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Biomedical subjects

R J Freer

Publications and source records attributed to R J Freer.

At least 55 records · Page 3Linked to original sources
PubMed1980

Synthesis and pharmacology of a noncompetitive antagonist of angiotensin-induced contractions of vascular smooth muscle. [Sarcosyl]1-[cysteinyl (s-methyl)]8-angiotensin II.

The synthesis of an angiotensin II (A II) antagonist, sarcosyl1-cysteinyl(S-methyl)8-angiotensin II [Sar1-Cys(Me)8-A II], showing partial organ selectivity and properties of a noncompetitive antagonist, is described. The compound was found to be an extremely potent antagonist on vascular smooth muscle both in vitro (pA2 for rabbit aorta approximately equal to 9.2) and in vivo on rat blood pressure (dose ratio of 103 for ED25 mm Hg during 1 microgram/kg per min infusion of antagonist). It was without effect on norepinephrine responses in both assay systems. In contrast, it was a considerably weaker antagonist on visceral smooth muscle (pA2 for guinea pig ileum = 8.5; pA2 for rat uterus = 7.9). Interestingly, in the vascular smooth muscle preparations, the compound also exhibited elements of a noncompetitive antagonist in that both the slope and maximum of the A II dose-response curves were reduced markedly. Qualitatively similar results were obtained with sarcosyl1-alanyl8-angiotensin II (Saralasin) on rabbit aorta. Moderate depression of maximum response was seen in guinea pig ileum but not in rat uterus. These effects on vascular smooth muscle were reversible in vitro but only partially reversible in vivo.

Angiotensin II↗
PubMed1979

Nuclear magnetic resonance conformational studies on the chemotactic tripeptide formyl-L-methionyl-L-leucyl-L-phenylalanine. A small beta sheet.

Previous work by several groups has shown that the combination of spin--spin coupling constants and spectral density components (derived from spin--lattice relaxation and/or nuclear Overhauser measurements) may aid in the task of conformational determination of peptides in solution. Using the peptide formyl-L-methionyl-L-leucyl-L-phenylalanine, which is a potent specific chemotactic agent for leucocytes, we show the following: (a) that 3JNHCH coupling constants are consistent with a high degree of rigidity in the peptide backbone in solution, (b) that 3H isotopic substitution in combination with relaxation data taken at different Larmor frequencies enables spectral density, and thence conformational, information to be obtained, (c) that side-chain conformations for this molecule mirror, in some aspects, those found in the solid state for other peptides containing the same residues, and (d) that temperature dependence of amide chemical shifts does not have direct implication concerning the existence of intramolecular hydrogen bonds in peptides. We are able to propose a family of conformations which appear to interchange rapidly on the NMR time scale and are characterized by a distribution of side-chain rotamers. The basic backbone conformation is, or closely approximates, a small beta antiparallel pleated sheet and as such suggests a possible mode of receptor--chemotactic peptide interaction.

Amino Acid Sequence↗
PubMed1979

Synthesis and pharmacology of a prohormone angiotensin antagonist.

A prohormone angiotensin antagonist, Sarcosyl1-Alanyl8-angiotensin I (Sar1-Ala8-A-I) was synthesized and its pharmacological properties were evaluated in three biological systems. It was found to be a good inhibitor in vivo in the rat blood pressure assay, somewhat less active in guinea pig ileum and a relatively weak antagonist in rat uterus. In vivo the inhibitory effect was greatly attenuated by the presence of the converting enzyme inhibitor BPP5alpha.

Angiotensin I↗
PubMed1979

Angiotensin-induced steroidogenesis in rabbit adrenal: effects of pH and calcium.

The effect of variations in pH and Ca2+ on angiotensin II (A-II)-induced steroidogenesis was tested on isolated adrenal glomerulosa cell suspensions. The results show that a reduction in pH from 7.4 to 6.5 produces both a shift to the left of the A-II dose-response curve as well as an increase in maximum steroid production. In contrast, removal of Ca2+ from the incubation medium virtually abolished steroidogenesis to A-II (5 X 10(-9)M(, KCl(10mM) and ACTH (250 microU/ml). The Ca2+ antagonist D-600, however, was less effective than simple removal of Ca2+ as 10(-4) M was required to block the steroidogenic response to these same agonists. The results indicate that the response characteristics of this system to A-II resemble most closely those seen with isolated arterial smooth muscle - especially rabbit aortic strips.

Adrenal Cortex↗
PubMed1979

Synthesis and pharmacological properties of [5-isoleucine]-, [8-isoleucine]-, and [5,8-diisoleucine]bradykinin.

Three bradykinin analogues have been synthesized in which the phenylalanine residue(s) at positions 5 and/or 8 have been substituted by isoleucine. All these analogues have weak bradykinin-like activity in isolated rat uterine smooth muscle or in rat blood pressure assay. No antagonistic activity was observed with any of these analogues. The importance of phenylalanine at positions 5 and 8 is discussed.

Amino Acid Sequence↗
PubMed1979

Synthesis of Nalpha-formyl-Met-Leu-Phe-OH: an inducer of chemotaxis in peritoneal polymorphonuclear neutrophils.

A chemotactic peptide CHO.Met.Leu.Phe.OH has been synthesized classically using the mixed anhydride procedure. The formyl group was introduced by coupling formic acid in the presence of dicyclohexylcarbodiimide to the partially protected triptide. The final product was obtained by treatment of the intermediate CHO.Met.Leu.Phe.OBzl with hydrogen fluoride. The ED50 of the peptide in the Boyden chamber assay was 7 x 10(-11) M; in the lysozyme release assay 2.4 x 10(-10) M and in the beta-glucuronidase release assay 2.6 x 10(-10) M. In a radioreceptor assay the ID50 of the peptide was 3.3 x 10(-10) M.

Chemotaxis, Leukocyte↗
PubMed1978

Correlation of the biological activity and solution conformation of [Asp1,Ile5]- and [Phe4,Tyr8]angiotensin II.

Angiotensin II is known to undergo a reversible conformational transition and a change in potency in rat uterus in vitro with pK approximately 6.5. We have shown by carbon-13 NMR that the conformational transition involves all-trans to partly cis isomerization of the His6-Pro7 peptide bond. Isomerization from all-trans at pH 6.8 to approximately 16% cis at pH 8.0 is therefore correlated with a 10-fold increase in biological activity for [Asp1,Ile5]-angiotensin II in rat uterus in vitro. Isomerization from all-trans at pH 6.8 to approximately 16% cis at pH 8.0 in the competitive inhibitor [Phe4,Tyr8]angiotensin II is correlated with exhibition of virtually no agonist activity at low pH to full agonist activity at high pH. An angiotensin II conformation with Pro7 in the cis form may therefore be the conformation with maximal binding or biological activity at the cellular receptor.

Angiotensin II↗
PubMed1978

Synthesis of two enzyme resistant enkephalin analogs possessing enhanced analgesic activity.

Two enzyme resistant analogs of methionine enkephalin (H-Try-Gly-Gly-Phe-Met-OH) have been synthesized and tested for morphine-like properties in the stimulated guinea pig ileum, rat tail-flick, mouse tail-flick and for stability in whole brain homogenates. The two analogs are: Nalpha-Methyl-Tyrosyl-Glycyl-Glycyl-Phenylalanyl-des-carboxy-Norleucine (I) and Tyrosyl-D-Alanyl-Glycyl-Phenylalanyl-des-carboxy-Norleucine (II). Both peptides were completely stable for 90 minutes when incubated with whole brain homogenate (rat) while methionine enkephalin was rapidly destroyed (t1/2=4 min at 37 degrees C). In addition each was more potent than methionine enkephalin in the stimulated guinea pig ileum assay and had good activity in the tail-flick test when given intraventricularly in mice or via indwelling catheters into the periaqueductal gray of rats. Each of these activities were blocked by naloxone. Interestingly, the antin-ociceptive activity of these peptides was much reduced in morphine tolerant animals.

Analgesics↗