T. Quesada

Renal effects of prolonged synthesis inhibition of endothelium-derived nitric oxide.

The aim of the present study was to investigate in conscious dogs the long-term effects of nitric oxide synthesis inhibition on glomerular filtration rate, sodium and water excretion, and plasma levels of renin and aldosterone. After a control period of 3 days, an inhibitor of endothelium-derived nitric oxide synthesis, NG-nitro-L-arginine-methyl ester, was infused for 3 consecutive days at a dose (50 ng/kg/min) that did not induce significant changes in arterial pressure (n = 6). The inhibition of nitric oxide synthesis led to a large and sustained decrease (p less than 0.05) in glomerular filtration rate of approximately 35%. This change was accompanied by a decrease (p less than 0.05) in urinary sodium excretion from 78.9 +/- 4.6 meq/day to 49.8 +/- 6.8, 60.1 +/- 4.2, and 53.5 +/- 9.0 meq/day by days 1, 2, and 3 of nitric oxide synthesis inhibition, respectively. Changes in fractional sodium excretion failed to achieve statistical significance. Nitric oxide synthesis inhibition also induced a significant and sustained decrease in urine flow rate. The decrease in glomerular filtration rate, natriuresis, and diuresis was accompanied by a 45% increase in plasma renin activity (p less than 0.05) and no change in plasma aldosterone concentration. By day 3 of the recovery period, glomerular filtration rate, natriuresis, diuresis, and plasma renin activity returned to values similar to those found during the control period. The administration of L-arginine during 3 consecutive days (5 micrograms/kg.min i.v.) did not modify any of the parameters measured but effectively prevented all the renal changes induced by the 3 days of nitric oxide synthesis inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of nitric oxide in mediating renal response to volume expansion.

The objective of the present study was to determine the role of endothelium-derived nitric oxide in mediating the renal response to extracellular volume expansion with isotonic saline (5% body weight). In anesthetized dogs (n = 7) and before volume expansion, nitric oxide synthesis was inhibited in the right kidney by continuous intrarenal infusion of NG-nitro-L-arginine-methyl ester (1 μg/kg/min). Arterial pressure and renal hemodynamics of both kidneys did not change significantly either during nitric oxide synthesis inhibition or during 5% volume expansion. However, in response to extracellular volume expansion, increases in natriuresis, diuresis, and fractional excretion of lithium (an index of proximal sodium reabsorption) were inhibited in the right kidney by 27%, 28%, and 41%, respectively, when compared with the contralateral kidney. Increases of renal interstitial hydrostatic pressure during 5% volume expansion were not statistically different between both kidneys. In another group of dogs (n = 4), the administration of L-arginine (0.5 mg/kg/min) into the right renal artery prevented the renal effects induced by the nitric oxide synthesis inhibitor during volume expansion. The findings in this study suggest that nitric oxide production plays an important role in regulating the renal response to extracellular volume expansion. The proximal tubule seems to be involved in the reduced renal excretory response to volume expansion during nitric oxide synthesis inhibition.

2-Methoxyestradiol attenuates hypertension and coronary vascular remodeling in spontaneously hypertensive rats.

OBJECTIVES Accumulating data provide evidence that some metabolites of 17beta-estradiol are biologically active and mediate multiple effects on the cardiovascular and renal systems. We investigated the effect of 2-methoxyestradiol (an active metabolite of estradiol with non-feminizing activity) on the development of hypertension and myocardial vascular remodeling in male and female ovarectomized SHR. METHODS Rats were divided into five groups: intact females, ovarectomized (OVX), OVX+ 2-methoxyestradiol (2ME), control males, and male+2ME. Systolic blood pressure was determined from 10 to 18 weeks. Structural changes in coronary vessels were quantified by an image analyzer. Immunoblotting of phosphorylated ERK1/2 and NADPH oxidase activity were performed on mesenteric arteries. RESULTS Treatment with 2ME reduced the increase in systolic blood pressure in male and ovarectomized rats to values not different from those obtained in intact females. Myocardial arterioles and small arteries showed significant increases in wall-to-lumen ratio and perivascular fibrosis in male and ovarectomized rats when compared with intact females. NADPH oxidase activity was increased in mesenteric arteries from males and ovarectomized females as compared with intact females. Finally, the expression of phosphorilated ERK1/2 were significantly higher in mesenteric arteries from male and ovariectomized animals than in those from intact females. Those effects of ovarectomy and gender differences were totally or partially prevented by treatment with 2-methoxyestradiol. CONCLUSIONS These data demonstrate that 2-methoxyestradiol protects the vasculature from hypertension-induced myocardial arterial remodeling in male and ovarectomized SHR, and that might be in part related to decreased superoxide generation and ERK1/2 activation.

Hemodynamic effects of hypertonic saline in the conscious rat.

The present study examines the role of vasopressin and the sympathetic nervous system on the hemodynamic effects of an infusion of hypertonic saline (NaCl 1.5 M) in conscious rats. The cardiovascular response to hypertonic saline was similar in both untreated and hexamethonium-pretreated rats. Mean arterial pressure increased by 15 mmHg as a consequence of the elevation of total peripheral resistance, while cardiac index was decreased. The administration of an antagonist to the pressor activity of vasopressin in rats with intact reflexes, partially decreased mean arterial pressure and total peripheral resistance and increased cardiac index toward basal values. In contrast, the hemodynamic response to hypertonic saline was totally reverted when the vasopressin antagonist was injected in the hexamethonium-pretreated rats. The results of the present study indicate that the hypertensive response induced by hypertonic saline in conscious rats is due to the vasoconstrictor effects of both vasopressin and the sympathetic nervous system.

Importance of Nitric Oxide and Prostaglandins in the Control of Rat Renal Papillary Blood Flow

The role of nitric oxide and prostaglandins in the control of rat renal papillary blood flow has been studied in anesthetized Munich-Wistar rats by use of laser Doppler flowmeter. Acute administration of N omega-nitro-L-arginine methyl ester (L-NAME) 10 mg/kg IV (n=8) increased mean arterial pressure by 27.8 +/- 3.6%, decreased papillary blood flow by 39.4 +/- 3.8%, and decreased renal blood flow by 47.4 +/- 1.9%. The subsequent administration of indomethacin (7.5 mg/kg IV) further decreased papillary blood flow (35.2 +/- 2.5%) without significant changes in mean arterial pressure or renal blood flow. In a second group (n = 6), administration of indomethacin before L-NAME decreased papillary blood flow by 39.6 +/- 2.1% without significantly altering mean arterial ressure or renal blood flow. The subsequent injection of L-NAME further decreased papillary blood flow (32.9 +/- 1.8%) and renal blood flow (49.8 +/- 6.6%) while increasing mean arterial pressure to a level not significantly different from that found in the first group. Autoregulation studies showed that L-NAME but not indomethacin reduced the renal perfusion pressure-renal blood flow relationship without altering autoregulation. However, both nitric oxide and prostaglandins importantly affected the renal perfusion pressure-papillary blood flow relationship because L-NAME and indomethacin significantly decreased this relationship in an additive fashion. Although both drugs reduced the sensitivity of the pressure-papillary flow relationship, only L-NAME affected autoregulation so that papillary blood flow was autoregulated at higher renal perfusion pressures. Thus, the present results indicate that both nitric oxide and prostaglandins control a similar percentage of rat renal papillary blood flow, but nitric oxide seems to be more important than prostaglandins as a mediator of the pressure-blood flow relationship. In contrast, only nitric oxide modifies the renal blood flow level, although it does not disturb whole-kidney blood flow autoregulation.

Role of protein kinase C in mesenteric pressor responses of rats with portal hypertension.

1 Hyporesponsiveness to vasoconstrictors is a characteristic abnormality of liver diseases of uncertain origin. In the present study, we have evaluated the involvement of protein kinase C (PKC) in the reduced pressor response to methoxamine (MTX) of a rat model of portal hypertension induced by partial portal vein ligation (PVL). Experiments were performed in the isolated and perfused mesentery. 2 The pressor response to MTX was reduced in PVL compared to that of control animals (Sham) and pretreatment with NG‐nitro‐L‐arginine (L‐NOARG, 10−4 m) or removal of the endothelium potentiated the response of both groups. However, only removal of the endothelium completely eliminated the reduced pressor response to MTX of the PVL vessels. 3 Pretreatment of the mesentric vessels with calphostin C (10−6 m), a PKC inhibitor, reduced the response to MTX of Sham to a level similar to that of untreated PVL vessels, but did not change that of PVL animals. 4 Mesenteric pressor responses to a PKC activator, phorbol 12,13‐dibutyrate (PDBu), were similar in vessels from both PVL and Sham rats and pretreatment with L‐NOARG or removal of the endothelium enhanced those responses while indomethacin (10−5 m) decreased them. In all cases, the responses to PDBU were similar in PVL vessels compared to Sham. 5 These results indicate that the reduced pressor response to MTX of the mesenteric vascular bed of PVL rats is due to an endothelial alteration, compatible with an enhanced production of nitric oxide. The lack of response to calphostin C in PVL vessels suggests an impairment in agonist‐induced PKC activation. Since direct activation of PKC induces a normal pressor response, it is concluded that the endothelial alteration interacts with the mechanism producing PKC activation, which results in a lower pressor response of the PVL mesenteric vaculature.

Cardiocirculatory responses to AII and AVP in conscious rats.

Cardiac and peripheral circulatory responses to changes in afterload with angiotensin II (AII) and vasopressin (AVP) were investigated in ganglion-blocked (hexamethonium) conscious rats. Cardiac output (CO) was measured by thermodilution. Both hormones were infused at a dose adjusted to increase mean arterial pressure 70% above baseline. AVP (11.4

Role of prostaglandins in mediating the renal effects of atrial natriuretic factor.

2.2 ng/kg/min. n = 6) decreased CO from 43.4