Alterations in polyamine levels in rat blood during pregnancy and lactation.

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Abstract
The concentration of circulating spermidine, the predominant polyamine in rat blood, increases significantly (P < .001) by the 6th day of pregnancy (22.45 .+-. 2.30 nmol/ml) when compared to age-matched virgin rats (12.15 .+-. 1.12 nmol/ml), with the largest increase occurring shortly before parturition. After birth spermidine levels fall, increase again to the highest level at the 3rd day of lactation (42.30 .+-. 6.09 nmol/ml), and then decline to virgin concentrations toward the end of lactation. The cellular elements of blood from virgin, pregnant and lactating rats contain over 89% of the total blood polyamine, with plasma containing less than 10%. Plasma spermidine is in the free noncovalently bound form. The blood concentration of spermine, as opposed to spermidine, does not increase during pregnancy or lactation. On a cell-to-cell basis, leukocytes contain over 160 times as much spermidine as erythrocytes. However, erythrocytes contain over 76% of the total blood spermidine per ml of whole blood. During pregnancy and lactation, spermidine increases significantly (P < 0.01) in erythrocytes, giving rise to increased concentrations observed in whole blood. The concentration of spermidine per erythrocyte in virgin, 15 day pregnant and 3 day lactating rats is 1.94 .+-. 0.06, 4.69 .+-. 0.93 and 5.83 .+-. 0.83 .times. 10-9 nmol, respectively. Ornithine decarboxylase, the 1st and possibly the rate-limiting enzyme in polyamine biosynthesis, increases asynchronestically in liver and kidney of pregnant and lactating rats during times when circulating spermidine concentrations are elevated.