Effect of Lactation upon Thyroid Secretion Rate in the Rat.

Abstract

1) Thyroid hormone secretion rate (TSR) was determined in lactating and non-lactating rats by administration of graded levels of L-thyroxine and measuring by radioiodine technics, subsequent suppression of thyroidal I¹³¹ output. 2) The average TSR of 2.2 μg/100 g L-thyroxine for lactating rats during the period of intense lactation (8–14 days postpartum) was significantly greater than the average of 1.3 μg/100 g for non-lactating rats of the same strain, age and weight range. These data are in accord with the concept that a hyperthyroid state is generally desirable for optimal milk secretion.