Renin and angiotensin tachyphylaxis

Tn the conscious dog, synthetic angioteiisin and crude hog renin produce dose-response curves which run strictly parallel if the max imum blood pressure attained is taken as the parameter. Repeated injections of small or medium closes of angioteitsiri or of small doses of renin do not l)roduce tachyphylaxis. In contrast, high closes of renin, as well as of angiotensin, diminish or abolish the pressor response to subsequent injections of the same substances. Furthermore, cros.s tachyphylaxis between renin and arigiotensin can be demon strated. infusions of renin and angiotensin in various dosages elicit characteristic blood pressure changes, which are very similar for both substances and also display tachyphy laxis at sufficiently high doses. It is concluded that so-called renin tachyphylaxis is, in fact, due to a diminished response to angiotensin. This might be takeii as an indirect proof that renin liberates aiigiotensiri not only iii vitro hut. also in the organism.

The effect of reserpine on the pressor response to injection of 2-halogenoethylamines

Dibenamine-like compounds sometimes caused an increase in blood pressure when injected intravenously in mammals. This response varied with species, with the preparation, and with the structure of the compound. The response became smaller after repeated injections. In spinal atropinized rats injected with hexamethonium 5 mg/kg this pressor effect produced by injection of the adrenaline antagonist, compound AT3 [ethylfluoren-9-yl(2-iodoethyl)amine hydriodide], was reduced by prior treatment for five days with 1 mg/kg reserpine. Acute adrenalectomy also reduced this effect of the adrenaline antagonist; reserpine plus adrenalectomy abolished it. Subsequent injection of adrenaline and noradrenaline restored it.

General and pulmonary hemodynamic effects of pure decapeptide angiotensin in normotensive man

Purified natural decapeptide angiotensin was infused intravenously at a constant rate for 32 minutes in 5 normotensive subjects. There was no significant change in the cardiac output. There were significant increases in the pulmonary artery, the pulmonary wedge, and the brachial artery pressures. There were significant increases in the systemic vascular and the total pulmonary resistances. There was no significant change in the pulmonary arteriolar resistance. The data indicate that angiotensin I produces peripheral arteriolar constriction and fail to demonstrate a concomitant pulmonary arteriolar constriction. Thus, they are consistent with an hypothesis implicating angiotensin as a causative agent in human essential hypertension.

A study of antagonists of 5-hydroxytryptamine and catechol amines on the rat's blood pressure

The effects of 5-hydroxytryptamine on the blood pressure of anaesthetized rats depended on the dose and the initial level of blood pressure. At medium blood pressure levels, 5-hydroxytryptamine gave a depressor response and sometimes a pressor response which was more evident with large doses. The depressor effect was less apparent or even absent at low, and more pronounced at high, blood pressure levels, and the converse applied to the pressor components. Adenosine also gave a depressor and pressor response. Lysergic acid diethylamide, dihydroergotamine, 1-(3,4-dichlorophenyl)-2-isopropylaminoethanol (a dichloro analogue of isoprenaline), dibenamine and 1-benzyl-5-methoxy-2-methyltryptamine antagonized 5-hydroxytryptamine and catechol amines. Lysergic acid diethylamide and 1-benzyl-5-methoxy-2-methyltryptamine were more effective against 5-hydroxytryptamine, 1-(3,4-dichlorophenyl)-2-isopropylaminoethanol and dibenamine against catechol amines; dihydroergotamine was equally effective against both groups. These antagonists fell into two groups according to their action against the two types of effects (depressor and pressor) of 5-hydroxytryptamine: lysergic acid diethylamide and 1-(3,4-dichlorophenyl)2-isopropylaminoethanol acted preferentially against depressor effects; 1-benzyl-5-methoxy-2-methyltryptamine and dibenamine preferentially against pressor; dihydroergotamine was not assignable to either group. Adenosine was affected similarly, but less than 5-hydroxytryptamine.

Factors influencing the hypertensive effect of eserine in the rat

Several factors influencing the hypertensive effect of eserine in the rat were investigated. Pretreatment with reserpine regularly depressed or abolished the hypertensive response to eserine. The slow intravenous infusion of either noradrenaline, dihydroxyphenylalanine or 5-hydroxytryptamine only occasionally restored the hypertensive effect of eserine in reserpine-treated rats. Bretylium and choline 2,6-xylyl ether bromide significantly depressed or even abolished the hypertensive effect of eserine. The effect of bretylium was stronger than that of choline 2,6-xylyl ether bromide. Cocaine was found to antagonize the action of bretylium on the response to eserine. In doses which significantly depressed the action of eserine bretylium did not inhibit the hypertension due to excitation of medullary centres induced by clamping the common carotid arteries. Lowering of body temperature abolished the hypertensive effect of eserine. Pretreatment with isopropylisoniazid did not antagonize the inhibitory action of reserpine on the hypertensive response to eserine. It is concluded that the present experiments indicate that the hypertensive effect of eserine in the rat is due to central activation of adrenergic nervous elements. Liberation of noradrenaline (and adrenaline) from the adrenals and from the blood vessels by eserine is an insignificant factor in producing the hypertensive response to eserine.

Evaluation of the pressor, cardiac, and renal hemodynamic properties of angiotensin II in man

These data demonstrate that in normal subjects angiotensin II is 10 times as potent as norepinephrine, which it resembles hemodynamically. An increase in the systolic pressure is associated with significant increase in diastolic pressure, increase in venous pressure, decrease in heart rate, slight decrease in cardiac output with striking increase in total peripheral resistance, decrease in renal blood flow, decreased glomerular filtration rate, increase in filtration fraction, arid slight decrease in urinary volume.

Preliminary studies of patients in shock suggest that angiotensin II is two or three times as potent as norepinephrine. Continuous administration is not associated with the development of resistance or tachyphylaxis, nor does sloughing of tissues occur when there is leakage outside the vein.

Cholinergic-like effects of hypertonic solutions

A consideration of the physiological effects of hypertonic solutions suggested that certain aspects might be cholinergic. This hypothesis has been investigated. Concentrated urea, glucose or salt solutions were rapidly injected intravenously into 25 anesthetized dogs. Systemic and pulmonary vascular pressures were monitored and compared with those obtained with acetylcholine. Data were collected before and after cervical vagotomy or treatment with physostigmine or atropine. The effects of hyperosmotic media and acetylcholine were similar. Both, in lower concentrations, produced transitory vasodilatation; bradycardia and cardiac irregularities became superimposed with stronger solutions. However, the hypertonic phenomena were ameliorated by vagotomy, unaffected by atropine and only partially potentiated by Eserine. Vasodilatation required a latent period of about 10 seconds beyond the circulation time. The evidence suggests that hypertonic materials evoke release of acetylcholine as a result of reflex and central nervous excitation. In addition, they exert a direct cholinergic-like action, mediated possibly through depolarization of cholinergically innervated effector cells from osmotic dehydration.

Effects of atropine and isoproterenol on cardiac output, central venous pressure, and mean transit time of indicators placed at three different sites in the venous system

Two milligrams of atropine given intravenously increased the cardiac output, the mean arterial pressure, and the heart rate and lowered the central venous pressure, stroke output, and peripheral resistance. Tsoproterenol given intravenously at the rate of 1 µg. per minute increased the cardiac output with only an average increase in pulse rate of nine beats per minute. The stroke volume was increased. The central venous pressure and the peripheral resistance were decreased. These observations on the circulation were made in the steady state. They demonstrate that the minute output of the heart can be increased by either a rise in rate or an increase in stroke volume in the presence of a fall in central venous pressure. They do not define the order of events leading to the steady state. When the indicator was placed in the superior vena cava, neither atropine nor isoproterenol changed the volume in which the indicator was diluted during its first circulation. Both atropine and isoproterenol decreased the volumes in which the indicators were diluted when they were injected into the antecubital or femoral veins.

Some pharmacological properties of brain ganglioside

The effects of a preparation of purified brain ganglioside and of neuraminic acid have been studied on various pharmacological test preparations. In concentrations of 10 mug/ml. or more, ganglioside stimulates the isolated guinea-pig ileum; graded responses are usually obtained. Various substances, known to antagonize the actions of other stimulant substances, fail to affect the response to ganglioside. Ganglioside and neuraminic acid neither stimulate the superior cervical ganglion of the cat nor do they affect ganglionic transmission. Ganglioside and neuraminic acid did not change the response of the frog rectus abdominis muscle to acetylcholine, nor did they affect the blood pressure of the cat. Ganglioside (2 mug/ml. or more) stimulates the isolated heart of Venus mercenaria, but the response, which develops slowly, decreases with repeated administration of ganglioside. The response is not blocked by 2-bromo-lysergic acid diethylamide and there is no indication that it is due to the liberation of endogenous 5-hydroxytryptamine or related indole compounds. For both the heart of Venus mercenaria and guinea-pig ileum, the activity demonstrated by brain ganglioside is specifically a property of the whole molecule, since neither neuraminic acid itself nor a preparation of brain ganglioside from which only two-thirds of its neuraminic acid had been removed are active.

Some pharmacological actions of synthetic analogues of angiotensinamide

In order to evaluate the importance of some structural features of asparagyl(1)-Valyl(5)-angiotensin II (angiotensinamide) for its pharmacological actions, the relative potencies of angiotensinamide and five peptide analogues were studied on the blood pressure of the rat, the isolated rat uterus and the isolated guinea-pig ileum. All the modifications of the angiotensinamide structure that were studied led to a decrease of potency which, however, was not the same on all three preparations. The importance of the guanido group, the phenolic group and the length of the peptide chain for the pharmacological activities of these peptides is discussed.

Decarboxylase inhibition and blood pressure reduction by alpha-methyl-3,4-dihydroxy-DL-phenylalanine

alpha-Methyl-3,4-dihydroxy-DLphenylalanine has been found to be an effective inhibitor of aromatic amino acid decarboxylation in man. This was shown by decreased formation of serotonin, tryptamine, and tyramine from the precursor amino acids. Reduction of amine biosynthesis is associated with lowering of blood pressure in hypertensive patients and a transient sedative effect.

Cardiac index during intravenous levarterenol infusion in man

Cardiac indices were determined by the Stewart-Hamilton indicator-dilution method during intravenous infusions of levarterenol in 25 human subjects. The rate and duration of the infusion as well as the increase in arterial pressure and bradycardia were varied in order to study their influences on the cardiac index.