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Biomedical subjects

R J Freer

Publications and source records attributed to R J Freer.

At least 37 records · Page 2Linked to original sources
PubMed1983

Acetylcholine potentiation of field stimulated rat vas deferens: a pre-synaptic muscarinic mechanism?

Acetylcholine (ACh) was found to markedly enhance the nerve stimulation induced twitch response of isolated, field-stimulated rat vas deferens (RVD). The ED200 (concentration which enhances the twitch response to 200% of control) for this potentiation was 6 X 10(-6)M with the maximum twitch response being increased by more than 3 fold (325 +/- 30%). Carbachol (ED200 = 8.5 X 10(-7)M) showed identical results. With each drug the potentiation was competitively antagonized by atropine (10(-7) - 10(-5)M). Physostigmine 10(-8) - 10(-6)M) both enhanced the basal twitch response (215 +/- 8% of control at 10(-5)M) and the sensitivity of the RVD to ACh (ED200 = 3.3 X 10(-7)M) but not to carbachol. Atropine, on the other hand reduced the basal twitch response by 18 +/- 3% at 10(-5)M. Hemicholinium (10(-4)M) also reduced the basal twitch responses by 23 +/- 5%. ACh (10(-7)M - 10(-5)M) did not modify the responses of unstimulated RVD to norepinephrine or KCl suggesting a pre-synaptic site of action. Taken together these results are compatible with the presence of a pre-junctional, excitatory muscarinic mechanism in the field stimulated RVD. That this cholinergic system may be of physiological significance is supported by the observations that atropine and hemicholinium depress while physostigmine enhances the twitch response in the absence of exogenous ACh.

Acetylcholine↗
PubMed1983

Characterization of the rat neutrophil formyl peptide chemotaxis receptor.

Numerous synthetic N-formylated peptides, believed to be the analogs of the naturally occurring initiating signal peptides produced by bacteria, are potent chemotactic agents for phagocytic cells in several species. The authors have characterized the receptor with moderately high affinity for the chemotactic peptide f-Met-Leu-[3H]Phe on the rat peritoneal neutrophils. When neutrophils are incubated with f-Met-Leu-[3H]Phe at 24 C, the binding is saturable and reversible. The receptor on the inflammatory rat neutrophils has an equilibrium dissociation constant (KD) of 3.4 x 10(-8) M at 24 C, and there are approximately 65,000 sites per cell. In addition, the potency of several of these chemotactic peptides in inducing lysosomal enzyme secretion and superoxide production correlated well with their ability to compete with f-Met-Leu-[3H]Phe for receptor binding. Structure activity studies further demonstrate that the fine specificity of the formyl peptide receptor has been conserved across species lines.

Acetylglucosaminidase↗
PubMed1982

Anti-f Met-Leu-Phe: similarities in fine specificity with the formyl peptide chemotaxis receptor of the neutrophil.

We have prepared antisera in both rabbits and rats against f Met-Leu-Phe conjugated to a variety of carrier proteins. Over 40 peptides with widely varying reactivity for the neutrophil formylpeptide receptor have been tested for their ability to bind to rabbit antibody raised against fMLP10-BSA. Structure-activity studies of peptides structurally related to f Met-Leu-Phe demonstrate that the N-formyl group is mandatory for maximum antibody binding activity. Methionine in position 1 and phenylalanine in position 3 are found to confer maximum binding activity. Stereoselectivity of the antibody-combining site also has been demonstrated. Comparison of the ability of the peptides to bind to the antibody receptor with their reactivity for the neutrophil has demonstrated a strong correlation in the rank order of reactivity of the numerous synthetic peptides: for the alpha NH2-acyl group, r = 0.94; for position 1, r = 0.90; for position 2, r = 0.97; and for position 3, r = 0.78. This strong correlation is seen across species lines with both rabbit and rat antibodies. Significant differences, however, in the specificity of the antibody and neutrophil receptors are seen at the carboxyl terminus of phenylalanine, and beyond the phenylalanine ring, r = 0.29. In addition, bacterial chemotactic factor-enriched butanol extracts from Escherichia coli culture filtrates can also bind to anti-f Met-Leu-Phe, affording additional evidence for the similarity in the structure of the bacterial chemotactic factor to the synthetic chemotactic peptides.

Animals↗
PubMed1981

Effect of insulin fragments on biological activity of insulin and desoctapeptide insulin. I. Potentiation of biological activities.

Four derivatives of the insuln B-chain COOH-terminal pentapeptide Arg-Gly-Phe-Phe-Tyr (B22-26) were synthesized and shown to be inactive alone. In the presence of submaximal concentrations of insulin or desoctapeptide insulin, peptides at concentrations of 10(-4) M and higher, markedly stimulated the actions of insulin on rat adipocytes including labeled glucose oxidation, activation of glycogen synthase, and stimulation of 2-deoxyglucose transport. The B-chain COOH-terminal heptapeptide, Gly-Phe-Phe-Tyr-Thr-Pro-Lys (B23-29) was inactive alone or in the presence of submaximal concentrations of insulin or desoctapeptide insulin, suggesting that argnine is required. Dose response curves of insulin, and desoctapeptide insulin for labeled glucose oxidation by rat adipocytes were shifted 1 log concentration unit to the left in the presence of peptide. Peptide shortened the lag time of labeled glucose oxidation and markedly enhanced the rate of 14CO2 production following the lag time. Peptides also enhanced insulin-like activities of concanavalin A and nonsuppressible insulin-like activity P.

Adipose Tissue↗
PubMed1981

Activation of (arachidonyl) phosphatidylinositol turnover in rabbit neutrophils by the calcium ionophore A23187.

The addition of the Ca2+ ionophore A23187 to rabbit neutrophils stimulated [14C]arachidonic acid incorporation into phosphatidylinositol and lysosomal enzyme secretion. A significant increase in phosphatidylinositol labelling was observed after a 2 min exposure to 0.1 microM-ionophore A23187. Maximum increases in rate of labelling were obtained with 1 microM-ionophore A23187 within 1 min, declining to basal rates after 15 min. Similarly, maximum rate of enzyme release occurred during the first 2 min of exposure to ionophore and release was essentially complete by 15 min. Threshold and peak ionophore A23187 concentrations for stimulating both processes were identical. In contrast with the specificity of phosphatidylinositol labelling induced by 1 microM-ionophore A23187 in the absence of cytochalasin B, ionophore also significantly stimulated labelling of phosphatidylserine and phosphatidylethanolamine in the presence of cytochalasin B. With a threshold ionophore concentration (0.1 microM), the enhanced incorporation of arachidonate was relatively specific for phosphatidylinositol in cytochalasin-treated cells. Ionophore A23187 did not accelerate labelling of phosphatidylinositol by [14C]acetate or [14C]glycerol, indicating that ionophore A23187 does not stimulate phosphatidylinositol synthesis de novo, although it did promote [14C]palmitate and [32P]Pi incorporation into neutrophil phosphatidylinositol. However, the increase in phosphatidylinositol labelling with these latter precursors was generally slower in onset and much more modest in magnitude than that observed with arachidonic acid. These results support the hypothesis that a Ca2+-dependent phospholipase, which acts on the arachidonate moiety of phosphatidylinositol, is responsible for initiating at least certain of the membrane events coupled to the release of secretory product from the neutrophil.

Animals↗
PubMed1981

Morphiceptin ( beta-casomorphin (1-4) amide): a peptide opioid antagonist in the field stimulated rat vas deferens.

The effect of Morphiceptin (H-Tyr-Pro-Phe-Pro-NH2) on opioid inhibition of field stimulated rat vas deferens (RVD) was studied. The morphiceptin was found to produce a weak inhibition of the twitch response of the RVD. In addition morphiceptin antagonized full agonists acting on the same receptor system (i.e. beta-endorphin selective antagonist for the delta receptor system of RVD by virtue of being a weak partial agonist.

Animals↗
PubMed1981

Inhibitory histamine receptors in the rat vas deferens.

The effect of histamine on the field stimulated rat vas deferens preparation was studied and compared to mouse vas deferens. Histamine produced a concentration dependent inhibition of rat vas deferens (ID50 14 microM) similar to that seen with mouse vas deferens (ID50 2.4 microM). Unlike mouse however, where only H2 receptors are observed, the histamine inhibition of rat vas deferens was attenuated by both H1, (diphenhydramine) and H2 (cimetidine) antagonists. It is concluded that rat vas deferens contains both H1 and H2 receptor types.

Animals↗
PubMed1980

Organ selective angiotensin antagonists: sarcosyl1-cysteinyl(S-methyl)8-angiotensin I.

An angiotensin antagonist, Sarcosyl1-Cysteinyl(S-Methyl)8-angiotensin I [Sar1-Cys(Me)8-ANG I] was synthesized and its pharmacological properties evaluated in vivo (rat blood pressure assay) and in vitro (rabbit aortic strips, guinea-pig ileum and rat uterus assays). It was found to be an extremely potent angiotensin II (ANG II) antagonist in the rat pressor assay (dose ratio for ANG II of 1300 during infusion of 5.0 micrograms/kg/min Sar1-Cys(Me)8-ANG I) and a moderately effective antagonist in guinea-pig ileum (pA2 congruent to 8.2). Moderate antagonism was also seen in the rabbit aortic strip preparation (pA2 congruent to 8.1) while the analog was inactive in the rat uterus assay. In each of the preparations where antagonist activity was observed there was evidence of non-competitive antagonism. Most striking was the inability of extremely high doses ( up to 125 micrograms ANG II/kg) of ANG II to overcome the Sar1-Cys(Me)8-ANG I blockade. In both the rat pressor and guinea-pig ileum assays the Sar1-Cys(Me)8-ANG I antagonism is completely abolished in the presence of the converting enzyme inhibitor SQ14225 (Captopril-Squibb). Organ selectivity of this analog is discussed in terms of the inherent activity of the active principle (i.e. the Sar1-Cys(Me)8-angiotensin II [Sar1-Cys(Me)8-ANG II] released by the action of converting enzyme) and the availability of converting enzyme in each bioassay.

Angiotensin I↗