Abstract
The lactose content of the mammary gland and plasma and the ion concentrations of the plasma were investigated in primiparous lactating rats after oxytocin (OT) administration. OT was given sc or iv at 1500 h on day 12 of lactation to mothers whose pups were removed 6 h earlier. At this time a large amount of milk was accumulated in the mammary glands. Mammary gland lactose content of animals injected sc with 10IU of OT was markedly reduced within 30 min and continued to decline to 120 min, whereas saline-injected controls maintained high levels throughout the experimental period. The value at 240 min in the OT-injected animals was 4.8% of that of the control. In contrast, the lactose concentration in plasma rose sharply up to 60 min and then returned to the baseline level at 240 min after OT injection. Potassium and calcium concentrations in plasma increased and plasma sodium decreased after OT injection. The iv administration of OT at graded doses (0.01, 0.1 and 1IU) resulted, at the end of 120 min, in a dose-dependent decrease in mammary gland lactose content with the higher 2 doses being statistically significant. These results indicate that OT administration to lactating rats shifts milk components from the mammary gland to the plasma.
