Hypocalcemic effect of salmon calcitonin following single and repeated nasal and intravenous administration in young rabbits.

The effect of the polypeptide salmon calcitonin (sCT) on serum calcium concentrations following intranasal and intravenous administration was studied in young rabbits. A small, hypocalcemic effect was observed after nasal administration of sCT without additives, indicating that the nasal sCT absorption was low. The absorption could be improved by addition of an absorption-enhancing adjuvant to the nasal preparation. The absorption, however, was still far from complete as was apparent from the much stronger effect of intravenously injected sCT. When a number of sCT doses were given during a 10-week period, the hypocalcemic effect per sCT dose in the young rabbits decreased after intravenous and, although less pronounced, after nasal administration. The decreased response to sCT is probably not related to the induction of neutralizing antibodies or desensitization of sCT receptors, but is more likely associated with the age-dependent level of bone activity.