Chronic lead exposure increases blood pressure and myocardial contractility in rats

We investigated the cardiovascular effects of lead exposure, emphasising its direct action on myocardial contractility. Male Wistar rats were sorted randomly into two groups: control (Ct) and treatment with 100 ppm of lead (Pb) in the drinking water. Blood pressure (BP) was measured weekly. At the end of the treatment period, the animals were anaesthetised and haemodynamic parameters and contractility of the left ventricular papillary muscles were recorded. Blood and tissue samples were properly stored for further biochemical investigations. Statistical analyses were considered to be significant at p<0.05. The lead concentrations in the blood reached approximately 13 µg/dL, while the bone was the site of the highest deposition of this metal. BP in the Pb-treated group was higher from the first week of lead exposure and remained at the same level over the next four weeks. Haemodynamic evaluations revealed increases in systolic (Ct: 96 ± 3.79 vs. Pb: 116 ± 1.37 mmHg) and diastolic blood pressure (Ct: 60 ± 2.93 vs. Pb: 70 ± 3.38 mmHg), left ventricular systolic pressure (Ct: 104 ± 5.85 vs. Pb: 120 ± 2.51 mmHg) and heart rate (Ct: 307 ± 10 vs. Pb: 348 ± 16 bpm). Lead treatment did not alter the force and time derivatives of the force of left ventricular papillary muscles that were contracting isometrically. However, our results are suggestive of changes in the kinetics of calcium (Ca++) in cardiomyocytes increased transarcolemmal Ca++ influx, low Ca++ uptake by the sarcoplasmic reticulum and high extrusion by the sarcolemma. Altogether, these results show that despite the increased Ca++ influx that was induced by lead exposure, the myocytes had regulatory mechanisms that prevented increases in force, as evidenced in vivo by the increased systolic ventricular pressure.