Histamine-induced hypocalcemia in the rat

The effect of histamine and betazole hydrochloride (Histalog) on serum calcium homeostasis in the rat was studied in these experiments. Either histamine base, histamine phosphate, betazole, or the appropriate control solution was injected intravenously into fasted, anesthetized 80-100 g male rats. Venous blood was collected before and at 30 and 60 min postinjection. Histamine base in doses of 0.5-2.0 mg/rat induced a significant hypocalcemic response 30 min postinjection which returned to baseline by 60 min. Likewise, the administration of 1.375 mg/rat of histamine phosphate (equivalent to 0.5 mg histamine base) also resulted in a significant fall in serum calcium concentration. However, betazole administration, in doses as high as 10 mg/rat, did not lower the serum calcium concentration. In the histamine experiments neither total protein nor hematocrit values differed from control at the time of hypocalcemia. Therefore the changes in serum calcium concentration cannot be explained by hemodilution. These experiments demonstrate that in the rat the administration of histamine results in a hypocalcemic response similar to that previously observed with gastrin.