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

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Abstract
The acute pressor effect of i.p. administered Cd was explored over the dose range 0.015-2 mg/kg in 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 caused tachycardia. Anesthetized rats gave a graded response, while conscious animals reacted in an all-or-none fashion. The increased pressor responsiveness of rats under pentobarbital could not be ascribed to its cardiac parasympatholytic effects, since sensitivity was not conferred on conscious rats when pretreated with atropine at a dose producing even greater tachycardia than that caused by pentobarbital. Nifedipine, which blocks Ca entry into smooth muscle cells, prevented the pressor response to Cd when given as pretreatment and terminated an ongoing response when give intercurrently. Possible mechanisms to account for the observed behavior are considered.