Changes in blood pressure control in aged rats.

The aging process is related to several changes in cardiovascular, metabolic and autonomic functions. However, descriptions of changes in arterial pressure (AP), baroreflex sensitivity and associated variations of serum glucose and insulin are controversial. The aim of this paper was to study AP, baroreflex sensitivity and changes in plasma levels of glucose and insulin of young (10 weeks, 239 +/- 4.3 g) and aged (18-24 months, 412 +/- 8.5 g) male Wistar rats. AP pulses were videotaped and processed on a microcomputer, using an analog-to-digital converter (beat-to-beat analysis). Baroreflex sensitivity was evaluated measuring heart rate changes induced by mean arterial pressure (MAP) variations produced by phenylephrine and sodium nitroprusside injections (N = 10 in each group). Plasma glucose (N = 10 in each group) and plasma insulin (N = 6 in each group) were quantified by a colorimetric enzymatic test and radioimmunoassay, respectively. There were no differences in systolic, diastolic or mean AP (110 +/- 5 vs 107 +/- 3 mmHg) between aged and young rats. The tachycardic response to the reduction of AP was impaired in aged compared to young rats (-1.95 +/- 0.29 vs -3.26 +/- 0.49 bpm/mmHg), while the bradycardic response to increases in AP was similar (-1.02 +/- 0.22 vs -1.5 +/- 0.26 bpm/mmHg). Basal levels of glucose (83 +/- 6 vs 62 +/- 4 mg/dl) and insulin (8.3 +/- 2 vs 4 +/- 0.5 microU/ml) were different. Thus, the reflex tachycardia evoked by a fall in AP is depressed in old rats.(ABSTRACT TRUNCATED AT 250 WORDS)