Intra-day variation of in vivo prostaglandin F2alpha formation in healthy subjects.

Prostaglandin F(2alpha) (PGF(2alpha)) is a major stable prostaglandin formed in vivo in physiological and pathophysiological situations and has mainly potent vasoconstrictive and pro-inflammatory properties. PGF(2alpha) is now used as an indicator of acute and chronic inflammation in human clinical settings but the extent of daily variation of PGF(2alpha)in vivo in healthy humans is unknown. We quantified levels of the PGF(2alpha) metabolite 15-keto-dihydro-PGF(2alpha) in 10 healthy males and females in spot urine samples during the day (including morning urine sample) and in 24-h urine during the same day. The intra-day coefficient of variation was 20.9%. However, the total mean value of 15-keto-dihydro-PGF(2alpha) in urine collected in the morning did not significantly differ from the mean level of 15-keto-dihydro-PGF(2alpha) in the 24-h urine samples in the 10 subjects. 15-Keto-dihydro-PGF(2alpha) levels in morning urine showed a positive linear correlation with levels of 15-keto-dihydro-PGF(2alpha) in 24-h urine (R=0.72, P<0.05). In conclusion, formation of PGF(2alpha) shows a biological variation within the day in healthy humans which should not be overlooked when planning a clinical study. Single morning urine samples can be used as an alternative to 24-h urine collections for quantification of PGF(2alpha) formation to simplify the sampling regime in larger clinical studies.