Factors affecting the acute pressor response to bolus cadmium injections

Tolerance to cadmium in the abdominal stretch response: a comparative study of cadmium and acetic acid

The intraperitoneal injection of cadmium (Cd) in mice produces a characteristic abdominal stretch response similar to that observed with acetic acid. Morphine, clonidine, and tripelennamine ED50 values were the same for inhibition of the response to Cd and to acetic acid. The ED50 values for aspirin and indomethacin were lower against the Cd than the acetic acid response. On repeated injections, Cd did but acetic acid did not produce tolerance to itself. Furthermore, the mice made tolerant to Cd were not cross-tolerant to acetic acid, but the acetic-acid-treated mice were cross-tolerant to Cd. These results suggest that Cd and acetic acid may produce the stretch response through different mechanisms, and the Cd-induced response might serve as a screening test for aspirin-like agents.

Influence of dosage, consciousness, and nifedipine on the acute pressor response to intraperitoneally administered cadmium

The acute pressor effect of intraperitoneally administered cadmium was explored over the dose range 0.015-2 mg/kg in both pentobarbital-anesthetized and conscious rats. The former first respondent at 0.031 mg/kg, and successive doublings of that dosage increased the highest pressures attained in a stepwise fashion until a dosage of 0.25 mg/kg, the maximally effective quantity, was reached. Arterial pressure did not rise in conscious rats until a dose of 1 mg/kg, which gave the maximum response within the range examined. Heart-rate changes with Cd were slight, and rarely significant at a given dosage, but pentobarbital invariably caused tachycardia. Anesthetized rats thus gave a graded response, while conscious animals reacted in an all-or-none fashion. The increased pressor responsiveness of rats under pentobarbital can not be ascribed to its cardiac parasympatholytic effects, since sensitivity was not conferred upon conscious rats when pretreated with atropine at a dose producing even greater tachycardia than that caused by pentobarbital. Nifedipine, which blocks calcium entry into smooth muscle cells, prevented the pressor response to cadmium when given as pretreatment and terminated an ongoing response when give intercurrently. Possible mechanisms to account for the observed behavior are considered.