Functional endocrine modification of the thyroid following ovariectomy in the canine.

The study involves bilateral ovariectomy in bitches followed by the monitoring of oestradiol, thyroxine and total triiodothyronine levels in order to study control mechanism alterations. Levels of oestradiol dropped significantly following surgery to reach basal concentrations after 2 weeks. Serum total thyroxine, free thyroxine and total triiodothyronine decreased following ovariectomy to stabilize in a steady state within 3 weeks of surgery. Levels of thyroid-binding globulin initially increased as a result of oestrogen ablation, thereafter levels decreased steadily. Modification of the hypothalamo-thyroxine-releasing hormone receptor site and changes in androgens and thyroid-binding globulins are discussed as possible causes for the changes in circulating thyroid hormone concentrations.