Effect of propranolol on plasma norepinephrine during sodium nitroprusside-induced hypotension

The sympathetic/beta-adrenergic pathway mediates irisin regulation of cardiac functions in zebrafish

Irisin is a 23 kDa myokine encoded in its precursor, fibronectin type III domain containing 5 (FNDC5). The exercise-induced increase in the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α) promotes FNDC5 mRNA, followed by the proteolytic cleavage of FNDC5 to release irisin from the skeletal or cardiac muscle into the blood. Irisin is abundantly expressed in skeletal and cardiac muscle and plays an important role in feeding, modulates appetite regulatory peptides, and regulates cardiovascular functions in zebrafish. In order to determine the potential mechanisms of acute irisin effects, in this research, we explored whether adrenergic or muscarinic pathways mediate the cardiovascular effects of irisin. Propranolol (100 ng/g B·W) alone modulated cardiac functions, and when injected in combination with irisin (0.1 ng/g B·W) attenuated the effects of irisin in regulating cardiovascular functions in zebrafish at 15 min post-injection. Atropine (100 ng/g B·W) modulated cardiovascular physiology in the absence of irisin, while it was ineffective in influencing irisin-induced effects on cardiovascular functions in zebrafish. At 1 h post-injection, irisin downregulated PGC-1 alpha mRNA, myostatin-a and myostatin-b mRNA expression in zebrafish heart and skeletal muscle. Propranolol alone had no effect on the expression of these mRNAs in zebrafish and did not alter the irisin-induced changes in expression. At 1 h post-injection, irisin siRNA downregulated PGC-1 alpha, troponin C and troponin T2D mRNA expression, while upregulating myostatin a and b mRNA expression in zebrafish heart and skeletal muscle. Atropine alone had no effects on mRNA expression, and was unable to alter effects on mRNA expression of siRNA. Overall, this research identified a role for the sympathetic/beta-adrenergic pathway in regulating irisin effects on cardiovascular physiology and cardiac gene expression in zebrafish.

Plethysmographic evaluation of the vascular effects of human calcitonin gene-related peptide in man

Calcitonin gene-related peptide (CGRP) is a neuropeptide with potent cardiovascular effects that include positive inotropic and chronotropic actions systemic vasodilation, and hypotension in animals and in man. The mechanism of action of CGRP is still, however, not clear, and in particular it is not known whether vasodilation by CGRP occurs by changes in cutaneous or in muscular blood flow, or both. The aim of the study was, therefore, to evaluate the cutaneous and muscular blood flow, at rest and after ischemic test, induced by an IV bolus 25 micrograms human CGRP infusion in 5 healthy normotensive volunteers, using a strain gauge plethysmographic procedure with venous occlusion. Human CGRP provoked a transient but significant decrease in systolic and diastolic blood pressure, associated with tachycardia, marked flushing, a significant increase in plasma noradrenaline, adrenaline, and cyclic AMP levels, and a slight, but significant, decrease in serum total calcium. Moreover, a significant increase in the carpal cutaneous blood flow at rest was observed, with no significant change in the lower extremity muscular blood flow at rest and after ischemic test. Finally human CGRP produced a significant increase in the venous partial O2 pressure and in the hematocrit and a significant decrease in the venous partial CO2 pressure. The results of the present study confirm the acute cardiovascular and metabolic effects of CGRP. In fact, hypotension, tachycardia, flushing, and the increased cutaneous blood flow indicate a systemic vasodilation by the neuropeptide, with a secondary sympathetic response, as documented by the augmented catecholamine and cyclic AMP plasma levels.

Comparison of intravenous nitroprusside, nitroprusside-captopril, and nitroglycerin for deliberate hypotension during posterior spine fusion in adults

Three techniques for deliberate hypotension (mean arterial pressure, 60 to 70 mmHg) were prospectively compared in adults undergoing posterior spine fusion. Patients received either IV sodium nitroprusside, sodium nitroprusside with oral captopril pretreatment, or IV nitroglycerin. Patient groups were comparable in age, sex, weight, baseline hemodynamic and laboratory parameters, duration of surgery, and duration of hypotension. Absolute blood loss was significantly less in the group receiving nitroglycerin; however, there were no differences between groups when corrected for operative exposure (milliliter per spine segment exposed). Nitroprusside was effective in producing target blood pressure in all patients. Nitroglycerin was ineffective in two patients and two other patients required greater than 20 micrograms/kg/min. Both groups receiving nitroprusside developed significant postinfusion increases in arterial pressure. Blood pressure fell significantly after induction of anesthesia in patients receiving captopril. Cardiac index, heart rate, pulmonary capillary wedge pressure, intrapulmonary shunt, and arterial blood gases were comparable and did not change significantly in any group. Systemic vascular resistance fell during infusion in all groups and remained depressed after infusion in patients receiving nitroglycerin. Plasma renin activity was significantly increased in the group receiving captopril due to loss of feedback inhibition of renin release and rose significantly during infusion in those patients receiving nitroprusside alone. There were no complications. Nitroprusside with and without captopril pretreatment was associated with postoperative increases in arterial pressure, although not to hypertensive levels, probably due to loss of captopril activity after single-dose administration. The use of nitroglycerin was limited by lack of potency. There was no demonstrable clinical advantage for any of the three techniques.

Effect of captopril on changes in plasma noradrenaline induced by sodium nitroprusside

There is much animal data to suggest that angiotensin II has a regulatory role in noradrenaline release. We sought evidence for such a mechanism in man by pretreating six normal volunteers with captopril (50 mg) or placebo and then infusing them with incremental doses of sodium nitroprusside. Pretreatment with captopril had no significant effect on the mean arterial pressure, heart rate or plasma noradrenaline response to sodium nitroprusside, despite increasing plasma renin activity. This suggests that in normotensive salt replete man, normal levels of angiotensin II do not exert any tonic effect on noradrenaline release.

Single and combined therapy for systemic hypertension with propranolol, hydralazine and hydrochlorothiazide: hemodynamic and neuroendocrine mechanisms of action

The antihypertensive mechanisms of single and combined therapy with a beta-adrenergic antagonist (propranolol) and a vasodilator (hydralazine) were investigated in 9 patients with moderately severe hypertension, who were receiving maintenance diuretic (hydrochlorothiazide) treatment. Hemodynamic and neuroendocrine responses were determined at rest and during lower body negative pressure, and dynamic and static exercise stress after the chronic administration of propranolol and hydralazine, given alone or in combination. All 3 drug regimens, each administered for at least 10 weeks, reduced blood pressure (p less than 0.05) compared with diuretic-only therapy in patients at rest, in both the supine and standing position, and during lower body negative pressure and dynamic exercise. There was a significant additive antihypertensive effect when propranolol and hydralazine were combined. Only combination therapy effectively lowered pressure during static exercise. The regimens produced divergent effects on the supine cardiac output: a decrease with propranolol (p less than 0.05), no change with combination therapy and an increase with hydralazine (p less than 0.05). Both hydralazine and combination therapy significantly reduced supine total peripheral resistance (p less than 0.05), whereas propranolol produced no change. All 3 drug treatments significantly reduced total peripheral resistance during upright rest and dynamic exercise (p less than 0.05), without changing cardiac output or maximal exercise capacity. During exercise, cardiac output was maintained in patients treated with propranolol and in those treated with combined therapy by increases in stroke volume (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Baroreflex sensitivity modulates vasodepressor response to nitroprusside

Baroreflex activity is a determinant of the homeostatic response to alteration in blood pressure. We examined the factors that determine the magnitude of the vasodepressor response to sequential incremental intravenous infusions of sodium nitroprusside (NP), 0.05 to 6.4 micrograms/kg/min, in eight male patients with essential hypertension. Each infusion level was of 10 minutes' duration. Change from control values of mean arterial pressure (delta MAP), heart rate (delta HR) and plasma norepinephrine (delta NE) were obtained at the end of each infusion level. Significant correlations were found between delta MAP vs log dose NP, delta HR vs delta MAP and delta NE vs delta MAP for each patient (p less than 0.05). However, the slopes of these relationships varied widely between subjects and were significantly correlated with the control blood pressure of each patient. In addition, the sympathetic responsiveness, as measured by delta NE vs delta MAP, was inversely correlated with the degree of vasodepressor response seen. Thus, the magnitude of the vasodepressor response was determined by two major factors: 1) the predrug blood pressure, possibly reflecting altered vascular geometry with hypertension; 2) the degree of sympathetic response, which probably acts by mediating the degree of reflex alpha-adrenergic-mediated arteriolar vasoconstriction.