Chronic arterial vasodilation, central hemodynamics, and cardiac hypertrophy in spontaneously hypertensive rats

Sexually dimorphic hemodynamic effects of intragastric ethanol in conscious rats

This study investigated the gender-related differences in hemodynamic effects of small to moderate doses of intragastrically (i.g.) administered ethanol in conscious rats. Changes evoked by ethanol (0.25, 0.5 or 1 g/kg) in mean arterial pressure (MAP), heart rate, cardiac index (CI), stroke volume (SV), and total peripheral resistance (TPR) were followed for 90 min in age-matched male and female Sprague-Dawley rats. Baseline values of MAP (121+/-2 vs. 124+/-2 mm Hg) were similar whereas CI (55+/-2 vs. 43+/-2 ml/min/100 g) and TPR (2.2+/-0.1 vs. 3.0+/-0.1 mm Hg/ml/min/100 g) were significantly (P<0.05) higher and lower, respectively, in female compared with male rats. In male rats, the middle dose (0.5 g/kg) of ethanol caused a slight increase in MAP due to significant (P<0.05) increases in CO whereas the other two doses (0.25 and 1 g/kg) had no effect on MAP. In female rats, MAP was not affected by ethanol (0.25 and 0.5 g/kg) and showed a significant reduction by the higher dose (1 g/kg) that was associated with decreases in CO and SV while TPR did not change. The hypotensive effect of ethanol (1 g/kg) in female rats started after 50 min, was maximal (13+/-1.7 mm Hg) at 70 min and remained so for the remaining 20 min of the study. Blood ethanol concentrations were similar in male and female rats. These findings suggest that the hemodynamic responses to i.g. ethanol are gender-related and that ethanol-evoked hypotension in female rats appears to involve a reduction in cardiac output.

Role of cardiac output in ethanol-evoked attenuation of centrally mediated hypotension in conscious rats

Our previous studies have shown that ethanol selectively counteracts centrally mediated hypotensive responses. This study investigated the role of cardiac output and peripheral resistance in the antagonistic interaction between ethanol and antihypertensive drugs. Changes in blood pressure, heart rate, cardiac index, stroke volume, and peripheral resistance elicited by clonidine and subsequent ethanol or saline administration were evaluated in conscious rats. The aortic barodenervated rat was employed because it exhibits greater hypotensive responses to clonidine compared with the intact rat. Aortic barodenervation elicited acute rises in blood pressure, heart rate, and peripheral resistance, whereas cardiac index and stroke volume were not altered. The blood pressure of conscious aortic barodenervated rats returned to sham-operated levels by 48 hours due to concomitant reductions in cardiac index and stroke volume; the peripheral resistance, however, remained significantly elevated. Clonidine (30 microg/kg, I.V.) elicited greater decreases in blood pressure in aortic barodenervated compared with sham-operated rats. The hypotension was caused by decreases in cardiac index and stroke volume because peripheral resistance did not change. Ethanol (1 g/kg, I.V.) counteracted the hypotensive effect of clonidine and raised blood pressure to levels higher than preclonidine values. Significant (P<.05) increases in cardiac index and stroke volume and decreases in peripheral resistance accompanied the pressor effect of ethanol. Additional control groups were included in the study to determine the selectivity of the interaction. A dose of hydralazine (0.5 mg/kg, I.V.) was used that produced similar hypotension to that evoked by clonidine in aortic barodenervated rats. Hydralazine-evoked hypotension was similar in denervated and control rats and resulted from significant reductions in peripheral resistance. Reflex increases in heart rate and stroke volume and hence cardiac output were observed. Ethanol given after hydralazine produced a short-lived pressor effect (<5 minutes versus 40 minutes in the case of clonidine) and counteracted the sympathetically mediated increases in cardiac output, stroke volume, and heart rate. These findings support our hypothesis that ethanol selectively counteracts hypotensive responses of central origin by reversing the reduction in cardiac output elicited by clonidine.

Brain 'ouabain' mediates sympathetic hyperactivity in congestive heart failure

In congestive heart failure (CHF), endogenous compounds with ouabainlike activity (OLA) may contribute to the maintenance of the circulatory homeostasis by peripheral as well as central effects. In the present study, we assessed changes in peripheral (plasma and left ventricle) and central (pituitary, hypothalamus, pons, and cortex) OLA in two animal models of CHF and determined whether brain OLA mediates sympathetic hyperactivity in CHF. Cardiomyopathic hamsters with their controls were studied at 9 months of age for tissue OLA. Rats were studied 4 weeks after acute coronary artery ligation for tissue OLA and sympathetic activity. In both models, left ventricular end-diastolic pressure was markedly increased. CHF was associated with significant increases in both plasma and tissue OLA in both models. In the brain, the most marked (twofold to threefold) increases occurred in the hypothalamus. In vitro, all OLA measured could be blocked by antibody Fab fragments (Digibind). Conscious rats with CHF showed elevated plasma catecholamines and enhanced responses of mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) to air stress and to intracerebroventricular (ICV) injection of the alpha 2-adrenergic receptor agonist guanabenz compared with sham-operated rats. ICV administration of the Fab fragments did not change resting RSNA or responses to air stress at 1 hour. However, 18 hours after injection of the Fab fragments, resting RSNA levels had significantly decreased compared with the control values, and plasma catecholamine levels had decreased to control values.(ABSTRACT TRUNCATED AT 250 WORDS)