Cardiovascular actions of human endothelin in conscious sheep

Whole body and renal noradrenaline release during acute infusion of endothelin-1 in conscious sheep

1. The present study investigated in conscious sheep the response of the sympathetic nervous system to a systemic infusion of 20 nmol/h endothelin-1 (ET-1), using a tritiated-noradrenaline (NA) tracer dilution technique. 2. Mean arterial pressure increased from 79 +/- 3 mmHg to a maximal level of 102 +/- 12 mmHg by 30 min of ET-1 infusion. 3. Total and renal NA kinetics were measured during this time. Total NA spillover was not affected by infusion of ET-1. In contrast, renal NA spillover decreased from a control level of 81 +/- 5 to 30 +/- 14 ng/min (P < 0.01) after 20 min and to 27 +/- 7 ng/min (P < 0.01) after 30 min of ET-1 infusion. 4. The present findings are consistent with the proposal that a direct vasoconstrictor action of ET-1 results in a paroreflex mediated reduction in renal sympathetic vasoconstrictor activity.

Haemodynamic and renal tubular effects of low doses of endothelin in anaesthetized rats

1. Renal haemodynamic and tubular transport responses to low-dose infusions (1 and 10 ng kg-1 min-1) of endothelin were investigated in anaesthetized rats. 2. Both doses caused transient increases in mean arterial blood pressure (17 +/- 5 mmHg, P < 0.05 at 1 ng kg-1 min-1) followed by sustained hypotension (-14 +/- 5 mmHg, P < 0.05), reduced renal vascular resistance (-42%, P < 0.05) and increased renal plasma flow (46%, P < 0.05). Glomerular filtration rate was unchanged. 3. Each dose caused profound diuresis and natriuresis. At 1 ng kg-1 min-1 urine flow rate and fractional water excretion increased 5-fold and fractional sodium excretion 10-fold. Fractional potassium excretion and solute-free water clearance were unaltered. 4. End-proximal fluid delivery estimated by lithium clearance doubled (P < 0.05) and fractional proximal and distal sodium reabsorption decreased 10-20% (P < 0.05). Absolute proximal reabsorption also fell with the higher dose. 5. Hypotension and natriuresis persisted for 30 min after terminating infusions. Time-control animals showed no changes in haemodynamics or renal tubular transport. 6. It is concluded that endothelin, at low concentrations, causes renal vasodilatation with concomitant natriuresis due to reduced sodium transport in proximal and distal nephron segments.

Endothelin: a new cardiovascular regulatory peptide

Endothelin, a recently discovered peptide produced by endothelial cells, contracts vascular strips in vitro with greater potency than any previously known vasoconstrictor. Infusions of pharmacologic doses of endothelin in vivo result in a prolonged pressor response and a preferential impairment of renal hemodynamic and excretory functions. Endothelin also directly stimulates the release of aldosterone from the adrenal gland and inhibits renin release in vitro. A highly sensitive and specific radioimmunoassay has confirmed that endothelin circulates in human plasma, and increased plasma endothelin levels have been associated with various cardiovascular disease states. This review summarizes the current knowledge about the molecular biologic features and physiologic actions of endothelin and also explores the role of endothelin, through its local and systemic function, as a regulator of vascular tone in normal and pathophysiologic states.

Haemodynamic effects of long-term endothelin infusion in conscious sheep

1. Synthetic human endothelin-1 was infused intravenously at 15 micrograms/h for 24 h to examine its cardiovascular actions in five conscious sheep. 2. Endothelin produced a maximum increase in mean arterial pressure (MAP) of +8 mmHg at 8 h, with an increase in calculated total peripheral resistance (CTPR) of +2.6 mmHg/L per min, whilst cardiac output (CO) was unchanged. At 24 h MAP was not significantly elevated, however CTPR had increased by +2.8 mmHg/L per min and CO had decreased by 0.9 L/min. 3. This study shows that long-term administration of endothelin produces sustained arterial vasoconstriction in sheep.