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G Fois

Publications and source records attributed to G Fois.

8 recordsLinked to original sources
PubMed2006

Structural depinning of Ne monolayers on Pb at T < 6/5 K.

We have studied the nanofriction of Ne monolayers with a quartz-crystal microbalance technique at temperatures below 6.5 K and in ultrahigh-vacuum conditions. Very homogeneous and smooth lead electrodes have been physically deposited on a quartz blank at 150 K and then annealed at room temperatures. With such a Pb-plated quartz-crystal microbalance, we have observed a pronounced depinning transition separating a low-coverage region, where the film is nearly locked to the oscillating electrode, from a high-coverage region characterized by slippage at the solid-fluid boundary. Such a behavior has been found to be very reproducible. These data are suggestive of a structural depinning of the solid Ne film when it becomes incommensurate with the lead substrate, in agreement with the results of an extensive molecular-dynamics study.

Journal Article↗
PubMed1983

Trypsin-activatable inactive renin in rat plasma.

1. Activation of inactive renin in rat plasma has been studied with different trypsin concentrations and incubation times at pH 6.2 and 4 degrees C. 2. Trypsin concentrations below 2 mg/ml, lower than endogenous rat plasma anti-trypsin activity, do not activate inactive renin, whereas maximal activation is obtained with trypsin at 6 mg/ml for 1 min at 4 degrees C, pH 6.2. 3. Under these conditions trypsin can cleave dialysable fragments from renin substrate. ANG I can be generated at 37 degrees C with a pH optimum of 5.3. Nevertheless, the ANG I formation at pH 6.2 was totally unaffected. 4. Incubations longer than 2 min with trypsin at 6 mg/ml can induce a direct cleavage of dialysable ANG I-containing fragments strongly interfering with the measurements of renin activity at pH 6.2. 5. On average 40% of the total renin measured in plasma of normotensive WK rats is in the inactive form, although a wide range of variation is observed.

Angiotensin I↗
PubMed1982

Active and inactive renin after a single dose of captopril in hypertensive patients.

In 25 hypertensive patients (15 with renal artery stenosis and 10 with essential hypertension), captopril, in a single 12.5 mg dose, caused a prompt decrease in arterial pressure without changing the heart rate. Plasma active and trypsin-activated renin significantly increases, whereas inactive renin and plasma aldosterone decreased. The plasma active/inactive renin ratio was also increased, suggesting that captopril, together with a release of active renin, may induce an in vivo activation of inactive renin. No correlations were found between blood pressure changes and both pretreatment and captopril-induced variations of active, inactive and trypsin-activated renin or the active/inactive ratio. However, the percent decrease in mean arterial pressure was significantly related to the increase in the active/inactive renin ratio in a group of patients whose blood pressure was brought to normal (r = -0.78; p less than 0.001). This finding suggests the possibility that vasodilating substances, in addition to inhibiting angiotensin II formation, might play some role both in exerting a full effect of captopril on blood pressure and in triggering the in vivo mechanisms of inactive renin activation.

Blood Pressure↗
PubMed1982

Studies on trypsin activation of inactive renin in rat plasma.

The experimental conditions of trypsin activation of inactive renin in rat plasma have been studied. Our results showed that the pH optimum of trypsin-activated renin is 6.2, the same as that of rat plasma active renin. Trypsin concentration and incubation time might also interfere with the activation process. Trypsin concentration below 2 mg/ml cannot activate inactive renin. Trypsin at a concentration of 6 mg/ml for 1 min. can cleave dialyzable fragments from renin substrate which can generate Angiotensin I at 37 degrees C with a pH optimum of 5.3 but which do not affect Angiotensin generation at pH 6.2. Longer incubations (more than 2 min.), on the contrary, can produce a cleavage at 4 degrees C of Angiotensin I containing fragments directly from renin substrate strongly interfering with measurements of renin activity at pH 6.2. Trypsin concentrations lower than endogenous rat plasma anti-trypsin activity do not activate inactive renin. Much higher concentrations of trypsin, however, are needed to obtain optimum activation of inactive renin. In average, 40% of the total circulating renin in rat plasma can be activated by trypsin.

Animals↗
PubMed1981

Trypsin activation of inactive renin in human plasma. An assessment of some methodological aspects.

The following methodological aspects of the use of trypsin as activator of inactive renin in human plasma have been studied: a) the effect of SBTI on renin activity and angiotensin; b) the reaction velocity of trypsin on inactive renin; c) the optimum trypsin concentration; d) the ability of human plasma to neutralize exogenous trypsin. Our results show that: 1) Some commercially available SBTI may exert an angiotensinase-like effect which can be abolished by PMSF. 2) At 4 degrees C activation of inactive renin reached a maximum within the first two minutes then no further activation could be demonstrated. 3) Trypsin 2 mg/ml yielded more inactive renin than trypsin 1 or 0.5 mg/ml. A higher concentration (3 mg/ml) gave substantially equivalent activation as (with) trypsin 2 mg/ml whereas when using a still higher concentration (4 mg/ml) a degradation of the renin system components could be noted. 4) Endogenous trypsin inhibitors can eventually inactivate exogenous trypsin up to 3 mg/ml. About 20% of renin is destroyed by trypsin 4 mg/ml within 2 min at 4 degrees C while an additional 40% is lost during the incubation at 37 degrees C if no SBTI is added.

Enzyme Activation↗
PubMed1980

[Methodology of renal vein renin study: comparison between simultaneous and sequential sampling (author's transl)].

Purpose of this study has been to compare the results obtained using two different procedures in blood sampling from the renal veins for measuring renal venous renin. The first is the classical procedure which employs three catheters for simultaneous sampling from both renal veins and from the inferior vena cava, or from an artery. The other one is a simplified procedure which employs a single catheter that allows blood to be collected in the following rapid sequential manner: right renal vein, inferior vena cava, left renal vein, inferior vena cava. We have studied 13 patients (8 with essential hypertension, 5 with unilateral renal artery stenosis). Two catheters were introduced through a femoral vein and inserted into both renal veins; a third catheter was inserted into the femoral artery; then the blood sampling was performed strictly simultaneously. Soon after, the blood sampling was repeated according to the above mentioned sequential single catheter procedure. PRA was measured by Angiotensin I radioimmunoassay, then the Renal Vein Ratios (RVRR) were calculated. Even though as average of less than 20 seconds elapsed between the blood sampling in a renal vein and that in inferior vena cava, our results demonstrate that the release of renin can vary so quickly that erroneous informations may be obtained unless a strictly simultaneous sampling of blood is performed. In conclusion, our study demonstrates that the only reliable renal vein renin sampling procedure must employ the simultaneous renal venous and arterial (or inferior vena cava) blood collection.

Adult↗