histamineinduced 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 80100 g male rats venous blood was collected before and at 30 and 60 min postinjection histamine base in doses of 0520 mgrat induced a significant hypocalcemic response 30 min postinjection which returned to baseline by 60 min likewise the administration of 1375 mgrat of histamine phosphate equivalent to 05 mg histamine base also resulted in a significant fall in serum calcium concentration however betazole administration in doses as high as 10 mgrat 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