Chronic ACE-inhibitor treatment and adrenergic mechanisms in spontaneously hypertensive rats

A Case Report of Lifesaving Intravenous Bolus Epinephrine Administration in a Case of Severe Refractory Anaphylactic Shock

Anaphylaxis is a life-threatening response to various types of allergens. Early recognition and management are crucial for reducing mortality. This case report highlights a 31-year-old male with a background of hypertension who presented to the emergency department with nausea, vomiting, right flank pain, headache, and elevated blood pressure (BP) of 212/134 mmHg. The patient was started on stat captopril 12.5 mg tablet and stat amlodipine 5 mg tablet for his high BP and stat diclofenac 75 mg (1 mg/kg) intramuscular (IM) for his flank pain. Two minutes later the patient started developing swelling of his mucosal membranes with no urticaria or rashes and his BP suddenly dropped and was unrecordable. First-line management was immediately initiated including the administration of two standard adult doses of IM epinephrine of 500 mcg each with a 5-minute interval. The BP remained undetectable; accordingly, a third IM epinephrine dose of 500 mcg was administered along with an intravenous (IV) epinephrine drip initiated at a rate of 4 mcg/min. The BP became 60/40 mmHg but kept dropping, thus an IV epinephrine bolus of 300 mcg (4 mcg/kg) was given along with the ongoing IV epinephrine drip. BP increased to 126/75 mmHg. While on the IV epinephrine drip the BP dropped again to 88/59 mmHg, a second IV epinephrine bolus of 200 mcg (2.6 mcg/kg) was given and the BP became 140/90 mmHg and recovery was achieved. Emergency cases require immediate recognition and intervention. Currently, IM epinephrine is the primary treatment for anaphylaxis. We hope our case report contributes to the database on severe refractory anaphylaxis by discussing a successful case where IV bolus epinephrine was used to prevent imminent cardiovascular collapse. Highlighting the need for appropriate escalation of management given the availability of physicians with expertise.

DPP4 (Dipeptidyl Peptidase-4) Inhibition Increases Catecholamines Without Increasing Blood Pressure During Sustained ACE (Angiotensin-Converting Enzyme) Inhibitor Treatment

BACKGROUND

DPP4 (dipeptidyl peptidase-4) inhibitors comprise a class of oral diabetes medication that have the potential for off-target cardiovascular effects. We previously showed that DPP4 inhibition attenuates the hypotensive effect of acute ACE (angiotensin-converting enzyme) inhibition and increases norepinephrine. Here, we investigated the effects of DPP4 during sustained ACE inhibition compared with during therapy with an ARB (angiotensin receptor blocker) or calcium channel blocker (neutral comparator) in a randomized, double-blinded crossover study.

METHODS

We enrolled 106 adults with type 2 diabetes and hypertension and 100 received intervention. Subjects were randomized to one of 3 blood pressure arms: ramipril, valsartan, or amlodipine for a total of 15 weeks and received 3 one-week crossover therapies in random order: placebo + placebo, sitagliptin + placebo, and sitagliptin + aprepitant separated by 4-week washout.

RESULTS

We found that DPP4 inhibition increased norepinephrine during ramipril but did not increase blood pressure. Aprepitant, a NK1 (substance P) receptor blocker, lowered standing heart rate during renin-angiotensin-aldosterone system blockade with ramipril or valsartan.

CONCLUSIONS

Increased catecholamines during concurrent ACE and DPP4 inhibition may contribute to cardiovascular complications in patients predisposed to heart failure.

Comparative study of the effects of lacidipine and enalapril on the left ventricular cardiomyocyte remodeling in spontaneously hypertensive rats

Antihypertensive medications are the most efficient drugs in achieving regression of myocardial hypertrophy in both clinical studies and animal models of hypertension. Nevertheless, there is a lack of clear and concise comparative study of their effects on the modulation of cardiomyocyte morphology and function. Here, we assessed the tissue-protective actions of 2 of these drugs, the calcium channel blocker lacidipine (3 mg/kg/day) and the angiotensin-converting enzyme-inhibitor enalapril (10 mg/kg/day) in vivo, after 8 weeks of treatment of 12-week-old spontaneously hypertensive rats, as well as in vitro, after short-term (4 min) application to isolated cardiomyocytes. Left ventricular hypertrophy (LVH) was compared at organ, tissue, and single-cell level. Our data showed that both drugs prevented the LVH of 20-week-old spontaneously hypertensive rats, but only lacidipine significantly decreased the cardiomyocyte size. Similarly, the single-cell contractility was significantly lowered in lacidipine-treated rats only. The effect of lacidipine was initiated shortly after exposure to the drug in a dose-dependent manner at 0.5 Hz, as well as at 2 Hz, with EC(50) of 10(-7) mol/L. These results can help in understanding the effects of these drugs on the prevention of LVH.

Angiotensin converting enzyme inhibition improves cardiac neuronal uptake of noradrenaline in spontaneously hypertensive rats

OBJECTIVES

It has been shown that a diminished sympathetic activity contributes to the hypotensive and cardioprotective actions of angiotensin converting enzyme (ACE) inhibitors (ACEI). Besides an inhibition of central sympathetic tone and peripheral noradrenaline release, we hypothesized that the interactions of ACEI with the sympathetic system may include a modulation of neuronal catecholamine uptake by peripheral nerves.

DESIGN

We investigated the influence of fosinopril on noradrenergic uptake into cardiac neurones in vitro and in vivo in acute and chronic models.

METHODS AND RESULTS

Acute administration of fosinoprilat to isolated perfused rat hearts increased the extraction of [3H]-noradrenaline from the perfusate by 39%. Treatment (14 days) of spontaneously hypertensive rats (SHR) with fosinopril (20 mg/kg per day) enhanced the cardiac uptake of i.v. administered [3H]-noradrenaline by 28%. The endogenous left ventricular content of noradrenaline was increased by 49% after an antihypertensive treatment of SHR with fosinopril (20 mg/kg per day). Identical increases in cardiac noradrenaline stores (53%) were observed in SHR treated with a blood pressure ineffective dose of fosinopril (0.2 mg/kg per day). The myocardial content of adrenaline was increased in parallel to noradrenaline after both dose regimes.

CONCLUSIONS

It is concluded that ACEI increases neuronal uptake of catecholamines in SHR in a blood pressure-independent manner. This effect occurs acutely and is independent of central sympathetic activity. Therefore, we hypothesize that ACEI modulate the activity of the cardiac noradrenaline transporter by direct activation. The improved uptake of noradrenaline may contribute to the antihypertensive and cardioprotective effects of ACEI.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

Attenuation by ACE inhibitor drugs of alpha-adrenoceptor sensitivity in human vessels: possible differences related to drug lipophilicity

AIMS

We investigated the effect of angiotensin converting enzyme inhibitors (ACEIs) on postsynaptic adrenoceptor sensitivity and compared the effect of the lipophilic ACEI, quinapril, and that of hydrophilic agent, enalapril in human vessels.

METHODS

Alpha-adrenoceptor sensitivity was evaluated using the dorsal hand vein compliance technique. The dose-response curves of vasoconstriction to phenylephrine and prostaglandin F2alpha were obtained in healthy male volunteers.

RESULTS

The ACEIs shifted the dose-response curve of phenylephrine to the right and raised the median effective dose (ED50; 189.3 (57.6 ng min(-1)) of phenylephrine. Following quinapril administration, ED50 increased to 481.1 (101.8 ngmin(-1) compared with 266.8 (55.8 ngmin(-1) after enalapril (95% CI for differences; 31.1-397.5 ng min(-1)). Quinapril administration had no effect on the dose-response curve of PGF2alpha.

CONCLUSIONS

ACE inhibition attenuates alpha-adrenoceptor sensitivity in human vessels. The effect of quinapril, a lipophilic ACEI, was greater than that of enalapril, a hydrophilic ACEI. Lipophilic ACEIs may be more potent in vasodilating effect than hydrophilic ACEIs. Angiotensin II concentration in tissue rather than that in plasma may contribute to the alpha-adrenoceptor sensitivity of the vessels.

Effects of candesartan cilexetil and enalapril on structural alterations and endothelial function in small resistance arteries of spontaneously hypertensive rats

It was previously observed that a significant regression of structural alterations and endothelial dysfunction in mesenteric small arteries of spontaneously hypertensive rats (SHRs) may be obtained after therapy with angiotensin-converting enzyme (ACE) inhibitors. It is not clear whether angiotensin II-type 1 receptor blockers may share this properties. We evaluated the effects of the ACE inhibitor enalapril and of the angiotensin II-receptor blocker candesartan cilexetil on structural alterations of mesenteric small resistance arteries, on cardiac mass, and on endothelial function in SHRs. Seventy-three rats were included in the study. Sixteen SHRs were treated with enalapril and 21 with candesartan cilexetil, whereas 18 Wistar-Kyoto (WKY) and 18 SHRs were untreated. Enalapril and candesartan cilexetil were administered in the drinking water from weeks 4 to 12 of age. Blood pressure was measured noninvasively every week. The rats were killed at the end of the treatment period, after 3 or 4 days of therapeutic washout. Heart weight/body weight ratio (HW/BW) was measured. Mesenteric arterioles were dissected and mounted on a micromyograph (Mulvany's technique). Then the media-to-lumen ratio (M/L) was evaluated. In addition, endothelium-dependent and endothelium-independent relaxation was evaluated by dose-response curves to acetylcholine (in the presence or absence of a bradykinin-receptor blocker and of indomethacin) and sodium nitroprusside. Systolic blood pressure was significantly reduced by both drugs, compared with untreated SHRs, although the hypotensive effect was greater with enalapril than with candesartan cilexetil. A significant reduction of M/L of mesenteric small arteries and of HW/BW was observed in SHRs treated with candesartan cilexetil or enalapril. A significant improvement of endothelial function, as evaluated by a dose-response to acetylcholine, was observed. The acetylcholine-induced vasodilatation was similar after addition to the organ bath of a selective blocker of bradykinin receptors, thus suggesting a minor role (if any) of the increased local availability of bradykinin, as a consequence of inhibition of ACE, in the improvement of endothelial function observed after enalapril treatment. In addition to a satisfactory antihypertensive effect observed with both drugs, candesartan cilexetil and enalapril were proven to be equally effective in reducing structural alterations in mesenteric small resistance arteries, in normalizing cardiac mass, and in improving endothelial function. The inhibition of bradykinin breakdown does not seem to be involved in the improvement of endothelial dysfunction observed with ACE inhibitors.

Angiotensin converting enzyme inhibition and calcium antagonism attenuate streptozotocin-diabetes-associated mesenteric vascular hypertrophy independently of their hypotensive action

OBJECTIVES

To investigate the relative roles of angiotensin II, bradykinin, and calcium-dependent pathways in the genesis of mesenteric vascular hypertrophy in experimental diabetes.

DESIGN

Streptozotocin-induced diabetic Sprague-Dawley rats were randomly allocated to these treatments for 24 weeks: no treatment; ramipril at a hypotensive dose; ramipril plus the bradykinin type 2 receptor blocker icatibant; icatibant alone; ramipril at a low dose; the angiotensin II type 1 receptor antagonist, valsartan; the dihydropyridine calcium antagonist, lacidipine; and the nondihydropyridine calcium antagonist mibefradil.

METHODS

Systolic blood pressure was serially measured every 4 weeks by tail-cuff plethysmography. We assessed the vascular architecture in sections of mesenteric arteries obtained after in-vivo perfusion, which were stained with an antibody to alpha-smooth muscle actin.

RESULTS

Both blood pressure and the mesenteric arterial wall: lumen ratio were reduced by administration of ramipril, at the high dose, either alone or in combination with icatibant, and also by valsartan. Treatment either with the low dose of ramipril or with the calcium antagonists lacidipine and mibefradil was associated with a decrease in the wall : lumen ratio of the mesenteric arteries without influencing blood pressure.

CONCLUSIONS

These findings demonstrate that blockade both of angiotensin II-dependent and of calcium-dependent pathways attenuates mesenteric vascular hypertrophy in experimental diabetes. Furthermore, the antitrophic effects of these antihypertensive agents may be independent of their hypotensive effects.

Early, short-term treatment with captopril permanently attenuates cardiovascular changes in spontaneously hypertensive rats

The purpose of the current study was to determine if early, short-term treatment of spontaneously hypertensive rats (SHR) with captopril would cause a persistent attenuation of the structural alterations of the heart, aorta, and coronary arteries that are commonly seen in adult SHR. Therefore, mating pairs of SHR were treated with captopril and the pups were kept on captopril (SHRC) or were taken off captopril at two months (SHROC). Untreated SHR and Wistar-Kyoto (WKY) rats were mated and served as controls. At 8-10 months of age, heart weight and left ventricular weight/body weight ratios were increased in SHR compared to WKY, SHRC, and SHROC. Aortic medial areas of SHR and SHROC were similar and were larger than WKY and SHRC. Nuclear density in SHR and SHROC was less than WKY and SHRC suggesting hypertrophy of the medial wall. In coronary vessels, medial thickness was greatest in SHR, while there was no difference among WKY, SHRC, SHROC. These data suggest that early, short-term treatment of SHR with captopril permanently attenuated the structural alterations in the heart and coronary vessels that are commonly seen in adult SHR.