Efficacy of ezetimibe/simvastatin 10/40 mg compared to doubling the dose of low-, medium- and high-potency statin monotherapy in patients with a recent coronary event.

OBJECTIVE: The aim of the study was to compare the efficacy/safety of doubling the dose of low-, medium- and high-potency statins on lipids/lipoproteins versus ezetimibe/simvastatin (EZE/SIMVA) 10/40 mg in patients with a recent coronary event. METHODS: In this open-label study, patients were stratified by baseline statin therapy (low, medium and high potency) and randomized equally to statin dose doubling or EZE/SIMVA 10/40 mg for 12 weeks. Primary analysis concerned change in low-density lipoprotein cholesterol for the whole population. Treatment-by-stratum interaction evaluated the consistency of treatment effect across statin potency strata. Post hoc analysis of between-group efficacy within strata was performed using ANCOVA. RESULTS: Within each stratum, EZE/SIMVA produced significantly greater reductions in low-density lipoprotein cholesterol, total cholesterol, apolipoprotein B and non-high-density lipoprotein cholesterol (HDL-C) compared to statin doubling. Numerical trends toward smaller between-group reductions were observed with higher-potency statins and reached statistical significance for apolipoprotein B and non-HDL-C. No significant between-group differences in HDL-C and C-reactive protein were observed within each stratum. EZE/SIMVA produced larger reductions in triglycerides versus low-potency statin, whereas it was similarly effective compared with intermediate-/high-potency statins. The safety/tolerability profiles of the treatments were similar across the strata. CONCLUSIONS: EZE/SIMVA 10/40 mg produced greater improvements in lipids with a similar safety profile compared to doubling the dose of low-, medium- and high-potency statins.

The effect of volatile fatty acids in acidified fermented piggery effluent on shiga-toxigenic and non-toxic resident strains of Escherichia coli.

AIMS: To examine the effects of acidified acidogenically fermented piggery effluent containing Volatile Fatty Acids (VFA) on shiga-toxigenic and resident strains of Escherichia coli (E. coli) as part of the development of a waste treatment process. METHODS AND RESULTS: Four shiga-toxigenic E. coli strains (O157:H7, 091.H-, 0111.H-, and 0123.H-) and four non-toxic resident enzootic strains were all killed by 3 h treatment with fermented piggery effluent liquor (153 mmol l(-1) total VFA) at pH 4.3. The shiga-toxigenic strains showed greater sensitivity after 1 h of treatment. The fermented liquor at pH 6.8 was not inhibitory. CONCLUSIONS: The shiga-toxigenic strains were no more resistant to the toxic effects of VFA than the non-toxic strains tested. SIGNIFICANCE AND IMPACT OF THE STUDY: Shiga-toxigenic strains and resident enzootic non-toxigenic strains are equally susceptible to inactivation by this waste treatment process and by acidified VFA in general.

Intrapericardial delivery of L-arginine reduces the increased severity of ventricular arrhythmias during sympathetic stimulation in dogs with acute coronary occlusion: nitric oxide modulates sympathetic effects on ventricular electrophysiological properties.

BACKGROUND: Nitric oxide (NO) modulates autonomic effects on myocardial contractility and sinus and atrioventricular nodal function of the heart. Whether NO influences autonomic actions on ventricular electrophysiological properties and arrhythmogenesis is not known. METHODS AND RESULTS: Four groups consisting of 43 autonomically denervated dogs were studied. To "superfuse" sympathetic nerves innervating the ventricles, test drugs were introduced into the pericardial sac for 30 minutes, and their effects on ventricular effective refractory period (ERP) and arrhythmia development were assessed before and during sympathetic stimulation (SS). In group 1 (n=12), ventricular ERPs showed no significant difference between control and superfusion with L-arginine, a NO precursor (222+/-20 versus 222+/-19 ms, P=.485). However, L-arginine significantly reduced SS-induced ERP shortening compared with control (9+/-7 versus 13+/-7 ms, P<.001). Simultaneous administration of N(G)-monomethyl-L-arginine (2 mg/mL) abolished the inhibitory effects of L-arginine (13+/-7 versus 13+/-7 ms, P=.885). In group 2 (n=15), the severity of ventricular arrhythmias significantly increased during SS. L-Arginine reduced this increase caused by SS. In group 3 (n=8), plasma norepinephrine spillover measured from the coronary sinus significantly increased during SS and was reduced by pericardial superfusion with L-arginine compared with control (6005.2+/-1525.6 versus 8503.4+/-2044.5 pg/min, P=.012). In group 4 (n=8), L-arginine pericardial superfusion significantly increased NO overflow measured from the coronary sinus during SS (93.25+/-59.20 versus 114.82+/-74.92 nmol/min, P=.043). CONCLUSIONS: Pericardial L-arginine reduces ERP shortening and increased severity of ischemic ventricular arrhythmias during SS in dogs. NO-induced reduction of norepinephrine release in the heart may be one of the underlying mechanisms.

Analysis of insulin-like growth factors (IGF)-I, and -II, type II IGF receptor and IGF-binding protein-2 mRNA and peptide levels in normal and nephrectomized rat kidney.

Immunocytochemistry, in situ hybridization, and radioimmunoassay were employed to examine the cellular distribution of mRNAs and proteins for IGF-I, II, IGF-II/M6P receptor, IGFBP2 as well as the levels of IGF-I and II in normal and unilaterally nephrectomized (Nx) adult rat kidneys. A similar distribution of immunoreactive IGF-I, and -II as well as IGF-II/M6P receptor was found in the principal cells of the cortical collecting duct and in all cells of the inner medullary collecting duct. In addition, immunostainable IGF-I and IGF-II/M6P receptor were noted in some inner medullary loops of Henle, while IGFBP2 was seen in the collecting ducts and loops of Henle of the inner medullar and the renal vasculature of all animals. By comparison, in situ hybridization revealed IGF-I mRNA only in the medullary thick ascending limbs while IGF-II mRNA was localized to the wall of the renal microvasculature in all kidneys. IGFBP2 mRNA was localized to the renal corpuscle and to inner medullary interstitial cells of all kidneys. These data suggest that renal IGF-I and IGFBP2 are synthesized at upstream sites along the nephron and then transported downstream for interaction with IGF receptors. Following nephrectomy, the renal levels of IGF-I peptide and mRNA were elevated at both 5 and 33 days post-nephrectomy, supporting a potential functional role for IGF-I in stimulating the structural and functional recovery in compensatory hypertrophy.

In vivo renal production and tubular secretion of tyramine.

Para-tyramine (p-TYM) is a predominant urinary amine in humans, rabbit, rat and dog, and its urinary excretion rate may reflect central nervous system pathophysiology. However, the source of urinary p-TYM is not known, nor have the mechanisms regulating its excretion been characterized. The present study, by using renal clearance techniques, examined the sources of urinary p-TYM and the mechanism of excretion in anesthetized rabbits. In all studies, the renal clearance of p-TYM was compared with that of norepinephrine (NE). Base-line delivery to the kidney of p-TYM in plasma was 8.6 +/- 1.6 ng/min (mean +/- S.E.M., n = 16), whereas the mean urinary excretion rate of p-TYM was 26.5 +/- 3.6 ng/min during the same period (P < .001 vs. delivery). In three separate series of experiments, either vehicle (n = 5) or a specific inhibitor of renal tubular organic cation secretion, cyanine 863 (6 mg/kg, n = 7), or a specific inhibitor of aromatic-amino acid-decarboxylase, alpha-mono-fluoromethyldopa (FMD, 4 mg/kg, n = 5), were infused i.v., Mean arterial pressure, glomerular filtration rate, renal plasma flow and urine flow rate were unchanged in all studies. The renal clearances of p-TYM (Cp-TYM) and NE (CNE) were unchanged only after vehicle. After cyanine 863, Cp-TYM was decreased to 36% of control (P < .01), whereas CNE decreased to 21% of its base-line value (P < .01). After FMD Cp-TYM was reduced to 2% of control (P < .05), whereas CNE decreased by 44% (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between insulin and norepinephrine on blood pressure and insulin sensitivity. Studies in lean and obese men.

To explore the interactions between insulin action and norepinephrine (NE) on blood pressure and muscle vascular resistance, we studied seven lean (66 +/- 1 kg) sensitive and seven age-matched obese (96 +/- 3 kg) insulin-resistant men after an overnight fast. Both groups were normotensive; however, the obese exhibited higher basal blood pressure, 90.8 +/- 2.2 vs. 83.4 +/- 1.6 mmHg, P < 0.04. Each subject was studied on two separate days during either saline (S) infusion or a euglycemic hyperinsulinemic clamp (I) achieving insulin concentrations of approximately 70 microU/ml. After 180 min of either S or I, NE was infused systemically at rates of approximately 50, 75, and 100 pg/kg per min. Glucose uptake was measured in whole body ([3-3H]glucose) and in leg by the balance technique. The results indicate: (a) the NE/pressor dose-response curve was decreased (shifted to the right) during I in lean but not in obese subjects, (b) I enhanced NE metabolic clearance by 20% in lean but not in obese, (c) NE decreases leg vascular resistance more in lean than in obese, and (d) NE causes a approximately 20% increase in insulin-mediated glucose uptake in both groups. In conclusion, insulin resistance of obesity is associated with an apparent augmented NE pressor sensitivity and decreased NE metabolic clearance. Both of these mechanisms can potentially contribute to the higher incidence of hypertension in obese man. Insulin resistance is likely to be a predisposing but not sufficient factor in the pathogenesis of hypertension. Because the obese group exhibited higher basal blood pressure, it is possible that our results reflect this difference. Further studies will be required to clarify this issue.

Effect of recombinant human growth hormone on adreno-cortical function, and on sodium and potassium homeostasis.

In the present study we examined the effect of treatment with recombinant human growth hormone (rhGH) on adrenocortical secretory function, as well as sodium and potassium balance. rhGH, 100 micrograms/kg per day, was given for 4 days. Both glucocorticoid and androgen secretion were unaffected by treatment as evidence by unchanged levels of cortisol and dehydroepiandrosterone-sulfate. rhGH resulted in retention of sodium and potassium and a decrease in serum potassium concentration, but neither aldosterone plasma levels nor urinary excretion rates changed until after treatment. During the rhGH washout phase, a natriuresis ensued, but this occurred slowly possibly in part because a higher serum potassium stimulated aldosterone secretion. In summary, short-term treatment with rhGH had no immediate effect on adrenocortical function, but caused pronounced retention of electrolytes. In the posttreatment period, there were increases in aldosterone secretion accompanied by delayed recovery from the retention of sodium.

Contributory role of lung pleura to release of anaphylactic mediators from guinea pig lung in response to ovalbumin or A23187.

Previous findings revealed greater contractile responses of guinea pig lung pleural surface strips to antigen or A23187 challenge than denuded lung parenchymal strips (lung strip devoid of any pleura). Moreover, we have identified a high density of mast cells distributed throughout the lung pleura. The present study examined mediators released from guinea pig lung pleural surface and denuded lung parenchyma fragments in response to immunologic challenge with ovalbumin (OA) or non-immunologic challenge with the ionophore A23187. Histamine levels were measured radioenzymatically; leukotrienes (LTs), prostaglandins (PGs) and thromboxane B2 (TXB2), a stable metabolite of thromboxane A2 (TXA2), were quantitated using an enzyme immunoassay. Histamine release reached a maximal level 3-5 min after OA challenge, whereas A23187-induced histamine release increased gradually in a time-dependent manner. Similar kinetics were observed in the release of LTs, PGs and TXA2. Pleural surface released a substantially (P < 0.05) greater amount of histamine to both challenges than denuded parenchyma. Moreover, histamine content in pleural surface was significantly (P < 0.05) higher than in denuded parenchyma. Pleural surface also released considerably (P < 0.05) more LTB4, LTC4, and LTE4 in response to OA and A23187 than denuded parenchyma. In contrast, pleural surface and denuded parenchyma released equivalent amounts of PGD2, PGE2, PGF2 alpha, and TXA2 in response to both challenges. The rank order of leukotriene release was LTC4 > LTE4 > LTB4, whereas that of prostanoid release was TXA2 >> PGD2 > or = PGF2 alpha >> PGE2. We conclude that pleural surface is the major source of histamine and leukotrienes released from guinea pig lung in vitro in response to OA and A23187, whereas both pleural surface and denuded parenchyma participate to the same extent in prostaglandin and TXA2 production after such challenges.

The interaction of norepinephrine excretion with blood pressure and race in children.

OBJECTIVE: The purpose of this study was to examine the relationship between urinary norepinephrine excretion and blood pressure, and to determine the influence of race on this relationship. Urinary norepinephrine was used to estimate renal and systemic sympathetic nervous system (SNS) activity. DESIGN: Fifty black and forty-nine white normotensive children aged 9-14 years had their blood pressure measured, and provided an overnight urine sample. METHODS: Urinary norepinephrine was measured by radioenzymatic assay. Excretion rates of norepinephrine were expressed per milligram urinary creatinine. RESULTS: Black children had age-adjusted mean diastolic and systolic blood pressure which was higher than in white children. For both blacks and whites, nocturnal urinary norepinephrine excretion rates were positively related to age-adjusted mean diastolic blood pressure, but not to systolic blood pressure. Norepinephrine excretion was significantly lower in black children compared with white children. CONCLUSION: These findings suggest that the higher blood pressures in black children were not causally related to greater SNS activity. The SNS may have been suppressed in black children, possibly by a greater expansion of plasma volume, alternatively, black children may have been more sensitive to the influences of the SNS than white children.

Measurement of insulin-like growth factor-II in physiological fluids and tissues. I. An improved extraction procedure and radioimmunoassay for human and rat fluids.

The measurement of serum insulin-like growth factors (IGFs) in serum is complicated by the presence of high affinity IGF-binding proteins. The accurate measurement of IGFs by radioligand binding assays requires that the interference from binding proteins be eliminated. Acid-gel chromatography, the standard method for removing binding proteins, is laborious and time consuming. Alternative methods for extracting serum IGFs include the use of HCl-ethanol treatment and reverse phase minicolumns. However, these methods are unsuitable for use with serum for some species, such as rat and sheep, due to incomplete removal of binding proteins. We developed a fast protein liquid chromatography size-exclusion chromatographic method for characterizing the presence of IGF-binding proteins in physiological fluids and used this method to systematically investigate different combinations of acids and organic solvents as potential extraction methods for IGFs. We developed and validated an improved extraction procedure that uses formic acid, Tween-20, and acetone. The new extraction method was used in conjunction with purified biosynthetic human IGF-II and a commercially available anti-IGF-II monoclonal antibody in the development of an improved RIA for IGF-II. The new RIA is sensitive (5.0 pg/tube), specific (IGF-I cross-reactivity, less than 1%), and reproducible [interassay precision (coefficient of variation), less than 9.2%). We measured the serum concentrations of IGF-II in adults and found a significant difference between normal subjects and individuals with insulin-dependent diabetes mellitus.

Measurement of insulin-like growth factor-II in physiological fluids and tissues. II. Extraction quantification in rat tissues.

The tissue distribution and developmental patterns of insulin-like growth factor-II (IGF-II) have not been investigated in rat tissues, primarily because of the lack of an efficient extraction method for IGF-II and a sensitive RIA. IGF-II was extracted from rat tissues by formic acid, and the extract was heated at an acidic pH and treated with acetone. The removal of binding proteins was demonstrated by fast protein liquid chromatography size exclusion column and the elimination of a dilutional bias in the RIA. Using rat IGF-II as standard, we optimized a RIA for the quantification of IGF-II in rat tissues. In adult rats, IGF-II was found in all 15 tissues examined, with the highest concentration in the pituitary, followed by kidney, seminal vesicles, intestine, and serum. This distribution is not only different from that of IGF-I, but also differs from that reported for IGF-II mRNA and IGF-II receptors, suggesting that the rates of synthesis and/or metabolism of IGF-II are tissue dependent. Developmentally, IGF-II levels fell postnatally in most tissues, a pattern similar to that of IGF-II mRNA and IGF-II receptor. This developmental pattern supports the hypothesis that IGF-II is important in early growth and development. A relatively homogeneous distribution was observed in the adult rat brain, a distribution also different from that reported for IGF-II mRNA. In the pituitary, the highest concentration was found in the posterior pituitary, followed by the intermediate and anterior pituitary. In conclusion, IGF-II is found in many tissues of adult rats. This observation supports an autocrine and/or paracrine roles for IGF-II.

Radioenzymatic assay for histamine: development and validation.

Radioenzymatic assays are sensitive analytic tools that use an enzyme to quantify a substrate for that enzyme. Purified histamine N-methyltransferase has been used as the basis for an assay for histamine. The sensitivity of the procedure is less than 10 fmol. The specificity of the assay is increased when the transferase reaction is carried out at 0-3 degrees C. Data documenting the precision of the assay, the stability of histamine in human plasma, and the gastric secretory rate of histamine are presented along with a chronologic description of the development of the technique.

Conversion of p-tyrosine to p-tyramine in the isolated perfused rat kidney: modulation by perfusate concentrations of p-tyrosine.

We used the isolated perfused rat kidney to evaluate the role of renal decarboxylation of p-tyrosine as the source of urinary p-tyramine. Kidneys were perfused with concentrations of p-tyrosine ranging from 0.02 mM to 2.0 mM. p-Tyramine was measured by a sensitive and specific radioenzymatic assay. An increase in the perfusate concentration of p-tyrosine resulted in a significant increase in p-tyramine production that was blocked by the addition of NSD-1015, an inhibitor of aromatic-1-amino decarboxylase (AADC). We conclude p-tyrosine is the precursor for the renal production of p-tyramine, renal AADC catalyzes the formation of urinary p-tyramine, synthesized p-tyramine is predominantly excreted in the urine, and p-tyramine synthesis is modulated by the arterial delivery of p-tyrosine to the kidney.

An assessment of plasma histamine concentrations during documented endotoxic shock.

Recent reviews of the literature involving histamine release during sepsis and endotoxemia have reported that the majority of the studies are inconclusive due to inadequate assays or experimental protocols. In a controlled experimental setting we have employed a specific and sensitive radioenzymatic assay to determine plasma histamine concentrations temporally during documented endotoxin-induced shock in the conscious rat. Cardiovascular and metabolic measurements for the control group (n = 7) were normal during the study period. Endotoxin (n = 8, LD/90-24 hrs.) induced an early transient hypotensive episode and increase in systemic vascular resistance and a sustained decrease in cardiac index and central venous pressure and increase in heart and respiratory rates. Hypoglycemia and hyperlacticemia were present at the end of the four-hour study period. The small intestine was severely hemorrhaged in all animals given endotoxin. Histamine concentrations for the control group were unchanged throughout the study period. Contrary to previous reports, this model of endotoxemia revealed unchanging histamine concentrations during the first 30 minutes which were temporally coincident with the characteristic early hypotensive episode evoked by endotoxin. The histamine concentrations at 60 and 240 minutes following endotoxin were increased two and three-fold, respectively, compared to the control group. Three of the 8 rats given endotoxin died before four hours; histamine concentrations in plasma taken when death appeared certain were 42, 91, and 174, compared to the control value of approximately 8 ng/ml. There was no clear association of the increases in plasma histamine with any of the parameters measured in this study: however, established histamine effects may have been masked by the pre-existing effects of other mediators known to be active during endotoxemia. In separate groups of animals endotoxin (n = 5) elicited early increases in plasma concentrations of norepinephrine (5-fold) and epinephrine (8-fold) that remained elevated for the 4-hour study period while the control group (n = 4) remained stable. This study establishes that a) plasma histamine concentrations are increased during endotoxemia, b) plasma histamine is not elevated during the initial hypotension episode following endotoxin, c) plasma histamine increases during the progression of endotoxic shock, and d) plasma histamine concentrations are extremely high prior to death.

Determination of norepinephrine levels in the adult human prostate.

Tissue levels of norepinephrine were measured in prostate tissue from 24 men ranging in age between 41 and 83 years. Prostatic tissue was obtained from men with subtle palpable prostate nodules undergoing transperineal needle biopsy. None of the patients were shown to have histologic evidence of adenocarcinoma. The severity of the symptoms of prostatism was evaluated prospectively using a standardized micturition symptom score questionnaire. Norepinephrine levels were quantified using a sensitive radioenzymatic assay (REA). Overall, the prostates contained relatively high levels of norepinephrine (1666 +/- 124 ng./gm.). Inverse correlations were observed between tissue norepinephrine levels and severity of symptoms of prostatism (r = -0.58; p = 0.003); age (r = -0.53; p = .008); and prostate size (r = -0.48; p = .02). Norepinephrine levels were also measured in tissue specimens obtained from men undergoing enucleation prostatectomy and transurethral resection of the prostate (TURP). The level of norepinephrine in these prostatectomy specimens (115 ng./gm.) was only 14% the level of the prostate biopsy specimens. The relatively low level of norepinephrine in the specimens obtained from patients with symptoms necessitating prostatectomy provides further evidence that norepinephrine levels are inversely related to the degree of symptomatic bladder outlet obstruction.

Leukotriene receptor antagonism and augmentation of beta-receptor-mediated events by LY171883.

LY171883, (1-[2-hydroxy-3-propyl-4-[4(1H-tetrazol-5-yl)butoxy)phenyl]etha none), a leukotriene (LT) D4/E4 receptor antagonist, was assessed in comparison with two well known phosphodiesterase inhibitors, isobutylmethyl-xanthine (IBMX) and theophylline, for its ability to augment beta-receptor-mediated responses. Relaxation of carbachol-contracted guinea-pig trachea by isoprenaline was enhanced by the three agents in a dose-dependent manner. A two-fold enhancement of isoprenaline-induced smooth muscle relaxation was produced by 2.5 microM IBMX, 28 microM LY171883, or 140 microM theophylline. Similar concentrations of IBMX or theophylline did not antagonize LTE4-induced tracheal contractions; LY171883 totally inhibited the response and had significant LTE4 receptor antagonist activity even at 10-fold lower concentrations. Antigen-induced release of histamine and LTC4 from guinea-pig lung was reduced by isoprenaline. Prior treatment with LY171883, IBMX, or theophylline did not enhance this action. Isoprenaline reduced histamine-induced bronchospasm in anaesthetized guinea-pigs. LY171883, 30 mg kg-1, or IBMX, 1 mg kg-1, did not affect the isoprenaline-induced decrease in the histamine response. IBMX, 3 mg kg-1, and theophylline, 30 mg kg-1, augmented the isoprenaline-induced bronchodilation. LTE4-induced bronchoconstriction was not affected by IBMX or theophylline whereas LY171883 antagonized this response at doses as low as 3 mg kg-1. Therefore, in both in-vitro and in-vivo test systems, LY171883 functioned primarily as a leukotriene receptor antagonist with minimal pharmacological activity attributable to its ability to potentiate isoprenaline.

Effect of treatment with biosynthetic human growth hormone (GH) on peripheral blood lymphocyte populations and function in growth hormone-deficient children.

GH influences the immune response. The mechanism is not known; however, the presence of receptors for GH on human lymphocytes as well as its ability to influence and modulate immune responses in animals suggest an association between GH and immune function in man. We evaluated the effect of recombinantly derived natural sequence human GH (hGH) on lymphocyte surface antigen expression, response to mitogenic stimulation, expression of interleukin-1 receptors, and production of anti-hGH antibodies in GH-deficient children. The only observed changes were a decrease in the percentage of B-cells and a transient increased reactivity to phytohemagglutinin stimulation. It appears from the results of our studies that the administration of hGH has a selective effect on lymphocyte immune function; however, we cannot eliminate a role for hGH in the initiation or regulation of antigen-mediated immune responses.

Release of histamine in rat hypothalamus and corpus striatum in vivo.

Histamine has remained a putative neurotransmitter for many years, partially because some of the criteria necessary to define it as a central nervous system neurotransmitter have not been established. The demonstration of in vitro release and the quantification of turnover as an indirect measure of release have been complicated by the histological evidence for multiple histamine pools in the central nervous system. In brain, there are multiple cell types which probably contain histamine. These cells include mast cells, neurolipomastocytoid cells, microvascular endothelial cells, and a histaminergic neuronal system which has been visualized using immunocytochemical methods. Using in situ brain microdialysis and a sensitive and specific radioenzymatic assay for histamine, we have identified histamine in the extracellular space of the rat hypothalamus and corpus striatum in vivo. Following neuronal selective stimuli, significant increases in extracellular histamine levels only were observed in the posterior hypothalamus, where dense histaminergic neuronal terminals have been described. However, after manipulations targeted towards histamine-containing mast cells, such increases were seen in both the posterior hypothalamus and corpus striatum. In summary, this study demonstrates that endogenous histamine can be released from the posterior hypothalamus by stimuli targeted towards histamine neurons and that histamine may also be released by non-neuronal mast cell elements.

Cross-reactivity of monomeric and dimeric biosynthetic human growth hormone in commercial immunoassays.

Commercial kits give different measurements for concentrations of growth hormone (GH, somatotropin) in serum. Most notably, a two-site monoclonal-antibody-based immunoradiometric assay (IRMA) from Hybritech routinely yields lower values than do conventional RIAs in which polyclonal antibodies are used. We used purified dimeric biosynthetic human GH as a model compound to investigate the specificity of five commercial immunoassays for size variants of GH. In all five assays, biosynthetic monomeric GH was significantly more potent than pituitary-derived standard GH supplied with the kits. Dimeric GH was significantly less potent than monomer in four of the five assays, and cross-reactivities varied more than fivefold, from 15% to 84%. Using three commercial kits selected for their specificity for dimeric GH, we measured GH in serum samples from 18 normal adults. The mean GH concentrations in serum--0.7 (Hybritech, IRMA), 1.8 (Diagnostic Products, RIA), and 3.1 (Cambridge, RIA) micrograms/L--differed significantly, but in the same rank order as that obtained in the experiments on dimer cross-reactivity.