Roles of estrogen and progesterone in modulating renal nerve function in the rat kidney

The maintenance of extracellular Na+ and Cl- concentrations in mammals depends, at least in part, on renal function. It has been shown that neural and endocrine mechanisms regulate extracellular fluid volume and transport of electrolytes along nephrons. Studies of sex hormones and renal nerves suggested that sex hormones modulate renal function, although this relationship is not well understood in the kidney. To better understand the role of these hormones on the effects that renal nerves have on Na+ and Cl- reabsorption, we studied the effects of renal denervation and oophorectomy in female rats. Oophorectomized (OVX) rats received 17β-estradiol benzoate (OVE, 2.0 mg·kg-1·day-1, sc) and progesterone (OVP, 1.7 mg·kg-1·day-1, sc). We assessed Na+ and Cl- fractional excretion (FENa+ and FECl- , respectively) and renal and plasma catecholamine release concentrations. FENa+ , FECl- , water intake, urinary flow, and renal and plasma catecholamine release levels increased in OVX vs control rats. These effects were reversed by 17β-estradiol benzoate but not by progesterone. Renal denervation did not alter FENa+ , FECl- , water intake, or urinary flow values vs controls. However, the renal catecholamine release level was decreased in the OVP (236.6±36.1 ng/g) and denervated rat groups (D: 102.1±15.7; ODE: 108.7±23.2; ODP: 101.1±22.1 ng/g). Furthermore, combining OVX + D (OD: 111.9±25.4) decreased renal catecholamine release levels compared to either treatment alone. OVE normalized and OVP reduced renal catecholamine release levels, and the effects on plasma catecholamine release levels were reversed by ODE and ODP replacement in OD. These data suggest that progesterone may influence catecholamine release levels by renal innervation and that there are complex interactions among renal nerves, estrogen, and progesterone in the modulation of renal function.

Differential effects of isoproterenol on the activity of angiotensin-converting enzyme in the rat heart and aorta

The excessive stimulation of beta-adrenergic receptors in the heart induces myocardial hypertrophy. There are several experimental data suggesting that this hypertrophy may also depend, at least partially, on the increase of local production of angiotensin II secondary to the activation of the cardiac renin-angiotensin system. In this study we investigated the effects of isoproterenol on the activity of angiotensin-converting enzyme (ACE) in the heart and also in the aorta and plasma. Male Wistar rats weighing 250 to 305 g were treated with a dose of (ñ)-isoproterenol (0.3 mg kg-1 day-1, N = 8) sufficient to produce cardiac hypertrophy without deleterious effects on the pumping capacity of the heart. Control rats (N = 7) were treated with vehicle (corn oil). The animals were killed one week later. ACE activity was determined in vitro in the four cardiac chambers, aorta and plasma by a fluorimetric assay. A significant hypertrophy was observed in both ventricular chambers. ACE activity in the atria remained constant after isoproterenol treatment. There was a significant increase (P<0.05) of ACE activity in the right ventricle (6.9 = 0.9 to 8.2 = 0.6 nmol His-Leu g-1 min-1) and in the left ventricle (6.4 ñ 1.1 to 8.9 ñ 0.8 nmol His-Leu g-1 min-1). In the aorta, however, ACE activity decreased (P<0.01) after isoproterenol (41 = 3 to 27 = 2 nmol His-Leu g-1 min-1) while it remained unchanged in the plasma. These data suggest that ACE expression in the heart can be increased by stimulation of beta-adrenoceptors. However, this effect is not observed on other local renin-angiotensin systems, such as the aorta. Our data also suggest that the increased sympathetic discharge and the elevated plasma concentration of catecholamines may contribute to the upregulation of ACE expression in the heart after myocardial infarction and heart failure

Increased angiotensin-converting enzyme activity in the left ventricle after infarction

An increase in angiotensin-converting enzyme (ACE) activity has been observed in the heart after myocardial infarction (MI). Since most studies have been conducted in chronically infarcted individuals exhibiting variable degrees of heart failure, the present study was designed to determine ACE activity in an earlier phase of MI, before heart failure development. MI was produced in 3-month old male Wistar rats by ligation of the anterior branches of the left coronary artery, control rats underwent sham surgery and the animals were studied 7 or 15 days later. Hemodynamic data obtained for the anesthetized animals showed normal values of arterial blood pressure and of end-diastolic pressure in the right and left ventricular cavities of MI rats. Right and left ventricular (RV, LV) muscle and scar tissue homogenates were prepared to determine ACE activity in vitro by measuring the velocity of His-Leu release from the synthetic substrate Hyp-His-Leu. ACE activity was corrected to the tissue wet weight and is reported as nmol His-Leu g(-1) min(-1). No significant change in ACE activity in the RV homogenates was demonstrable. A small nonsignificant increase of ACE activity (11 + 9 percent; P>0.05) was observed 7 days after MI in the surviving left ventricular muscle. Two weeks after surgery, however, ACE activity was 46 + 11 percent (P<0.05) higher in infarcted rats compared to sham-operated rats. The highest ACE activity was demosntrable in the scar tissue homogenate. In rats studied two weeks after surgery, ACE activity in the LV muscle increased from 105 + 7 nmol His-Leu g(-1) min (-1) in control hearts to 153 + 11 nmol His-Leu g(-1) min(-1) (P<0.05) in the remaining LV muscle of MI rats and to 1051 + 208 nmol His-Leu g(-1) min(-1) (P<0.001) in the fibrous scar. These data indicate that ACE activity increased in the heart after infarction before heart failure was demonstrable by hemodynamic measurements. Since the blood vessels of the scar drain to the remaining LV myocardium, the high ACE activity present in the fibrous scar may increase the angiotensin II concentration and decrease bradykinin in the cardiac tissues surrounding the infarcted area. The increased angiotensin II in the fibrous scar may contribute to the reactive fibrosis and hypertrophy in the left ventricular muscle surviving infarction.

Calpain activity of hypertrophic hearts from hypertensive rats

Heart tissue contains large amounts of the Ca²+ -activated protein-ase calpain which has been assigned a specific function in the turnover of muscle protein. The objective of the present study was to determine calpain (E.C. 3.4.22.17)-like activity in homogenates of left ventricle from hypertensive rats that developed ventricular hypertrophy. Calpain activity was assayed using heat-denaturated azocasein as a substrate in the presence of 1 mM calcium and corrected by subtraction of the Ca²+ -independent activities. Tha latter were measured in the presence of 1 mM EGTA and the products read at 440nm. Male Wistar rats (225g) were assgned to control (N=8, normal drinking water), salt (N=6, drinking water containing 1 percent NaCl) and DOCA-salt (N=6, deoxycorticosterone acetate, 8 mg/Kg, sc, twice a week for 20 days plus drinking water containing 1 percent NaCl) groups. SHR (N =6, spontaneously hypertensive rats) were also used. The calpain activity of the control group was at 3.90 ñ 0.22 mU/g wet weight tissue. Hypertension induced significant left ventricular hypertrophy in DOCA-salt rats (26 percent) and in SHR (54 percent) and a 30 percent decrease in calpain activity in both groups (P < 0.01). In the high salt load (salt group) calpain activity was also decreased, but this was not accompanied by hypertrophy...

Heart prolyl endopeptidase activity in one-kidney, one clip hypertensive rats

1. Heart mass, prolyl endopeptidase activity and fractionated proteins from heart tissue were studied in one-kidney, one clip hypertensive rats (N=6) and compared to sham-operated rats (N=6). 2. Body weigh, arterial pressure and tissue mass were measured 4 weeks after artery clipping Z-Gly-Pro-p-nitroaniline hydrolysis was used to measure tissue prolyl endopeptidase activity in the homogenate. Protein was fractionated into the soluble and myofibrillar fractions. 3. In the normotensive rats, prolyl endopeptidase activity expressed in terms of protein specific activity (µM substrate hydrolyzed h-1 mg supernatant protein-1) occurred in atria and was 2.5-fold higher than in the ventricles (3.79 ñ 0.20 vs 1.44 ñ 0.02, P<0.05). In the one-kidney, one clip hypertensive rats, the left ventricle tissue increased 1.7-fold (2.27 ñ 0.11 vs 3.72 ñ 0.11 mg wet weight tissue/g body weight, P<0.001), the soluble protein fraction (54.86 ñ 3.60 vs 57.38 ñ 6.64 mg/g wet weight tissue) was unchanged, while the myofibrillar fraction increased 1.9-fold (118.9 ñ 9.09 vs 229.8 ñ 8.47 mg/g wet weight tissue, P<0.001). 4 The specific activity of the atrial and ventricular prolyl endopeptidase decreased in atria and increased in ventricles as the result of hypertension (3.79 ñ 0.2 vs 2.84 ñ 0.13 and 1.44 ñ 0.02 vs 1.87 ñ 0.13; respectively). These regional differences in prolyl endopeptidase enxyme content caused by one-kidney, one clip hypertension in neurosecretory and non-neurosecretory heart areas suggest that this enzyme plays a local role in the turnover of specific polypeptides