Abstract

The growth hormone response to acute hypercalcemia was studied in 9 normal subjects. Growth hormone, calcium, glucose, phosphate and magnesium levels were determined at 30-min intervals during 4-h infusions. Infusions, performed in random order in the subjects, consisted of either normal saline at 3 ml/min for / h or 15 mg calcium/kg (calcium gluconate at 3 ml/min for 3 h followed by normal saline for the fourth hour. Significant hypercalcemia (P less than 0.05) was achieved within 60 min and maintained throughout the infusion. No change in calcium concentrations occurred during normal saline infusions, and phosphate, glucose and magnesium were unchanges in all studies. Growth hormone levels were significantly higher (P less than 0.05) at 60 min and all subsequent determinations during calcium infusion when compared to normal saline infusions. In 6 of the subjects, standard l-dopa provocative testing with an oral dose of 500 mg was preformed during normal saline and calcium infusions identical to those described above. Peak growth hormone responses did not differ significantly following l-dopa during saline or calcium infusion. These results suggest that an acute increase in circulating calcium promotes greater basal growth hormone secretion without a synergistic increase in hypothalamic mediated growth hormone release by l-dopa.