Abstract
Summary
The milk yield of rats was determined on days 14, 16, 18 and 20 by separating the litters from their dams for 10 hours, then injecting 2 USP units of oxytocin and allowing the young to nurse for 30 minutes. Immediately prior to test milking on days 16 and 20 an experimental group of 15 rats was injected with 1.25 ml of 25% sodium citrate to cause convulsions (tetany) due to the decrease in ionized plasma calcium. The milk yield of these rats was greatly reduced in comparison with their own previous production and in comparison with the milk yield of the control group on the same day. It is suggested that the contractility of the mammary gland myoepithelial cells by oxy-tocin is greatly reduced by the lack of plasma calcium. Thus the decreased milk yield of parathyroidectomized rats is due to a reduction in the synthesis of milk and interference with the removal of the milk secreted.
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