The importance of growth hormone and liothyronine in induced hypocalcaemia in hypophysectomized animals.

The resistance to hypocalcaemia induced by synthetic salmon calcitonin (SCT) was studied in intact and hypophysectomized rats. The recovery from hypocalcaemia was greatly impaired in the latter group, but this was normalised by small doses of purified human growth hormone (GH). The initial hypocalcaemic response to SCT was delayed in the hypophysectomized rats. This was not affected by treatment with GH, but normalised by substitution with liothyronine. We conclude that GH accelerates the recovery from hypocalcaemia in hypophysectomized animals, perhaps by a stimulation of parathyroid activity, while thyroid hormone accelerates the initial hypocalcaemic response to SCT, probably by restoring the reduced rate of bone resorption.