Recent experiments demonstrated increased isobaric arterial compliance and distensibility in hypertensive patients, which could be explained by a decrease in arterial wall stress, when assessed at constant pressure. We investigated the effect of hypertension on the mechanical properties of the carotid arterial wall, and especially wall stress, assessed in vivo in spontaneously hypertensive rats (SHR). Right carotid artery internal diameter (ID) and wall thickness (WT) were continuously monitored in 30 week old anesthetized SHR (n = 8) or their normotensive controls (WKY, n = 7), using a high resolution (1 micron) transcutaneous A-mode echo-tracking system (NIUS 2), coupled to a measurement of left carotid arterial pressure (micromanometer). Mean arterial pressure was 123 +/- 6 in WKY and 202 +/- 2 mmHg in SHR (p < 0.01). Mechanical parameters were calculated at mean pressure from ID and WT-pressure curves (*: p < 0.01 vs WKY). There was no difference between the groups for ID (WKY: 1.13 +/- 0.07; SHR: 1.20 +/- 0.06 mm, NS) and mid-wall stress (WKY: 10.5 +/- 1.2; SHR: 10.5 +/- 0.7 10(5) dynes/cm2, NS) while WT was increased in SHR (WKY: 105 +/- 8; SHR: 191 +/- 16 microns, p < 0.01). In SHR, incremental modulus (wall rigidity) was increased (WKY: 0.86 +/- 0.09; SHR: 1.96 +/- 0.25 10(7) dynes/cm2, p < 0.01) while distensibility (WKY: 1.77 +/- 0.16; SHR: 0.54 +/- 0.06 10(-3) mmHg-1, p < 0.01) and compliance (WKY: 1.84 +/- 0.30; SHR: 0.61 +/- 0.07 10(-3) mm2/mmHg, p < 0.01) were decreased.(ABSTRACT TRUNCATED AT 250 WORDS)