Development of morphologically dominant follicles is associated with fewer metabolic disturbances in amenorrheic women with polycystic ovary syndrome: a pilot study.

OBJECTIVES: To determine if amenorrheic women with polycystic ovary syndrome (PCOS) demonstrate ultrasonographically detectable changes in follicle population. METHODS: Sixteen women with PCOS reporting the absence of menses for more than 3 months were enrolled in the study. Subjects had a physical examination, fasting blood tests and two transvaginal ultrasound scans spaced 1 month apart. In cases where evidence of a morphologically dominant follicle (≥ 10 mm in diameter) occurred, subsequent ultrasound scans were performed to determine the fate of the dominant follicle. Differences in total follicle population, maximum follicle diameter and clinical, hormonal and metabolic features were determined. RESULTS: Forty-four percent of subjects showed changes in follicle population of 6-10 follicles and 37% showed changes in follicle population of > 10. Maximum follicle diameters ranged between 5.4 and 33.0 mm. Four subjects demonstrated follicle diameters ≥ 10 mm. Of those who developed dominant follicles, two subjects ovulated, one subject developed a persistent anovulatory follicle and the dominant follicle regressed in the remaining subject. Diagnostic criteria for PCOS were similar among women that did or did not develop dominant follicles (menstrual cycle length, P = 0.880; hirsutism score, P = 0.809; free androgen index, P = 0.991; total follicle count, P = 0.199). However, lower glycosylated hemoglobin (P = 0.047) and insulin levels (P = 0.049) and better insulin sensitivity (P = 0.048) were noted in women who attained dominant follicles. CONCLUSION: Amenorrheic women with PCOS demonstrate changes in follicle population that are consistent with active follicle growth and regression despite prolonged periods of anovulation. Morphologic selection occurs in amenorrheic women and attainment of dominant follicles is associated with improved metabolic status.

Possible cyclic nucleotide regulation of calcium mediating myocardial contraction.

An inhibitor of adenylate and guanylate cyclases was tested on strips of left atria from rabbits. Effects of catecholamines (cardiotonic) and of acetylcholine (cardiodepressive) were blocked, and positive force-frequency was converted to negative. Ouabain produced only contracture without positive inotropy. The cardiotonic effect of increased calcium remained. Data suggest that cyclic nucleotides modulate calcium associated with these stimuli.

Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome (HHH) presenting with acute fulminant hepatic failure.

We report on two Aboriginal patients with the hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome. Both presented with acute hepatic failure with severe hypertransaminasemia and coagulopathy, prompting evaluation for emergent liver transplantation. The diagnosis of HHH syndrome was based on the presence of typical metabolic abnormalities. A protein-restricted diet and L-arginine or L-citrulline supplementation were immediately started, with rapid normalization of liver function test results and other biochemical abnormalities. Molecular analysis of the SLC25A15 gene showed that the two patients were homozygous for the common French Canadian mutation (F188Delta). The diagnosis of HHH syndrome should be considered in patients with unexplained fulminant hepatic failure. There does not appear to be a genotype-phenotype correlation for this presentation, inasmuch as the only other reported patient presenting with this picture had two different point mutations. Early identification and prompt treatment of these patients is crucial to avoid liver transplantation and can be life saving.

Excessive formation of hydroxyl radicals and aldehydic lipid peroxidation products in cultured skin fibroblasts from patients with complex I deficiency.

Previous studies suggest oxygen free radicals' involvement in the etiology of cardiomyopathy with cataracts. To investigate the role of free radicals in the pathogenesis of the cardiomyopathy with cataracts and complex I deficiency, fibroblasts from patients were assessed for hydroxyl radical formation and aldehydic lipid peroxidation products with and without redox active agents that increase free radicals. The rate of hydroxyl radical formation in patient cells was increased over 2-10-fold under basal conditions, and up to 20-fold after menadione or doxorubicin treatment compared with normal cells. We also found an overproduction of aldehydes in patient cells both under basal conditions and after treatment. Both hydroxyl radicals and toxic aldehydes such as hexanal, 4-hydroxynon-2-enal, and malondialdehyde were elevated in cells from patients with three types of complex I deficiency. In contrast, acyloins, the less toxic conjugated products of pyruvate and saturated aldehydes, were lower in the patient cells. Our data provide direct evidence for the first time that complex I deficiency is associated with excessive production of hydroxyl radicals and lipid peroxidation. The resultant damage may contribute to the early onset of cardiomyopathy and cataracts and death in early infancy in affected patients with this disease.

Simple method for the quantitative analysis of endogenous folate catabolites p-aminobenzoylglutamate (pABG) and its acetamido (apABG) derivative in human serum and urine by liquid chromatography-tandem mass spectrometry.

OBJECTIVE: To develop a routine method for quantitative measurement of the folate catabolites p-aminobenzoylglutamate (pABG) and acetamidobenzoylglutamate (apABG) in serum and urine using liquid chromatography-tandem mass spectrometry (LC-MS/MS). DESIGN AND METHODS: Urine, serum and aqueous standards were thawed. Two microliters of d3-glutamic acid (d3-Glu; 1 mmol/L) was added to 200 uL of specimen as internal standard. The samples were acidified with 4 uL 6N HCL, and aliquots were precipitated with 2 volumes (412 uL) of acetonitrile. For urine specimens 30 volumes (6.18 mL) of acetonitrile was used. Samples were centrifuged at 1900 x g for 10 min and the supernatant (10 microL) injected into a Biorad CAT/MET analytical column fitted to the LC-MS/MS. Detection of the catabolites was by selective multiple ion monitoring (multiple SRM) of the respective transitions. Urine and serum samples were analysed in a group of healthy volunteers and in anonymous samples from patients being tested for PTH and urinary catecholamines. RESULTS: pABG and apABG eluted at 5.2 and 4.74 min, respectively while the d3-glutamic acid eluted at around 7 min. Limit of quantitation (LOQ) for both catabolites was 10 nmol/L (which is equivalent to 33.3 fmol for a 10 microL injection). Limit of detection (LOD) was 1 nmol/L based on a signal to noise ratio of 5:1. A linear calibration curve was obtained from 10 to 100 nmol/L for serum specimens and from 10 to 200 micromol/L for urines. Imprecision for spiked serum samples (n=10) was between 2.5 and 20% for apABG and 4.5 and 21% for pABG (at 10 and 100 nmol/L, respectively). Imprecision for spiked urine samples (n=10) was between 2.9 and 4.0% for apABG and 6.0-12.7% for pABG. Recoveries were between 80 and 122% for serum samples and between 92 and 102% for urine specimens. Total folate catabolites in random urine samples from volunteers (n=5) are 2.9+/-2.3 umol/L (mean+/-S.D.). This group also had total serum catabolites of 11.9+/-7.6 nmol/L and serum folate of 35.3+/-5.8 nmol/L. Serum from patients being tested for PTH (n=11) had serum folate levels of 27.0+/-10.4 nmol/L with total serum catabolites of 20.4+/-23.8 nmol/L. Levels of serum folate and total catabolites in pregnant women (n=18) were 33.9+/-22.7 and 11.4+/-8.7 nmol/L, respectively. Mean urinary folate catabolites in patients being tested for urinary catecholamines (n=19) was 581.8+/-368.4 nmol/L. CONCLUSION: A simple, reliable and highly specific method by LC-MS/MS for detecting and quantifying the folate catabolites pABG and apABG was developed. This enables, for the first time, the routine clinical analysis of folate utilization in patients.

Studies of normal and nephritic rat glomerular basement membrane.

Solubilization of the normal glomerular basement membrane with various solvents revealed that the material is held together by hydrogen and disulfide linkages as well as ionic salt bridges which ionize at around pH 10.0. Pronase digestion indicated that differences in susceptibility to enzyme digestion exist between normal and nephritic membrane. Titration of a urea-insoluble material indicated that some alteration must have taken place in the association between various components of the nephritic basement membrane. Chemical analysis of alkali-solubilized fractions suggested that greater alkali susceptibility of the nephritic material may be present. A collagen-like material resembling both tendon and dog basement membrane collagen in its amino acid composition was isolated. It contained 10% hexose, but in addition to glucose and galactose, mannose was also detected. A glycopeptide fraction obtained by pronase and collagenase digestion has a carbohydrate composition similar to the collagen-like material above. These substances probably represent incompletely digested fragments of the basement membrane.

Doxorubicin-induced acute changes in cytotoxic aldehydes, antioxidant status and cardiac function in the rat.

Doxorubicin (DOX)-induced cardiotoxicity is thought to be caused by free radical-mediated mechanisms. An in vivo rat model was developed to investigate the DOX-induced cascade of early biochemical changes focusing on the central role of the aldehydic lipid peroxidation products. Antioxidant status was evaluated by glutathione measurements. Creatine Kinase (CK) activity was measured as an index of cardiac injury. Development of functional abnormalities were documented by echocardiography. The results showed that aldehydes in rat plasma and heart tissues increased significantly following DOX treatment. The changes occurred early, peaked around 2 h after DOX administration, and the levels declined or returned to baseline value within 8-24 h. Toxic aldehyde levels including malondialdehyde, hexanal and 4-hydroxy-non-2-enal also increased. Acyloin levels, metabolic products of aldehydes, increased early and then decreased in plasma, and there was a significant decrease in heart tissues after DOX treatment. GSH levels decreased early, then increased by 24 h, while GSSG levels decreased initially, then increased after DOX treatment, suggesting early depletion of GSH and a later rebound phenomenon. CK levels were elevated after treatment. The functional abnormalities were documented by stress echocardiography in some rats although the changes were not consistent at such an early stage following treatment. Our data confirmed the involvement of free radicals, and suggested that the cytotoxic aldehydes play a central role in initiating the steps that lead to functional impairment of the myocardium following DOX administration. Scavengers and the metabolic removal of some of the aldehydes also play a role in protecting the myocardium against injury.

Cyclic AMP modulation of calcium accumulation by sarcoplasmic reticulum from fast skeletal muscle.

The role of cyclic 3',5'-AMP in modulating sarcoplasmic reticulum from fast skeletal muscle was studied. The rate of Ca2+ uptake was stimulated in the presence of protein kinase plus 1 micron cyclic AMP. The stimulation was absent when denatured protein kinase was used. When an adenylate cyclase inhibitor was added, the uptake rates fell to 55% of control. This decrease in rate was partially overcome by 1 micron cyclic AMP. A modulating role for cyclic AMP in fast skeletal muscle is proposed.

The cardiac sarcoplasmic reticulum-glycogenolytic complex. A possible effector site for cyclic AMP.

Cardiac sarcoplasmic reticulum-glycogenolytic complex, isolated as a single peak on sucrose density gradient, may function as a "compartmented" effector site for cyclic AMP resulting in modulation of both glycogenolysis and calcium transport. The conversion of phosphorylase b to a is stimulated by ATP and inhibited by protein kinase inhibitor. Cyclic AMP alone stimulated neither phosphorylase b to a conversion nor calcium uptake. An inhibitor of adenylate cyclase depressed both calcium uptake and phosphorylase activation and both functions were subsequently stimulated by micromolar concentrations of cyclic AMP. Endogenous phosphorylation of sarcoplasmic reticulum was also inhibited by adenylate cyclase inhibitor and the inhibition was reversed by cyclic AMP. These results suggest that the sarcoplasmic reticulum of cardiac muscle is an internal effector site for cyclic AMP which may regulate both calcium and metabolism. It appears that cyclic AMP formation in vitro is not the rate-controlling step in the activation sequence.

Determination of free and protein-bound methadone and its major metabolite EDDP: enantiomeric separation and quantitation by LC/MS/MS.

OBJECTIVE: To measure free and protein-bound R- and S-enantiomers of methadone and its major metabolite, 2-ethylidine-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in serum. METHODS: To determine free fraction, samples were filtered using ultrafiltration membranes with a molecular weight cut-off of 10,000 Da and extracted using liquid-liquid extraction. The solvent extract was evaporated and reconstituted in mobile phase for analysis by LC/MS/MS. Total analyte was determined by extracting unfiltered samples. Enantiomeric separation was by chiral chromatography. RESULTS: LC conditions resulted in baseline separation of R- and S-EDDP, and 85% resolution of methadone enantiomers. Precision of spiked specimens for both R- and S-methadone and R- and S-EDDP was less than 10% at 100 nM, and did not exceed 20% at 10 nM. CONCLUSIONS: Using minimal sample clean-up and a total instrument run-time of 10 min, a rapid, sensitive and highly specific method was developed for quantitation of free and total R- and S-enantiomers of methadone and EDDP.

Free and bound enantiomers of methadone and its metabolite, EDDP in methadone maintenance treatment: relationship to dosage?

OBJECTIVES: To determine the effects of metabolism and protein binding on the relationship between administered dose, blood levels of R methadone and biological response by measuring the free and protein-bound forms of the R and S enantiomers of methadone and EDDP, its metabolite. DESIGN AND METHODS: To measure free and total drug, trough levels were collected from 45 methadone clients. To measure free methadone, samples were filtered using ultrafiltration with a MW weight cut-off of 10,000 and extracted using liquid-liquid extraction. The solvent was evaporated and samples reconstituted in mobile phase for analysis by LC/MS/MS. Total analyte was determined by extracting unfiltered samples. Enantiomeric separation of methadone and EDDP was by chiral chromatography. RESULTS: The presence of unmetabolized methadone suggested that none of the patients were very fast metabolizers. R and S forms were metabolized at the same rate at all administered doses. Free R methadone levels correlated both with methadone dose and with the total amount of R methadone. The free fraction of R methadone (%free R) was higher at lower doses than at high doses, varied from 5 to 25% and was inversely proportional to the total dose of administered drug in a relationship that was logarithmic and non-linear. CONCLUSIONS: By measuring the free, biologically active form of the drug, we were unable to account for the large variations in dose required between different patients to prevent the onset of withdrawal symptoms. The reason for the large range in dosage may be multifactorial.

Diabetic nephropathy in hypertransfused patients with beta-thalassemia. The role of oxidative stress.

OBJECTIVE: Pathogenesis of diabetes-related microvascular complications involving oxidative damage by free radicals has been demonstrated. Free radical generation has been shown to derive largely from iron. Our objectives, therefore, were to determine if there is an increased incidence and/or an accelerated course of nephropathy in patients with diabetes, secondary to transfusional hemochromatosis, and to examine whether free radical activity contributes to the development of this complication. RESEARCH DESIGN AND METHODS: We evaluated nine patients with homozygous beta-thalassemia, complicated by clinically overt diabetes, for diabetic nephropathy over a 7-year period. Lipid peroxidation was quantified by measuring the presence of 20 saturated and unsaturated aldehydes, and results were compared with five normotensive type 1 diabetic patients without iron overload. RESULTS: Nephropathy developed in five of nine patients (55%) after a mean duration of overt diabetes of 3.6 +/- 2.0 years. Three patients showed evidence of progressive microalbuminuria over a 7-year period (24.7-46.2, 52.2-430.1, and 17.7-54.3 micrograms/min, respectively). Two patients with borderline microalbuminuria (19.9 and 14.5 micrograms/min, respectively) demonstrated stable albumin excretion rates over the follow-up period. Total aldehyde concentration was significantly higher in beta-thalassemia diabetic patients, compared with nonthalassemic diabetic control subjects (8,106 +/- 1,280 vs. 4,594 +/- 247 nmol/l; P < 0.0001). The three patients with progressive microalbuminuria demonstrated significantly higher total aldehyde concentration, compared with the other beta-thalassemia diabetic patients with stable albumin excretion (9,428 +/- 337 vs. 7,445 +/- 1,003 nmol/l; P < 0.01). Serum vitamin E concentrations were significantly lower in beta-thalassemia patients with diabetes, compared with diabetic patients without iron overload (12.1 +/- 6.0 vs. 25.9 +/- 11.4 mumol/l; P = 0.02). Serum vitamin C concentrations did not differ between the two groups. Multiple regression analysis demonstrated total aldehyde concentration to be the most significant predictor for the development of microalbuminuria (P = 0.01), followed by the duration of diabetes (P = 0.02) and glycemic control (P = 0.02). CONCLUSIONS: Early development and an accelerated course of diabetic nephropathy in iron-loaded patients with beta-thalassemia are observed. These findings may be attributed to high oxidative stress in these patients, which is secondary to iron-derived free radicals and to the patients' diminished antioxidant reserves.

Cardiac function and cytotoxic aldehyde production in a murine model of chronic iron-overload.

OBJECTIVES: To determine the relationship between the total chronic dose of iron administered, ex-vivo cardiac function and the concentrations of cytotoxic aldehydes in heart tissue of a murine model. METHODS: In the first experiment, 34 male B6D2F1 mice were randomized to receive intraperitoneal injections of 5, 10 or 20 mg of iron dextran for three weeks, or a placebo control. The mice were subsequently randomized to undergo ex-vivo assessment of cardiac function. In the second experiment, free radical generation, quantified by the presence of 20 separate cytotoxic aldehydes, was assessed in heart tissue of 40 mice that were randomized to receive chronic treatment with various concentrations of iron dextran (100 mg to 300 mg total chronic dose administered), placebo treatment with saline, or no treatment at all (baseline). RESULTS: Iron-loaded groups displayed dose-dependent depressions of heart rate, systolic pressure, developed pressure, coronary pressure, -dP/dt and +dP/dt, and increases in diastolic pressure. Monotonic dose-dependent increases in total heart aldehydes were observed in the iron-treated groups (r-0.97, p < 0.0001), whereas no significant differences were observed between baseline or time-placebo control groups. CONCLUSIONS: While no single mechanism is likely to account for the complex pathophysiology of iron-induced heart failure, our findings show that chronic iron-loading in a murine model results in dose-dependent alterations to cardiac function; and results in free radical mediated damage to the heart, as measured by excess concentrations of cytotoxic aldehyde-derived peroxidation products. This is the first description of the effects of excess iron on cardiac function assessed by an ex-vivo Langendorff technique in a murine model of chronic iron-overload.

Induction of a wide range of C(2-12) aldehydes and C(7-12) acyloins in the kidney of Wistar rats after treatment with a renal carcinogen, ferric nitrilotriacetate.

An iron chelate, ferric nitrilotriacetate (Fe-NTA), induces renal proximal tubular necrosis associated with lipid peroxidation and oxidative DNA damage that finally leads to a high incidence of renal cell carcinoma in rodents. In the present study, we investigated what kinds of C(2-12) saturated and unsaturated aldehydes and C(7-12) acyloins, metabolites of saturated aldehydes, are produced in the kidney and liver within 24 h after single i.p. administration of 15 mg Fe/kg of Fe-NTA, or after repeated (1 or 3 wk) i.p. administration of 5-10 mg Fe/kg of Fe-NTA. Amounts of twenty one aldehydes and five acyloins were determined by capillary column gas chromatography-negative-ion chemical ionization mass spectrometry with ammonia as reagent gas. Most of the aldehydes and all the acyloins measured revealed a significant dose-dependent increase 1 to 3 h after single administration in the kidney, among which 4-hydroxy-2-nonenal (HNE) showed the highest increase (27.3-fold) and malondialdehyde (MDA) was the most abundant aldehyde (2.40 nmol/100 mg wet tissue). In the liver, however, the increase in aldehydes and acyloins was less prominent. After repeated administration of Fe-NTA, only 9 aldehydes (ethanal; furfural; trans,trans-2,4-heptadienal; nonanal; trans-2,cis-6-nonadienal; HNE; decanal; trans-4,cis-4-decenal; MDA) and 4 acyloins (3-hydroxyheptan-2-one; 3-hydroxyoctan-2-one; 3-hydroxynonan-2-one; 3-hydroxydodecan-2-one) showed a significant increase. Immunohistochemistry further demonstrated an increased amount of HNE-modified and MDA-modified proteins in the renal proximal tubules after repeated Fe-NTA administration. Some of the aldehydes measured such as HNE and MDA are reportedly cytotoxic, genotoxic and mutagenic. Accumulation of these aldehydes may play a role in this renal carcinogenesis model.

Cytotoxic aldehydes as possible markers for childhood cancer.

Concentrations of 22 known aldehydes (byproducts of lipid peroxidation), 5 acyloins, free and total carnitine and acylcarnitines were measured in plasma and urine obtained from pediatric patients with various forms of cancer before any treatment, and following treatment with doxorubicin or daunorubicin. Aldehydes, before the initiation of chemotherapy, were significantly elevated in cancer patients compared to controls. Aldehydes such as hexanal, heptanal, and malondialdehyde were strikingly higher in samples from cancer patients, while trans 4-cis-4-decenal was the prominent aldehyde in the blood of controls. In addition, in each form of cancer the pattern of aldehydes appeared to be unique when compared to controls, or to others forms of cancer. In cancer patients receiving chemotherapy there was a general trend toward a reduction 24 h after both the first and after the fifth doxorubicin dose. These changes however were not significant statistically due to large inter-patient variation. Free and total plasma carnitine levels remained in the normal range, and there were no abnormal acylcarnitines detected in urine. Possible hypotheses to explain the elevations in aldehydes, and the reasons for the changed aldehyde profiles in different forms of cancer are discussed.

L-carnitine attenuates doxorubicin-induced lipid peroxidation in rats.

Doxorubicin (DOX) was administered intraperitoneally to rats in six equal, 2.5 mg/kg doses over a 2-week period with or without L-carnitine. Injury was monitored by echocardiography, release of myosin light chain-1 (MLC-1), and by measurement of aldehydic lipid peroxidation products. General observation revealed that DOX alone caused more ascites than DOX plus L-carnitine. Animals sacrificed 2 h after the sixth dose had significantly higher aldehyde concentrations than 2 h after a single dose of DOX. Aldehydes in plasma and heart remained elevated for 3 weeks after the final dose of DOX, whereas L-carnitine prevented or attenuated the DOX-induced increases in lipid peroxidation. The increase in MLC-1 2 h after the sixth dose of DOX was greater than after a single dose, suggesting cumulative damage. Echocardiography did not detect either early injury or the protective effects of L-carnitine. These data indicate that lipid peroxidation following DOX occurs early, and parallels the cumulative characteristics of DOX-induced cardiotoxicity. The protective effects of L-carnitine may be due to improved cardiac energy metabolism and reduced lipid peroxidation.

Barth syndrome: clinical observations and genetic linkage studies.

Barth syndrome is an X-linked recessive condition characterized by skeletal myopathy, cardiomyopathy, proportionate short stature, and recurrent neutropenia, but with normal cognitive function. Some, but not all patients, exhibit carnitine deficiency and/or the presence of 3-methylglutaconic and ethylhydracylic acids in urine. Recently the mutation causing Barth syndrome was localised to the Xq28 region by linkage analysis. We report 6 cases of Barth syndrome from 4 families and highlight the fact that neuromuscular and cardiovascular symptoms and the severity of infections tend to improve with age, while short stature persists. Also previously unreported was myopathic facies and nasal quality to speech in our cases. The urinary organic acid abnormalities and plasma carnitine deficiency were inconsistent findings. We propose that they may be epiphenomena rather than indicators of the primary metabolic defect, and that the primary defect or defects in this disorder may lie in the mitochondrial electron transport chain.

A biochemical, histochemical, and electron microscopic study on the effects of iron-loading on the hearts of mice.

Acute iron poisoning and chronic iron overload are well-known causes of myocardial failure. Although the exact mechanism is not known, excess iron-catalyzed free radical generation is conjectured to play a role in damaging the myocardium and altering cardiac function. We report here on the effects of acute and chronic iron-loading on the total iron concentration, glutathione peroxidase activity, and cytotoxic aldehyde production in the heart of a murine model (n = 35). Light microscopic examination for the presence of ferrous and ferric iron was undertaken following histochemical staining for these species. In addition, examination of representative samples by transmission electron microscopy was performed. Our findings show that iron-loading can result in significant increases in total iron concentrations, alterations to glutathione peroxidase activity, and increases in cytotoxic aldehyde concentrations in the hearts of mice. Furthermore, we observe that iron-loading can significantly alter and damage various cellular constituents (e.g., mitochondria, lysosomes, sarcoplasmic reticulum) and this may have bearing on the mechanism of iron-induced heart failure.

Clofibrate does not alter cyclic nucleotide metabolism in muscle.

Clofibrate is a hypolipidemic agent that causes muscle protein breakdown in rats, and an acute muscular syndrome in man. It also inhibits adenylate cyclase in fat tissue. Muscle protein metabolism has been shown to be regulated by cyclic nucleotides. In the present experiments were measured several parameters of cyclic nucleotide metabolism to determine the role that cyclic nucleotides play in clofibrate-induced muscle protein degradation. It was found that clofibrate treatment did not alter cyclic nucleotide levels, nor did it change the activities of basal or hormone-stimulated adenylate cyclase, or cyclic nucleotide phosphodiesterase in muscle. Our results suggest that muscle protein breakdown in clofibrate-treated rats is not regulated by cyclic nucleotides.

Human parathyroid adenoma adenylate cyclase: stimulation by histamine that is blocked by cimetidine.

Recent evidence suggests that the histamine receptor blocking agent cimetidine can decrease parathyroid hormone release from human parathyroids. To determine the mechanism for inhibition we examined the ability of histamine 1 X 10(-5) moles/liter to stimulate adenylate cyclase in a particulate membrane preparation from 13 human parathyroid glands. Histamine significantly increased adenylate cyclase activity as compared to control; however, the degree of stimulation was variable among the individual tissue samples. Enzyme stimulation was dose dependent over the concentration range of 1 X 10(-7) to 1 X 10(-4) moles/liter. Cimetidine at 1 X 10(-4) moles/liter completely abolished the histamine mediated increase in activity, but did not block the epinephrine-induced stimulation. The identification of an adenylate cyclase system in certain human parathyroid adenomas that is stimulated by histamine and blocked by cimetidine may offer a basis for the pharmacologic alteration of parathyroid hormone secretion.