Abstract
Summary
Thyroparathyroidectomy was performed in 44 lactating rats on day 7 postpartum. Successful replacement therapy was started immediately after surgery with optimal level of T4 (3 μ 100 g day), 2 × 40 USP units PTH day (corresponding to 29-30 USP units 100 g day) and 1 USP unit OXT for complete milk removal on days 14-18. Litter weight and milk yield on day 14 reached levels of normal animals given optimal amounts of T4 (3 μg 100 g day) and 1 USP unit OXT for milk yield test. Discontinuation of PTH on day 13 resulted, within 6-18 hours, in 10 fatal attacks of tetany in a group of 12. Withdrawal of PTH on day 14 coincided with 10 hour isolation period for milk yield test. A group of 15 such animals survived considerably longer than previous group, due, it is believed, to gradual inhibition of lactation and reduction in blood Ca removed during separation period. In 11 rats which succumbed to tetany later, milk yield was significantly higher on day 15 as compared to day 14, 29 hours after last PTH injection. Nine rats which lactated normally without exhibiting signs of tetany during 4 day period after withdrawal of PTH, were considered to have (accessory) parathyroid tissue. It is tentatively proposed to consider 29-30 USP units of PTH/100 g/day as estimate of parathyroid secretion rate in this strain of intensively lactating rats under beneficial influence of optimal T4 level.
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