Role of epinephrine in the development of hypertension in Dahl salt-sensitive rats

Lack of influence of circulating adrenaline on blood pressure in normotensive and hypertensive rats

The relationship between circulating adrenaline and blood pressure was examined by manipulating plasma adrenaline levels in both normotensive and hypertensive rats: bilateral adrenalmedullectomy was performed in spontaneously hypertensive rats and stroke-prone spontaneously hypertensive rats; adrenaline bitartrate was infused chronically (25-32 micrograms/kg/h s.c.) into Wistar Kyoto, Sprague Dawley and stroke-prone rats via osmotic minipumps. Arterial and venous catheters were subsequently implanted for direct measurement of mean arterial pressure, blood sampling and drug administration in conscious rats. Adrenaline infusion for 5-6 weeks in Wistar Kyoto rats did not affect resting blood pressure (118 +/- 3 versus 119 +/- 1 mmHg in controls) even though plasma adrenaline was elevated 12-fold. Plasma noradrenaline was marginally elevated. Blood pressure was also unaffected by adrenaline infusion in Sprague Dawley or stroke-prone hypertensive rats. One week after adrenal medullectomy, plasma adrenaline was reduced 89% in spontaneously hypertensive rats, but blood pressure was unaffected. Ten weeks after adrenal medullectomy in young stroke-prone rats, resting blood pressure was slightly higher (167 +/- 2 mmHg) than in control rats (157 +/- 2 mmHg), although adrenaline was reduced by 34% in plasma and 67% in adrenal glands. Nitroprusside was infused acutely to lower blood pressure and reflexly elevate plasma noradrenaline. Neither of these responses were affected by chronic adrenaline infusion or adrenal medullectomy. In both adrenaline-infused Wistar Kyoto and medullectomised stroke-prone rats, autonomic blockade reduced blood pressure to a similar extent as in controls, indicating that the degree of sympathetic vasoconstriction was not altered by either treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac adenylyl cyclase, beta-adrenergic receptors, and G proteins in salt-sensitive hypertension

The present study investigated whether high salt intake (8%) in Dahl salt-sensitive and salt-resistant rats with and without hypertension produces a heterologous desensitization of cardiac adenylyl cyclase as observed in various types of hypertension and human heart failure. In membranes from Dahl salt-sensitive rats on a high-salt diet (8%) basal, isoproterenol-, 5'-guanylylimidodiphosphate-, and forskolin-stimulated adenylyl cyclase was reduced compared with the low-salt (0.4%) group and Dahl salt-resistant rats on either 0.4% or 8% sodium chloride. The activity of the catalyst was depressed, and the expression of the immunodetectable inhibitory G proteins Gi alpha was increased in Dahl salt-sensitive rats on 8% sodium chloride, whereas the density of beta-adrenergic receptors and the activity of the stimulatory G protein Gs alpha reconstituted into Gs alpha-deficient S49 cyc- mouse lymphoma cell membranes were unchanged in any condition studied. We conclude that high salt intake in salt-sensitive hypertensive Dahl rats produces hypertension, cardiac hypertrophy, and heterologous desensitization of cardiac adenylyl cyclase. The latter alteration is due to an increase of Gi alpha proteins and a depressed catalyst activity of adenylyl cyclase. The results demonstrate that heterologous adenylyl cyclase desensitization can precede the development of contractile dysfunction in later stages and can occur independently of changes in beta-adrenergic receptors.

Sucrose does not raise blood pressure in rats maintained on a low salt intake

Diets high in sucrose or fructose have been shown by others to induce a modest elevation of blood pressure in rats. The present experiments were conducted to determine whether the sucrose-induced increase of blood pressure is dependent on the intake of sodium chloride. Four groups of Sprague-Dawley rats were studied: 1) a group maintained on a low salt diet and distilled water (0.45% sodium chloride, no added sucrose), 2) a low salt-high sucrose group (0.45% sodium chloride diet and 7% sucrose in distilled water), 3) a high salt group (4% sodium chloride diet and distilled water), and 4) a high salt-high sucrose group on a diet adjusted daily to maintain the same high intakes of sodium chloride and sucrose as those of groups 2 and 3. Systolic blood pressures were measured by tail-cuff plethysmography during weeks 1-3 of treatment, and direct mean arterial blood pressures were recorded in conscious animals during week 4. Animals on the high salt diet gained weight more slowly than those on the low salt intake. On the low sodium chloride intake, blood pressures were not affected by high dietary sucrose (group 1 versus 2). In contrast, on the high sodium chloride intake, blood pressures were 10-14 mm Hg higher in sucrose-drinking animals than in water-drinking animals (group 3 versus 4). The increments in blood pressures of the high sodium chloride-high sucrose group were not accompanied by greater increments in body weight compared with the animals on the high sodium chloride intake alone.(ABSTRACT TRUNCATED AT 250 WORDS)