Abstract
1. Dogs were treated with growth hormone for three months under controlled conditions, dietary calcium absorption efficiency was measured by administration of47Ca and45Ca, and calcium pool size, pool turnover, bone mineral accretion, and endogenous fecal calcium excretion were measured using the I.V.45Ca tracer. Identical studies were performed in each animal, at the end of a five-month equilibration period, and at the end of the three-month period of growth hormone administration. 2. Dietary calcium absorption efficiency increased and endogenous fecal calcium excretion decreased as a result of growth hormone administration. Urine calcium fell slightly. Although direct balances were not determined, these changes indicate a positive calcium balance shift in association with treatment. 3. Growth hormone had no effect on the size of the miscible calcium pool, but increased mineral incorporation into bone by 21-41%. Return of calcium from bone was reduced, consistent with the positive balance shift, but to an unmeasured extent. 4. Parallel kinetic and morphometric measurement of skeletal turnover performed on adjacent long bone sections indicated a consistent positive correlation between estimates derived by the two methods, with kinetic estimates tending to be slightly higher than the morphometric, particularly at low levels of skeletal remodeling.