Endogenous-circulating melatonin was significantly higher ( P < or = 0.01 ) following melatonin ( urine : 152.94 gh ( -1 ) ( 74.51 ) , plasma : 43,554.57 pM ( 33,527.11 ) ) than placebo ( urine : 0.86 gh ( -1 ) ( 0.40 ) , plasma : 152.06 pM ( 190.55 ) ) .