Effects of Endogenous Thyrocalcitonin and Vitamin D 3 on Milk Yield in Parathyroidectomized and Thyroparathyroidectomized Rats 1

Abstract

Summary

Thirty-three lactating rats were divided into 6 groups: (A) normal control, (B) sham-operated control, (C) parathyroidectomized (PTX), (D) PTX plus 8000 IU of vitamin D₃/day, (E) thyroparathy-roidectomized (TPTX), (F) TPTX plus 3 μg of L-T₄/100 g of body wt/day plus 8000 IU of vitamin D₃/day. Milk production in (A) and (B) were not significantly different but were higher (p<0.05) than other four groups. Group C was significantly less than 1) on days 18 and 20 only, while E was significantly less than F in all 4 days. PTX was less severe on milk production than TPTX and took a longer time to manifest the detrimental effects. Vitamin D₃ at 8000 IU/day ameliorated the symptoms of PTX but did not completely replace PTH for normal lactation. PTH seems essential for lactating mammary glands for normal lactation in rats. Endogenous TCT seems not essential for milk production. Thyroxine probably has some calcium mobilizing effect similar to PTH.