Acute intravenous calcitonin: failure to modify systemic blood pressure

Calcium and a principal calcium-regulating hormone, PTH, have been characterized as possessing vasoactive properties in the spontaneously hypertensive rat (SHR). Calcitonin is another calcium-regulating peptide with primary, but opposing effects on many of the same target organs, and capable of modifying both extracellular and intracellular calcium distribution. We sought to determine whether calcitonin, like PTH, exhibits vasoactivity in the SHR and its control, the Wistar-Kyoto rat (WKY). Three male SHR and 3 male normotensive WKY received intravenous injections (range 1-100 micrograms/kg) of synthetic human calcitonin. Seven SHR and 7 WKY received equivalent doses of the more potent peptide, synthetic salmon calcitonin. Intraarterial pressure was monitored continuously. Neither analog of calcitonin produced significant changes in blood pressure. Serum ionized calcium levels 30 minutes postinjection were unchanged from baseline in the WKY; in the SHR, postinjection serum ionized calcium levels were significantly lower than baseline values (pre = 1.12 +/- 0.01 mmol/l vs. post 1.08 +/- 0.01 mmol/l, p less than 0.05). We conclude that calcitonin modifies extracellular calcium, but does not have demonstrable, acute systemic cardiovascular effects.