Nitric oxide limits the eicosanoid-dependent bronchoconstriction and hypotension induced by endothelin-1 in the guinea-pig

CONTRIBUTION OF PROSTANOID TP RECEPTORS TO THE PRESSOR AND INTRARENAL HAEMODYNAMIC RESPONSE TO ENDOTHELIN

Previous studies have shown that endothelin (ET)-1 stimulates thromboxane (Tx)A(2) production and so we hypothesized that inhibiting prostanoid TP receptors would prevent the pressor and intrarenal haemodynamic response to an acute infusion of ET-1. 2. Male Sprague-Dawley rats were anaesthetized with Inactin (Sigma Chemical, St Louis, MO, USA; 50 mg/kg) and catheters were inserted into the femoral artery and vein for recording mean arterial pressure (MAP) and infusion of ET-1 and receptor antagonists, respectively. A jugular vein catheter was used for the infusion of bovine serum albumin (6.2% in saline) during surgery (1.25% bodyweight). The pressor response to a 1 h infusion of ET-1 (6 pmol/kg per min) was determined in rats that had been pretreated with vehicle (0.9% NaCl) or the TP receptor antagonist SQ29548 (2 mg/kg per h). Laser Doppler single-optic fibres were implanted in the left kidney for the measurement of medullary blood flow (MBF) and cortical blood flow (CBF). 3. Prostanoid TP receptor blockade completely inhibited the acute pressor response to ET-1; the change in MAP was 14 2% versus -3 4% in vehicle and SQ29548 groups, respectively (P<0.05). Endothelin-1 reduced CBF (-15.2 3.3%), a response that was not significantly changed by SQ29548 (-6.2 7.6%). Similarly, the ET-1-mediated response in MBF was not altered by the TP receptor antagonist (7.7 4.9 vs 6.5 5.2%). 4. To determine the influence of the ET(B) receptor in modulating the response to ET-1 during TP receptor blockade, additional groups were pretreated with A-192621, an ET(B) receptor-selective antagonist (10 mg/kg, i.v.). A-192621 potentiated the increase in MAP produced by ET-1 (32 5%; P<0.05 vs ET-1 alone). SQ29548 significantly inhibited, but did not completely block, the increase in MAP produced by ET-1 during ET(B) antagonist treatment (18 4%; P<0.05). Endothelin-1-induced decreases in CBF were significantly enhanced in rats that were pretreated with A-192621, whereas ET-1 also significantly decreased MBF following A-192621 treatment. During ET(B) receptor blockade, TP receptor inhibition had no effect on the ET-1-mediated response of CBF and MBF. 5. These results suggest that TP receptor activation is not involved in the renal haemodynamic responses to ET-1. However, TP receptor activation contributes to the acute pressor response to ET-1, but does not account for the potentiated increase in MAP during ET(B) receptor blockade.

Intravenous and Intrapulmonary Administration of Honey Solution to Healthy Sheep: Effects on Blood Sugar, Renal and Liver Function Tests, Bone Marrow Function, Lipid Profile, and Carbon Tetrachloride-Induced Liver Injury

Safety of intravenous (i.v.) or intrapulmonary administration of different concentrations of honey and their effects on blood sugar, renal and liver function tests, bone marrow function, lipid profile, and carbon tetrachloride (CCl(4))-induced liver damage were studied. Healthy sheep of either sex, 6-8 months old, were assigned randomly into the following groups: sheep received i.v. infusion of 5% honey in normal saline at 10-day intervals for 50 days and were compared with sheep that received 5% dextrose; sheep received higher doses of honey (50 g of honey) by i.v. infusion daily for 10 days; sheep received four higher doses of honey (80 g each dose) for 2 weeks; sheep received subcutaneous injection of CCl(4) after four doses of i.v. infusion of 80 g of honey, and estimations of serum gamma-glutamyl transpeptidase (SGGT), serum glutamic oxaloacetic transaminase (SGOT), and serum glutamate pyruvate transaminase (SGPT) were performed daily for 10 days postinjection; sheep received i.v. infusion of 40 g of honey, and blood sugar estimation was performed for 3 h at 30-min intervals after infusion and compared with sheep that received 5% dextrose; sheep received rapid i.v. injection of 40% honey or 40% dextrose, and blood sugar was estimated before and after injection; sheep received various concentrations of honey in distilled water (0.5 mL/1.5 mL, 0.75 mL/1.75 mL and 1.2 mL/2.2 mL), and blood sugar estimation was performed before and after inhalation. Results showed that i.v. or intrapulmonary administration of honey did not cause any adverse effect. Intravenous delivery of honey by slow infusion caused improvement of renal and hepatic function, bone marrow function, and lipid profile. It reduced SGOT, SGPT, triglyceride, cholesterol, blood urea nitrogen, and blood sugar and elevated serum protein, serum albumin, hemoglobin, white blood cell, and neutrophil percentage. Similar results were obtained with the use of higher doses of honey. CCl(4) caused mild elevation of SGPT and SGGT and lowering of SGOT in sheep that received repeated i.v. administration of honey before administration of CCl(4), whereas in control sheep CCl(4) caused significant elevation of all the liver enzymes. Intravenous infusion of 40 g of honey caused elevation of blood sugar for 90 min postinfusion, whereas it decreased blood sugar at 2 and 3 h postinfusion as compared with fasting blood sugar. Dextrose caused significant elevation of blood sugar at all time intervals. Similar results were obtained with the use of 10% dextrose or 80 g of honey. Addition of honey to dextrose caused less hyperglycemia as compared with dextrose alone. Acute injection of 20 mL of 40% dextrose significantly elevated blood sugar for 3 h postinjection, whereas little elevation in blood sugar was obtained after injection of 40% honey; the difference between honey and dextrose was significant. Inhalation of honey caused significant lowering of blood sugar during and after inhalation as compared with fasting blood sugar and water inhalation. The effect was greater with a higher concentration of inhaled honey. It might be concluded that slow i.v. infusion or rapid i.v. injection of honey in different concentrations was safe and could lower blood sugar and improve renal, hepatic, and bone marrow functions and lipid profile. Intravenous honey had a hepatoprotective effect against CCl(4)-induced liver injury. Inhaled honey was safe and reduced blood sugar significantly.

Function of the endothelinB receptor in cardiovascular physiology and pathophysiology

One of the two receptors by which the potent vasoactive effects of endothelin (ET)-1 are mediated is the ET(B) receptor (ET(BR)), which is found in several tissues, but, more importantly from a cardiovascular point of view, on the endothelial cell. The endothelial cell also has the unique capability of releasing ET-1, as well as other factors, such as the endothelial-derived relaxing factors and prostacyclin, which counteract the myotropic effects of the peptide. The secretory and contractile responses to ET-1 rely on G-protein-coupled ET(BR)s, as well as ET(A)-G-protein-coupled receptor-like proteins. The mitogenic properties of ET-1 via ET(A) receptors (ET(AR)s) coupled to mitogen-activated protein kinases and tyrosine kinases on the vascular smooth muscle may occur in conjunction with the anti-apoptotic characteristics of the endothelial ET(BR)s. Interestingly, most of the relevant antagonists and agonists for both ET(AR)s and ET(BR)s have been developed by the pharmaceutical industry. This highlights the therapeutical potential of compounds that act on ET receptors. In normal as well as in physiopathological conditions, the ET(BR) plays an important role in the control of vascular tone, and must be taken into account when using ET receptor antagonists for the treatment of cardiovascular diseases. For the management of congestive heart failure, renal failure and primary pulmonary hypertension, the most recent literature supports the use of selective ET(AR) antagonists rather than mixed antagonists of ET(AR)s and ET(BR)s. Nonetheless, validation of this view will have to await the first clinical trials comparing the actions of ET(A) to mixed ET(A)/ET(B) receptor antagonists.

Pressor and pulmonary responses to ET-1(1-31) in guinea-pigs

1. Endothelin-1(1-31) (ET-1(1-31); 0.25 to 4 nmol kg(-1); i.v.) induced, in the guinea-pig, graded increases in MAP and an indomethacin-sensitive enhancement of pulmonary insufflation pressure (PIP). At all doses, ET-1(1-31) induced a monophasic pressor response, except at 4 nmol kg(-1), which caused a rapid and transient response (first phase: over first 10 min after injection) followed by a more slowly-developing and sustained (second phase: between 10 and 45 min after injection) increase in MAP. ET-1(1-31) was 4 to 10 fold less potent than ET-1 on PIP responses. 2. Phosphoramidon (5 and 10 mg kg(-1)) reduced both pressor and PIP effects of ET-1(1-31). Thiorphan (0.25 and 2.5 mg kg(-1)) did not affect the pressor responses to ET-1(1-31) although its PIP effects were markedly reduced by the NEP inhibitor. A selective endothelin-converting enzyme (ECE) inhibitor, CGS 35066 (1 mg kg(-1)), significantly reduced the second phase pressor response and increase in PIP triggered by ET-1(1-31). 3. The second (but not the first) pressor phase of ET-1(1-31) (4 nmol kg(-1)) was markedly reduced by BQ-123 (selective ET(A) antagonist), whereas the increase of PIP was significantly reduced by BQ-788 (selective ET(B) antagonist). Co-administration of BQ-123 plus BQ-788 abolished ET-1(1-31)-induced increase in PIP, but blockade of the second pressor phase afforded by BQ-123 was now reversed. 4. In guinea-pig isolated perfused lungs, ET-1(1-31) (50 nM) induced the release of prostacyclin and thromboxane A(2), which was inhibited by BQ-788 (5 nM) or thiorphan (25 microM), but not BQ-123 (1 microM). 5. These results suggest that ET-1(1-31) enhances MAP. Its sustained, but not transient, pressor effects are mediated via ET(A) receptor activation. Furthermore, ET-1(1-31) increases airway resistance in vivo and triggers prostacyclin and thromboxane A(2) release from perfused lungs predominantly via ET(B) receptor activation. ET-1(1-31) failed to display any selectivity of action towards either ET(A) or ET(B) receptors in these models. 6. We suggest that, in order to raise MAP, ET-1(1-31) requires conversion to ET-1, predominantly by ECE and to a lesser extent neutral endopeptidase 24.11, whereas the reverse holds true regarding its pharmacological effects in airways.