In vitro metabolism of [3H]-(-)-noradrenaline (3H-NA), 0.2 mumol/l, was measured in rat endometrial and myometrial slices at different stages of gestation and compared with that in dioestrous rats. Metabolism of 3H-NA, 0.2 mumol/l, was measured in rat placental slices from day 14 of gestation onwards. 2. 3H-NA was metabolized mainly by deamination in rat myometrium, with [3H]-3,4-dihydroxyphenylethylene glycol, (3H-DOPEG) being the major metabolite. Cocaine, 30 mumol/l, inhibited 3H-DOPEG formation and the amount of 3H-NA remaining in the tissue. O-methylated metabolite formation was unaffected by cocaine. 3. O-methylation and deamination were equally active pathways for metabolizing 3H-NA in rat endometrium. O-methylation to [3H]-normetanephrine (3H-NMN) predominated in the placenta. In both tissues O-methylated metabolite formation was inhibited by 30 mumol/l cocaine. 4. In myometrium, metabolite formation per gram was constant in the first half of pregnancy and was similar to that in dioestrous animals. By day 17 of gestation, however, [3H]-O-methylated deaminated metabolites (3H-OMDA), comprising 3-methoxy, 4-hydroxy-phenylethylene glycol and vanillylmandelic acid, and 3H-NMN formation were less than in dioestrous animals. 5. Endometrial 3H-NMN and 3H-DOPEG formation per gram were higher in rats at day 5 of gestation than in dioestrous rats but metabolite formation per gram declined thereafter to reach values equal to (3H-DOPEG) or less than (3H-OMDA and 3H-NMN) those in dioestrous rats. 6. 3H-NMN and 3H-OMDA formation per gram decreased from day 14 to day 20 of gestation in rat placentae.(ABSTRACT TRUNCATED AT 250 WORDS)
