Is supine rest necessary before blood sampling for plasma metanephrines?

BACKGROUND: The impact of blood sampling in sitting vs supine positions on measurements of plasma metanephrines for diagnosis of pheochromocytoma is unknown. METHODS: We compared plasma concentrations of free metanephrines in samples from patients with primary hypertension obtained after supine rest with those obtained in the sitting position without preceding rest. We also assessed the effects on diagnostic test performance retrospectively in patients with and without pheochromocytoma, and we calculated cost-effectiveness for pheochromocytoma testing. RESULTS: Upper reference limits of plasma free metanephrines were higher in samples obtained from seated patients without preceding rest than from supine patients with preceding rest. Application of these higher upper reference limits to samples from supine patients with pheochromocytoma decreased the diagnostic sensitivity from 99% to 96%. In patients without pheochromocytoma, adjusting the plasma concentration for the effects of sitting while preserving the 99% sensitivity by use of the supine upper reference limits increased the number of false-positive test results from 9% to 25%. CONCLUSIONS: To preserve high diagnostic sensitivity we recommend the use of upper reference limits determined from blood samples collected in the supine position. Under these conditions, negative test results for blood samples obtained with patients sitting are as effective for ruling out pheochromocytoma as negative results from samples obtained after supine rest. Repeat testing with samples obtained in the supine position offers a cost-effective approach for dealing with the increased numbers of false-positive results expected after initial sampling in the sitting position.     

Simultaneous Pharmacokinetic Modeling of Gentamicin,Tobramycin and Vancomycin Clearance from Neonates to Adults: Towards a Semi-physiological Function for Maturation in Glomerular Filtration

Purpose

Since glomerular filtration rate (GFR) is responsible for the elimination of a large number of water-soluble drugs, the aim of this study was to develop a semi-physiological function for GFR maturation from neonates to adults.

Methods

In the pharmacokinetic analysis (NONMEM VI) based on data of gentamicin, tobramycin and vancomycin collected in 1,760 patients (age 1 day–18 years, bodyweight 415 g–85 kg), a distinction was made between drug-specific and system-specific information. Since the maturational model for clearance is considered to contain system-specific information on the developmental changes in GFR, one GFR maturational function was derived for all three drugs.

Results

Simultaneous analysis of these three drugs showed that maturation of GFR mediated clearance from preterm neonates to adults was best described by a bodyweight-dependent exponent (BDE) function with an exponent varying from 1.4 in neonates to 1.0 in adults (Cl_GFR?=?Cl_drug*(BW/4 kg)^BDE with BDE?=?2.23*BW^?0.065). Population clearance values (Cl_drug) for gentamicin, tobramycin and vancomycin were 0.21, 0.28 and 0.39 L/h for a full term neonate of 4 kg, respectively.

Discussion

Based on an integrated analysis of gentamicin, tobramycin and vancomycin, a semi-physiological function for GFR mediated clearance was derived that can potentially be used to establish evidence based dosing regimens of renally excreted drugs in children.     

Cytokinin signaling regulates cambial development in poplar

Although a substantial proportion of plant biomass originates from the activity of vascular cambium, the molecular basis of radial plant growth is still largely unknown. To address whether cytokinins are required for cambial activity, we studied cytokinin signaling across the cambial zones of 2 tree species, poplar (Populus trichocarpa) and birch (Betula pendula). We observed an expression peak for genes encoding cytokinin receptors in the dividing cambial cells. We reduced cytokinin levels endogenously by engineering transgenic poplar trees (P. tremula × tremuloides) to express a cytokinin catabolic gene, Arabidopsis CYTOKININ OXIDASE 2, under the promoter of a birch CYTOKININ RECEPTOR 1 gene. Transgenic trees showed reduced concentration of a biologically active cytokinin, correlating with impaired cytokinin responsiveness. In these trees, both apical and radial growth was compromised. However, radial growth was more affected, as illustrated by a thinner stem diameter than in WT at same height. To dissect radial from apical growth inhibition, we performed a reciprocal grafting experiment. WT scion outgrew the diameter of transgenic stock, implicating cytokinin activity as a direct determinant of radial growth. The reduced radial growth correlated with a reduced number of cambial cell layers. Moreover, expression of a cytokinin primary response gene was dramatically reduced in the thin-stemmed transgenic trees. Thus, a reduced level of cytokinin signaling is the primary basis for the impaired cambial growth observed. Together, our results show that cytokinins are major hormonal regulators required for cambial development.     

Adherence and satisfaction of rheumatoid arthritis patients with a long‐term intensive dynamic exercise program (RAPIT program)

Objective

To evaluate adherence and satisfaction of patients with rheumatoid arthritis (RA) in a long‐term intensive dynamic exercise program.

Methods

A total of 146 RA patients started an intensive (strength and endurance training for 75 minutes, twice a week, for 2 years) exercise program (Rheumatoid Arthritis Patients In Training) aimed at improving physical fitness. Program attendance and satisfaction were examined. Additional assessments at baseline were done to find possible predictors of attendance.

Results

Median (interquartile range) age and disease duration of the patients were 54 (45–61) and 5 (3–10) years, respectively. After 2 years, 118 (81%) patients still participated in an exercise class. The median attendance rate of all patients was 74%. Low attendance was weakly associated with high disease activity, low functional ability, and low quality of life at baseline but not with the severity of joint damage at baseline. At the end, 78% of all participants would (strongly) recommend the program to other RA patients.

Conclusion

Adherence and satisfaction of RA patients with an intensive dynamic exercise program over a prolonged time can be high. Disease severity parameters do not strongly predict the compliance of participants in an intensive exercise program.

     

A Sertoli cell-selective knockout of the androgen receptor causes spermatogenic arrest in meiosis

Androgens control spermatogenesis, but germ cells themselves do not express a functional androgen receptor (AR). Androgen regulation is thought to be mediated by Sertoli and peritubular myoid cells, but their relative roles and the mechanisms involved remain largely unknown. Using Cre/loxP technology, we have generated mice with a ubiquitous knockout of the AR as well as mice with a selective AR knockout in Sertoli cells (SC) only. Mice with a floxed exon 2 of the AR gene were crossed with mice expressing Cre recombinase ubiquitously or selectively in SC (under control of the anti-Müllerian hormone gene promoter). AR knockout males displayed a complete androgen insensitivity phenotype. Testes were located abdominally, and germ cell development was severely disrupted. In contrast, SC AR knockout males showed normal testis descent and development of the male urogenital tract. Expression of the homeobox gene Pem, which is androgen-regulated in SC, was severely decreased. Testis weight was reduced to 28% of that in WT littermates. Stereological analysis indicated that the number of SC was unchanged, whereas numbers of spermatocytes, round spermatids, and elongated spermatids were reduced to 64%, 3%, and 0% respectively of WT. These changes were associated with increased germ cell apoptosis and grossly reduced expression of genes specific for late spermatocyte or spermatid development. It is concluded that cell-autonomous action of the AR in SC is an absolute requirement for androgen maintenance of complete spermatogenesis, and that spermatocyte/spermatid development/survival critically depends on androgens.     

Recombinant factor VIIa enhances deposition of platelets with congenital or acquired alpha IIb beta 3 deficiency to endothelial cell matrix and collagen under conditions of flow via tissue factor-independent thrombin generation

A novel approach to treat bleeding episodes in patients with Glanzmann thrombasthenia (GT) and perhaps also in patients receiving alpha IIb beta 3 inhibitors is the administration of recombinant factor VIIa (rFVIIa). The mechanism of action of rFVIIa in these patients is, however, still unclear. We studied the effect of rFVIIa-mediated thrombin formation on adhesion of alpha IIb beta 3-deficient platelets under flow conditions. Adhesion of alpha IIb beta 3-deficient platelets to the extracellular matrix (ECM) of stimulated human umbilical vein endothelial cells or to collagen type III was studied using a model system with washed platelets and red cells. When alpha IIb beta 3-deficient platelets were perfused over the surface at arterial shear rate for 5 minutes, a low surface coverage was observed (GT platelets, mean +/- SEM, 37.5% +/- 5.0%; normal platelets preincubated with an RGD-containing peptide, 7.4% +/- 2.1%). When rFVIIa, together with factors X and II, was added to the perfusate, platelet deposition significantly increased (GT platelets, mean +/- SEM, 67.0% +/- 4.3%; normal platelets preincubated with an RGD-containing peptide, 48.2% +/- 2.9%). The same effect was observed when normal platelets were pretreated with the commercially available anti-alpha IIb beta 3 drugs abciximab, eptifibatide, or tirofiban. It was shown that tissue factor-independent thrombin generation (presumably induced by binding of rFVIIa to adhered platelets) was responsible for the increase in platelet deposition. In conclusion, defective adhesion of alpha IIb beta 3-deficient platelets to ECM can be restored by tissue factor-independent rFVIIa-mediated thrombin formation. The enhanced generation of platelet procoagulant surface facilitates fibrin formation, so that lack of platelet aggregate formation might be compensated for.     

Survivin: a novel neuroendocrine marker for pheochromocytoma

OBJECTIVE: To study survivin expression in human adrenal medulla and in benign and malignant pheochromocytoma tissue as a tool to predict tumor metastatic potential and prognosis. DESIGN: Blinded study to assess the role of the anti-survivin antibody in chromaffin cells. METHODS: We performed immunohistochemistry with a purified rabbit-polyclonal anti-survivin antibody on 39 formalin-fixed and paraffin-embedded pheochromocytoma/paraganglioma specimens, and on 10 normal adrenal medulla samples from patients unaffected by a chromaffin cell tumor. Fourteen samples were from 14 patients with benign pheochromocytoma (<8 year follow-up, mean 5.2 years), 18 specimens were from 12 patients with malignant pheochromocytoma (<13 year follow-up, mean 6.3 years), 5 samples were from 2 patients with malignant paraganglioma (<6 year follow-up, mean 4 years), and 2 specimens from 2 patients with benign paraganglioma (<7 year follow-up, mean 5.5 years). Malignancy was defined by metastases in non-chromaffin tissues. Staining intensity with the anti-survivin antibody was scored from 0 (none) to 3+ (heavy). Tissues from human kidney, breast, and melanoma served as controls. RESULTS: All pheochromocytoma/paraganglioma specimens stained either 2+ or 3+. By analysis of variance (ANOVA), there was no statistically significant difference between the staining intensity of benign and malignant samples. All normal adrenal medulla specimens stained positively with anti-survivin but to a lesser degree than the chromaffin cell tumors (P<0.01). CONCLUSIONS: Based on these findings, we conclude that (i) survivin may represent a novel neuroendocrine marker for chromaffin cell tumors, and (ii) survivin does not appear to reliably distinguish benign from malignant pheochromocytomas/paragangliomas and thus does not identify patients at risk of recurrent disease.