Synthesis of [8-alpha-hydroxyisocaproic acid]oxytocin. Biological activities and comparison of its in vivo uterine actions to those of deamino-[8-alpha-hydroxyisocaproic acid]oxytocin, deamino-oxytocin and oxytocin

The synthesis and biological activities of [8-alpha-hydroxyisocaproic acid]oxytocin are reported. The in vivo uterine responses to [8-alpha-hydroxyisocaproic acid] oxytocin are prolonged and those to deamino-[8-alpha hydroxyisocaproic acid] oxytocin (as well as those we have previously reported for deamino-oxytocin) are very prolonged as compared with those of oxytocin. Time courses of the in vivo uterine responses to deamino-[8-alpha-hydroxyisocaproic acid]oxytocin and deamino-oxytocin (as followed by plotting the intervals between the individual contractions of a response vs. time after peptide injection) differ from those to [8-alpha-hydroxyisocaproic acid]oxytocin and oxytocin.

Biofunctional evaluation of a hydrogen bond stabilizing the beta-turn in the acyclic part of oxytocin

In a continued effort to determine the importance of the hydrogen bonds for stabilization of the biologically active conformation of oxytocin, deamino-[9-glycolicamide] oxytocin was synthesized in order to study, in this respect, the hydrogen bond between the peptide N--H of Gly9 and the C=0 of Cys6. In this analog the amide linkage between residues at positions 8 and 9 is replaced by an ester. Thus the residue at position 9 cannot be involved in hydrogen bond formation with the C=O of Cys6. Deamino-[9-glycolicamide] oxytocin exhibited 134 +/- 13 U/mg and 355 +/- 48 U/mg of uterotonic activity in absence and in presence, respectively, of Mg2+, 108 +/- 8 U/mg of milk-ejecting activity, 0.35 +/- 0.03 U/mg of pressor activity and 2.5 +/- 0.1 U/mg of antidiuretic activity. It is concluded that the hydrogen bond under question is not critical for the conformation required for biofunctional interaction of oxytocin with its receptors in the uterus, mammary gland and other target organs.

[On preclotting of woven Dacron vascular prostheses (author's transl)]

The role and the clinical value of common protocols of preclotting for a woven Dacron vascular prosthesis have been investigated. A comparative study of blood loss was carried out for Standard Woven De Bakey protheses inserted in a specially constructed extracorporeal blood circuit with canine models. The system detected transport of blood across the wall of the prostheses. These measurements were supplemented by gravimetric assessment of blood clot density and scanning electronmicroscopy examination of the internal surfaces of the prostheses. The pre-operative protocols investigated included : absence of pre-treatment, precoagulation with anticoagulant-free blood and various techniques using heparinized blood subsequent to an initial blood contact (modified method of Sauvage). The effect of using heparinized animals was also investigated. Leakages in unclotted prostheses could be reduced almost five fold by any precoagulation technique. Heparinization did not cause a significant increase in leakage and considerably improved the quality of the newly deposited blood product lining on the prostheses which consisted almost entirely of fibrin and eliminated any embolization.

Studies on the importance of the asparagine residue in oxytocin. Synthesis and some pharmacological properties of [1-alpha-mercaptoacetic acid, 5-isoasparagine] oxytocin

[1-Alpha-Mercaptoacetic acid, 5-isoasparagine] oxytocin was synthesized to study the effects of moving the side chain carboxamide group of the amino acid residue in position 5 of oxytocin from the beta to the alpha position. The analog has an isoasparagine residue in position 5 and the 20-membered ring size of oxytocin is maintained by substituting cysteine in position 1 of oxytocin by alpha-mercaptoacetic acid. The analog was found to possess 0.098 +/- 0.002 U/mg of uterotonic activity but no milk-ejecting, antidiuretic or rat pressor activity could be detected. The substance did not inhibit the uterotonic or milk-ejecting activity induced by oxytocin nor the antidiuretic or rat pressor responses to the USP posterior pituitary standard. These results, together with the data available in the literature, indicate that an analog of oxytocin lacking the asparagine residue in position 5 is neither an agonist nor an antagonist. The observations may mean that the asparagine residue is critically important for the interaction of oxytocin with its receptor.

A SEM investigation of the trauma to prostheses and arteries during vascular reconstruction procedures

Scanning electron microscopy was used to diagnose incidents of trauma and the pattern of healing following surgical implantation of microporous blood vessel substitutes. Vascular reconstruction procedures using autogenous or synthetic prosthetic materials inflict damage to the adjacent tissues as well as the prosthesis. This effects the thrombotic behavior and healing pattern of the area. The prognoses for long term success are, as a consequence, directly influenced. Various vessel occluding devices were evaluated on canine models with respect to their ability to damage blood vessels at the clamped site. The impact of suture needles on tissues and prosthetic materials was also considered. Of the various vessel clamping devices which are commercially available, those which have elastomeric shields on the clamping components were found to be the most satisfactory. The development of less traumatic surgical devices and possible modifications in the surgical protocols are discussed with the aim of further reducing surgical trauma.

Biofunctional evaluation of a hydrogen bond linking the ring and tail beta-turns of oxytocin

Deamino-[8-N-methylleucine]oxytocin and deamino-[8-alpha-hydroxyisocaproic acid]oxytocin were synthesized to study the importance of hydrogen bonding between the carboxamide carbonyl of asparagine and the peptide N-H of leucine in stabilizing the biologically active conformation of oxytocin. The analogs were synthesized by coupling deaminotocinoic acid with Pro-Leu(Me)-Gly-NH2 and Pro-HyIc-Gly-NH2, respectively. (HyIc is alpha-hydroxyisocaproic acid). Deamino-[8-N-methylleucine]oxytocin was found to possess 48 +/- 7 units of uterotonic activity, 33 +/- 5 units of avian vasodepressor activity, and 3.15 +/- 1.5 units of antidiuretic activity per mg; deamino-[8-alpha-hydroxyisocaproic acid]oxytocin possessed 134 +/- 12 units of uterotonic activity, 31 +/- 3 units of avian vasodepressor activity, 9.6 +/- 3.0 units of antidiuretic activity, and 0.26 +/- 0.02 unit of pressor activity per mg. Neither of the analogs possesses the peptide N-H at residue 8 required for the formation of a hydrogen bond with the asparagine carboxamide; however, both can assume the conformation needed to evoke the characteristic biological activities of oxytocin although in lower potency. It is concluded that such a hydrogen bond does not constitute a conformational constraint that is essential for hormone action.

Conformational studies on [Pro3, Gly4]-oxytocin in dimethyl sulfoxide by 1H nuclear magnetic resonance spectroscopy: evidence for a type II beta turn in the cyclic moiety

A model for oxytocin has been previously proposed in which residues 3 and 4 occupy the corner positions in a beta turn (Urry, D. W., & Walter, R (1971) Proc. Natl. Acad. Sci. U.S.A. 68, 956). The analogue [Pro(3),Gly(4)]-oxytocin (PGO) was used in proton magnetic resonance (1H NMR) studies designed to probe the contribution of these corner positions in forming a beta turn. Comparison of various 1H NMR parameters obtained at 220 MHz for backbone amide protons of PGO with those for the corresponding protons of oxytocin suggests that, to a first approximation, these two peptides may have similar backbone conformations in )CD3)2SO. Theoretically, the L-Pro lead toGly sequence in positions 3 and 4 of PGO would allow the formation of either a type I or type II beta turn. The two coupling constants between vicinal amide and C alpha protons for Gly(4) of PGO in (CD3)2SO are compatible with a type II beta turn in which 04, the dihedral angle about the bond between the backbone C alpha and N' atoms of Gly4, is appromximately +92 degrees, but not with a type I beta turn. A survey of peptides studied in other laboratories by X-ray and/or 1H NMR with reported type II beta turns with L-Pro lead toGly or Gly lead to Gly sequences in the corner positions revealed a close correlation between chemical shifts and vicinal coupling constants for the glycl residue in the second corner position. It is suggested that this criterion can form an additional basis for the characterization of beta turns. More studies are needed to determine the particular type of beta turn manifest in the cyclic moiety of oxytocin per se, although a reasonable working hypothesis is that oxytocin, similar to PGO, has a type II beta turn.

[Binding sites for 3H-Leu-enkephalin in rat straitum]

The binding of 3H-Leu-Enkephalin to a particulate fraction from Rat striatum has been investigated in the presence of 20 mum bacitracin which prevents its hydrolysis. After deduction of a low-affinity, "non-saturable" component, the saturation kinetics at equilibrium provide evidence for two distinct saturable sites. The first exhibits Michaelis kinetics with a Kd value of 2.7 +/- 0.1 nM; both morphine and naloxone compete with the binding of 3H-Leu-Enkephalin on this site but not on the second one. The marked decrease in binding of 3H-Leu-Enkephalin observed in the presence of high concentration of sodium ions indicates that these two pentapeptides have the same properties as morphinomimetic analgesics. Taken together, these data indicate that the first site is identical to the "opiate receptor", while the nature of the second saturable site remains to be established.

Importance of the third amino acid residue of oxytocin for its action on isolated rat uterus: study of relationship between hormone conformation and activity

In a continued effort to relate the three-dimensional structure of a peptide hormone to its biological activity, the dose-response relationships of [3-phenylalanine] oxytocin (oxypressin), with an aromatic amino acid residue in position 3, and [3-beta-cyclohexylalanine]oxytocin, with an aliphatic amino acid residue to position 3, were determined in the rat uterine assay in vitro and compared to that of oxytocin. Oxypressin has not only a lower affinity for the smooth muscle receptor than the natural hormone, but also a decreased maximal response (efficacy). [3-beta-Cyclohexylalanine]oxytocin exhibits an even lower affinity than oxypressin, but retains the same maximal response as oxytocin. A reorientation of the tyrosine sidechain, caused by the presence of a neighboring aromatic sidechain in position 3, away from the surface of the 20-membered ring is though to remove the phenolic hydroxyl group from its optimal position in the "active center" of oxytocin and give rise to the reduced efficacy of oxypressin.

Oxytocin analogues with combined high smooth muscle and negligible antidiuretic activities. Investigation of position 7 in neurohypophyseal hormones

The proline residue in position 7 of oxytocin occupies one of the four corner positions in the two beta turns proposed for the preferred conformation of the pituitary hormone. It has been suggested that synthetic modifications of the residues in these corner positions will yield analogues in which one or more of the biological activities of the parent hormone is highly accentuated in terms of potency relative to other activities. In a continued effort to test this hypothesis the following analogues of oxytocin were prepared: [7-glycine]oxytocin, [1-beta-mercaptopropionic acid,7-glycine]oxytocin, [7-alanine]oxytocin, and [1-beta-mercaptopropionic acid,7-alanine]oxytocin. These peptides were found to possess the following specific activities, respectively: rat uterotonic, 65 +/- 2, 355 +/- 3, 22 +/- 1, 123 +/- 4; avian vasodepressor, 5.3 +/- 0.8, 17 +/- 0.4, 4.8 +/- 0.1, 9.8 +/- 0.5; rat antidiuretic, less than0.01, 0.062, 0.081 +/- 0.01, 0.17 +/- 0.01; rat pressor, 0.3, 0.5, 0.4, 0.5 unit/mg. Thus the analogues retain high uterotonic activity but exhibit strongly diminished renal and vascular activities relative to oxytocin. Especially noteworthy is [1-beta-mercaptopropionic acid,7-glycine]oxytocin with its high uterotonic activity but very low antidiuretic and pressor activities. The activity profile of this analogue combined with the fact that it is only slowly enzymatically degraded warrants further investigations of this peptide for clinical applications.

Synthesis of nucleoside diphosphates and triphosphates by a salmon milt enzyme preparation

A cell-free enzyme preparation capable of forming nucleoside (or deoxynucleoside) di- and tri-phosphates from the corresponding nucleoside monophosphates in the presence of adenosine triphosphate (ATP) was prepared from immature salmon milts. The preparation was not free from phosphatase activities. The corresponding nucleoside (or deoxynucleoside) di- and tri-phosphates were readily formed from cytidine monophosphate, adenosine monophosphate, uridine monophosphate, and deoxyuridine monophosphate; guanosine monophosphate, deoxycytidine monophosphate, inosine monophosphate, and deoxyribosylthymine monophosphate were poorer substrates. The reaction required ATP. Guanosine triphosphate, uridine triphosphate, cytidine triphosphate, deoxyribosylthymine triphosphate, and inosine triphosphate could replace ATP, though they were in general less effective. With cytidine monophosphate as substrate, the formation of cytidine triphosphate was accelerated by Mg++, Ca++, Mn++, Co++, Ni++, and CN−, and was inhibited by Cu++, Ag+, Zn++, Hg++, F−, iodoacetate, p-hydroxymercuribenzoate, and ethylenediaminetetraacetate. Neither glutathione nor 2-mercaptoethanol in concentrations of between 1 × 10−3 and 1 × 10−1 M protected the enzyme. The optimum pH was 7.5–8.0. The enzyme was very unstable, losing two-thirds of its activity in 1 hour at 30 °C. Under optimum conditions with cytidine monophosphate as substrate, 8.5 μmoles of cytidine triphosphate were formed per hour per milligram of protein nitrogen at 25 °C.

THE REACTION OF SULFONYLIMIDO INTERMEDIATES WITH AROMATIC COMPOUNDS

Thermolysis of methanesulfonyl azide in aromatic solvents gives methanesulfonamide and the isomeric methanesulfonanilides. The orientation of the latter and the relative reactivities of the aromatic substrate towards attack by the methylsulfonylimido intermediate have been studied quantitatively. The high reactivity and also great selectivity of the attacking species are interpreted in terms of a rate-determining addition process to give a sulfonylaziridine derivative followed by a product-determining ring opening and rearrangement to the substituted anilides. Partial rate factors are discussed, as are possible mechanisms for the formation of the methanesulfonamide. The methanesulfonylimido intermediate must be abstracting two hydrogen atoms synchronously from the aromatic substrate.