Search PubMed⌕ Search

Biomedical subjects

C Poulos

Publications and source records attributed to C Poulos.

At least 19 recordsLinked to original sources
PubMed2000

Mathematical modelling of insect neuropeptide potencies. Are quantitatively predictive models possible?

The potencies of natural adipokinetic hormones and synthetic variants have been determined in Locusta migratoria using the lipid mobilisation assay in vivo, and/or the acetate uptake assay in vitro. These data are combinations of previously published and unpublished data (a total of sixty-nine analogues), and form data sets for the construction of mathematical models of the hormone potencies. The sequence variations of amino acids in both natural and artificial adipokinetic hormone analogues were described using continuous descriptor scales z(1)', z(2)', and z(3)', each previously published scale being derived from various properties of the amino acids. By means of these z'-scales and partial least squares regression we attempted to model the potencies in Locusta migratoria of adipokinetic hormones in the two assays. Correlations (r(2) values) between predicted and actual potencies of the different peptides were up to 0.73. We discuss the potential of the partial least squares method for formulating quantitative relationships between different hormone structures and their potencies, and describe how the procedure might be used in structure-activity prediction with the construction of an optimised peptide data set.

Amino Acid Sequence↗
PubMed1995

GR 73,632 and [Glu(OBzl)11]substance P are selective agonists for the septide-sensitive tachykinin NK1 receptor in the rat urinary bladder.

The existence of a septide-sensitive subtype of the tachykinin NK1 receptor has been recently proposed. In the rat isolated urinary bladder, the non-peptide NK1 receptor antagonist RP 67,580 exhibits a higher affinity towards septide (pKB 7.57) than towards [Sar9]substance P sulfone (pKB 7.00). In this study we have investigated the pharmacological profile of the non-mammalian tachykinin physalaemin, of the synthetic NK1 receptor agonist GR 73,632 (delta-aminovaleryl[LPro9,NMeLeu10]substance P(7-11)) and of [Glu(OBzl)11]substance P in relation to the putative existence of a septide-sensitive receptor. The activity of [Glu(OBzl)11]substance P at the NK1, NK2 and NK3 receptor was assayed in the guinea-pig ileum NK1 receptor assay (EC50 26 nM), in the rabbit pulmonary artery NK2 receptor assay (weak agonist activity) and in the rat portal vein NK3 receptor assays (no appreciable activity up to 1 microM). GR 73,632, [Glu(OBzl)11]substance P and physalaemin, all produced concentration-dependent contractions of the rat isolated urinary bladder, with EC50 values of 17, 79, and 9 nM, respectively. The responses to the three agonists were very slightly or not modified by the NK2 receptor antagonist SR 48,968 (1 microM). RP 67,580 (0.3-3 microM) produced a concentration-dependent rightward shift of the curve to GR 73,632, [Glu(OBzl)11]substance P and physalaemin without producing depression of their maximal response. Schild plot analysis indicated the competitive nature of the antagonism. The affinity (pKB) of RP 67,580 towards physalaemin, GR 73,632 and [Glu(OBzl)11]substance P was 7.12, 7.56 and 7.95, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Clinical results from intracytoplasmic sperm injection at monash IVF.

The impact of a modification of the intracytoplasmic sperm injection (ICSI) technique on fertilization and pregnancy rates was examined in a retrospective analysis of 171 consecutive ICSI treatment cycles (156 patients). Patients were selected for ICSI on the basis of severe oligoasthenozoospermia (65 patients) or following conventional in vitro fertilization (IVF) with failed or poor fertilization (70 patients). Seven patients in which epididymal or testicular sperm was used, 10 patients with sperm antibodies and 4 patients with retrograde ejaculation or who required electro-ejaculation were also treated with ICSI. In the first 105 cycles (102 patients), single sperm, rendered immotile, were injected into the ooplasm of 979 metaphase II (M II) oocytes using an established technique (Method 1). In the following 66 cycles (513 M II oocytes injected), the ICSI procedure was modified by increased aspiration of the oolemma to ensure the intracytoplasmic deposition of sperm (Method 2). The patient groups did not differ between the two injection procedures. The normal (two pronuclear) fertilization rate increased significantly (P < 0.001) from 34.3% with Method 1 to 73.1% with Method 2, with no difference in the oocyte degeneration rate (4.3% v. 4.5% respectively). The incidence of failed fertilization was significantly (P < 0.01) reduced from 17.1% (18 cycles) to 1.6% (1 cycle) with the change in technique. As a consequence of the increased fertilization rates with Method 2, more embryos were available for assessment and transfer, and a pregnancy rate per oocyte retrieval of 21.2% was obtained for Method 2. Fertilization, embryo transfer and pregnancies were obtained in all patient groups treated with ICSI.(ABSTRACT TRUNCATED AT 250 WORDS)

Australia↗
PubMed1994

Synthesis and biological activity of NK1 substance P selective agonists by modifying the methionyl residue.

A series of analogues of substance P, where the Met11 residue was replaced by Glu(OCH2CH3), Glu(OBzl) and Hse(CH3), were synthesized in order to investigate the effect on agonist activity of modifications at the C-terminal residue. The biological activities in the guinea-pig ileum assay (NK1 receptor) and rat [text says rabbit] pulmonary artery (NK2 receptor) indicate that replacement of the SCH3 group of Met11 of substance P by the COOBzl or OCH3 groups favour interaction with the NK1 receptor and increase selectivity towards this receptor subtype.

Amino Acid Sequence↗
PubMed1994

Synthesis and biological activity of NK1 tachykinin antagonists not containing D-residues.

A series of analogues of the previously reported NK1 tachykinin antagonist [Orn6, Glu(OBzl)11]-SP6-11-OBzl has been synthesized and tested in order to investigate the effects on antagonistic activity of modifications at the C-terminal residue. The biological activity in the guinea-pig ileum assay (NK1 receptor) indicates that the two aromatic rings introduced in the C-terminal part of the peptide are both essential for the expression of antagonistic activity.

Amino Acid Sequence↗
PubMed1994

Microinjection: choice of embryo transfer technique.

Subzonal sperm microinjection (SUZI) is indicated in severe oligoasthenozoospermia, in which the total count of motile sperm is inadequate for in vitro fertilization (IVF), and in cases with repeated failure of fertilization. Sperm for microinjection are selected following centrifugation on a Percoll gradient and stimulation with pentoxifylline and 2-deoxyadenosine. Motile sperm (2-10 per egg) are injected into the perivitelline space and fertilized oocytes are then cultured for two days prior to transfer into the Fallopian tube (tubal embryo stage transfer, TEST) or uterus. During 1992, SUZI results showed a total fertilization rate of 30% (19% were 2 pronuclear, 11% were polyspermic), a transfer rate of 55% and pregnancy rates of 15.2% per transfer and 8.3% per cycle. Recent pregnancy data in mild-moderate male factor infertility showed that gamete intrafallopian transfer (GIFT) results were consistently superior to TEST or IVF, suggesting a beneficial effect of the tubal environment on fertilization and early embryonic development. Accordingly, the combination of SUZI followed by the immediate transfer of injected oocytes into the Fallopian tube, the MIFT procedure, was explored. An initial study of 21 consecutive microinjection candidates showed a clinical pregnancy rate of 24% per cycle. Information regarding fertilization and polyspermy rates was available from supernumerary oocytes in 90% of patients. A randomized, controlled trial comparing MIFT with SUZI or TEST in severe male factor infertility is required to confirm the improved pregnancy rate in MIFT cycles.

Embryo Transfer↗
PubMed1994

Analogues of the C-terminal fragments of neurokinins with modifications at their C-terminal methionyl residue. Structure-activity studies.

Analogues of SP4-11 have been synthesized in which the methionyl residue is replaced successively by the Glu(OCH2CH3), Glu(OBzl), Hse(CH3) and Glu(CONHCH3) residues, and analogues of NKA4-10 and NKB4-10 have been prepared in which the methionyl residue is replaced by the Hse(Bzl) and Hse(CH3) residues, respectively. The SP4-11 analogues were tested in three in vitro preparations representative of NK-1, NK-2 and NK-3 receptor types. Substitution of the SCH3 group of the Met11 side chain by the groups COOCH2CH3 and COOBzl has little affect on the agonist activity in NK-1 preparations, while in NK-2 the corresponding analogues are more potent than the parent octapeptide; that substituted with COOBzl being 8.2 times more potent than SP4-11. In NK-3 preparations all analogues are weak agonists. The selectivity of all the analogues is reduced compared with the corresponding hexapeptide analogues. The SP4-11 analogues, along with those of NKA4-10 and NKB4-10, were tested for their binding ability in the three receptor subtypes above. The SP4-11 analogues show reduced affinity for NK-1 receptors, while the NKA4-10 and NKB4-10 analogues have almost the same affinities as NKA and NKB for NK-2 and NK-3 receptors, respectively. The effect of the lipophilicity of the Met11 side chain, especially when a phenyl group is present in the side chain, at the NK-2 receptor is discussed.

Amino Acid Sequence↗
PubMed1994

Synthesis and biological activity of locust AKH-I and its analogues with modifications at the threonine residues.

A convenient method of synthesis, using a combination of solid and liquid phase methodology, for locust Adipokinetic Hormone-I (AKH-I) and its analogues with modifications at the threonine residues are reported. The N-terminal nonapeptide acid of AKH-I is synthesized in the solid phase using the 2-chlorotrityl chloride resin and the Fmoc/t-Bu strategy. Quantitative cleavage of the nonapeptide acid from the resin, with the tert-butyl type side-chain protection intact, is achieved with a mixture of acetic acid/trifluoroethanol/dichloromethane. The nonapeptide acid is then coupled in solution to the threonine derivatives, H-Thr-NH2 or H-Thr(Bzl)-NH2, with the DCC/HOBt method. The efficiency of this approach in the synthesis of AKH-I is demonstrated by the high yields and purity of the synthesized peptides. All the synthesized peptides were tested in two ways: first, in a lipid mobilization assay in locusts in vivo; and second, in a novel assay in vitro concerned with the uptake of radiolabelled acetate into locust tissue. Replacement of the hydroxyl hydrogen in Thr5 of locust AKH-I by the bulky and highly lipophilic tert-butyl group reduced the potency markedly, whereas efficacy is unaffected, but when the hydroxyl hydrogen of Thr10 in AKH-I is replaced by a benzyl group, the activity of the resulting analogue is identical to that of the natural peptide. Structure-activity relationships are discussed.

Amino Acid Sequence↗
PubMed1994

A case of successful use of reproductive technology for a couple with subfertility due to retrograde ejaculation, where artificial insemination had failed.

A case history of a couple where the infertility was due to retrograde ejaculation is presented; when conventional treatment with artificial insemination using sperm isolated from postejaculatory urine failed, IVF and GIFT technology was applied. This resulted in a pregnancy which unfortunately failed at 3 months, unrelated to the method of conception. This case report highlights the possible use of IVF/GIFT for yet another type of male subfertility.

Adult↗
PubMed1993

Synthesis of a potent antagonist of substance P by replacing the CH2SCH3 and the alpha-carboxamide groups of the methionine at [Orn6]-SP6-11 by benzyl ester groups.

Analogues of [Orn6]-SP6-11 have been synthesized in which the CH2SCH3 group of Met11 is replaced by a COOCH3 or a COOBzl group. These analogues, which were tested for agonist and antagonist activity in three in vitro preparations representative of NK-1, NK-2 and NK-3 receptor types, were full agonists at NK-1 receptors, showed very weak agonist activity at NK-2, receptors and were weak antagonists at NK-3 receptors. The above analogues were modified by substituting the alpha-carboxamide of residue 11 by a COOCH3 and a COOBzl group, respectively. The resulting analogues were found to be devoid of agonist activity in each of the functional assays. However, they showed weak antagonist activity at each receptor subtype, with the exception of the dibenzyl analogue, which was a potent and selective NK-1 receptor antagonist. It is concluded that appropriate modification of the side chain of Met11 and its alpha-carboxamide leads to a potent and selective at NK-1 receptor antagonist.

Amino Acid Sequence↗
PubMed1993

Synthesis of potent antagonists of substance P by modifying the methionyl and glutaminyl residues of its C-terminal hexapeptide and without using D-amino acids.

Analogues of [Orn6]-SP6-11 have been synthesized in which the Met11-NH2 residue is replaced by the alpha, gamma-dimethyl, alpha, gamma-dibenzyl and alpha, gamma-di-tert-butyl esters of glutamic acid. These analogues were tested in three in vitro preparations representative of NK-1, NK-2 and NK-3 receptor types for agonist and antagonist activity. The dimethyl analogue is a selective full agonist in the NK-1 receptor type and a weak antagonist in the other two receptor types, while the dibenzyl and the di-tert-butyl analogues are potent antagonists in the NK-1 receptor type and weak antagonists in the other two receptor types. It is concluded that appropriate modification at the alpha-carboxamide and the side chain of the methionine residue of substance P may induce antagonism without using D-amino acids.

Amino Acid Sequence↗
PubMed1992

Synthesis and biological activity of analogues of the C-terminal hexapeptide of substance P with modifications at glutaminyl and methioninyl residues. Structure-activity studies.

Analogues of [Orn6]-SP6-11 have been synthesized in which the methionyl residue is replaced by glutamine gamma-carboxamide substituted derivatives. These analogues where tested in three in vitro preparations representative of NK-1, NK-2 and NK-3 receptor types. Substitution of the SCH3 group of the Met11 side chain by CONHCH3, CON(CH3)2, CONHPh and CONCH3Ph groups results in analogues which are full agonists in NK-1 and NK-2 preparations with the exception of the Glu[N(CH3)2]11 and the Glu(NHCH3)11 analogues, which are partial agonists at NK-1 and NK-2 receptors respectively. The Glu(NHCH3)11 analogue shows selectivity for the NK-1 receptor type and is equipotent to the Glu(NCH3Ph)11 analogue in the same receptor type. The latter analogue is 2.84 times more potent than the parent hexapeptide in the NK-2 preparation. The Glu(NHPh)11 analogue is a full agonist in the NK-3 preparation and equipotent to the parent hexapeptide, in contrast to the other analogues in which Met has been replaced by glutamine gamma-carboxamide substituted residues. It is concluded that for NK-1 receptor type the lipophilic character of Met11 side chain is not a determining factor for activity but it is an important factor for activity in the NK-2 receptor type and has a stronger effect when a phenyl group is present, thus leading to analogues which are full agonists and more potent than the parent hexapeptide.

Amino Acid Sequence↗
PubMed1991

Application of carboxylic-phosphinic mixed anhydrides in the fragment peptide synthesis of protected analogues of substance P.

Mixed carboxylic-phosphinic anhydrides derived from peptide acids and 1-oxo-1-chlorophospholane have been applied in the synthesis of the protected [Leu11]-SP by the fragment coupling strategy. The yields from fragment couplings were ca. 75%, the products were of high purity while the conditions of formation and coupling of the corresponding mixed phosphinic anhydrides, for optimum yields, have been evaluated.

Amino Acid Sequence↗
PubMed1991

Synthesis of a potent agonist of substance P by modifying the methionyl and glutaminyl residues of the C-terminal hexapeptide of substance P. Structure-activity relationships.

Analogues of [Orn6]-SP6-11 have been synthesized in which the Met11 residue is replaced by glutamate gamma-alkylesters. These analogues were tested in three in vitro preparations representative of NK-1, NK-2, and NK-3 receptor types. Substitution of the SCH3 group of the Met11 side chain by a COOR (R = methyl, ethyl, n-propyl, n-butyl, cyclohexyl) group results in analogues which are full agonists in NK-1 and NK-2 preparations but show little agonist activity in the NK-3 preparation. When the SCH3 group is replaced by a t-butyl ester group and the resulting analogue is a full agonist in all the above preparations and more active than the parent hexapeptide and SP-OCH3 at NK-1 receptors. It is concluded that for activity at NK-1 receptors methionine can be replaced by gamma-t-butyl glutamate without loss of activity, whilst at NK-2 and NK-3 receptors the above substitution increases the activity of [Orn6]-SP6-11. Other gamma-alkyl esters of the glutamic acid reduce its biological activity.

Amino Acid Sequence↗
PubMed1991

Application of 2-chlorotrityl resin in solid phase synthesis of (Leu15)-gastrin I and unsulfated cholecystokinin octapeptide. Selective O-deprotection of tyrosine.

The carboxyl terminal dipeptide amide, Fmoc-Asp-Phe-NH2, of gastrin and cholecystokinin (CCK) has been attached in high yield through its free side chain carboxyl group to the acid labile 2-chlorotrityl resin. The obtained peptide resin ester has been applied in the solid phase synthesis of partially protected (Leu15)-gastrin I utilising Fmoc-amino acids. Quantitative cleavage of this peptide from resin, with the t-butyl type side chain protection intact is achieved using mixtures of acetic acid/trifluoroethanol/dichloromethane. Under the same conditions complete detritylation of the tyrosine phenoxy function occurs simultaneously. Thus, the solid-phase synthesis of peptides selectively deprotected at the side chain of tyrosine is rendered possible by the use of 2-chlorotrityl resin and Fmoc-Tyr(Trt)-OH. The efficiency of this approach has been proved by the subsequent high-yield synthesis of three model peptides and the CCK-octapeptide.

Amino Acid Sequence↗