Jean-Pierre Dausse

Specific Binding of [3H]Rauwolscine to α2-Adrenoceptors in Rat Cerebral Cortex: Comparison Between Crude and Synaptosomal Plasma Membranes

Abstract: [3H]Rauwolscine, a specific, potent, radiolabelled α2‐antagonist, binds to distinct high‐ and low‐affinity α2‐adrenoceptors in crude membrane preparations of the rat cerebral cortex. The concentration of high‐affinity α2‐adrenoceptors was increased by addition of sodium ions or guanylnucleotides. In synaptosomal plasma membrane preparations, only the low‐affinity component was found. Neither sodium or guanylnucleotides caused any increase in the concentration of these low‐affinity receptors for [3H]rauwolscine.

PATTERNS OF MESSENGER RNA EXPRESSION FOR alpha1-ADRENOCEPTOR SUBTYPES IN HUMAN CORPUS CAVERNOSUM

PURPOSE The present study evaluated the expression of alpha1-adrenoceptor subtypes in human corpus cavernosum. MATERIALS AND METHODS The mRNA encoding alpha1a, alpha1b and alpha1d subtypes were assessed by RNA-directed complementary cDNA synthesis followed by Taq DNA amplification. The level of alpha1 mRNA was calculated in arbitrary optical density units and normalized with respect to the length of the respective cDNA fragments. RESULTS We found that alpha1a, alpha1b and alpha1d adrenoceptor subtypes are expressed in human corpus cavernosum, with a predominant expression of the alpha1a subtype. CONCLUSION These results suggest that alpha1a-adrenoceptor subtype is important and that understanding the biochemical and functional characteristics of this subtype may lead to the development of specific antagonists in the treatment of impotence.

Hypertension in cafeteria-fed rats: alterations in renal α2-adrenoceptor subtypes

Obesity is a major cause of human essential hypertension and there are clear evidences that abnormal kidney functions play a key role in obesity hypertension. Feeding rats a cafeteria diet has been extensively used as an experimental model to study obesity and energy balance expenditure. The present study investigated whether rats fed a cafeteria diet develop hypertension with alterations in renal alpha2-adrenoceptor subtype distribution. Weight gain induced by feeding rats a cafeteria diet during 8 weeks was associated with a marked increase in blood pressure. Insulin levels were higher in these hypertensive rats, leading to a decreased plasma glucose/insulin ratio. Based on radioligand-binding studies using [3H]-RX821002 and selective competitors, a raise in alpha2-adrenoceptor density that was solely due to an increased alpha2B-adrenoceptor subtype density was detected in the kidney of the cafeteria-fed rat. Furthermore, reverse transcription-polymerase chain reaction (RT-PCR) experiments showed an overexpression of the gene encoding the alpha2B-adrenoceptor subtype in these rats. On the other hand, despite a similar mRNA level, the alpha2A-adrenoceptor subtype was no more detectable by radioligand-binding studies in the kidney of the cafeteria-fed rat. In conclusion, cafeteria-fed rats are hypertensive, with renal alterations in alpha2-adrenoceptor distribution. These alterations, which are not related to genetic factors, may play a key role in the onset of hypertension.

Regulation of white adipocyte guanine nucleotide binding proteins Gsα and Giα1–2 by testosterone in vivo: Influence of regional fat distribution

Abstract The influence of the androgenic status on the steady-state amounts of Gi α 1–2 and Gsα subunits was compared in hamster fat cell membranes from the femoral subcutaneous (FSC) and epididymal (EP) adipose tissues, using immunoblotting experiments. In sham-operated hamsters, Gi α 1–2 and Gsα steady-state amounts found in FSC fat cells were 38% and 40% reduced, respectively, as compared to EP adipocytes. In EP fat cells, castration induced a down-regulation of both Gi α 1–2 (−39%) and Gsα (−33%), whereas testosterone replacement restored Gsα, but not Gi α 1–2 levels, to control values. In contrast, these G protein α-subunits were insensitive to the androgenic status in FSC fat cells. These data provide the first evidence that the androgenic status can modulate the expression of both the Gi α 1–2 and Gsα subunits of the fat cell adenylate cyclase regulatory Gi and Gs proteins and that this modulation depends on the anatomical origin of these cells.

Insulinemia and pancreatic α2-adrenoceptors in salt-sensitive (SBH) and salt-resistant (SBN) Sabra rats: effect of high salt diet

Studies in humans have suggested that hyperinsulinemia might play an important role in salt sensitivity and in the later development of high blood pressure. This possibility has been tested in this study on Sabra rats, an animal model of salt-induced hypertension. Salt-sensitive (SBH) and salt-resistant (SBN) Sabra rats have been submitted to either a normal (0.2% NaCl) or a high salt (8% NaCl) diet for 6 weeks. Comparisons of blood pressure, basal glucose and insulin levels, and insulin response to glucose overload (1 g/kg) have been made. As pancreatic alpha2-adrenergic receptors are implicated in the control of insulin release, their densities have been determined on plasma membranes by saturation studies with [3H]-RX-821002 as the specific radioligand. Under normal diet, blood pressures were respectively 133 +/- 9 and 108 +/- 10 mm Hg (n = 6) in SBH and SBN. Basal glucose and insulin levels and insulin response to glucose overload were found to be significantly higher in SBH than in SBN. In contrast, alpha2-adrenergic receptor densities were lower (P < .001) in SBH when compared to SBN. High salt diet increased (P < .01) blood pressure, decreased basal glucose (P < .01) and insulin (P < .001) levels only in SBH. However, when compared to SBN the insulin response to glucose overload was maintained higher in SBH. Alpha2-adrenergic receptor densities and difference between SBH and SBN did not differ from those found in normal diet. In conclusion, the salt-induced high blood pressure of salt-sensitive Sabra rats is not associated with hyperinsulinemia and insulin resistance. Indeed, an improvement in the insulin sensitivity appears to be induced by either a high salt diet or high blood pressure.

Differential sodium regulation between salt-sensitive and salt-resistant sabra rats is not due to any mutation in the renal α2B-adrenoceptor gene

A defect in sodium modulation of density and agonist affinity of renal alpha 2-adrenoceptor exists in normotensive salt-resistant Sabra (SBN) rats when compared to hypertensive salt-sensitive (SBH). A highly conserved aspartic acid residue in the second helix has been implicated in sodium regulation of alpha 2-adrenoceptor-ligand interactions. As the alpha 2B-adrenoceptor subtype is preponderantly present in kidney of SBH and SBN rats, a mutation might distinguish this subtype between SBH and SBN rats. From this study, no difference between SBH and SBN alpha 2B-adrenoceptor gene could be demonstrated in terms of nucleotide sequence. These data suggest that in Sabra rats, the differential sodium regulation in density and agonist affinity between renal SBH and SBN alpha 2-adrenoceptor may have another origin than the alpha 2B-adrenoceptor encoding gene.