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Replacement Therapy in Lactating Thyroparathyroidectomized Rats¹

Department of Dairy Husbandry, University of Missouri, Columbia

ABSTRACT

Thyroparathyroidectomy was performed in 58 albino rats at Day 4 of lactation. The mother rats lost considerable body weight after the operation due, at least partially, to a reduced food intake. Replacement therapy was started immediately after operation. All animals received daily 3.5 µg. 1-thyroxine/100 g. body weight and graded amounts of parathormone (PH) until Days 13 and 14 of lactation, respectively.

Based on the litter weight increase, daily injections of ten, 2 x 20 and 3 x 20 U.S.P. units of PH did not restore lactation to average control levels, whereas seven animals with presumed accessory parathyroid tissue reached normal or better than control levels. However, based on the weight of milk obtained on Day 14 of lactation under standardized conditions, expressed as per cent of the litter body weight as a criterion, 3 x 20 U.S.P. units PH/day resulted in successful replacement therapy in ten animals. Many incidents of tetany were recorded after discontinuing the PH supply and also in excellent lactating animals which were given 2 x 20 U.S.P. units PH/day. The withdrawal of PH on Day 13 resulted on Day 14 of lactation in a reduced blood calcium level, tetany, nervousness, depressed food intake and body weight, irregular nursing, disturbed lactogenic hormone discharge from the pituitary gland, presumably in an interruption of the let-down mechanism, and in markedly reduced milk yields.

¹ Contribution from Missouri Agricultural Experiment Station, Journal Series No. 2033. Approved by the Director.

² Research Fellow of Federal Ministry of Nutrition and Agriculture, Bonn, Federal Republic of Germany. This investigation was supported in part by research grants from Public Health Serice.