AimMaintenance of the blood and extracellular volume requires tight control of endothelial macromolecule permeability, which is regulated by cAMP signalling. This study probes the role of the cAMP mediators rap guanine nucleotide exchange factor 3 and 4 (Epac1 and Epac2) for in vivo control of microvascular macromolecule permeability under basal conditions.MethodsEpac1−/− and Epac2−/− C57BL /6J mice were produced and compared with wild‐type mice for transvascular flux of radio‐labelled albumin in skin, adipose tissue, intestine, heart and skeletal muscle. The transvascular leakage was also studied by dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) using the MRI contrast agent Gadomer‐17 as probe.ResultsEpac1−/− mice had constitutively increased transvascular macromolecule transport, indicating Epac1‐dependent restriction of baseline permeability. In addition, Epac1−/− mice showed little or no enhancement of vascular permeability in response to atrial natriuretic peptide (ANP), whether probed with labelled albumin or Gadomer‐17. Epac2−/− and wild‐type mice had similar basal and ANP‐stimulated clearances. Ultrastructure analysis revealed that Epac1−/− microvascular interendothelial junctions had constitutively less junctional complex.ConclusionEpac1 exerts a tonic inhibition of in vivo basal microvascular permeability. The loss of this tonic action increases baseline permeability, presumably by reducing the interendothelial permeability resistance. Part of the action of ANP to increase permeability in wild‐type microvessels may involve inhibition of the basal Epac1‐dependent activity.

A full-length cDNA clone encoding barley dihydroflavonol-4-reductase was isolated from a kernel-specific cDNA library by screening with the cDNA of the structural gene (A1) for this enzyme from maize. Subsequently, the gene corresponding to the barley dihydroflavonol-4-reductase cDNA was cloned and sequenced. The gene contains three introns at the same positions as in the Zea mays gene, corresponding to the positions of the first three of the five introns present in the genes of Petunia hybrida and Antirrhinum majus. In vitro transcription and translation of the Hordeum vulgare cDNA clone yielded a protein which converts dihydroquercetin into 2,3-trans-3,4-cis-leucocyanidin with NADPH as cofactor. The protein has a deduced amino acid sequence of 354 residues and a molecular weight of 38,400 daltons. Dihydroflavonol reductases of barley, maize, petunia and snapdragon are highly polymorphic in the NH2- and C-terminal parts of the polypeptide chain while a central region of 324 residues contains 51% identical amino acids. This identity increases to 81% when only the barley and maize enzymes are compared. Recessive mutants in the Ant18 gene tested so far lack dihydroflavonol-4-reductase activity and accumulate small amounts of dihydroquercetin but have retained activity for at least two other enzymes in the flavonoid pathway. In testa-pericarp tissue of mutants ant18-159, ant18-162 and ant18-164, wild-type levels of steady state mRNA for dihydroflavonol reductase have been measured, while mRNA for this enzyme is not transcribed in mutant ant18-161. These data are consistent with the proposal that the Ant18 locus carries the structural gene for dihydroflavonol-4-reductase of barley.

The serotonin 5-HT 2A receptor is suspected to be involved in a number of psychiatric disorders, including schizophrenia. In particular, atypical antipsychotics have antagonistic effects on the 5-HT 2A receptors, supporting a specific role of the 5-HT 2A receptor in the pathophysiology of this disease. The aim of this study is to investigate cortical and subcortical 5-HT 2A binding in neuroleptic-naive schizophrenic patients. Fifteen neuroleptic-naive patients diagnosed with schizophrenia (age 27.5 ± 4.5 years), 11 men and 4 women, and 15 healthy control subjects matched for age (28.5 ± 5.7 years) and gender underwent a 40 min positron emission tomography (PET) study using the 5-HT 2A antagonist, [18 F]altanserin, as a radioligand. PET images were co-registered to 3 T magnetic resonance images (MRIs) for each individual subject, and ROIs were applied automatically onto the individual MRIs and PET images. The cerebellum was used as a reference region. The binding potential of specific tracer binding (BP p ) was used as the outcome measure. No significant difference was seen in cortical receptor distribution between patients and controls. An increase in 5-HT 2A receptor binding in the caudate nucleus was detected in the group of schizophrenic patients (0.7 ± 0.1) when compared to the healthy controls (0.5 ± 0.3) (p ¼ 0.02). Our results confirm other in vivo findings of no difference in cortical 5-HT 2A receptor binding between first-episode antipsychotic-naive schizophrenic patients and age-and gender-matched healthy control subjects. However, a preliminary finding of increased 5-HT 2A binding in the caudate nucleus requires further investigation to explore the relation of subcortical and cortical 5-HT 2A receptor binding.