Vasopressor actions

Like-wise angiotensin II (9 or 30 rat units per mouse) failed to augment erythropoiesis in polycythemic mice (25). However, similar quantities of both renin and angiotensin II increased blood pressure when administered intravenously to normal rats and mice (Fig. lO). Neither the REF nor the incubation mixture of REF and serum produced any vasopressor action. On the contrary, a slight drop in blood pressure was observed with the REF-serum mixture. This mild vaso-depressor action of the mixt-ure of REF and serum noted in rats and the report of a kinin-forming enzyme in the light-mitochondrial fraction of rat kidneys (2) led us to test the effect of bradykinin on erythropoiesis. Intravenous injections of 2.0 and 20 ug of bradykinin triacetate evoked no demonstrable erythropoietic response in polycythemic mice (Fig. lO). This agent did, however, produce the expected drop in blood pressure of rats. 

Injection of a second dose after the pressor effects of the first have worn off usually causes little or no response, the vascular system remaining insensitive for several hours. This may be due to the appearance of an anti-vaso-pressin in the organism, or, more likely, to the exhaustion of a contractile factor in the vessel walls. Birds for some unexplained reason appear to be immune from the vasopressor action of pituitary extracts. In man, the constricting effect on the capillaries is very conspicuous in the blanching of the skin that follows subcutaneous injection. 

Intake of a large amount of sodium chloride negates the antihypertensive effects of diuretics. Other mechanisms, such as direct vasodilating action, decreased responsiveness to vasopressor agents, stimulation of prostacyclin [35121 -78-9] production, and reduction in the intracellular calcium... 

Dopamine (Intropin) [Vasopressor/Adrenergic] Uses Short-tOTn use in cardiac decompensation secondary to X contractility when no hypovolemia is present T organ p fusion (at low dose) Action Renal dose 2-5 mcg/kg/min Inotropic dose 5-10 mcg/kg/min Pressor dose >10 mcg/kg/min Dose Adults Feds. 5-20 mcg/kg/min by cont inf, start at 5 and t by 5 mcg/kg/min to 20 mcg/kg/min max to effect (mix 400 mg in 250 mL DjW to make 1600 mcg/mL) (see Table 1-3) Caution [C, ] Contra Pheochromocytoma (adrenal gland tumor), VF, sulfite sensitivity Disp Inj 40, 80, 160 mg/mL, premixed 0.8, 1.6, 3.2 mg/mL SE Tach, vasoconstriction, 4- BP, HA, N/V, dyspnea Notes >10 mcg/kg/min X renal p fiision Interactions t Effects W/ a-blockers, diuretics, ergot alkaloids, MAOIs, BBs, anesthetics, phenytoin X effects W/ guanethidine EMS Correct hypovolemia before use use microdrip set or inf pump check soln- discolored... 

Phenylephrine, Nasal (Neo-Synephrine Nasal) (OTC) [Vasopressor/Decongestant] Uses Can be used prior to nasal intubation and NG tube insCTtion to reduce bleeding Action a-Adren gic agonist Dose Adults Feds. 1—2 sprays/nostril q4h (usual 0.25%).Caution [C, +/—] HTN, acute pancreatitis, H, coronary Dz, NAG, h5 pCTth5Toidism Contra Bradycardia, arrhythmias Disp Nasal soln (0.125-0.25%) SE Arrh5rthmias, HTN, nasal irritation, dryness, sneezing, HA Interactions May -1- effects OF nitrates EMS Ocular instillation may dilate pupil... 

Mechanism of Action A vasopressor that forms the active metabolite desglymido-drine, an alphaj-agonist, activating alpha receptors of the arteriolar and venous vasculature. Therapeutic Effect Increases vascular tone and BP. 

It is a vasopressor agent with some structural similarity to adrenaline and has a powerful alpha receptor stimulant action. The pressor response is accompanied by reflex bradycardia. It is used as a nasal decongestant and mydriatic agent and also in the treatment of paroxysmal supraventricular tachycardia. 

Metaraminol has a longer duration of action than some other vasopressors and care should be taken to avoid inducing hypertension. The dose is 0.5-5 mg as a slow intravenous bolus. If necessary, 15-100 mg may be diluted in normal saline (500 ml) and given by infusion. The dose of methoxamine is 2-5 mg intravenously. 

Vasopressin also plays an important role in the short-term regulation of arterial pressure by its vasoconstrictor action. It increases total peripheral resistance when infused in doses less than those required to produce maximum urine concentration. Such doses do not normally increase arterial pressure because the vasopressor activity of the peptide is buffered by a reflex decrease in cardiac output. When the influence of this reflex is removed, eg, in shock, pressor sensitivity to vasopressin is greatly increased. Pressor sensitivity to vasopressin is also enhanced in patients with idiopathic orthostatic hypotension. Higher doses of vasopressin increase blood pressure even when baroreceptor reflexes are intact. 

Mechanism of Action Inhibit angiotensin-converting enzyme (ACE), resulting in decreased plasma angiotensin II which leads to decreased vasopressor activity and decreased aldosterone secretion ... 

Malinowska, B., Schlicker, E., 1993a. Effects of Hi and H3 agonists on the neurogenic vasopressor response in the pithed rat. Agents Actions 38, C254-C256. 

These agents reduce sympathetic outflow from vasopressor centers in the brainstem but allow these centers to retain or even increase their sensitivity to baroreceptor control. Accordingly, the antihypertensive and toxic actions of these drugs are generally less dependent on posture than are the effects of drugs that act directly on peripheral sympathetic neurons. 

Current concepts of resuscitation after local anesthetic cardiotoxicity have been reviewed (17). Vasopressin may be a logical vasopressor in the setting of hypotension, rather than adrenaline, in view of the dysrhythmogenic potential of the latter. Amiodarone is probably of use in the treatment of dysrhythmias. Calcium channel blockers, phenytoin, and bretyllium should be avoided. In terms of new modes of therapy targeted at the specific action of local anesthetics, lipid infusions, propofol, and insulin/ glucose/potassium infusions may all have a role, but further research is necessary. 

Patients with severe hyperthyroidism can have an occult cardiomyopathy that makes them extremely sensitive to beta-blockers. The long duration of action of sotalol in this case necessitated prolonged inotropic and vasopressor support. A shorter-acting beta-blocker, such as esmo-lol, could theoretically be safer in such cases. 

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