Reduced uptake of noradrenaline into storage vesicles from the pregnant uterus

A noradrenaline (NA) storage vesicle fraction was isolated from the uteri of virgin as well as pregnant guinea-pigs. The uptake of 3H-NA into respective vesicle fractions was compared. Total uptake of 3H-NA in the presence of Mg2+ (2.5mM) and ATP (2.5 mM) at 30 degrees C after 20 min was 6.0 +/- 1.4 pmol . mg-1 in uterus fractions from virgin guinea-pigs as compared to 1.87 +/- 0.41 pmol . mg-1 in uterus fractions from pregnant animals. When desipramine (5mM) was added in order to block neuronal uptake the corresponding figures were 4.75 +/- 0.92 and 0.51 +/- 0.18 pmol . mg-1, respectively. Thus in the presence of desipramine (5mM) uptake was reduced by 21.4% in fractions from virgin uteri but by 72.7% in fractions from pregnant uteri. Reserpine (0.1 microM) inhibited uptake of 3H-NA by 34% in fractions from virgin uteri and by 46% in fractions from pregnant uteri. Our results indicate a decreased amount of functional storage vesicles in uteri of guinea-pigs at term pregnancy and are consistent with the proposed degeneration of adrenergic nerves during pregnancy.