Central and peripheral effects of repeated stress and high NaCl diet on neuropeptide Y.

Fludrocortisone reduces plasma norepinephrine in healthy humans, but forearm vascular and pressor responses to norepinephrine are potentiated. The effects of fludrocortisone on sympathetic nerve activity in healthy humans are not known. To investigate these effects we evaluated muscle sympathetic nerve activity, heart rate, and arterial pressure in 11 healthy volunteers during three protocols: (1) before and on day 7 of fludrocortisone (0.4 mg/d) treatment with ad libitum diet (n = 6); (2) before and on day 7 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 7); and (3) before and on day 2 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 4). Placebo did not alter any parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of fludrocortisone on sympathetic nerve activity in humans.

Cardiovascular effects of melanocortins

G protein-mediated signaling plays a decisive role in blood pressure regulation and the phenotype of vascular smooth muscle cells (VSMCs); however, the relevance of proteins that restrict G protein activity is not well characterized in this context. Here, we investigated the influence of regulator of G protein signaling 5 (RGS5), an inhibitor of Gαq/11 and Gαi/o activity, on blood pressure and the VSMC phenotype during experimental hypertension. In mice, loss of RGS5 did not affect baseline blood pressure, but prevented hypertension-induced structural remodeling. RGS5-deficient arterial VSMCs did not acquire a synthetic phenotype as evidenced by their inability to decrease the abundance of contractile markers-α-smooth muscle actin and smooth muscle-myosin heavy chain-or to proliferate under these conditions. Mechanistically, hypertensive pressure levels or biomechanical stretch are sufficient to increase the expression of RGS5. Loss of RGS5 severely impairs the activation of RhoA and stress fiber formation. In stretch-exposed VSMCs, RhoA activity was amplified upon inhibition of PKC, which mimics the downstream effects evoked by RGS5-mediated inhibition of Gαq/11 signaling. Collectively, our findings underline that RhoA activation may depend on the restriction of G protein activity and identify RGS5 as a mechanosensitive regulatory protein that is required to promote the synthetic VSMC phenotype as a prerequisite for structural renovation of the arterial wall during hypertension.-Arnold, C., Demirel, E., Feldner, A., Genove, G., Zhang, H., Sticht, C., Wieland, T., Hecker, M., Heximer, S., Korff, T. Hypertension-evoked RhoA activity in vascular smooth muscle cells requires RGS5.

Hypertension-evoked RhoA activity in vascular smooth muscle cells requires RGS5.

Chapter 6 – The Sympathetic Nervous System in Acute and Chronic Blood Pressure Elevation

To elucidate the role of the dopaminergic system in the maintenance of hypertension in the deoxycorticosterone acetate (DOCA)/NaCl hypertensive rat, the responses of mean arterial pressure (MAP), plasma norepinephrine (NE), epinephrine (E), and prolactin (PRL) to intravenous (iv) administration of bromocriptine, a dopamine agonist, and hexamethonium bromide, a ganglion blocker, were examined in conscious, unrestrained 4-wk DOCA/NaCl hypertensive rats. Bromocriptine was administered to adrenomedullectomized (ADMX) rats to assess the role of the adrenal medulla in its depressor effect. Bromocriptine (50, 250, and 500 micrograms/kg) and hexamethonium (3 and 30 mg/kg) caused dose-dependent decreases in MAP that were greater in DOCA/NaCl rats than in uninephrectomized controls. Basal plasma NE, E, and PRL were significantly higher in DOCA/NaCl rats than in controls. Bromocriptine (500 micrograms/kg iv) decreased plasma PRL to undetectable levels and increased plasma E significantly without changing NE levels in DOCA/NaCl and uninephrectomized control rats. In ADMX rats bromocriptine (500 micrograms/kg iv) decreased MAP, PRL, and NE without affecting E levels. These results suggest that the depressor response to bromocriptine could be related to inhibition of sympathetic outflow without participation of the adrenal medulla. The hyperprolactinemia and enhanced depressor response to bromocriptine observed in DOCA/NaCl animals suggest that the dopaminergic system might be altered in this model of hypertension.

Enhanced depressor effect of bromocriptine in the DOCA/NaCl hypertensive rat.

To examine the role of the sympathetic nervous system in the development of deoxycorticosterone acetate (DOCA)/NaCl hypertension and to test the hypothesis that the responsiveness of the sympathetic nervous system to stress is enhanced during the developmental phase of hypertension in this model before resting sympathetic activity becomes increased, DOCA/NaCl-treated rats and uninephrectomized control animals were studied after 3, 7, 14, and 28 days of treatment. Basal plasma norepinephrine and epinephrine in conscious, unrestrained resting DOCA/NaCl-treated rats were the same as in controls at 3, 7, and 14 days but were significantly elevated at 28 days of treatment. Ganglionic blockade resulted in a significantly greater decrease in mean arterial pressure in DOCA/NaCl rats than in controls at 14 and 28 days of treatment. At 14 days, DOCA/NaCl rats exhibited significantly greater increments in plasma norepinephrine and epinephrine following cold stress than did H2O controls. Basal plasma prolactin levels were elevated and release of dopamine from isolated superfused mediobasal hypothalami reduced in 28-day DOCA/NaCl hypertensive rats. These results indicate that sympathetic nervous system activity increases progressively during the development of DOCA/NaCl hypertension and that the sympathoadrenal system is hyperresponsive to environmental stress even early in the course of DOCA/NaCl treatment and suggest that hypothalamo-hypophyseal function is altered in this model of hypertension.

S. Nagahama

Papers

Enhanced depressor effect of bromocriptine in the DOCA/NaCl hypertensive rat.

Hyperresponsiveness of monoaminergic mechanisms in DOCA/NaCl hypertensive rats.