Effects of indomethacin on steroid-induced changes in pressor responsiveness in man

Vascular Dysfunction in Horses with Endocrinopathic Laminitis

Endocrinopathic laminitis (EL) is a vascular condition of the equine hoof resulting in severe lameness with both welfare and economic implications. EL occurs in association with equine metabolic syndrome and equine Cushing’s disease. Vascular dysfunction, most commonly due to endothelial dysfunction, is associated with cardiovascular risk in people with metabolic syndrome and Cushing’s syndrome. We tested the hypothesis that horses with EL have vascular, specifically endothelial, dysfunction. Healthy horses (n = 6) and horses with EL (n = 6) destined for euthanasia were recruited. We studied vessels from the hooves (laminar artery, laminar vein) and the facial skin (facial skin arteries) by small vessel wire myography. The response to vasoconstrictors phenylephrine (10⁻⁹–10^-5M) and 5-hydroxytryptamine (5HT; 10⁻⁹–10^-5M) and the vasodilator acetylcholine (10⁻⁹–10^-5M) was determined. In comparison with healthy controls, acetylcholine-induced relaxation was dramatically reduced in all intact vessels from horses with EL (% relaxation of healthy laminar arteries 323.5 ± 94.1% v EL 90.8 ± 4.4%, P = 0.01, laminar veins 129.4 ± 14.8% v EL 71.2 ± 4.1%, P = 0.005 and facial skin arteries 182.0 ± 40.7% v EL 91.4 ± 4.5%, P = 0.01). In addition, contractile responses to phenylephrine and 5HT were increased in intact laminar veins from horses with EL compared with healthy horses; these differences were endothelium-independent. Sensitivity to phenylephrine was reduced in intact laminar arteries (P = 0.006) and veins (P = 0.009) from horses with EL. Horses with EL exhibit significant vascular dysfunction in laminar vessels and in facial skin arteries. The systemic nature of the abnormalities suggest this dysfunction is associated with the underlying endocrinopathy and not local changes to the hoof.

How do glucocorticoids cause hypertension: role of nitric oxide deficiency, oxidative stress, and eicosanoids

The exact mechanism by which glucocorticoid induces hypertension is unclear. Several mechanisms have been proposed, although there is evidence against the role of sodium and water retention as well as sympathetic nerve activation. This review highlights the role of nitric oxide-redox imbalance and their interactions with arachidonic acid metabolism in glucocorticoid-induced hypertension in humans and experimental animal models.

Cardiovascular consequences of cortisol excess

Cushing's syndrome is a consequence of primary or, more commonly, secondary oversecretion of cortisol. Cardiovascular disease is the major cause of morbidity and mortality in Cushing's syndrome, and excess risk remains even in effectively treated patients. The cardiovascular consequences of cortisol excess are protean and include, inter alia, elevation of blood pressure, truncal obesity, hyperinsulinemia, hyperglycemia, insulin resistance, and dyslipidemia. This review analyses the relationship of cortisol excess, both locally and at tissue level, to these cardiovascular risk factors, and to putative mechanisms for hypertension. Previous studies have examined correlations between cortisol, blood pressure, and other parameters in the general population and in Cushing's syndrome. This review also details changes induced by short-term cortisol administration in normotensive healthy men.

Glucocorticoid hypertension due to the use of bleaching skin cream, a case report

We report on an unusual case of a 28-year old African woman who developed glucocorticosteroid induced arterial hypertension after abusive use of a skin bleaching cream. Glucocorticosteroids exert their effect at many different sites involved in blood pressure regulation: in particular at the level of the kidney, blood vessels and the heart. The exact incidence of arterial hypertension after prolonged cutaneous glucocorticosteroid administration is unknown. The mechanism of glucocorticosteroid induced hypertension is discussed.

Glucocorticoid-induced hypertension: from mouse to man

1. Adrenocorticotrophic hormone (ACTH) raises blood pressure in humans, sheep, rat and mouse. In rat and humans, but not sheep, the hypertension can be explained by glucocorticoid excess. 2. In both rat and humans, the hypertension is associated with a rise in cardiac output and renal vascular resistance. 3. In both rat and humans, the nitric oxide system is implicated in glucocorticoid hypertension. 4. In both rat and humans, hypertension due to naturally occurring glucocorticoids is not prevented by drugs that block classical glucocorticoid or mineralocorticoid receptors. 5. Abnormalities in glucocorticoid metabolism may contribute to some forms of 'essential' hypertension.

Cortisol inhibits cholinergic vasodilation in the human forearm

Exogenous cortisol raises blood pressure (BP) in humans and there is accumulating evidence of abnormalities of glucocorticoid activity in essential hypertension. In this study we tested the hypothesis that exogenous cortisol attenuates the cholinergic dilator response in the forearm circulation. Fourteen healthy normotensive men were studied. Using bilateral forearm venous plethysmography, we examined forearm blood flow responses to intra-arterial acetylcholine (ACh) and sodium nitroprusside (SNP) pre- and post-NG-monomethyl-L-arginine (LNMMA) after 2 or 5 days of oral cortisol or placebo in a randomized, double-blind crossover study. Exogenous cortisol increased supine systolic (P < .05) and standing systolic (P < .05) BP and produced expected metabolic changes and suppressed serum cortisol concentration (P < .001). Baseline forearm blood flow did not differ between placebo and cortisol treatments at 2 or 5 days. Cholinergic vasodilatation was impaired after cortisol administration, reaching statistical significance at 5 days (P < .05). Cortisol did not affect responses to SNP. NG-monomethyl-L-arginine inhibited cholinergic vasodilatation in placebo-treated groups but had no additional effect in the presence of cortisol. These results support our hypothesis and suggest that the mechanism of impaired cholinergic dilatation in glucocorticoid-treated subjects involves abnormalities of the endothelial nitric oxide system.

Adrenocorticotrophic hormone-induced hypertension in the rat: effects of the endothelin antagonist bosentan

1. The effects of the endothelin antagonist bosentan on adrenocorticotrophic hormone (ACTH)-induced hypertension were examined in the conscious male Sprague-Dawley rat. 2. In order to confirm endothelin antagonism, 18 rats were randomly divided into two groups: receiving either (i) endothelin-1 (0.125, 0.25, 0.5 and 1 nmol/kg, i.v.); or (ii) endothelin-1 at these doses following bosentan (100 mg/kg gavage) and mean arterial pressure recorded (study A). Subsequently, 40 male rats (320 +/- 5 g) were randomly divided into four groups (n = 10): (i) Sham (0.9% saline, s.c.) + 5% acacia gum gavage; (ii) ACTH (500 micrograms/kg per day, s.c.) + 5% acacia gum gavage; (iii) Sham injection + bosentan (100 mg/kg per day) gavage; or (iv) ACTH + bosentan. Six control days (C1-C6) were followed by 11 treatment days (T0-T10). Systolic blood pressure, water intake, urine volume, food intake and bodyweight were measured every second day (study B). 3. Bosentan significantly attenuated the endothelin-1-induced blood pressure rise at 0.125 nmol/kg (P < 0.05), but not at higher doses. 4. Bosentan at a dose which attenuated endothelin-1-induced blood pressure increase had no effect on either blood pressure or metabolic parameters in ACTH-treated rats. 5. These results suggest that endothelin does not play a major role in ACTH-induced hypertension.

Hemodynamic profile of corticotropin-induced hypertension in the rat

OBJECTIVES

To examine hemodynamic variables in corticotropin-induced hypertension in rats and the effects of reversal of the hypertension by L-arginine on the hemodynamic profile.

METHODS

Sixty male Sprague-Dawley rats were randomly divided into four groups: sham treatment (0.9% NaCl, injected subcutaneously); 0.5 mg/kg corticotropin per day, subcutaneously; 0.6% L-arginine in food plus sham; and L-arginine plus corticotropin. Systolic blood pressure, water and food intakes, urine volume, and body weight were measured every second day. After 10 days mean arterial blood pressure was measured by intra-arterial cannulation, and cardiac output, and renal, mesenteric, and hindquarter blood flows were determined using transonic small animal flowmeters.

RESULTS

Injection of corticotropin increased blood pressure, water intake, urine volume, and plasma sodium concentration, and decreased body weight and plasma potassium concentration. It increased cardiac output (P < 0.01), mesenteric blood flow (P < 0.05), and renal vascular resistance (P < 0.05), and decreased renal blood flow (P < 0.05), but did not change calculated total peripheral resistance, hindquarter blood flow, mesenteric or hindquarter vascular resistance. L-arginine prevented corticotropin-induced rises in blood pressure (P < 0.001) and renal vascular resistance (P < 0.05), and a fall in renal blood flow (P < 0.05), but did not affect other hemodynamic variables.

CONCLUSION

The hemodynamic profile of corticotropin-induced hypertension in the rat is characterized by a rise in cardiac output and renal vascular resistance, a fall in renal blood flow, but no change in total peripheral resistance, hindquarter blood flow, mesenteric vascular resistance, or hindquarter vascular resistance. L-arginine prevented corticotropin-induced rises both in blood pressure and in renal vascular resistance in the rat. These data suggest that the increase in renal vascular resistance might play a role in corticotropin-induced hypertension in the rat.

Glucocorticoids and hypertension in man

Abnormalities of cortisol production or metabolism are involved in the genesis of hypertension in Cushing's syndrome, apparent mineralocorticoid excess and liquorice abuse and possibly in chronic renal failure and essential hypertension. We have studied the physiological mechanisms by which cortisol raises blood pressure in short term studies of cortisol administration in normal men. Cortisol induced hypertension cannot be explained by increases in vasopressor or decreases in vasodepressor hormone concentrations, or by any increase in sympathetic nervous activity. The hypertension is accompanied by substantial sodium retention but a significant component of the blood pressure rise is sodium independent. The hypertension is characterized by an increase in cardiac output but a rise in output is not essential for the rise in blood pressure. Our working hypothesis is that cortisol induced hypertension is a consequence of increases in renal vascular resistance.

Mechanisms of cortisol-induced hypertension in humans

There is emerging evidence that cortisol plays a significantly greater role in human hypertension than previously thought. Apart from the well recognized role of cortisol in the hypertension of Cushing's syndrome, local cortisol excess has been recognized as responsible for rare forms of hypertension such as apparent mineralocorticoid excess and licorice abuse and more recently implicated in the hypertension of chronic renal failure, hypertension related to low birth weight and essential hypertension. Although cortisol-induced hypertension is characterized by sodium retention and volume expansion, studies with synthetic glucocorticoids or sodium restriction suggest that the hypertension is, to a substantial degree, independent of sodium and volume. Increase in cardiac output is not essential for cortisol-induced blood pressure rise but the precise role of increases in total or regional peripheral resistance as a primary mechanism has nto been determined. Increased pressor responsiveness, particularly to catechols, is a prominent feature but whether these changes are sufficient to account for the hypertension remains unclear. There is no evidence for increased sympathetic nervous activity as judged by measurements of plasma catcholamines, neuropeptide-Y, or resting noradrenaline spillover rate. Responses to mental stress or maximal hand-grip are unchanged and baroreflex sensitivity is increased. Octreotide profoundly reduced the elevated plasma insulin concentrations seen with cortisol administration but had no effect on the rise in blood pressure.

Studies on the mechanisms of glucocorticoid hypertension in humans

Hypertension is a common feature of both Cushing's syndrome, which is relatively rare, and iatrogenic steroid administration, which is much more common. Cardiovascular mortality and morbidity are very significant in patients with both naturally occurring and iatrogenic disease. The mechanism of glucocorticoid induced hypertension in man remains undefined. Contrary to previous notions, it does not reflect urinary sodium retention or volume expansion. Increased pressor responsiveness may be an important contributor to the rise in blood pressure.

Pressor responsiveness in corticosteroid-induced hypertension in humans

In previous studies short-term cortisol increased cold pressor responses and the rise in forearm vascular resistance accompanying intra-arterial norepinephrine without an increase in overall resting sympathetic nervous activity. The present study examined whether these alterations in pressor response are glucocorticoid or mineralocorticoid effects, or both. Normal male subjects (n = 12) received either fludrocortisone, 0.3 mg daily (n = 6), or dexamethasone, 3 mg daily (n = 6), for 7 days. Hemodynamic studies were performed before and on day 7 of treatment. Fludrocortisone increased body weight from 69.3 +/- 1.8 to 71.1 +/- 2 kg (p less than 0.001), cardiac output from 5.0 to 6.0 l/min (+/- 0.1, p less than 0.01), mean arterial pressure from 82 +/- 1 to 91 +/- 1 mm Hg (p less than 0.001), cold pressor responsiveness from 13.0 to 39.0 mm Hg/ml per 100 ml per minute (R units) (+/- 4.3, p less than 0.01), and forearm vascular response to intra-arterial norepinephrine (F = 59.4, p less than 0.01) and angiotensin II (F = 30.8, p less than 0.01) infusions. Total peripheral resistance fell from 22.0 to 20.1 mm Hg/l per minute (+/- 0.3, p less than 0.05). Dexamethasone did not increase cardiac output, 5.1 to 5.2 l/min (+/- 0.1), or body weight but did increase mean arterial pressure from 82 +/- 3 to 91 +/- 3 mm Hg (p less than 0.001), cold pressor responsiveness from 8.6 to 17.1 R units (+/- 2.8, p less than 0.05), and forearm vascular response to intra-arterial norepinephrine (F = 33.0, p less than 0.01) and angiotensin II (F = 54.9, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Thromboxane mediates renal hemodynamic response to infused angiotensin II

Since we had found that angiotensin II (Ang II), but not phenylephrine (PE), increased the excretion of thromboxane (Tx) and raised mean arterial pressure (MAP) by a Tx-dependent mechanism, we tested the role of TxA2 in mediating Ang II-induced changes in renal hemodynamics. For series 1, groups of anesthetized rats received an i.v. infusion of Ang II (50 ng.kg-1.min-1). When infused with a vehicle, Ang II increased MAP, renal vascular resistance (RVR) and the excretion of TxB2 factored by GFR. A PGH2-TxA2 receptor antagonist, SQ-29,548, or three days of pretreatment with a TxA2 synthase inhibitor UK-38,485, which reduced excretion of TxB2 by 80%, blunted the rise in MAP and RVR induced by Ang II. In contrast, three days of pretreatment with indomethacin did not alter the renal vascular response to Ang II. For series 2, groups of rats received Ang II at a higher rate (500 ng.kg-1.min-1) while the RPP was stabilized at +11 to +15 mm Hg with a suprarenal aortic clamp. SQ-29,548 and UK-38,485 both prevented Ang II-induced reductions in GFR and blocked 80% of the increase in RVR. For series 3, infusions of phenylephrine at an equipressor dose to series 2 of 30 micrograms.kg-1.min-1 with control of RPP at +14 mm Hg also increased RVR but this was not blunted by SQ-29,548.

IN CONCLUSION

1.) infusion of Ang II increases excretion of filtered TxB2, causes dose-dependent increases in RVR and, at high doses, reduces GFR.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrocortisone-induced hypertension in humans: pressor responsiveness and sympathetic function

Oral hydrocortisone increases blood pressure and enhances pressor responsiveness in normal human subjects. We studied the effects of 1 week of oral hydrocortisone (200 mg/day) on blood pressure, cardiac output, total peripheral resistance, forearm vascular resistance, and norepinephrine spillover to plasma in eight healthy male volunteers. Although diastolic blood pressure remained unchanged, systolic blood pressure increased from 119 to 135 mm Hg (SED +/- 3.4, p less than 0.01), associated with an increased cardiac output (5.85-7.73 l/min, SED +/- 0.46, p less than 0.01). Total peripheral vascular resistance fell from 15.1 to 12.2 mm Hg/l/min (SED +/- 1.03, p less than 0.05). Resting forearm vascular resistance remained unchanged, but the reflex response to the cold pressor test was accentuated, the rise in resistance increasing from 10.5 mm Hg/ml/100 ml/min (R units) before treatment to 32.6 R units after treatment (SED +/- 6.4, p less than 0.025). The rise in forearm vascular resistance accompanying intra-arterial norepinephrine (25, 50, and 100 ng/min) was also significantly greater after hydrocortisone, increasing from an average of 14.9 +/- 2.4 R units before treatment to 35.1 +/- 5.5 R units after hydrocortisone (SED +/- 6.0, p less than 0.05). A shift to the left in the dose-response relation and fall in threshold suggested increased sensitivity to norepinephrine after treatment. Measurement of resting norepinephrine spillover rate to plasma and norepinephrine uptake indicated that overall resting sympathetic nervous system activity was not increased. The rise in resting blood pressure with hydrocortisone is associated with an increased cardiac output (presumably due to increased blood volume).(ABSTRACT TRUNCATED AT 250 WORDS)