The effects of glucagon, 1 or 10 μg/100 g body weight, on serum calcium were studied in intact and thyroparathyroidectomized rats. The animals either had received no treatment or had been given parathyroid extract or vitamin D in doses which produced hypercalcemia. Serum calcium was determined before and again at 1, 3 and 5 hr after glucagon administration. Glucagon produced modest decreases in the serum calcium in all rats except some of the thyroparathyroidectomized ones given no pretreatment in which the serum calcium was abnormally low. There was a significant correlation between the serum calcium and the hypocalcemic response to glucagon. In tissue culture experiments with embryonic rat bone labeled with 45Ca, glucagon inhibited the release of 46Ca induced with either parathyroid hormone or dibutyryl- 3′, 5′-adenosine monophosphate. The inhibition by glucagon of parathyroid hormone action was partially overcome with larger concentrations of parathyroid hormone. The results indicate that inhibition of bone resorption may be a factor in the hypocalcemic response to glucagon.
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