Hannsjorg W. Seyberth

Bartter's syndrome: A disorder characterized by high urinary prostaglandins and a dependence of hyperreninemia on prostaglandin synthesis

Urinary prostaglandins E2 and F2alpha were measured by gas chromatography-mass spectrometry in three adult women and an adolescent girl with Bartters syndrome. On a constant metabolic diet prostaglandin E2 ranged from 293 to 1,221 ng/day (mean, 640 ng/day) and exceeded the normal range for adults of 76 to 281 ng/day in all patients. Prostaglandins F2alpha ranged from 291 to 1,061 ng/day (mean, 747 ng/day) in the adult women. Only in a young girl did prostaglandins F2alpha (1,677 ng/day) clearly exceed the normal range for adults of 422 to 871 ng/day. Treatment with indomethacin, which decreased urinary prostaglandin E-like material by 69 per cent or more, did not affect blood pressure. Plasma renin activity, which ranged from 5.2 to 22.2 ng/ml/hour (patients supine) and from 23.3 to 30.4 ng/ml/hour (patients upright), and urinary aldosterone, which ranged from 14.0 to 45.6 ng/day, decreased by 79, 65 and 52 per cent, respectively. The clearance of creatinine was lower for the eight or nine days of treatment, the balances of sodium and potassium were positive, and serum potassium was higher than in control. Ibuprofen, an inhibitor of prostaglandin synthetase which differs in structure from indomethacin, produced metabolic effects which were qualitatively similar to those of indomethacin. The results indicate that the renal synthesis of prostaglandins is increased in Bartters syndrome and that prostaglandins mediate the hyperreninemia and hyperaldosteronism which characterize the disorder. The over-production of prostaglandins by the kidney could be proximal cause of the syndrome, or secondary to intrarenal changes of an unknown nature. This study provides additional evidence for an important role for prostaglandins in the release of renin.

Increased arachidonate in lipids after administration to man: Effects on prostaglandin biosynthesis

Ethyl arachidonate was administered orally to 4 healthy male volunteers in a dose of 6 gm daily for a 2 to 3 wk period after a 1O‐day control period. The increased intake of this precursor of the dienoic prostaglandins resulted in significant increases in the relative and absolute amount of arachidonate in plasma triglycerides, phospholipids, and cholesteryl esters. Similar changes in lipid composition were noted in platelets. The excretion of 7 α‐hydroxy‐5, 11‐diketotetranorprostane‐1 ,16‐dioic acid, the major urinary metabolite of E prostaglandins in man, was increased by an average of 47% in 3 of the 4 volunteers. Platelet reactivity was assessed by determining the threshold concentration of adenosine diphosphate (ADP) necessary to induce secondary, irreversible aggregation of platelet‐rich plasma. This threshold concentration dropped significantly in all volunteers (10% to 60% of control values). It is concluded that the biosynthesis and function of prostaglandins can be augmented in man by oral administration of an esterified precursor fatty acid.

Relation between plasma concentration of indomethacin and its effect on prostaglandin synthesis and platelet aggregation in man.

The dose and plasma levels of indomethacin correlated with inhibition of prostaglandin synthesis as measured both by urinary excretion of the major metabolite of prostaglandin E2 (PGE‐M) and by the release of prostaglandin E drom thrombin‐stimulated platelets. Considerable intersubject variability was observed in the suppression of PGE‐M excretion. In some patients 37.5 mg indomethacin daily, usually considered subtherapeutic, caused suppression. Maximal suppression (>90%) occurred in some after a daily dose of 75 mg, whereas 150 mg was required to achieve this level of inhibition in others. Suppression of the excretion of PGE‐M by 60% occurred when the end of the dosage interval plasma levels of indomethacin were in the range 0.05 to 0.3 µg/ml, which implies that a somewhat higher average steady‐state concentration during the dosage interval was required to achieve this effect. A similar degree of inhibition of the release of PGE2 on thrombin‐stimulated platelets was associated with the same range of plasma levels. Upon discontinuation of the drug, the levels of indomethacin in plasma decreased exponentially; inhibition of the release of PGE2 from platelets by indomethacin declined linearly with time and in parallel with the logarithm of the diminishing plasma levels.

Quantification of the major urinary metabolite of the E prostaglandins by mass spectrometry: Evaluation of the method's application to clinical studies

Measurement of 7alpha-hydroxy-5,11-diketotetranoprostane-1,16-dioic acid, (PGE-M), the major urinary metabolite of prostaglandin E1 and E2 in man provides a useful indicator to monitor prostaglandin biosynthesis. For quantitative analysis of this prostaglandin metabolite and the stable-isotope dilution techniqe of selected ion monitoring (SIM) is employed using gas-liquid chromatography-mass spectrometry. The preparation of the bis(D3-methyloxime), bis-methyl ester of PGE-M containing a tritium tracer in position 2 which was used as internal standard for the SIM method is described. The synthesis of this internal standard includes the biosynthetic conversion of 11-hydroxy-9,15-diketoprostanoic acid to PGE-M by the rabbit. The intra-assay coefficient of variation of this SIM method ranged between 4.0 to 6.7 percent. The recovery of authentic, underivatized PGE-M added to urine was 93 +/- 3% (mean +/- SEM, n=17). The levels of PGE-M excreted in urine were higher (p less than 0.001) in males than in females (15.2 +/- 1.9 mug/24 hours (n=24) and 3.3 +/- 0.3 mug/24 hours (n=17), respectively. These levels were in close agreement with values published previously. No significant difference in excretion of PGE-M between the sexes was observed in the pre-pubertal age-grou (male: 2.9 +/- 0.8 mug/24 hours, n=5; female: 3.1 +/- 0.9 mug/24 hours, n=5) or in the age-group of 45-80 years (male: 9.3 +/- 1.1 mug/24 hours, n=21; female: 7.3 +/- 0.9 mug/24 hours, n=12). The amount of PGE-M excreted decreased significantly after administration of indomethacin or acetyl salicylic acid in therapeutic doses. The concomitant reduction of the urinary excretion of PGE-M (68 to 85% decrease) and prostaglandin E (73 to 100% decrease) after indomethacin treatment in each case (n=8) is evidence that a diminished urinary PGE-M output reflects a decrease in prostaglandin E biosynthesis.

Prostaglandin-mediated hypercalcemia in the VX2 carcinoma-bearing rabbit☆

Prostaglandin biosynthesis and metabolism were studied in the VX2 carcinoma-bearing rabbit, an animal model of prostaglandin-mediated hypercalcemia. All the identification and quantification of the prostaglandins were done by gas chromatography-mass spectrometry. The tumor incubated in vitro converted exogeneous arachidonic acid principally to PGE2. Biosynthesis from endogenous precursor lipids yields mainly PGE2 and PGF2alpha. The 100,000 x g supernatant fluid of the tumor did not contain any metabolizing enzymes. Significant hypercalcemia developed between the first and second week after tumor implantation. The levels of the major plasma metabolite of PGE2, 15-keto-13,14-dihydro-PGE2, became elevated at one week, had risen 25-fold by the end of the second week, and at the fourth week were elevated to 256 times the pre-incubation levels. The concentration of 15-keto-13,14-dihydro-PGF2alpha in plasma rose in parallell but to a lesser degree. 7alpha-hydroxy-5,11-diketotetranor-prostane-1,16-dioic acid, the major urinary metabolite of the E prostaglandins, was elevated two weeks after tumor implantation and rose until the fifth week. Indomethacin treatment lowered both serum calcium and the plasma level of 15-keto-13,14-dihydro-PGE2.

The role of prostaglandins in the pathogenesis of human disease: elucidation with stable isotopic methods

Prostaglandins are extremely potent biogenic compounds and as such are formed in quite small amounts in vivo. The total body production of prostaglandin E2 (PGE2), for example, is less than one µmol per day. Accordingly, the prostaglandins have provided a number of analytical challenges that have been soluble only by the use of selected ion monitoring with mass spectrometry. This is accomplished ultimately by employing stable-isotope-labelled compounds both as internal standards and as carriers.

PROSTAGLANDINS AS MEDIATORS OF THE HYPERCALCEMIA ASSOCIATED WITH CERTAIN HUMAN CANCERS

In a subset of patients with hypercalcemia caused by solid tumors, the elevated serum calcium is dependent on an increased metabolism of arachidonic acid via the cyclooxygenase pathway. Such patients excrete increased amounts of the major urinary metabolite of PGE 2 in the urine, and the administration of aspirin or indomethacin will restoreserum calcium levels to normal. Complete reversal of the hypercalcemia is seen only in those patients who have no evidence of bone metastases by X-Ray or bone scan. When such patent evidence of bone metastases is present in patients excreting high levels of the prostaglandin E metabolite, serum calcium will be reduced significantly but only slightly by the inhibitors ofthe fatty acid cyclooxygenase. In hypercalcemic patients who do not excrete elevated amounts of PGE metabolite, aspirin and indomethacin do not lower serum calcium, indicating that such patients have prostaglandin independent hypercalcemia.