Neutral endopeptidase and angiotensin I converting enzyme insertion/deletion gene polymorphism in humans.

Neutral endopeptidase (NEP) hydrolyses angiotensins (Ang) I and II and generates angiotensin-(1-7) [Ang-(1-7)]. In humans, the insertion/deletion (I/D) angiotensin-I converting enzyme (ACE) gene polymorphism determined plasma ACE levels by 40%. In rats, a similar polymorphism determines ACE levels which are inversely associated to NEP activity. The objective of this study is to evaluate the relationship between ACE expression and plasma NEP activity in normotensive subjects and in hypertensive patients. In total, 58 consecutive patients with hypertension, evaluated in our Hypertension Clinic, were compared according to their ACE I/D genotypes with 54 control subjects in terms of both plasma ACE activity and NEP activities. Plasma ACE activity was elevated 51 and 70% in both DD ACE groups (normotensives and hypertensives) compared with their respective ID and II ACE groups (P<0.001). A significant effect of the ACE polymorphism and of the hypertensive status on ACE activity was observed (P<0.001). In normotensive DD ACE subjects, NEP activity was 0.30+/-0.02 U/ml, whereas in the normotensive II ACE and in the normotensive ID ACE subjects NEP activity was increased 65 and 48%, respectively (P<0.001). In the hypertensive DD ACE patients, NEP activity was 0.47+/-0.03 U/mg. An effect of the I/D ACE genotypes on NEP activity (P<0.04) and an interaction effect between the I/D ACE genotype and the hypertensive status were also observed (P<0.001). These results are consistent with a normal and inverse relationship between the ACE polymorphism and NEP activity in normotensive humans (as is also observed in rats). This normal relationship is not observed in hypertensive patients.

[Early prevention of experimental left ventricular hypertrophy in experimental hypertension and angiotensin II levels]. / Prevención precoz de hipertrofia ventricular izquierda en la hipertensión experimental y concentraciones de angiotensina II.

INTRODUCTION: Angiotensin II levels can be partially inhibited during chronic administration of angiotensin converting enzyme (ACE) inhibitors, limiting from a clinical point of view its efficacy in the treatment of hypertension. There are few studies relating ACE activity directly with early prevention of left ventricular hypertrophy (LVH) in systemic hypertension during the administration of an ACE inhibitor (ACEI). AIM: To evaluate the effects of early ACE inhibition with perindopril on the development of hypertension, LVH and levels of angiotensin II (Ang II) in plasma as well as in LV in the rat Goldblatt model (Gb; 2 kidneys-1 clip), 2 weeks after surgery. RESULTS: Systolic blood pressure and relative LV mass increased by 42% and 20% respectively, in the Gb group (p < 0.001). Plasma and LV ACE activities were significantly higher in the Gb rats compared with the control rats. Plasma and LV Ang II levels also increased by 129% and 800%, respectively. Perindorpil prevented hypertension and LVH development by inhibiting plasma ACE (and also LV ACE), and also circulation Ang II in plasma and in the LV. CONCLUSIONS: In this experimental model of hypertensive LVH, there is an early activation of plasma and cardiac ACE. Early administration of an ACE inhibitor prevents the development of hypertension and LVH by inhibiting the increases of plasma and LV Ang II.

Angiotensin I-converting enzyme modulates neutral endopeptidase activity in the rat.

Angiotensin I is a substrate for both ACE and for neutral endopeptidase 24.11 (NEP). We hypothesized that high ACE expression is related to low NEP activity. Accordingly, circulating and tissue NEP and ACE activities were measured by fluorometry in homozygous rats (F(0) and F(2)) for the Lewis microsatellite allele (LL, low ACE) and for the Brown Norway microsatellite allele (BB, high ACE). Plasma, lung, and aortic ACE activities in F(0) and F(2) were higher in BB rats than in LL rats (P<0.01), whereas left ventricular ACE activity was similar in both genotypes. In contrast, NEP activity in the LL group was higher in the serum, aorta, and lungs in F(0) and F(2) homozygous (P<0.05). Plasma ACE activity was inversely correlated with serum (r=-0.6 and -0.598 in F(0) and F(2), respectively; P<0.03) and lung NEP activities (r=-0.77 in F(0) and r=-0.59 in F(2), P<0.01). Aortic ACE and NEP activities were also correlated (r=-0.696 and -0.584 in F(0) and F(2), respectively; P<0.03). In conclusion, genetically determined high ACE expression in rats is inversely related to tissue NEP activity, which could determine lower angiotensin-(1-7) tissue levels.

Reproducibility of plasma angiotensin-converting enzyme activity in human subjects determined by fluorimetry with Z-phenylalanine-histidyl-leucine as substrate.

Despite the major physiologic role of angiotensin-converting enzyme (ACE), few studies have evaluated the ideal conditions for measuring human plasma ACE activity, specifically when using Z-phenylalanine-histidyl-leucine as substrate. This study, performed in volunteer patients, assessed the reproducibility of human plasma ACE activity measured by fluorimetry with Z-phenyl-histidyl-leucine as the substrate. After blood centrifugation, plasma was stored under different conditions until processing. The following sources of variability were evaluated: (1) the interval to centrifugation of blood after collection, (2) the temperature and (3) safe time for storing the plasma after cold centrifugation, (4) the effect of fasting. Plasma ACE activity was 20.6+/-7.7 U/mL, 20.9+/-8 U/mL, and 20.5+/-7.9 U/mL (n = 25) when samples were centrifuged immediately, after 1 hour of blood sampling, and after 3 hours of blood sampling, respectively (not significant). In plasma kept at -20 degrees C, ACE activity was not different after 1 week (17.4+/-4.3 U/mL) nor after 1 month (17.9+/-4 U/mL), whereas baseline ACE was 16.7+/-4.3 U/mL (n = 10). In plasma stored at -80 degrees C, ACE activity was 15.5+/-5.7 U/mL after 1 month (baseline 15+/-5.3 U/mL; not significant; n = 12). No evidence for hydrolysis of the reaction product of ACE (his-leu dipeptide) was observed in plasma samples kept for 1 month at -20 degrees C or at -80 degrees C (by high-performance liquid chromatography analysis). In plasma obtained before breakfast, ACE activity was 12.8+/-7.1 U/mL, and it was 12.3+/-7.5 U/mL 2 hours afterwards (not significant; n = 12). Thus, to determine human plasma ACE activity by fluorimetry with reliability, with Z-phenylalanine-histidyl-leucine used as a substrate, there is a safe interval of at least 3 hours before blood centrifugation at -4 degrees C. Plasma may be kept at -20 degrees C or at -80 degrees C for at least 4 weeks before final processing. Fasting does not influence its enzymatic activity.

Omeprazole, a specific gastric secretion inhibitor on oxynticopeptic cells, reduces gizzard erosion in broiler chicks fed with toxic fish meals.

The relation between gizzard erosion-black vomit (GE-BV) and gastric secretion is not completely understood. A pharmacological approach to reduce the presence of GE-BV in chicks due to fish meal in diets is also unknown. In this study the use of omeprazole, a H+/K+ ATPase inhibitor, and fish meals of different biotoxicological characteristics, showed that: 1) Omeprazole decreased total gastric acid content, GE scores and severe GE (SGE) cases, in a dose-dependent manner. This reduction was significant at levels higher than 20 mg omeprazole/Kg body weight (BW)/day (p < 0.01). The addition of 50 mg omeprazole/kg BW/day almost completely prevented the incidence of SGE cases and reduced in 50% GE score in chicks (p < 0.01). 2) A significant reduction in specific mortality, near 90%, was also seen with all toxic fish meals when omeprazole (50 mg/Kg BW/day) was added to experimental diets in comparison to control groups. However, no mortality was observed when omeprazole was added to diets containing non-toxic fish meals. 3) In chicks fed with toxic fish meals, addition of different amounts of omeprazole to diets changed the relative weight of proventriculus (p < 0.01) and gizzard (p < 0.05). Maximum effect was obtained with omeprazole concentration higher than 50 mg/Kg BW/day. 4) Omeprazole did not change feed intake in chicks fed with toxic fish meal. However, in some fish meal a reduction on weight gain was observed with the addition of omeprazole.

Binding and production of insulin-like growth factor-I in rat mammary gland.

1. Mammary tissue from pregnant rat presents low and high affinity IGF-I functional receptors. 2. Mammary explants from pregnant and lactating rats secrete IGF-I and its production was related to the developmental stage of the gland. 3. An inverse relationship between IGF-I production and tissue binding capacity was observed.

Epidermal growth factor increases cyclic AMP levels in pregnant rat mammary gland explants.

Addition of epidermal growth factor (EGF) to a rat mammary organ culture results in increase levels of intracellular cyclic AMP. This dose dependent EGF effect occurs at physiological concentrations of the hormone and was maximal in early and middle pregnancy.

[Beta adrenergic receptors in circulating lymphocytes of patients with chronic heart failure]. / Receptores beta adrenérgicos en linfocitos circulantes de pacientes con insuficiencia cardiaca crónica.

Severe decompensated chronic heart failure is associated to increased levels of circulating catecholamines and decreased density of myocardial beta-adrenergic receptors. In 14 patients with stable, class II-III heart failure we studied circulating lymphocytes to determine the number of beta adrenergic receptors, the dissociation constant of 3H dihydroalprenolol (kd) and the intracellular content of cyclic AMP (AMPc). Results (mean +/- SEM) were compared to those obtained in 10 healthy controls. The number of beta receptors was significantly decreased (105 +/- 16 vs 185 +/- 24, fmol/mg of membrane protein, p less than 0.01). No differences were found in Kd (1.65 +/- 0.2 vs. 1.36 +/- 0.28 nm) nor the level of AMPc (7.9 +/- 2.1 vs 7.1 +/- 2.9 pmol/mg protein), respectively. The decreased number of beta adrenergic receptors in the circulating lymphocytes may be related to the increased level of circulating catecholamines that have been shown to be present during exercise in these patients.