Urinary excretion of TXB2 after angiotensin converting enzyme inhibition in hypertensive patients

Thromboxane inhibition improves renal perfusion and excretory function in severe congestive heart failure

OBJECTIVES

The aim of this study was to evaluate whether thromboxane inhibition can favorably affect renal perfusion and clinical conditions in patients affected by severe heart failure.

BACKGROUND

The renal formation of the vasoconstrictor thromboxane A(2) (TxA(2)) is increased during cardiac failure.

METHODS

By oral administration of picotamide (a renal TxA(2) synthase and TxA(2)/prostaglandin H(2) receptor inhibitor), we blocked renal TxA(2). Fourteen patients in New York Heart Association functional class IV were studied according to a randomized, double-blinded, cross-over design. Each of the two eight-day periods of testing was preceded by a three-day period during which certain vasoactive medications were stopped.

RESULTS

Daily 24-h total urinary thromboxane B(2) (TxB(2)), the stable metabolite of TxA(2), dropped at the end of picotamide treatment (p < 0.01 vs. baseline). Compared with placebo, effective renal plasma flow and the glomerular filtration rate increased (p < 0.01 and p < 0.05, respectively), thus leading to a significant decrease in the filtration fraction (p < 0.01). Renal vascular resistance decreased consistently (p < 0.01). In all patients, picotamide treatment was associated with an increase in diuresis and natriuresis (p < 0.001 vs. baseline). Plasma creatinine decreased (p < 0.05 vs. baseline). Patients also showed improvement in several clinical parameters, including a significant decrease in both pulmonary and venous pressure (p < 0.01 vs. baseline).

CONCLUSIONS

These results indicate that renal thromboxane formation plays an important role in renal vascular resistance in patients with severe heart failure, such as those described in the present study. Inhibition of TxA(2) improves renal hemodynamics and kidney function and favorably affects indexes of cardiac performance.

Preliminary observations of the acute effects of selective serum thromboxane inhibition and angiotensin converting enzyme inhibition on blood pressure and renal hemodynamics in hypertensive humans

CGS 13080, a selective thromboxane synthetase inhibitor, was given intravenously (0.6 mg/kg over 6 hours) to eight hypertensive (diastolic 95-115 mm Hg) euvolemic caucasian females on their customary salt intake (24 hour urine Na: 142.9 +/- 14.8 meq). No change occurred in blood pressure or glomerular filtration rate (GFR): 95.2 +/- 7.2, control versus 95.0 +/- 9.0, CGS 13080 (ml/min); or renal plasma flow (RPF): 363.2 +/- 34.2, control, versus 373.2 +/- 31.2, CGS 13080, (ml/min). Prostaglandin production was altered: platelet generation of thromboxane B2 83.3 +/- 10.9, control, versus 5.4 +/- 1.8, CGS 13080 (ng/hr) (P less than .001); urinary prostaglandin E (PGE) 249.0 +/- 56.3, control, versus 443.9 +/- 79.8, CGS 13080 (ng/6 hr) (P = .06); urinary 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) 188.6 +/- 23.4, control, versus 287.9 +/- 21.8, CGS 13080 (ng/6 hr) (P = .01); urinary thromboxane B2 54.8 +/- 12.9, control, versus 58.6 +/- 20.3 CGS 13080 (ng/6 hr) (P = NS). Serum levels of renin, angiotensin II and aldosterone were not altered by CGS 13080. Captopril when dosed to lower diastolic blood pressure 5-7 mm Hg did not significantly affect GFR, RPF or RVR. Nor did it affect platelet generation of thromboxane B2 or urine concentrations of PGE, 6-keto-PGF1 alpha or thromboxane B2. Captopril did increase renin levels 1.2 +/- 0.2, control, versus 2.9 +/- 1.1, captopril (ng/ml/hr) (P = NS), but did not statistically change angiotensin II, or aldosterone levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction between indomethacin and captopril or enalapril in healthy volunteers

In this study eight healthy volunteers were involved in a randomized, cross-over trial in which they were treated with either 25 mg of captopril b.i.d. or 20 mg of enalapril o.i.d. alone or in combination with 50 mg of indomethacin b.i.d. in order to detect a difference between both converting enzyme inhibitors when interacting with indomethacin. Before and after each 4-d treatment period, blood pressure (determined by random zero sphygmomanometer), body weight, plasma renin activity, angiotensin converting enzyme, plasma potassium, serum creatinine and the 24-h urinary excretion of 6-keto-prostaglandin F1 alpha were measured. Indomethacin attenuated the decrease of supine diastolic blood pressure during treatment with captopril, but not with enalapril. However, the initial decrease of blood pressure on captopril was greater than on enalapril. Both converting enzyme inhibitors had no effect on the urinary excretion of 6-keto-prostaglandin F1 alpha, while indomethacin reduced it. The results suggest a difference between captopril and enalapril in interaction with indomethacin.

Role of the endogenous angiotensin II in the antihypertensive effect of MK 421 in rats made hypertensive by norepinephrine or vasopressin

To assess the mechanism by which inhibitors of angiotensin converting enzyme (ACE) lower blood pressure, we evaluated the role of endogenous angiotensin II in the antihypertensive effect of MK 421, a long-lasting ACE inhibitor, in rats made hypertensive by chronic infusion of norepinephrine or vasopressin. The hypertensive effect of norepinephrine (1.8 mg/kg/day, ip) or vasopressin (7.2 U/kg/day, ip) was inhibited by the simultaneous administration of MK 421 (6 mg/kg/day, ip). Additional administration of angiotensin II at a subpressor dose (36 micrograms/kg/day, ip) did not revert the antihypertensive effect of MK 421 in rats made hypertensive by chronic infusion of norepinephrine or vasopressin. The present results suggest that the hypotensive effect of ACE inhibitors may depend on a reduced sensitivity of the vasculature to vasoconstrictor substances. In addition, it is also suggested that the suppressed angiotensin II may not be essential for the antihypertensive effect of ACE inhibitors in rats made hypertensive by chronic infusion of norepinephrine or vasopressin.

Role of thromboxane A2 in the hypotensive effect of captopril in essential hypertension

We have previously reported that captopril stimulates thromboxane A2 synthesis in patients with essential hypertension. In the present study, the hypotensive effects of captopril and OKY-046, a selective inhibitor of thromboxane A2 synthetase, were studied in nine patients with essential hypertension to determine whether thromboxane A2 is involved in the regulation of blood pressure. A single oral dose of OKY-046 (400 mg) decreased urinary thromboxane B2 (a stable metabolite of thromboxane A2) excretion significantly (from 113 +/- 19.0 to 51.0 +/- 6.1 pg/min; p less than 0.01) and increased urinary sodium excretion significantly (from 73.0 +/- 15.3 to 113.0 +/- 14.4 microEq/min; p less than 0.01), but no change was observed in mean arterial pressure. The administration of OKY-046 (600 mg/day) for 3 days induced a significant and sustained decrease in urinary thromboxane B2 excretion, but it did not affect the mean arterial pressure. Although captopril (50 mg) alone induced a significant increase in urinary thromboxane B2 excretion (from 91.4 +/- 11.0 to 297.3 +/- 30.8 pg/min; p less than 0.001) and a significant decrease in mean arterial pressure (from 97.0 +/- 4.7 to 88.1 +/- 5.1 mm Hg; p less than 0.01), captopril in combination with OKY-046 induced a decrease both in urinary thromboxane B2 excretion (from 70.8 +/- 12.3 to 54.2 +/- 14.7 pg/min; p less than 0.01) and in mean arterial pressure (from 105.1 +/- 3.8 to 84.2 +/- 3.6 mm Hg; p less than 0.01). Thus, the hypotensive effect of captopril was potentiated by OKY-046. OKY-046 did not affect the changes in plasma renin activity and plasma aldosterone concentration and blunted urinary prostaglandin E2 and 6-keto-prostaglandin F1 alpha excretion in response to captopril. These results indicate that thromboxane A2 counteracts the hypotensive effect of captopril in patients with essential hypertension.

No evidence on significant roles of the prostaglandin-thromboxane and kallikrein-kinin system in the antihypertensive effect of MK 421 in rats made hypertensive by norepinephrine or vasopressin

Inhibition of angiotensin converting enzyme by MK 421 (6 mg/kg/day ip) induced a significant increase in urinary kinin excretion in norepinephrine-infused rats (1.8 mg/kg/day ip), whereas it had no effect on urinary prostaglandin E2 excretion. In contrast, MK 421 did not induced any significant changes in urinary kinin and prostaglandin E2 excretion in vasopressin-infused rats (7.2 U/kg/day ip). The simultaneous administration of indomethacin (10 mg/kg/day sc), OKY 046 (12 mg/kg/day sc) or aprotinin (100,000 units/kg/day sc) did not affect the antihypertensive effect of MK 421 in rats made hypertensive by chronic infusion of norepinephrine or vasopressin. The present results suggest that the hypotensive effect of MK 421 may depend on a reduced sensitivity of the vasculature to vasoconstrictor substances. In addition, it is also suggested that neither the prostaglandin-thromboxane or kallikrein-kinin systems are essential for the antihypertensive effect of MK 421 in these models of hypertension.