Intra-day variation of in vivo prostaglandin F2α formation in healthy subjects

Prostaglandin F2α (PGF2α) is a major stable prostaglandin formed in vivo in physiological and pathophysiological situations and has mainly potent vasoconstrictive and pro-inflammatory properties. PGF2α is now used as an indicator of acute and chronic inflammation in human clinical settings but the extent of daily variation of PGF2αin vivo in healthy humans is unknown. We quantified levels of the PGF2α metabolite 15-keto-dihydro-PGF2α 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-PGF2α in urine collected in the morning did not significantly differ from the mean level of 15-keto-dihydro-PGF2α in the 24-h urine samples in the 10 subjects. 15-Keto-dihydro-PGF2α levels in morning urine showed a positive linear correlation with levels of 15-keto-dihydro-PGF2α in 24-h urine (R = 0.72, P < 0.05). In conclusion, formation of PGF2α 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 PGF2α formation to simplify the sampling regime in larger clinical studies.