolase activity in plasma

We have previously reported that certain fetal tissues including the lung and kidney have an increased platelet-activating factor (PAF) content and enzymatic mechanism for its elevated biosynthesis during the latter stages of pregnancy. In contrast, in the maternal plasma compartment of both the rabbit and human, a decreased capacity to inactivate PAF has been demonstrated. The PAF acetylhydrolase in the fetal plasma is also suppressed. The present study was undertaken to determine the mechanism(s) involved in the regulation of PAF acetylhydrolase. The 17 alpha-ethynylestradiol was administered (intraperitoneal [i.p.] 2.5 mg/kg body wt 5 days) to female and male rats. The plasma PAF acetylhydrolase activity decreased 5-fold. A decrease was observed when a concentration of the estrogen as low as 50 micrograms/kg was employed. The injection of dexamethasone (i.p., 1.3 mg/kg body wt, 5 days) to male and female rats resulted in a 3-fold increase in the plasma PAF acetylhydrolase activity. The activity returned to the values prior to hormone treatment 4 days after cessation of treatment. Testosterone and progesterone were without effect on plasma acetylhydrolase activity. The change in PAF acetylhydrolase activity caused by estrogen and the glucocorticoid was reflected by a change in the activity in the HDL fraction and not due to the presence of an inhibitor or activator in the plasma of the hormone-treated animals. Human serum obtained from a group of women, in which the 17 beta-estradiol concentration was elevated in preparation for an in vitro fertilization procedure, showed an inverse relationship between the plasma estrogen concentration and the PAF acetylhydrolase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine, the dopamine D2 receptor and pituitary tumours

Dopamine plays an important role in the hypothalamic-pituitary axis where its major effects are to inhibit pituitary hormone secretion and cell division. Chronic dopamine deficiency has been postulated as a cause of pituitary tumour formation and several lines of evidence exist to suggest that a functional deficiency may develop as a result of defective dopamine receptor action. The available data suggest that a number of sites in the dopamine-D2 receptor-second messenger pathways may be implicated. These abnormalities are reflected in the variety of responses to dopamine and its agonists which have been observed in pituitary tumours both in the clinical situation and in cultured cells in vitro. Whilst it seems likely that the primary defect in pituitary tumour formation lies within the pituitary itself, the role of hypothalamic factors in facilitating tumour growth remains to be explored. Further studies of the dopamine receptor and its function will be of value not only in pathophysiological studies of human pituitary adenomas, but also in the development of new pharmacological agents to treat patients with these tumours.

Developmental expression of glycogenolytic enzymes in rabbit tissues: possible relationship to fetal lung maturation

Glycogen can be degraded in mammalian tissues by one of three isozymes of glycogen phosphorylase, termed muscle (M), liver (L) and brain (B) after the tissues in which they are preferentially expressed in adult animals, or by members of the family of alpha-glucosidases. In the current study, we have examined the developmental expression of these enzymes and their respective mRNAs in rabbit tissues, with particular emphasis on the developing lung, a tissue in which glycogen serves as an important source of carbon for surfactant phospholipid biosynthesis. Native gel activity assays and RNA blot hybridization analysis revealed that the B isoform of glycogen phosphorylase predominates in fetal and adult lung tissues, accompanied by a low level of expression of the M isoform. Total B and M phosphorylase activities increased during fetal lung development, with a peak at day 28 of gestation, then decreased to the adult level at term. This peak in activity coincided with the peak period of glycogen degradation in developing lung. While the increase in M isozyme activity was correlated with an increase in the level of its mRNA, B isoform mRNA showed no significant alteration during development, suggesting that the increase in B isoform activity is determined by a posttranscriptional mechanism. Analysis of phosphorylase mRNA levels in developing liver, skeletal muscle, brain and heart revealed a diverse expression pattern. The L isozyme mRNA was predominant at all time points in liver, the M isozyme was predominant at all time points in muscle, the B isozyme was predominant at all time points in brain, and heart contained a mixture of B and M mRNA in roughly equal ratios at all time points. Thus, our studies of phosphorylase mRNA in the rabbit provide no evidence for general predominance of the B isozyme in fetal tissues, or for isozyme 'switching' from the B to the L or M forms during development, as has been suggested by others. In addition to the increase in phosphorylase activity, acid, but not neutral alpha-glucosidase activity was found to increase significantly during fetal lung development, again with a peak at day 28 of gestation. Interestingly, RNA blot hybridization analysis with a probe for lysosomal alpha-glucosidase revealed no change in the level of expression of its 4 kb transcript in developing lung. Instead, we observed induction of a structurally related mRNA of 7.4 kb that peaked at day 28 of gestation. Hybridization with a sucrase/isomaltase-specific oligonucleotide excluded the possibility that the 7.4 kb transcript encodes this protein.(ABSTRACT TRUNCATED AT 400 WORDS)

c-myc hypermutation is ongoing in endemic, but not all Burkitt's lymphoma

Deregulation of c-myc oncogene secondary to chromosomal translocation appears to play an essential role in the genesis of both endemic (African) Burkitt's lymphoma (eBL) and sporadic Burkitt's lymphoma (sBL). In most eBL, mutations in or near exon 1 disrupt normal c-myc regulatory sites. We examined c-myc sequences from a patient with sBL and two patients with eBL to determine (1) whether mutation is ongoing as the tumor clone expands, (2) the nature of mutations in the protein-coding exons 2 and 3, and (3) the extent of c-myc hypermutation in the two clinical forms of BL. Using the polymerase chain reaction (PCR), we amplified segments of c-myc from bulk tumor samples, cloned the products into plasmid vectors, and sequenced multiple subclones of each segment. The mutation frequencies in the control (remission bone marrow) and sBL tumor subclones were 0.65 x 10(-4) and 3.0 x 10(-4) (mutations/base), respectively (P greater than .25). Subclones from the two eBLs exhibited mutation frequencies of 20 x 10(-4) and 16 x 10(-4), respectively (P less than .001 v control). In addition to the consensus mutations seen in one eBL, a random pattern of unshared mutations was observed throughout c-myc in both samples, demonstrating that mutations may be introduced in a stepwise fashion. We noted a clear excess of transitions over transversions (30:9), which is qualitatively similar to the pattern observed in diverse examples of eukaryotic gene mutation. These data demonstrate that c-myc hypermutation is an ongoing process as the eBL tumor clone expands, is qualitatively different from immunoglobulin gene hypermutation, and is not a universal feature of BL, perhaps reflecting the nature of the translocation or the stage of tumor cell maturation.

The dopamine D2 receptor is expressed in GH3 cells

Some pituitary tumours respond to dopamine by decreasing the release of prolactin and/or GH and by inhibition of tumour growth. Certain tumours are unresponsive. Dopamine D2 receptor high-affinity binding is impaired in these tumours, and the rat GH3 cell line behaves in a similar way. The hypothesis that the dopamine-binding defect results from impaired D2 receptor gene expression has been tested in the present study. On Northern blots, D2 receptor mRNA was present in both normal rat pituitary cells and in GH3 cells. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis identified a putative D2 receptor protein in normal and GH3 cell membranes. The lack of effect of dopamine in GH3 cells does not reflect the absence of D2 receptor gene expression.

Antibodies in patients with recurrent respiratory papillomatosis treated with lymphoblastoid interferon

Serum specimens from 53 evaluable patients enrolled in a clinical trial of lymphoblastoid interferon in recurrent respiratory papillomatosis were screened for the presence of interferon-binding antibodies by an indirect enzyme immunoassay and evaluated for neutralizing antibody measured as the inhibition of antiviral activity. Immunoglobulin G antibodies that specifically bound lymphoblastoid interferon were detected in 66% (35 of 53) of patients; neutralizing antibody was detected in 11 of the 35 patients having binding antibody (and in none of the patients who were negative for binding antibody). The incidence of detectable neutralizing antibody in this study population was 20.8% (11 of 53), which is markedly higher than in previous reports of lymphoblastoid interferon in patients with other diseases (i.e., less than 1% incidence). The cumulative dose received at the time of detection of neutralizing antibody ranged from 163 to 385 MU per square meter of body surface. Neutralizing antibody was detectable at a median time of 120 days after initiation of interferon therapy, and binding antibody appeared earlier in those patients (median 59 days) than in patients in whom only binding antibody was produced (median 116 days). Despite the tendency of binding antibody to appear either in patients in whom neutralizing antibody was eventually formed, the detection of binding antibody was not necessarily predictive of the subsequent development of neutralizing antibodies. Binding antibody persisted after neutralizing antibodies had become undetectable.(ABSTRACT TRUNCATED AT 250 WORDS)