Application of Drug–Receptor Theories to Angiotensin

1973 ◽  
Vol 51 (9) ◽  
pp. 665-672 ◽  
Author(s):  
F. Rioux ◽  
W. K. Park ◽  
D. Regoli
Keyword(s):  
New York ◽  
Smooth Muscle ◽  
Rabbit Aorta ◽  
Biologically Active ◽  
Mass Action ◽  
Intrinsic Activity ◽  
Rat Stomach ◽  
Response Curves ◽  
Threshold Phenomenon ◽  
Specific Receptors

The myotropic action of angiotensin II has been studied on two smooth muscle preparations: the strip of rat stomach and of rabbit thoracic aorta. Contractions evoked by angiotensin are not modified by atropine, methysergide, and diphenhydramine on the rat stomach or by phentolamine, methysergide, and diphenhydramine on the rabbit aorta. It appears that angiotensin acts directly on specific receptors and not through release of acetylcholine on the stomach or of noradrenaline on the aorta. Interference by intramural prostaglandins is excluded because angiotensin is equally active on tissues pretreated or not with indomethacin.Dose–response curves obtained with angiotensin on the two tissues are close to the theoretical curves predicted by the mass–action law. The relations stimulus effect is linear, indicating that the extent of the contraction is proportional to the number of receptors occupied by the agonist. No threshold phenomenon or spare receptor capacity could be demonstrated in either tissue. It is therefore concluded that the interaction of angiotensin with its specific receptors in the two smooth muscle preparations can be analyzed quantitatively with the occupation theory by applying the concepts of affinity and intrinsic activity as defined by Ariens in 1964. (Molecular pharmacology. Vol. 1. The mode of action of biologically active compounds. Academic Press, New York.)

Myotropic affinities of angiotensin II and des-Asp1-angiotensin II in rabbit aorta and femoral artery by microassay

1979 ◽  
Vol 57 (11) ◽  
pp. 1256-1266 ◽  
Author(s):  
William H. Waugh ◽  
Theodore E. Bales
Keyword(s):  
Angiotensin Ii ◽  
Femoral Artery ◽  
Rabbit Aorta ◽  
Mass Action ◽  
Intrinsic Activity ◽  
Angiotensin Receptors ◽  
Response Curves ◽  
Contractile Responses ◽  
Increased Sensitivity ◽  
Dose Dependent

Dose-dependent isometric contractions to [Asp1,Ile5]-angiotensin II (AII) and des-Asp1-[Ile5]-angiotensin II (AIII) were obtained with 3-mm-wide rings of rabbit thoracic aorta and femoral artery in microbaths. A period of 2.5–3 h was required to obtain reproducible contractile responses of increased sensitivity. Contractions developed faster and they were much more forceful but less sustained in femoral arterial rings than in aortic rings. Noncumulative dose–response curves with AII and AIII were parallel and reached the same maximum. Peak contractile responses were linearly proportional to the receptor stimulation predicted from the mass action equation and the concept of intrinsic activity relating bath dosage of agonist to the number of myotropic receptors occupied by AII and by AIII. These findings validated measurement of the myotropic affinities of both tissues for AII and AIII by the obtained ED50 values. In 0.6-mL baths, developed with the use of a meshed screen for reoxygenation, the apparent affinities of aortic muscle for AII and AIII averaged 0.149 and 0.0030 nM, respectively. The mean affinities were much greater at 0.594 and 0.236 nM, respectively, in femoral arterial muscle. The myotropic affinity for AIII relative to that for AII averaged 2.26% in the aorta but 40.8% in the femoral artery. The apparent affinities were reduced and contractions less forceful in 0.24-mL baths without regassing. The results suggest that AII and AIII may stimulate the same angiotensin receptors in aorta and femoral artery and that the receptors may be different in structure or immediate environment in these two vascular tissues.

Receptors for bradykinin in rabbit aortae

1977 ◽  
Vol 55 (4) ◽  
pp. 855-867 ◽  
Author(s):  
D. Regoli ◽  
J. Barabé ◽  
W. K. Park
Keyword(s):  
Dose Response ◽  
Rabbit Aorta ◽  
Inhibitory Effect ◽  
Mass Action ◽  
Response Curves ◽  
Terminal Fragment ◽  
Mass Action Law ◽  
New Type ◽  
Specific Receptors ◽  
Stimulation Of

Rabbit aorta strips respond to bradykinin (BK) and to the C-terminal fragment of BK, the octapeptide 1-8 BK (Octa) with sustained contractions which are presumably due to the stimulation of specific receptors, because they remain unchanged in presence of phentolamine, methysergide, mepyramine, 8-Leu-ATII, and indomethacin. Experimental dose–response curves of BK and Octa are very similar to the theoretical curves predicted by the mass-action law and show the classical hyperbolic shape; ratios of doses producing 16% and 84% of maximum effects are 1:20 for Octa and 1:19 for BK. The relations of stimulus and effect are linear, suggesting that the extents of the contractions are proportional to the number of receptors occupied by the agonists.Structure–activity studies performed with fragments and analogues of BK and with analogues of Octa have shown that 8-Phe is essential for activation of the aortic receptor, and plays an important role for the affinity. The octapeptide 1-8 sequence is more favorable than the nonapeptide, because BK (pD2 = 6.40) is less potent than Octa (pD2 = 7.19) and 9-Ala BK is a partial agonist.Antagonists for both Octa and BK have been found by replacing 8-Phe with aliphatic residues (Ala, Nle, Leu, Leu-OMe) in the octapeptide. Affinities of 8-Leu-Octa (pA2 = 6.75) and 8-Leu-OMe-Octa (pA2 = 6.66) for the aortic receptors are fairly high and the antagonism appears to be of the competitive type because pA2 – pA10 is close to 0.95 for both compounds.The inhibitory effect of these two compounds are specific for Octa and BK. It is concluded that rabbit aortae contain a new type of receptor for BK, different from those found in the intestine and the uterus of several species.

The Pressor and Myotropic Effects and the Antagonistic Properties of Several Analogues of Angiotensin II

1972 ◽  
Vol 50 (2) ◽  
pp. 99-112 ◽  
Author(s):  
D. Regoli ◽  
W. K. Park
Keyword(s):  
Angiotensin Ii ◽  
Chemical Structure ◽  
Biological Activities ◽  
Unnatural Amino Acid ◽  
Intrinsic Activity ◽  
Rat Stomach ◽  
Response Curves ◽  
Isolated Organs ◽  
The Right ◽  
The Relationship

The substitution of an unnatural amino acid, 1-aminocyclopentanecarboxylic acid (Acpc), for each of the eight amino acids of angiotensin (AT) has been used to study the relationship between chemical structure and biological activities of angiotensin. The pressor and the myotropic activities of the various ATII derivatives have been tested on the rat blood pressure and on three isolated organs: rat isolated colon, rat stomach strip, and rabbit isolated kidney.The results indicate that 6-His and 8-Phe are essential for the activities of angiotensin II. Moreover, (8-Acpc)-ATII, but not (6-Acpc)-ATII, antagonizes the pressor and myotropic effects of ATII and ATI. αE and pD2 of all analogues have been estimated on the isolated rat stomach strip to evaluate intrinsic activity and affinity for the receptors. (1-, (2-, (3-, (4-, and (5-Acpc)-ATII have the same intrinsic activities as ATII, while those of (6-, (7-, and (8-Acpc)-ATII are much lower.Analogues of ATII substituted in position 8 antagonize specifically the myotropic and pressor effects of ATII and ATI. On the contrary, the effects of other smooth muscle stimulating agents (acetylcholine, 5-hydroxytryptamine, bradykinin, and vasopressin) are not modified.Log dose response curves of ATII and ATI are shifted to the right in the presence of antagonists, but remain parallel. The antagonism is rapidly reversible and may be competitive.

Characterization of receptors for angiotensin in the rat vas deferens

1979 ◽  
Vol 57 (4) ◽  
pp. 417-423 ◽  
Author(s):  
J. Magnan ◽  
D. Regoli
Keyword(s):  
Smooth Muscle ◽  
Vas Deferens ◽  
Proteolytic Enzymes ◽  
Rabbit Aorta ◽  
Rat Vas Deferens ◽  
Converting Enzyme ◽  
Response Curves ◽  
Sympathetic Nerve Stimulation ◽  
The Right

Experiments were performed in the rat vas deferens to characterize the receptor for angiotensin mediating the potentiation of the sympathetic nerve stimulation by this peptide. For this purpose we measured the order of potency of various angiotensins, the affinity of two specific and competitive antagonists, and we compared the effects of several angiotensins in tissues desensitized by angiotensin II.The potency of natural angiotensins follows the order: ATII > ATI > ATIII the relative potency of a few analogues which resist degradation by proteolytic enzymes as well as the potency of three L-Ala analogues of ATII show similar changes as those observed in other smooth muscle preparations (e.g. the rabbit aorta).Affinity of antagonists was evaluated by measuring pA2 and is higher for [Leu8]-ATII than for [des-Asp1, Leu8]-ATII. Both antagonists appear to be competitive since they displace the dose-response curves of ATII and ATIII to the right without changing the slope of the curves. Desensitization with ATII renders the tissues insensitive to ATIII and to other angiotensins without changing the response of the tissues to substance P.ATII does not modify the action of exogenous NA on nonstimulated tissues. ATI has no direct effect since its action is completely blocked in the presence of an inhibitor of the converting enzyme (SQ. 14225), while the responses of the vas deferens to ATII and substance P are unaltered.It is concluded that the receptor for ATII in the rat vas deferens is of the same type as the receptor mediating contraction of the rabbit aorta.

Metabolism of angiotensin II and some analogs in intact strips and in muscle preparations of rabbit aortae

1978 ◽  
Vol 56 (1) ◽  
pp. 39-47 ◽  
Author(s):  
J. Magnan ◽  
D. Regoli
Keyword(s):  
Smooth Muscle ◽  
Angiotensin Ii ◽  
Smooth Muscle Cells ◽  
Rabbit Aorta ◽  
Muscle Preparation ◽  
Response Curves ◽  
Aortic Strip ◽  
Complete Relaxation ◽  
Maximal Tension ◽  
Apparent Diffusion

The purpose of this work was twofold: (a) to develop a muscle preparation of the rabbit aorta free of adventitia and endothelium, and (b) to measure the metabolism of angiotensin II (ATII) in this preparation. The muscle was prepared by 'shucking-off' the adventitia layer and by eliminating the endothelium. Concentration–response curves to ATII and noradrenaline (NA) measured in the muscle preparation provided pD2 values for ATII and NA not significantly different from those observed in the intact aortic strip. However, the maximal tension developed by the two agonists averaged 20–30% of the maximal tension of the intact strips. Apparent diffusion of ATII, in and out of the tissue, was faster in the muscle while NA diffusion was not significantly different. Metabolism of ATII was measured at the plateau of contraction and after complete relaxation in both the muscle and the intact strip. Ten percent of ATII was metabolized at the plateau of the contraction and 50% after complete relaxation. Heptapeptide 1–7 was the metabolite found in both preparations. 1-β-Asp ATII was also broken down to heptapeptide 1–7 while 1-β-Asp,8-Phe-OMe-ATII resisted the degradation and was found unchanged even after 90 min of incubation. It is suggested that the enzyme which inactivates ATII is located in the smooth muscle cells and that it is a carboxypeptidase.

Receptors for bradykinin in intestinal and uterine smooth muscle

1977 ◽  
Vol 55 (6) ◽  
pp. 1270-1285 ◽  
Author(s):  
J. Barabé ◽  
J.-N. Drouin ◽  
D. Regoli ◽  
W. K. Park
Keyword(s):  
Smooth Muscle ◽  
Direct Action ◽  
Rabbit Aorta ◽  
Maximum Effect ◽  
Academic Press ◽  
Response Curves ◽  
Rat Uterus ◽  
Hexyl Ester ◽  
Stimulus Effect ◽  
General Pharmacology

An attempt has been made to characterize receptors for bradykinin (BK) in two smooth muscle preparations (cat ileum and rat uterus) sensitive to BK. Studies have shown that contractions of the two isolated organs produced by BK result from a direct action of this peptide on specific receptors. Since (a) experimental dose–response curves of BK in the two preparations are superimposed to the theoretical ones calculated with the equation of Clark (Clark, A. J. 1937. General pharmacology. Verlag von J. Springer, Berlin), (b) ratios between doses producing 16 and 84% of maximum effect correspond to 1:28 (cat ileum) and 1:19 (rat uterus), and (c) relations stimulus–effect are linear and with a slope of 1.0 (cat ileum) and 1.1 (rat uterus), we choose to interpret these findings with the approach proposed by Clark (1937) and elaborated by Ariens (Ariens, E. J. 1964. Molecular pharmacology. Academic Press Inc., London).Studies on the structure–activity relationships performed with fragments and analogues of BK do not allow for a precise distinction of groups responsible for affinity or for the activation of receptors, and actually show that 1-Arg, 4-Gly, 5-Phe, 8-Phe, and 9-Arg are essential for the interaction. Analogues more potent than BK were obtained by replacing 8-Phe with Tyr(Me) and Trp, while 8-Cha BK keeps full activity. When tested for antagonism, all the analogues and the fragments are inactive; some of these compounds were found to potentiate the activity of BK in the rat uterus.Cyproheptadine (CH), dihydrochlorprothixene (DHCP), phenylalanine-octyl ester (POE), and β-phenylanaline-hexyl ester (β-PHE), as well as 5-Tyr(Me),8-Tyr(Me) BK, and 8-Leu-OMe Octa BK were tested for antagonism. CH, DHCP, POE, and β-PHE (at concentrations ranging from 10−6 to 10−5 M) reduce the myotropic effects of BK in the two preparations. The antagonism is nonspecific for BK, since the effects of other agonists acting on receptors different from those of BK are also reduced. Maximal responses to BK as well as to the other stimulants are significantly diminished, indicating that the antagonism is of the noncompetitive type. 5-Tyr(Me),8-Tyr(Me) BK and 8-Leu-OMe Octa BK did not exert any antagonistic action.Evidence is presented in favour of the interpretation that the receptors for BK in the two preparations are of the same type, and differ from the receptor of the rabbit aorta.

A smooth muscle active factor isolated from renal cortex of the rabbit

1977 ◽  
Vol 232 (2) ◽  
pp. F84-F91
Author(s):  
C. B. Brown ◽  
D. E. Drum ◽  
N. K. Hollenberg
Keyword(s):  
Smooth Muscle ◽  
Renal Cortex ◽  
Proteolytic Enzymes ◽  
Renal Medulla ◽  
Rabbit Aorta ◽  
Water Soluble ◽  
Intrinsic Activity ◽  
Rat Colon ◽  
Muscle Actions ◽  
Muscle Responses

Homogenates of rabbit renal cortex contained a water-soluble material with striking activity on smooth muscle derived from the rabbit aorta, rat stomach, and guinea pig ileum--but not rat colon or chick rectum. Evidence derived from the spectrum of its pharmacologic activity, the influence of specific competitive antagonists on the smooth muscle responses to the factor, the influence of proteolytic enzymes and its elution position during molecular sieve filtration on Sephadex G-10 made it unlikely that the factor was a prostaglandin, renin, angiotensin, a catecholamine, serotonin, bradykinin, a nucleotide, a small organic product of local metabolism, or a small ion. The agent was not found in extracts of renal medulla, spleen, myocardium, or lung. The smooth muscle response to the factor was blocked by phenoxybenzamine. The renal cortical factor in subthreshold concentration also potentiated responses of the rabbit aorta to angiotensin and norepinephrine. The factor's intrinsic activity and ability to potentiate the smooth muscle actions of endogenous vasoconstrictors make it a candidate as a mediator of smooth muscle responses in a number of states.

Characteristics Of The Contractions Induced By Prostaglandin E2-Like Activity In The Rat Stomach Strip And By Thromboxane A2-Like Activity In The Rabbit Aorta And Mesenteric Artery

1981 ◽  
Author(s):  
F J Zijlstra ◽  
J E Vincent
Keyword(s):  
Angiotensin Ii ◽  
Mesenteric Artery ◽  
Thromboxane A2 ◽  
Rabbit Aorta ◽  
Prostaglandin E ◽  
Rat Stomach ◽  
Cascade System ◽  
Response Curves ◽  
Rabbit Mesenteric Artery

The dose-response curves obtained in the measurement of the prostaglandin E (PGE) and thromboxane-A2 (TxA2)-like activity using a cascade system cons isting of a rat stomach strip , a rabbit aorta strip and a mesenteric artery were determined. The following linear relat ionships were observed:log dose-activity for PGE2 and the stomach strip , do se-activity for angiotensin II (All) and the rabbit aorta, log dose-log activity for angiotensin II and the rabbit mesenteric artery.The do se-activity curves for All and TxA2 are different when the rabbit aorta is used whereas the log dose-log activity curves are much more similar for the rabbit mesenteric artery. Therefore, AI I can only be used as a reference substance in the last case. A comparison was made of the TxA2 like activity measured by bioassay and the TxB2 determined by a radioimmunoassay in platelets after aggregation. The curves were parallel when the TxA2 like activity was measured with the mesenteric artery.The different contractile characteristics of these organs should be taken into account in the determination of the PGE2 like and TxA2 like activity with these tests.

Co-expression of prepro-adrenomedullin with a putative adrenomedullin receptor gene in vascular smooth muscle

1999 ◽  
Vol 96 (5) ◽  
pp. 493-498 ◽  
Author(s):  
Dominic J. AUTELITANO ◽  
F. TANG
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Receptor Gene ◽  
Biologically Active ◽  
Potent Vasodilator ◽  
Specific Receptors ◽  
High Concentrations ◽  
Active Release ◽  
Ribonuclease Protection ◽  
Vasodilator Action

The prepro-adrenomedullin (prepro-AM) gene encodes several biologically active peptides, including the potent vasodilator AM. At least part of the vasodilator action of AM appears to be mediated via interactions with receptors on vascular smooth muscle cells (VSMC); however, the specific receptors involved are not known. The aim of the present study was to identify putative AM receptor genes that are co-expressed with AM in cultured rat aortic VSMC that may mediate the actions of AM. AM mRNA was shown to be expressed in rat aortic VSMC cultures. In acute (4 h) secretion studies, only 20% of the total immunoreactive AM was intracellular, with the majority (80%) found in the medium, indicating active release of AM peptide from VSMC. Using highly specific ribonuclease protection analysis, mRNAs encoding three putative AM receptors [L1, calcitonin-receptor-like receptor (CRLR) and RDC1] were shown to be present at high concentrations in RNA extracts from lung. In cultured VSMC, however, whereas RDC1 mRNA was expressed at relatively high concentrations, transcripts encoding CRLR and L1 were not detected. The co-expression of prepro-AM mRNA with the RDC1 receptor implies that AM may act in a localized manner via this receptor to modulate VSMC function.

The rabbit mesenteric vein: a specific bioassay for substance P

1978 ◽  
Vol 56 (4) ◽  
pp. 603-609 ◽  
Author(s):  
A. Bérubé ◽  
F. Marceau ◽  
J. N. Drouin ◽  
F. Rioux ◽  
D. Regoli
Keyword(s):  
Substance P ◽  
De Novo ◽  
Smooth Muscles ◽  
High Sensitivity ◽  
Mass Action ◽  
Response Curves ◽  
Mesenteric Vein ◽  
Mass Action Law ◽  
New Type ◽  
Specific Receptors

The anterior mesenteric vein of the rabbit responds to substance P with dose-dependent contractions and is among the vascular smooth muscles most sensitive to this peptide. In spite of its high sensitivity to numerous other agents, including angiotensin and bradykinin, the rabbit mesenteric vein can be made selective for substance P by the use of specific inhibitors that will prevent the myotropic effects of acetylcholine, catecholamines, histamine, 5-hydroxytryptamine, and of the two above-mentioned peptides, without modifying the contractions elicited by substance P. It appears that this peptide acts directly on specific receptors and not through the release of neurotransmitters. Interference by intramural prostaglandins is excluded because substance P is equally active on tissues pretreated with indomethacin or untreated.Dose–response curves obtained with substance P are close to the theoretical curves predicted by the mass action law. The rabbit mesenteric vein contains a new type of receptor for bradykinin, recently identified (REGOLI, D., MARCEAU, F., and BARABÉ, J. 1978. De novo formation of vascular receptors for bradykinin. Can. J. Physiol. Pharmacol. 56, in press.). The action of bradykinin on this receptor can be prevented with the use of specific and competitive inhibitors and, therefore, the mesenteric vein will distinguish between peptides of the kinins or of the substance P types.

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