Differences between the sexes and the effects of surgery and anesthesia on the urinary excretion rate of eicosinoids in the rat.

Measurements were made of PGE2, PGF2 and TXB2 in the urine of male and female Munich-Wistar rats. Initial urine were collected in the awake state in metabolic cages and were followed by collections of ureteral urine during surgery and anesthesia both before and during cyclooxygenase inhibition with indomethacin. The excretion rate of all eicosinoids in the awake state was similar between the sexes. PGE2 excretion remained unaffected after anesthesia/surgery in both sexes indicating that providing plasma volume is maintained, the PGE2 system is not activated by the stress of anesthesia/surgery. Near complete inhibition of PGE2 was observed during indomethacin administration in both sexes. TXB2 excretion rates rose in both males and females with anesthesia/surgery and were slightly suppressed during indomethacin in males only. PGF2 excretion rose following surgery/anesthesia and was statistically significant in female rats. During indomethacin, TXB2 excretion was moderately reduced in male rats and unaffected in the female. Near complete inhibition of PGF2 was observed during indomethacin in both sexes. The urinary eicosinoid responses to indomethacin seen in these studies failed to provide an explanation for our earlier observations of a fall in renal vascular resistance in the female rat, studied under anesthesia and during indomethacin administration.

Renal synthesis and urinary excretion of eicosanoids during pregnancy in rats.

We tested whether vasodilatory prostaglandins (PGs) mediate the adaptation of the maternal renal circulation to pregnancy by assessing production of PGs by kidney tissues in vitro. We reasoned that if PGs are crucial, then local synthetic rates of these hormones would most likely be increased. Glomeruli harvested from gravid rats of gestational days 6, 12, and 20 did not demonstrate greater basal or stimulated syntheses of PGF2 alpha, PGE2, or 6-keto-PGF1 alpha than those from virgin controls. Production of PGE2 and 6-keto-PGF1 alpha by renal cortical slices obtained from pregnant rats was not greater than that of virgins either. Urine 24-h excretory rates of PGE2 and 6-keto-PGF1 alpha, but not PGF2 alpha, were significantly increased during pregnancy (all P less than 0.05 from prepregnant levels). During midgestation, when urinary excretion of PGE2 and 6-keto-PGF1 alpha was greatest, medullary syntheses of these PGs were found to be comparable between virgin and gravid animals. The present study, which fails to show augmented synthesis of PGs by renal tissues derived from gravid rats, is consistent with our previous investigation in which cyclooxygenase inhibition did not reduce the gestational increase of renal hemodynamics or restore the attenuated renal pressor responsiveness to exogenous angiotensin II. Taken together, we conclude that in rats, PGs most likely do not mediate the alterations in the renal circulation observed during pregnancy.

Purification and quantitative analysis of urinary prostanoids in human and in rat by packed and capillary gas chromatography-negative-ion chemical-ionization mass spectrometry.

We describe a method for the quantitative analysis of prostaglandin (PG) E2 and the major urinary metabolites PGI2 and thromboxane (Tx) A2 in human and in rat by combined gas chromatography and negative-ion chemical-ionization mass spectrometry. The procedure is based on the sequential use of small columns with distinct properties combined with a thin-layer chromatography step, for the extraction and the purification of urinary prostaglandins. The compounds are then analysed as their pentafluorobenzyl ester-O-methyloxime-trimethylsilyl ether derivatives, using either packed or capillary columns. Deuterated analogues are used as internal standards. The method was established by using tritiated prostaglandins covering the extremes of polarity in order to optimize the recovery of prostanoids as well as the quality of the chromatograms and spectra. The overall recovery was 24%. Standard curves were obtained by the same procedure and found to be reproducible, with a maximal day-to-day variation of +/- 5%. The relatively simple approach required for the sequential extraction and purification of prostaglandins on small columns of distinct properties, combined with the highly specific and highly sensitive method of detection, places this procedure among the most reliable method for measuring urinary prostanoids in both humans and animals. In addition, the procedure is faster than classical approaches and necessitates smaller amounts of samples and solvents.

Effects of low-dose aspirin on responses to furosemide.

We assessed the effects of low-dose aspirin (0.5 and 15 mg/kg/d) on renal prostaglandin synthesis and action in healthy volunteers using intravenous furosemide as a stimulus. Inhibition of platelet cyclo-oxygenase was assessed by changes in serum thromboxane B2 (TXB2) level. After one week of treatment, ten healthy subjects did not show any change in weight, blood pressure, or diuretic and natriuretic responses to furosemide with either dose of aspirin. Serum TXB2 level was reduced to 3% of control by aspirin 0.5 mg/kg/d and to 0.1% by the higher dose. In contrast, urine excretion of TXB2 was only reduced to 68% and 51% of the placebo value, whereas 6-keto-prostaglandin F1 alpha (6kPGF1 alpha) excretion was not decreased by either dose. Furosemide produced a transient increase in excretion rates of TXB2 and 6kPGF1 alpha that was of lesser duration than the diuretic response. These transient increases were slightly reduced by aspirin. Baseline plasma renin activity was not affected by either dose of aspirin. The brisk increment in plasma renin activity seen ten minutes after furosemide, as well as later values (30 and 240 min) were not changed by aspirin. We conclude that chronic low-dose aspirin can profoundly affect platelet PG production without affecting stimulated renal PGI2 production or plasma renin activity. There is a modest reduction in urine TXB2 excretion that is consistent with a primarily renal source of this metabolite.