The Effect of Hypertensive Episodes and Cardiac Hypertrophy on the Canine Cardiac Baroreflex

Abstract

1. Left ventricular (LV) hypertrophy has been implicated in the reduction of baroreflex sensitivity present in hypertension. The aim of the current study was to investigate the mean arterial pressure-heart rate reflex (MAP-HR) in a model which induced left ventricular hypertrophy but no sustained blood pressure elevation. 2. Five mongrel dogs were exposed to transient blood pressure elevation of between 20 and 30 mmHg, through hindlimb compression using a pneumatic pressure suit, for 7 h per day, 6 days per week for 6 weeks. Resting blood pressure was not altered by the 6 week hindlimb compression intervention. 3. Echocardiographically determined LV mass (mean +/- s.e.m.) was 116.0 +/- 7.4 g prior to hindlimb compression (baseline) and elevated to 125.4 +/- 8.1 g (P = 0.003) after 6 weeks of compression. A reduction in the early (E) to late (A) transmitral diastolic flow ratio (E/A) from 1.80 +/- 0.06 at baseline to 1.54 +/- 0.09 (P = 0.037) after the 6 week intervention suggested that cardiac compliance was reduced. 4. The maximum gain of the MAP-HR reflex, studied using the 'steady-state' drug technique, when blood pressure was normal, showed a trend for reduction from 3.85 +/- 0.43 beats/min per mmHg at baseline to 3.10 +/- 0.45 beats/min per mmHg (P = 0.067) after 6 weeks of compression. This gain reduction became significant after beta-adrenoceptor blockade with propranolol (3.13 +/- 0.55 vs 2.32 +/- 0.25 beats/min per mmHg; P = 0.039). Covariant analysis showed a significant inverse correlation between LV mass and maximum gain (r = 0.96; P < 0.001) during the 6 week compression period.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction in infarct size by local estrogen does not prevent autonomic dysfunction after stroke

“…32). The BRS is depressed after the onset of several cardiovascular pathologies (6,7,9,12,(15)(16)(17)20), including stroke (30,41). Prior administration of systemic estrogen significantly reduces (ϳ50%) the infract size in various animal models of stroke, including permanent MCAO (3-5, 13, 31, 41, 42), and our laboratory has recently demonstrated that intravenous estrogen injection 30 min before MCAO in male rats completely reversed the resulting autonomic dysfunction (36).…”

Left Ventricular Changes in Isolated Office Hypertension

“…Our study does not explain the underlying mechanism leading to the development of LV changes in IO hypertension, but it may be speculated that transient BP increases, caused by exaggerated responses to mild stress, such as during medical evaluation, may have an effect on cardiac growth, leading to hypertrophy. One study 35 in dogs showed that concentric LV hypertrophy can be produced by intermittent compression of the dogs' limbs to increase BP. Furthermore, experimental studies have shown that brief episodes of cardiac pressure overload are sufficient to induce growth-related genes and protein synthesis in the heart.…”