Parathyroid Hormone and Thyrocalcitonin Function in Adrenalectomized Rats

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Abstract
The effect of adrenalectomy on the ability of the parathyroids or appropriate cells in the thyroid in the rat to respond to low or high calcium challenge was studied. Using 200 g male rats the following experimental groups were included: controls, parathyroidectomized (PTX), adrenalectomized (ADX), parathyroidectomized- adrenalectomized concurrently, parathyroidectomized 5 days after adrenalectomy, thyroidectomized (TX) and thyroidectomizedadrenalectomized concurrently. High calcium challenge was administered by intraperitoneal injection of 5 mg Ca/100 g body wt in 2 injections. The following results were noted: 1) Adrenalectomy alone had little or no effect on plasma calcium and phosphate levels under the conditions of these experiments, though it decreased urinary excretion of phosphate and increased by 30% the plasma concentration of 45Ca administered 2 weeks prior to the experimental studies. 2) Parathyroidectomy in adrenalectomized rats differed from that in adrenal-intact rats in that the rate of fall in plasma calcium was slightly retarded; in that the rats survived for the duration of the experiments despite plasma calcium as low as 5 mg/100 ml; and in that the temporary rise in renal calcium excretion which normally follows parathyroidectomy was negated. 3) Adrenalectomy did not affect the differences in plasma calcium levels produced in TI and TX animals by calcium administration but did negate similar differences seen in plasma radiocalcium concentrations. Also, calcium injection into adrenalectomized rats produced a higher and more persistent increased plasma phosphate level in both TI and TX animals. It is concluded that, while adrenalectomy causes definite changes in calcium transport in bone, both parathyroid hormone and thyrocalcitonin secretion or activity compensate for these changes such that little or no effect is produced on stable plasma calcium levels. (Endocrinology86: 1075, 1970)

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