Effect of alpha-adrenergic stimulation on prostacyclin and renin release in the rat kidney

Renal thromboxane A2 synthesis in the Lyon hypertensive rat

The aim of the present study was to assess the mechanisms by which norepinephrine (NE) increased the synthesis of prostanoids and revealed a hyperactivity of the Thromboxane (Tx) A2 synthase in the Lyon genetically hypertensive (LH) rat kidney. To this purpose, the effects of NE (1.2 x 10(-8) to 9.6 x 10(-7) M) on renal function and prostanoid synthesis were assessed in isolated perfused kidneys following beta-adrenoceptor blockade by sotalol (10(-5)M) and compared to those of equipressor concentration of an alpha 2-adrenoceptor agonist, BHT 933 (3.5 x 10(-4) M) and angiotensin II (AII) (7.7 x 10(-9) M). Kidneys were isolated from eight week-old male LH rats and from their normotensive (LN) and low blood pressure (LL) controls and perfused in a single pass system. In baseline conditions, sotalol did not modify renal function or urinary prostanoids in any of the three strains. Following NE stimulation, it potentiated the increase in renal vascular resistance of LL and LN controls but not that of LH rats. The pressure-natriuresis and the urinary prostanoids remained unchanged. BHT 933 elicited a weak stimulation of prostanoid release while AII markedly increased it and revealed, as did NE, the hyperactivity of the TxA2 synthase. It is concluded that the NE-induced stimulation of prostanoid synthesis does not involve beta-adrenoceptors and is unrelated to the associated hemodynamic changes. These results also demonstrate that the increased renal synthesis of TxA2 observed in LH rat kidney is not a specific response to alpha-adrenoceptor stimulation and is likely to involve activation of the phosphoinositide pathway.

Adrenergic stimulation of renal prostanoids in the Lyon hypertensive rat

Young, genetically hypertensive Lyon (LH) rats exhibited an increased renal in vivo turnover of norepinephrine and an elevated urinary excretion of thromboxane B2 when compared with normotensive (LN) and low blood pressure (LL) controls. Therefore, the effects of norepinephrine (1.2 x 10(-8) to 9.6 x 10(-7) M) and of phenylephrine (5 x 10(-8) to 1.9 x 10(-6) M) on renal function and the urinary excretion of prostanoids were assessed in isolated perfused kidneys of 8-week-old LH, LN, and LL rats. In addition, the effects of norepinephrine were assessed before and during thromboxane A2/prostaglandin H2 receptor blockade by AH23848 (4 x 10(-6) M). Before drug infusion, LH kidneys differed from those of LN and LL controls by having an elevated renal vascular resistance and a decreased natriuresis and glomerular filtration rate; the urinary output of prostaglandin E2 and F2 alpha, of 6-ketoprostaglandin F1 alpha, and of thromboxane B2 was similar in the three strains. The constrictor effects of norepinephrine and phenylephrine were significantly increased in LH rat kidneys compared with LL but not with LN controls, and their pressure-natriuresis was markedly reduced. Norepinephrine and phenylephrine induced a 10- to 20-fold dose-dependent increase in the synthesis of the four prostanoids, which was more pronounced in LH than in LN and LL rats for thromboxane B2 only. AH23848 infusion significantly reduced the vascular effects of norepinephrine and increased the natriuretic response of LH but not of LN and LL rat kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal prostaglandin synthesis by the isolated perfused rat kidney

In order to assess the main characteristics of the prostaglandin (PG) biosynthesis by the isolated perfused rat kidney, the urinary and venous outputs of PGE2, PGF2alpha, 6-keto-PGF1alpha and of thromboxane (Tx)B2 were followed during 120 min after an equilibration period of 30 min. Single pass kidneys were perfused with a Krebs-Henseleit solution added with Polygeline at a constant flow rate providing a perfusion pressure about 90 mm Hg. From the beginning of the study, major differences could be observed in the renal biosynthetic rate of the 4 PG studied which were mainly excreted into the venous effluent. During the perfusion, urinary and venous outputs of PGE2, PGF2alpha and of TxB2 remained stable whereas those of 6-keto-PGF1alpha sharply increased and were found inversely related to the glomerular filtration rate (r = -0.95; p n 0.001). Finally, the urinary and venous outputs of each of the four PGs studied were found positively related. It is concluded that the isolated perfused rat kidney is a valuable preparation for studying the biosynthesis of PGs and that, at least in thi model, the urinary excretion of PGs is a good index of their renal synthesis.

Vasoactive hormones in the renal response to systemic sepsis

The pathophysiology of renal dysfunction in generalized sepsis remains unknown. In this study, 24 hours after surgical induction of peritonitis in 20 volume-loaded sheep, three patterns of renal function were seen. In group 1 (n = 8), glomerular filtration rate (GFR) decreased by 70%, urine volume by 85%, absolute sodium excretion by 95%, and fractional sodium excretion by 83%. Group 2 (n = 4) exhibited similar sodium retention but GFR did not fall. Group 3 (n = 8) showed no change in GFR or urine volume and only minimally reduced sodium excretion. Mean arterial pressure fell 17% in group 1 only; central venous pressure, pulmonary capillary wedge pressure, and plasma volume were maintained at or above presepsis values in all groups. Cardiac index was either increased or unchanged, and renal plasma flow was maintained in all groups; there was thus no hemodynamic evidence to suggest volume contraction. Histologic examination showed only minor changes with no consistent pattern. Renal functional changes correlated with other manifestations of severe sepsis--GFR and sodium retention correlated significantly with increased cardiac index, decreased systemic vascular resistance, pulmonary arterial hypertension, leukopenia, hypoproteinemia, and hypoglycemia. All of these changes were most marked in group 1. In groups 1 and 2, plasma renin activity (PRA) increased and urinary kallikrein excretion decreased. PRA correlated inversely with GFR, urine volume, and sodium excretion; urinary kallikrein excretion correlated positively with urine volume and sodium excretion. Urinary excretion of 6-keto-PGF1 alpha was increased in groups 1 and 2 and correlated inversely with mean arterial pressure in group 1 animals. During sepsis, urinary thromboxane B2 excretion continued at presepsis values in all groups. The results suggest that unusual reciprocal changes in activity of the renin-angiotensin and renal kallikrein-kinin systems may play a role in the renal response to sepsis. PGI2 synthesis is increased and may affect systemic hemodynamics and renal function; the role of thromboxane A2 in this context is unknown.

Sodium balance as a determinant of prostacyclin production by isolated rat aorta

The present study investigates whether the synthesis of prostacyclin (PGI2) in isolated rat aorta is dependent on the state of sodium balance of the animals. Three groups of ten rats each were included into the study. Two of them were fed a diet low in NaCl for 10 days with group I receiving 0.9% saline and group II distilled water as drinking fluid. Group III received a regular rat chow containing approximately 0.8 mmol day-1 of sodium, also for 10 days. At the end of the dietary protocol, systolic arterial blood pressure was significantly higher in group I (109.9 +/- 2.4 mmHg) as compared to group II (101.0 +/- 2.4 mm Hg; P less than 0.05) and group III animals (102.2 +/- 1.6 mm Hg; P less than 0.05). Generation of PGI2-like activity was determined in portions of the animals' isolated aorta using a platelet aggregation bioassay following incubation in 0.05 M Tris buffer (pH 9.3) for 12, 15, and 30 min, respectively. During these incubation times, generation of PGI2-like activity averaged 48.6 +/- 3.5, 57.8 +/- 4.3 and 68.3 +/- 3.2 pmol mg-1 in group III animals, which had received the regular rat chow, with similar values in the low salt group II (50.2 +/- 2.5, 57.7 +/- 2.7 and 72.9 +/- 3.7 pmol mg-1). Aortic generation of PGI2-like material was significantly suppressed in the high salt group I (37.5 +/- 2.8, 46.2 +/- 3.2 and 61.3 +/- 4.0 pmol mg-1; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of dietary alteration of prostaglandin synthesis on blood pressure and the reversal of hypertension in the one-kidney, one-clip rat

This study examined the effect of diet-induced changes in prostaglandin synthesis on systolic blood pressure in one-kidney, one clip (1k, 1C) hypertensive rats and on the fall in blood pressure after unclipping. It tested the hypothesis that inhibition of prostaglandin synthesis exacerbates hypertension in this model and prevents complete reversal after unclipping. Rats with sustained hypertension within 8 weeks of renal artery clipping were fed synthetic diets supplemented to 20% of total energy with either safflower oil (linoleic acid) or a mixture of cod liver oil (90%) (containing eicosapentaenoic acid) and linseed oil (10%) (containing linolenic acid) for 4 weeks. The latter oil mixture resulted in a predictable reduction in kidney PGE2 and 6-keto PGF1 alpha (hydrolysis product of PGI2), aortic 6-keto PGF1 alpha and serum TXB2. However, at the end of 4 weeks dietary treatment there were no differences in systolic blood pressure between the two diet groups, and the blood pressure fall 24 hours after unclipping was similar. These findings therefore do not support a role for prostanoids in the maintenance or reversal of 1K, 1C hypertension.

Effects of alpha-agonist on renin and prostaglandin E2 release in anesthetized dogs

The relationship between renin release and renal prostaglandin (PG) production induced by the alpha-agonists methoxamine and alpha-methylnorepinephrine was examined in anesthetized dogs. Both intrarenal infusions of methoxamine (1, 3, and 5 micrograms/min) and alpha-methylnorepinephrine (0.37, 1, and 2 micrograms/min) resulted in a dose-dependent decrease in renal blood flow to a slight degree. Methoxamine dose-dependently increased the renin secretion rate but failed to increase the PGE2 secretion rate. In contrast, alpha-methylnorepinephrine failed to affect the renin secretion rate but dose-dependently increased the PGE2 secretion rate. The effect of methoxamine (5 micrograms/min) on renin release was abolished by the intrarenal alpha 1-adrenoceptor blockade with prazosin (3 micrograms/min) but was not affected by the intrarenal alpha 2-adrenoceptor blockade with yohimbine (30 micrograms/min). The effect of alpha-methylnorepinephrine (2 micrograms/min) on PGE2 release was abolished by yohimbine but not by prazosin. These results suggest that there is a dissociation between renin release and renal PG production induced by alpha-agonists and that renal alpha 1- and alpha 2-adrenoceptors may participate in renin and PGE2 release, respectively.

Role of prostaglandins during reversal of one-kidney, one-clip hypertension in the rat

Unclipping the one-kidney, one-clip rat returned blood pressure to normotensive levels within 24 h and was associated with a substantial increase in urinary PGE2 and 6-keto PGF1 alpha excretion. Prior treatment with indomethacin (6.0 mg/kg) markedly reduced urinary prostaglandins after clip removal and attenuated the fall in blood pressure. Aspirin (100 mg/kg) treatment, which reduced 6-keto PGF1 alpha to a lesser degree without altering PGE2 excretion, had no significant effect on the blood pressure fall. It is suggested that in the one-kidney, one-clip rat prostaglandins are released as the result of exposing the unclipped kidney to elevated arterial pressure, and that these contribute to the subsequent fall in blood pressure.

Frusemide releases renin in the rat kidney when prostacyclin synthesis is suppressed

The effect of inhibiting prostaglandin (PG) synthesis on basal and frusemide-stimulated renin secretion was examined in the rat isolated perfused kidney. The stable PGI2 derivative, 6-keto PGF1 alpha, was measured by radioimmunoassay in urine collected from the kidney. Treatment of rats with indomethacin (3.0 mg kg-1) reduced 6-keto PGF1 alpha excretion from 121.3 +/- 39.1 (n = 9) to 15.5 +/- 6.6 (n = 9) pg min-1 (P less than 0.02) but had no effect on basal renin secretion. Renal perfusion pressure, flow rate and vascular resistance were similar in treated and control rats. Mean urine flow was lower after treatment. Infusion of frusemide (250 micrograms min-1) did not alter 6-keto PGF1 alpha excretion in control or indomethacin-treated (P greater than 0.05) rats. Although renin secretion was increased during frusemide infusion, there was no significant difference between control (1,806 +/- 384 ng angiotensin I (AI) min-1) and treated (2,310 +/- 554 ng AI min-1) rats (P greater than 0.05). Propranolol, at a dose (8 micrograms min-1) which suppressed renin secretion after isoprenaline stimulation, had no effect on the response to frusemide in indomethacin-treated rats. These results demonstrate that frusemide-stimulated renin secretion in the rat kidney does not require intact renal PGI2 synthesis and is independent of beta-adrenergic mechanisms.

Urinary 6-keto PGF1 alpha and PGE2 in two kidney-one clip hypertension in the rat

The 24 hour urinary excretion of 6-keto PGF1 alpha and PGE2 was compared in 2 kidney-1 clip rats developing hypertension within 12 weeks of renal artery clipping with rats remaining normotensive over this period. Although systolic blood pressure was markedly elevated in the hypertensive (210 +/- 5.1 mm Hg), in contrast with the normotensive (141 +/- 1.9 mm Hg) group, urinary levels of 6-keto PGF1 alpha (26.1 +/- 3.4 and 22.1 +/- 2.7 ng/24 h, respectively) and PGE2 (52.8 +/- 28 and 53.3 +/- 10.8 ng/24 h) were not significantly different. Treating the 2 kidney-1 clip normotensive group with indomethacin (3.0 mg/kg, by intraperitoneal injection) twice-weekly for 3 weeks reduced 6-keto PGF1 alpha excretion from 22.1 +/- 2.7 to 8.4 +/- 2.2 ng/24 h (P less than 0.002) and PGE2 from 53.3 +/- 10.8 to 8.7 +/- 1.8 ng/24 h (P less than 0.002) but did not change blood pressure when compared with a similar group given buffer vehicle only. These findings do not support a role for renal prostaglandins in 2 kidney-1 clip hypertension in the rat.