Daniel Benzoni

Aging-Associated Sensory Neuropathy Alters Pressure-Induced Vasodilation in Humans

Healthy skin is protected from pressure-induced ischemic damage because of the presence of pressure-induced vasodilation (PIV). PIV relies on small sensory nerve fibers and endothelial function. Since aging alters both nervous and vascular functions, we hypothesized that PIV is altered with aging. We compared PIV in non-neuropathic and neuropathic older subjects (60-75 years) with that of young subjects (20-35 years). Laser Doppler flowmetry was used to evaluate the cutaneous responses to local pressure application, acetylcholine, and local heating. Quantitative sensory tests were used to evaluate sensory-nerve-fiber function. The non-neuropathic older subjects had an impaired PIV (12+/-7% increase in blood flow with pressure) compared with young subjects (62+/-4%, P<0.001). In the presence of peripheral neuropathy, the older subjects were totally deprived of PIV, leading to early pressure-induced cutaneous ischemia (-31+/-10%, P<0.001). This inability of the skin to adapt to localized pressure in older subjects is related to the severity of the sensory-fiber dysfunction rather than to endothelial dysfunction, which was comparable between the non-neuropathic (141+/-19% increased blood flow with acetylcholine, P<0.05) and neuropathic older subjects (145+/-28% increase, P<0.05) compared with young subjects (234+/-25% increase).

Interactions between nitric oxide and prostanoids in isolated perfused kidneys of the rat.

1 The present study was aimed to assess the interaction between nitric oxide (NO) and thromboxane (Tx) A2‐prostaglandin (PG) H2 in single‐pass perfused isolated kidneys of the rat. 2 Noradrenaline (NA, 63 and 110 nM) dose‐dependently elevated the renal vascular resistance (RVR), the glomerular filtration rate (GFR) and the urinary excretion of sodium (UNaV). Infusion of Nγ‐nitro‐L‐arginine methyl ester (L‐NAME, 100 μm), an inhibitor of NO synthesis, enhanced the effects of NA on RVR and on UNaV, but decreased those on GFR. The TxA2‐PGH2 (TP) receptor blockade by GR32191B (10 μm) attenuated this potentiating effect of L‐NAME. 3 When renal perfusion pressure was stepwise increased from 90 to 150 mmHg, L‐NAME similarly decreased renal perfusion flow rate and GFR. 4 The venous excretion of TxB2 and 6‐keto‐PGF1α was increased by L‐NAME in baseline conditions as well as after NA or increasing renal perfusion pressure (RPP). 5 These results suggest that: (1) TxA2 and PGH2 play an important role in the overall effect of the renal prostanoids, (2) NO strongly interacts with the cyclo‐oxygenase pathway and reduces the prostanoid synthesis in the kidney, and (3) the pressor effect of L‐NAME partly relies upon the vasoconstrictor effect of TxA2 and PGH2.

URINARY EXCRETION OF PROSTANOIDS DURING SLEEP IN OBSTRUCTIVE SLEEP APNOEA PATIENTS

1. Given the unexplained frequent association between systemic hypertension and obstructive sleep apnoea (OSA), the secretion of prostanoids during sleep was investigated (more specifically, the ratio of prostacyclin (PGI2) to thromboxane A2 (TxA2), since they have marked opposite effects on vascular tone). Prostacyclin has vasodilating effects, whereas thromboxane results in vasoconstriction.

A new radioimmunoassay for urinary thromboxane B2 with prior purification by high performance liquid chromatography

In order to assess the role of the renally formed thromboxane A2 in humans, a new radioimmunoassay was developed for the determination of the urinary excretion of thromboxane B2, the stable metabolite of thromboxane A2. Urines were extracted with ethylacetate and thromboxane B2 was separated from the other primary prostaglandins by a reversed phase high performance liquid chromatography using water, acetonitrile and acetic acid (71:29:0.1) as mobile phase with an overall recovery of 44.1% +/- 1.3 (n = 42). The radioimmunoassay, performed on the fraction containing thromboxane B2 used a sensitive (less than 1pg) and highly specific antibody (final dilution: 1/460 800) that we have raised in the rabbit. The coefficient of variation was found lower than 5% in the usable part of the standard curve and the inter-assay reproducibility was at 7.3%. The 24-hour urinary excretion of thromboxane B2 measured in 26 healthy adults established at 109 +/- 12.9 ng/24h in men and at 99.5 +/- 9.2 ng/24 h in women. Therefore, it differed from that of the other prostaglandins by lower values devoid of sex-related differences.

A new technique for the measurement of urinary 6-keto-prostaglandin F1α: normal values in adults

Abstract A new sensitive and specific radioimmunoassay for measurement of urinary 6-keto-prostaglandin F1α is described. In this technique, 6-keto-prostaglandin F1α was first extracted and separated from prostaglandins F2α, F1α, E2, E1, A2 and A1 by using an original high performance liquid chromatographic method with an overall recovery of 74.4 ± 0.9%. The radioimmunoassay used a highly specific antibody raised in the rabbit. The sensitivity of the method was 1.8 pg. Between-assay reproducibility was at 7.7%. As previously reported for prostaglandins E and Fα, the urinary excretion of 6-keto-prostaglandin F1α, measured in 28 healthy adult subjects, was found to be significantly (p

20-Hydroxyeicosatetraenoic acid and renal function in Lyon hypertensive rats.

To evaluate the contribution of cytochrome P450 (CYP450) metabolites of arachidonic acid in the increased renal vascular resistance and blunted pressure-natriuresis response exhibited by Lyon hypertensive (LH) rats, the effects of an intrarenal infusion of 17-octadecynoic acid (3 microM), an inhibitor of the formation of epoxyeicosatrienoic and 20-hydroxyeicosatetraenoic acids, were compared in 8-week-old LH and low blood pressure (LL) control rats. 17-Octadecynoic acid failed to affect renal function in LL rats. In contrast, it reduced renal vascular resistance and shifted the pressure-natriuresis relationship to lower pressures in LH rats. Blockade of thromboxane-endoperoxide (TP) receptors with GR 32191B prevented the renal vasodilator response to 17-octadecynoic acid but not its natriuretic action. Miconazole (1 microM), an inhibitor of epoxygenase activity, had no effect on renal function in LH rats. These results indicate that CYP450 metabolites of arachidonic acid, likely 20-hydroxyeicosatetraenoic acid, contribute to the resetting of the pressure-natriuresis relation in LH rats and that the renal vasoconstrictor effects of 20-hydroxyeicosatetraenoic acid in LH rats may be related to activation of TP receptors.

Plasma Lipids in Genetically Hypertensive Rats of the Lyon Strain

Of the four standardized strains of genetically hypertensive rats, only the Lyon hypertensive rats spontaneously exhibit a higher body weight than their normotensive controls. In order to determine if this increased body weight is associated with alterations in the lipid metabolism, plasma triglycerides (TG), phospholipids (PL), total cholesterol (TPC), and high-density lipoprotein cholesterol (CHDL) were followed in Lyon hypertensive (LH), normotensive (LN), and lowtensive (LL) male rats between 5 and 32 weeks of age. TG were stable with age in LL and LN but increased in LH rats. PL decreased in LL, remained stable in LN, but increased with age in LH rats. TPC and CHDL were stable in LL and LN and increased with age in LH rats. Plasma lipids were not related to the blood pressure level, but were postively related to the body weight in the hypertensive strain. Thus, starting at the age of 5 weeks, LH rats exhibit spontaneously a significant increase in blood pressure, body weight, and plasma lipid concentrations.

Adrenergic stimulation of renal prostanoids in the Lyon hypertensive rat.

Young, genetically hypertensive Lyon (LH) rats exhibited an increased renal in vivo turnover ofnorepinephrine and an elevated urinary excretion of thromboxane B2 when compared withnonnotensive (LN) and low blood pressure (LL) controls. Therefore, the effects of norepinephrine(1.2 xlO−8 to 9.6 lO−7 M) and of phenylephrine (5xlO−8 to 1.9x10−6 M) on renal functionand the urinary excretion of prostanoids were assessed in isolated perfused kidneys of8-week-old LH, LN, and LL rats. In addition, the effects of norepinephrine were assessed beforeand during thromboxane A2/prostaglandin H2 receptor blockade by AH23848 (4xlO−6 M).Before drug infusion, LH kidneys differed from those of LN and LL controls by having anelevated renal vascular resistance and a decreased natriuresis and glomerular filtration rate;the urinary output of prostaglandin E2 and F2a, of 6-ketoprostaglandin Fla, and of thromboxaneB2 was similar in the three strains. The constrictor effects of norepinephrine andphenylephrine were significantly increased in LH rat kidneys compared with LL but not withLN controls, and their pressure‐natriuresis was markedly reduced. Norepinephrine andphenylephrine induced a 10- to 20-fold dose-dependent increase in the synthesis of the fourprostanoids, which was more pronounced in LH than in LN and LL rats for thromboxane B2only. AH23848 infusion significantly reduced the vascular effects of norepinephrine andincreased the natriuretic response of LH but not of LN and LL rat kidneys. In conclusion,isolated perfused kidneys from LH rats exhibit an increased production of thromboxane A2,which enhances the renal effects of norepinephrine and therefore could participate in thedevelopment of hypertension of the Lyon model.

Radioimmunoassay for urinary prostaglandins E and Fα: normal values in different age groups

Abstract A new radioimmunoassay for urinary prostaglandins E and F α is described which allows the extraction and Chromatographie separation of urinary prostaglandins with an overall recovery of 80.5% and 89.3% for prostaglandins E 2 and F 2α respectively. The antibodies raised in the rabbit could not distinguish prostaglandins of series 1 and 2 but were found highly specific towards their metabolites and other primary prostaglandins. The sensitivity of the assay developed was at 2.2 pg for prostaglandin E and 2pg for prostaglandin F α . This assay was applied to normal adults of both sexes; it was shown that the daily urinary excretion of prostaglandins F ga and E was greater in men than in women. In children aged from 1 to 114 months, the urinary excretion of prostaglandins increased with age. This increase was more marked during the first two years of life and was significantly related to age.

Major cardiovascular risk factors in Lyon hypertensive rats. A correlation analysis in a segregating population

Objective To investigate the association of blood pressure with the other major cardiovascular risk factors in a large population of back-cross to Lyon hypertensive (LH) rats. Methods Mean arterial pressure was recorded in male freely moving Lyon normotensive (LN), LH, F1 and back-cross to LH rats aged 30 weeks. Plasma cholesterol, triglycerides, insulin, creatinine, urea, fibrinogen and haematocrit levels, and the insulin:glucose ratio were measured in 31-week-old rats and 24 h albuminuria in 6-week-old rats. Results Adult LH rats exhibited a significant increase in plasma lipids, insulin, fibrinogen, creatinine, urea and haematocrit levels compared with LN rats. In young LH rats, at an age at which blood pressure is slightly increased, albuminuria was increased to a greater extent than expected from their blood pressure levels. In the adult back-cross to LH rats, only the plasma cholesterol level was associated with blood pressure. Moreover, the plasma cholesterol level was related to fibrinogen and haematocrit levels. Finally, in the same rats, albuminuria developed early in life was positively related to hypercholinesterolaemia measured later in life. Conclusion Plasma cholesterol, fibrinogen, haematocrit levels and early albuminuria could act synergistically in the enhancement or the development, or both, of vascular and kidney damage in the LH rat. Most interestingly, the association between plasma cholesterol level and blood pressure indicates that, as in essential hypertension, hypercholesterolaemia is a major phenotype associated with hypertension in the LH rat.