Mechanism of lipid bilayer perturbation by bactericidal membrane-active small molecules

Membrane-active small molecules (MASMs) are small organic molecules designed to reproduce the fundamental physicochemical properties of natural antimicrobial peptides: their cationic charge and amphiphilic character. This class of compounds has a promising broad range of antimicrobial activity and, at the same time, solves some major limitations of the peptides, such as their high production costs and low in vivo stability. Most cationic antimicrobial peptides act by accumulating on the surface of bacterial membranes and causing the formation of defects when a threshold is reached. Due to the drastically different structures of the two classes of molecules, it is not obvious that small-molecule antimicrobials act in the same way as natural peptides, and very few data are available on this aspect. Here we combined spectroscopic studies and molecular dynamics simulations to characterize the mechanism of action of two different MASMs. Our results show that, notwithstanding their simple structure, these molecules act just like antimicrobial peptides. They bind to the membrane surface, below the head-groups, and insert their apolar moieties in the core of the bilayer. Like many natural peptides, they cause the formation of defects when they reach a high coverage of the membrane surface. In addition, they cause membrane aggregation, and this property could contribute to their antimicrobial activity.

Use of an Innovative Simple Method for Anaerobiosis in the Diagnosis and Management of Infections in Two Unusual Cases

Technical limitations restrict routine anaerobe isolation from clinical materials in resource-limited laboratories. An innovative two steps combustion candle jar technique may be suitable for such setup. This system was tried with one case of chronic osteomyelitis developed on supracondyler compound fracture. Porphyromonas spp. was isolated and identified. Vancomycin was recommended based on in vitro sensitivity test, but the leg was amputed after receiving a resistant drug gentamycin. While in another child with hydrocephalous, V-P shunt associated infection by Peptostreptococcus anaerobius was successfully controlled by sensitive drug vancomycin. These two eye-opener cases insisted us for large scale application of the technique.

Cyclization and unsaturation rather than isomerisation of side chains govern the selective antibacterial activity of cationic-amphiphilic polymers

The influence of cyclization and unsaturation on the hydrophobic side chains of cationic-amphiphilic polymers towards antibacterial activity and mammalian cell toxicity is reported.

Isosteric substitution in cationic-amphiphilic polymers reveals an important role for hydrogen bonding in bacterial membrane interactions

The important role of hydrogen bonding in the interactions of cationic-amphiphilic polymers with bacterial membranes has been reported.

Biomimetic antibacterial polymers, the functional mimics of antimicrobial peptides (AMPs), targeting the bacterial cell membrane have been developed to combat the problem of antibiotic resistance. Amphiphilicity, a balance of cationic charge and hydrophobicity, in these polymers has been shown to be pivotal for their selective interactions with anionic lipid membranes of bacteria instead of zwitterionic mammalian (human erythrocyte) membranes. However, it is unclear if and to what extent hydrogen bonding in amphiphilic antibacterial polymers contributes to this membrane binding specificity. To address this, we employ isosteric substitution of ester with amide moieties that differ in their potency for hydrogen bonding in the side chains of N-alkyl maleimide based amphiphilic polymers. Our studies reveal that amide polymer (AC3P) is a potent antibacterial agent with high membrane-disrupting properties compared to its ester counterpart (EC3P). To understand these differences we performed bio-physical experiments and molecular dynamics (MD) simulations which showed strong interactions of AC3P including hydrogen bonding with lipid head groups of bacterial model lipid bilayers, that are absent in EC3P, make them selective for bacterial membranes. Mechanistic investigations of these polymers in bacteria revealed specific membrane disruptive activity leading to the delocalization of cell division related proteins. This unprecedented and unique concept provides an understanding of bacterial membrane interactions highlighting the role of hydrogen bonding. Thus, these findings will have significant implications in efficient design of potent membrane-active agents.

Anaerobic culture on growth efficient bi-layered culture plate in a modified candle jar using a rapid and slow combustion system

Success for maximum isolation of anaerobes depends on maintaining critically low oxygen levels throughout and growth in a reduced medium with exclusion of inhibitory substances. Hence a dual system was used equipped with candle combustion for instant exhaustion of major part of oxygen from a sealed jar, along with acidified steel wool for residual oxygen purging. For inhibitory substances removal, test anaerobes were grown on anaerobic medium layered on buffer charcoal agar bed. After 48 hours incubation average colony sizes were compared with that of growths in conventional Gas-Pak system. Better growths were noted in the innovative system.

DNA base excision repair of 5-hydroxymethyl-2'-deoxyuridine stimulates poly(ADP-ribose) synthesis in Chinese hamster cells

5-Hydroxymethyl-2'-deoxyuridine (hmdUrd) is incorporated into DNA as a thymidine analog resulting in extensive substitution of thymine residues with 5-hydroxymethyluracil (hmUra) residues. These hmUra residues are then subject to excision by action of hmUra-DNA glycosylase. 3-Aminobenzamide (3AB), an inhibitor of poly(ADP-ribose) synthesis, is toxic to cells that incorporate and repair hmdUrd. To demonstrate that incorporation and repair of hmdUrd stimulates synthesis of poly(ADP-ribose) from intracellular NAD, V79 hamster cells were treated with hmdUrd and intracellular NAD levels were measured. Following hmdUrd treatment, NAD levels fell markedly (80-90%) within 4 h and remained low for at least 10 h, before partially recovering by 24 h. The degree of NAD lowering was dose dependent and paralleled net hmdUrd incorporation. The NAD lowering was largely prevented by concurrent treatment with 4 mM 3AB. No effects on NAD levels were seen following treatment with deoxythymidine or bromodeoxyuridine, which are incorporated into DNA but, in contrast to hmdUrd, are not repaired. When the incorporation of hmdUrd into DNA was blocked with hydroxyurea or aphidicolin, no NAD lowering was seen. HmdUrd also did not produce lowering of NAD concentrations in mutant cell strains deficient in the ability either to incorporate hmdUrd into DNA or to repair hmdUrd from DNA. These results demonstrate that synthesis of poly(ADP-ribose) resulted directly from the incorporation into DNA of the nucleoside hmdUrd and its subsequent repair. These results unequivocally demonstrate that the initiation of normal DNA base excision repair by itself, and not DNA damage per se, is a sufficient stimulus for the induction of poly(ADP-ribose) synthesis.

Opioid modulation of oxytocin release from spinal cord synaptosomes

Regulation of oxytocin release from spinal cord synaptosomes was investigated using in vitro preparations. Experiments were designed to determine whether opioid peptides regulate oxytocin release from spinal cord synaptosomes, as they do from synaptosomes derived from neurohypophysis. Oxytocin release was evoked by the addition of 56 mM KCl in synaptosomes prepared from thoracic and lumbosacral parts of the spinal cord. Addition of 5 microM naloxone, 1 min prior to the addition of the stimulus, caused a significant (p < 0.025) increase of oxytocin release. Prior addition of 5 microM dynorphin, demonstrated a significant (p < 0.01) decrease whereas addition of 5 microM [D-Ala2,N-Me-Phe4,Gly-ol]-enkephalin showed no effect on KCl-induced OT release. The results suggest that spinal cord OT release is under inhibitory control of opioid peptides and the opioids act via the kappa opioid receptor.

The release of oxytocin from spinal cord synaptosomes by high KCl depolarizing stimulus: a calcium dependent process

Oxytocin (OT) release from synaptosomes isolated from the thoracic (T) and lumbosacral (LS) regions of the spinal cord was evoked by 56 mM potassium chloride (KCl). The release mechanism was shown to be a calcium dependent process. The ability of high KCl to evoke OT release from isolated nerve terminals in a calcium dependent manner provides additional support for the role of OT as a neurotransmitter in the spinal cord.

Isotonic and hypertonic saline act as stressful stimuli for oxytocinergic system of the pituitary, hypothalamus and spinal cord

We have recently demonstrated that immobilization stress leads to an increase in the spinal cord oxytocin content in the rat. The current experiments were undertaken to determine if other stressors have similar effect on the spinal cord oxytocin levels. Male Long Evans rats were injected either with isotonic or hypertonic saline and sacrificed either 15 minutes or 3 hours after saline injection. Oxytocin content of the neurohypophysis, hypothalamus and spinal cord were determined by specific radioimmunoassay in Sep-pak extracted samples. The results demonstrate that both isotonic and hypertonic saline act as stressful stimuli and reduce oxytocin content of the pituitary and hypothalamus when the rats were sacrificed within 15 minute following the injection. Spinal cord oxytocin content was also affected by isotonic and hypertonic saline administration; oxytocin content decreased if rats were sacrificed after a short period (15 min) and increased if rats were sacrificed after a long period (3 hours). These results, together with those reported earlier, support the hypothesis that stressors, in general, affect the spinal cord oxytocin content.

Changes in oxytocin and vasopressin content in posterior pituitary and hypothalamus following pantethine treatment

Pantethine, a cysteamine precursor, depletes somatostatin in the cerebral cortex and hypothalamus and prolactin in the anterior pituitary and hypothalamus. This study investigated the effect of pantethine on oxytocin and arginine vasopressin content in the posterior pituitary and hypothalamus. Male Long-Evans rats were injected intraperitoneally with escalating doses of pantethine (i.e., 146.7 mg, 293.4 mg and 586.6 mg/100 gm body weight). Hormone content was determined by radioimmunoassay. Three hours after pantethine treatment, the oxytocin content in the posterior pituitary and the hypothalamus was markedly reduced with all doses of the drug. Vasopressin content in the posterior pituitary and hypothalamus was decreased but to a lesser extent than oxytocin and only with the highest dose of pantethine. Pantethine may act to reduce oxytocin and vasopressin content through intracellular conversion to cysteamine. The exact mechanism of action of pantethine on oxytocin and vasopressin remains to be elucidated.

Solid-phase synthesis of 16 potent (selective and nonselective) in vivo antagonists of oxytocin

We describe the synthesis and some pharmacological properties of 16 new in vivo antagonists of oxytocin. These are based on modifications of three peptides: A, B, and C. A is our previously reported potent and selective antagonist of the vasopressor (V1 receptor) responses to arginine-vasopressin (AVP)/weak oxytocin antagonist, [1-(beta-mercapto-beta,beta-pentamethylenepropionic acid), 2-O-methyltyrosine]arginine-vasopressin (d(CH2)5[Tyr(Me)2]AVP. B reported here, the Ile3 analogue of A, is d(CH2)5[Tyr(Me)2]AVT (5 below) and C is our previously reported potent nonselective oxytocin antagonist/AVP V1 antagonist, [1-(beta-mercapto-beta,beta-pentamethylenepropionic acid),2-O- methyltyrosine,8-ornithine]vasotocin (d(CH2)5[Tyr(Me)2]OVT). The following substitutions and deletions, alone or in combination, were employed in A, B, and C: 1-deaminopenicillamine (dP); D-Tyr(Alk)2 (where Alk = Me or Et), D-Phe2; Val4, Thr4; delta 3-Pro7; Lys8, Cit8; desGly9, desGly-NH2(9), Ala-NH2(9); Leu-NH2(9); Arg-NH2(9). The 16 new analogues are (1) d(CH2)5[D-Tyr(Me)2]AVP, (2) d(CH2)5[D-Tyr(Me)2, Val4,delta 3-Pro7]AVP, (3) d(CH2)5[D-Tyr-(Et)2, Val4,Lys8]VP, (4) d(CH2)5[D-Tyr(Et)2,Val4,Cit8]VP, (5) d(CH2)5[Tyr(Me)2]AVT, (6) d(CH2)5[Tyr(Me)2,Lys8]VT, (7) dP[Tyr(Me)2]AVT, (8) dP[Tyr(Me)2,Val4]AVT, (9) d(CH2)5[D-Tyr(Me)2, Val4]AVT, (10) d(CH2)5[D-Phe2,Val4]AVT, (11) d(CH2)5[Tyr(Me)2,Thr4]OVT, (12) d(CH2)5[Tyr(Me)2,Thr4,Ala-NH2(9)]OVT, (13) d(CH2)5[Tyr(Me)2,Thr4,Leu-NH2(9)]OVT, (14) d(CH2)5[Tyr(Me)2,Thr4,Arg-NH2(9)]OVT, (15) desGly-NH2(9),d(CH2)5[Tyr(Me)2,Thr4]OVT, (16) desGly9,d(CH2)5[Tyr(Me)2,Thr4]OVT. 1-4 are analogues of A, 5-10 are analogues of B, and 11-16 are analogues of C. Their protected precursors were synthesized either entirely by the solid-phase method or by a combination of solid-phase and solution methods (1 + 8 or 8 + 1 couplings). All analogues were tested in rats for agonistic and antagonistic activities in oxytocic (in vitro, without and with Mg2+, and in vivo) assays as well as by antidiuretic and vasopressor assays. All analogues exhibit potent oxytocic antagonism in vitro and in vivo. With an in vitro pA2 (in the absence of Mg2+) = 9.12 +/- 0.09, dP[Tyr(Me)2]AVT is (7) one of the most potent in vitro oxytocin antagonists reported to date. Fifteen of these analogues (all but 6) appear as potent or more potent in vivo oxytocin antagonists than C (pA2 = 7.37 +/- 0.17). Analogues 1-9 and 14 are potent AVP V1 antagonists. Their anti-V1 pA2 values range from 7.92 to 8.45. They are thus nonselective oxytocin antagonists.(ABSTRACT TRUNCATED AT 400 WORDS)

Oxytocin and vasopressin are present in human and rat pancreas

Immunoreactive oxytocin and vasopressin were found in human and rat pancreatic extracts. The pancreatic oxytocin and vasopressin eluted on Sephadex G-75 gel filtration chromatography and on reverse phase high pressure liquid chromatography in the same positions as their respective reference preparations. The immunoreactive oxytocin was biologically active in the rat milk ejection assay. The presence of oxytocin and vasopressin in human and rat pancreatic extracts suggests the possibility of local synthesis of both hormones. The neurohypophysial hormones are known to be endocrine mediators of insulin and glucagon release. The finding of oxytocin and vasopressin in the pancreas raises the possibility, although yet unproven, of local synthesis and perhaps a paracrine function for the neurohypophysial peptides upon pancreatic hormone release or for a local function upon the liver.

Effects of cysteamine on blood pressure: possible mediation through vasopressin release

Cysteamine (beta-mercaptoethylamine, CSH) has been reported to have various effects on the neuroendocrine system. Reports indicate CSH decreases pituitary oxytocin (OT) without affecting pituitary vasopressin (VP). However, preliminary studies from our laboratory strongly indicate that CSH has an effect on VP release. Experiments were conducted with dibenzyline-treated, urethane-anesthetized, male Sprague-Dawley (SD) rats. Rats were injected with 4 mU of standard VP and 4 mg/100 g of CSH. Administration of VP resulted in an increase in mean arterial pressure (MAP) of 23.5 +/- 3.2 mm Hg. Administration of CSH resulted in a consistent, immediate decrease in MAP of 13.0 +/- 2.0 mm Hg prior to an increase of 21.0 +/- 2.6 mm Hg. The effects due to VP and CSH were strikingly different; the CSH-induced MAP rise took longer to peak and to return to baseline. Both the VP- and CSH-induced MAP rise were markedly inhibited by a prior administration of a specific VP antagonist d(CH2)5[Tyr(Me)]AVP. In addition, the typical increase in MAP observed in SD rats following CSH administration was substantially reduced when the same dose was administered in homozygous diabetes insipidus (HODI) rats. The data presented here strongly suggest that CSH-induced MAP elevation is due to the release of VP from the pituitary gland.

Immobilization stress affects oxytocin and vasopressin levels in hypothalamic and extrahypothalamic sites

Oxytocin (OT) and vasopressin (VP) have been localized in various sites within the central nervous system outside the classic hypothalamo-neurohypophyseal axis. This study investigated the effect of immobilization stress on the levels of OT and VP in the hypothalamus, pons-medulla, and the cervical, thoracic, and lumbosacral segments of the spinal cord. Male Long Evans rats were immobilized for 1 min and sacrificed by guillotine. The tissues were dissected out and homogenized in 0.1 N HCl. The hormone content was determined by radioimmunoassay (RIA) in Sep-pak extracted samples. The data show a decrease in OT content of 33.6% (P less than 0.02) and 42.4% (P less than 0.01) in the hypothalamus and pons-medulla, respectively. In the spinal cord, however, OT levels were increased by 39.1% (not significant), 51.1% (P less than 0.05), and 87.6% (P less than 0.001) in the cervical, thoracic, and lumbosacral segments respectively. The VP content of the hypothalamus and pons-medulla did not change. However, in the spinal cord, the VP content was also increased by 101.4% (P less than 0.01) and by 143.7% (P less than 0.01) in the cervical and lumbosacral segments. The levels of VP in the thoracic segment did not change. The data demonstrate that stress can alter hypothalamic and extra-hypothalamic levels of OT as well as spinal cord levels of VP. The exact physiological effects of these changes, particularly within the spinal cord, remain to be elucidated.

Cyclic variations in spinal cord levels of oxytocin and vasopressin during the stages of the rat estrous cycle

Oxytocin (OT) and vasopressin (VP) have been localized to numerous central nervous system locations outside the classic hypothalamo-neurohypophyseal tract including all levels of the spinal cord. To date, the physiological function of these peptides within the spinal cord is unknown. The purpose of this study was to determine if the variations exhibited by pituitary OT and VP during the stages of the estrous cycle in the rat were also present in the spinal cord. The stage of the estrous cycle was determined by vaginal smears in female Long Evans rats. Following decapitation, the cervical, thoracic, and lumbosacral segments of the spinal cord were isolated and homogenized, and the hormones were extracted from the tissue with the Sep-pak method. OT and VP content were determined by RIA. A cyclic variation in spinal cord OT and VP was present, with maximal levels occurring in diestrus, a time in the estrous cycle when LH and estradiol levels are lowest. Our results suggest that spinal cord OT and VP may be regulated by ovarian hormones. These data represent the first documented changes in spinal cord levels of OT and VP under physiological conditions.

Elimination of vasopressin analgesia following lesions placed in the rat hypothalamic paraventricular nucleus

Pain thresholds are increased following central administration of arginine vasopressin (AVP), an effect which appears not to be mediated through opioid analgesic processes. In addition to magnocellular projections to the posterior lobe of the pituitary gland and parvocellular projections to the zona externa of the median eminence, the paraventricular nucleus (PVN) of the hypothalamus contains VP parvocellular neurons which also project to extrahypothalamic structures involved in pain inhibition. The present study examined whether AVP analgesia as measured by the tail-flick test was altered in animals with lesions placed in the PVN at either 7 or 35 days after surgery. VP levels in the pons-medulla and the lumbo-sacral spinal cord were measured by radioimmunoassay, as well as VP-like immunoreactivity in the PVN and spinal cord with immunocytochemistry. Lesions placed in the PVN eliminated AVP analgesia on the tail-flick test at both 7 and 35 days after surgery, and decreased radioimmunoassayable VP by 59% in the lumbo-sacral spinal cord and 36% in the pons-medulla. The extent of the lesions ranged from complete destruction of the PVN to partial sparing of ventro-medial PVN cells with VP-like immunoreactivity. These data indicate that the PVN is a critical structure for the integrity of AVP analgesia.

Hypothalamic oxytocin: a cerebrovascular modulator in man?

Immunocytochemical studies in normal rats show an association between oxytocin (OT) neurons and cerebral blood vessels. This is supported by the finding of neurophysin (NP) immunoreactivity in blood vessels and pia-arachnoid tissue of rats with hereditary vasopressin (VP) and VP-NP deficiency. OT and OT-NP fibers were visualized in pia-arachnoid and blood vessels at the base of the brain and, to a lesser extent, over the dorsal surface. OT constricts human basilar artery with a threshold response in the 10(-10) M range, and an ED50 of 4.8 X 10(-9) M. These observations suggest that extrahypothalamic projections of OT neurons may modulate cerebrovascular function.

Extrahypothalamic neurohypophysial peptides in the rat central nervous system

Vasopressin (VP) and oxytocin (OT) have been identified in a number of extrahypothalamic areas, both by immunohistochemistry and by radioimmunoassay. Because of the incomplete nature of the data available, we have conducted a survey of the VP and OT concentrations in the rat central nervous system. VP and OT were readily detectable in all areas studied. With the exception of the amygdala, OT concentrations were generally 2-4 times those of VP. The physiological function of neurohypophysial hormones in these extrahypothalamic areas is essentially unknown.

Morphine, beta-endorphin and [D-Ala2] Met-enkephalin inhibit oxytocin release by acetylcholine and suckling

Morphine inhibits suckling-induced oxytocin (OT) release in lactating mice. Since beta-endorphin and enkephalins have several actions in common with morphine, the action of these opioid peptides on OT release was investigated. In anesthetized lactating rats, OT release was achieved by intraventricular injection of acetylcholine (ACh) or by the physiological stimulus of suckling. The amount of OT released was estimated by comparing milk-ejection responses to these stimuli to those following known amounts of intravenous (IV) OT. Both beta-endorphin and [D-Ala2]Met-enkephalin inhibited ACh-induced and suckling-induced OT release. Naloxone antagonized opiate inhibition in both cases.

Vasopressin concentrations in hypophysial portal plasma: insignificant reduction following removal of the posterior pituitary gland

This study was designed to determine the relative contribution of vasopressin-secreting nerve terminals in the median eminence compared to those in posterior pituitary to the high concentrations of the hormone in hypophysial portal blood. Vasopressin was measured by radioimmunoassay in plasma obtained by microcannulation of individual long portal veins of 8 intact male Long-Evans rats (2.0 +/- 0.44 ng/ml SEM), and in 8 in which the posterior pituitary was removed just prior to collection (1.5 +/- 0.3 ng/ml SEM). Since there was no significant difference /p = 0.23, NS) in the concentration of vasopressin in portal plasma after removal of the posterior pituitary gland, these results suggest that the direct vasopressin pathway to the median eminence is the major source of vasopressin in portal blood of the rat.

Design and synthesis of potent in vivo antagonists of oxytocin

We have previously shown that the substitution of 8-ornithine and 2-O-methyltyrosine alone and in combination in [1-deaminopenicillamine] oxytocin (dPOT) brought about enhancements in antagonistic potencies to responses to oxytocin in vivo. To explore the effects of these substitutions in analogs of dPOT containing larger alkyl substitutents on the beta carbon at position 1 and on the tyrosine residue at position two, the following six analogs were synthesized: [1-(beta-mercapto-beta, beta-diethylpropionic acid), 8-ornithine] vasotocin (1, dEt2OVT); (1-beta-mercapto-beta, beta-cyclopentamethylenepropionic acid), 8-ornithine] vasotocin (2, d(CH2)5OVT): [1-beta-mercapto-beta, beta-diethylpropionic acid), 2-O-methyltyrosine, 8-ornithine]vasotocin [3, dEt2 Tyr(Me)OVT]; [1-(beta-mercapto-beta, beta-diethylpropionic acid), 2-O-ethyltyrosine, 8-ornithine]vasotocin [4, dEt2 Tyr(Et)OVT]; [1-beta-mercapto-beta', beta-cyclopentamethylenepropionic acid), 2-O-methyltyrosine, 8-ornithine]vasotocin [5, d(CH2)5 Tyr(me)OVT]: [1-beta-mercapto-beta, beta-cyclopentamethylenepropionic acid), 2-O-methyltyrosine, 8-ornithine]vasotocin [6,d(CH2)5 Tyr(Et)OVT]. The required protected intermediates were synthesized by a combination of solid-phase synthesis and by individual 8 + 1 couplings in solution. All six analogs antagonize the actions of oxytocin on the rat uterus in the absence of Mg2+, in the presence of 0.5 mM Mg2+ and in situ. They also antagonize milk ejection responses to oxytocin, and the vasopressor responses to arginine vasopressin, and all have very low antidiuretic activities. With pA2 values of 7.35 +/- 0.08 and 7.37 +/- 0.17, respectively, compounds 3 and 5 are the two most potent in vivo antagonists of oxytocin reported to date.

The design of effective in vivo antagonists of rat uterus and milk ejection responses to oxytocin

Several new synthetic analogs of the oxytocin antagonist [1-deaminopenicillamine]oxytocin have been prepared and tested for their abilities to inhibit responses to oxytocin by the isolated rat uterus in the absence and presence of Mg++, by the rat uterus in situ, and by the rat mammary gland in situ. Substituting 2-O-methyltyrosine in [1-deaminopenicillamine]oxytocin strikingly enhances antagonism of all uterin responses, and [1-deaminopenicillamine, 2-O-methyltyrosine]oxytocin and its 4-threonine analog are also potent inhibitors of the milk ejection response. Substituting 2-phenylalanine in [1-deaminopenicillamine]oxytocin also enhances antagonistic activities in all uterine assays, but [1-deaminopenicillamine, 2-phenylalanine]oxytocin retains agonistic activity on milk ejection assays. From these studies we can conclude that changes in the 1-position (1-deaminopenicillamine substitution) and the 2-position (2-O-methyltyrosine or 2-phenylalanine substitution) can have additive effects on antagonistic activities. Substitution of an 8-ornithine also enhances inhibitory potency in vivo, and this effect may also be additive to those of the substitutions in 1- and 2-positions. These findings provide many clues that may lead to the design of even more effective antagonists; several of the analogs reported here appear to the most effective antagonists of oxytocin in vivo yet reported and may be useful agents in further studies on the physiological functions of endogenous oxytocin.

Synthetic antagonists of in vivo responses by the rat uterus to oxytocin

As part of a program in which we are attempting to synthesize in vivo antagonists of oxytocin, the following four analogues were synthesized and tested for antagonistic activities in rat uterus and rat vasopressor assay systems: [-(beta-mercapto-beta,beta-diethylpropionic acid), 4-threonine]oxytocin (1, dEt2TOT), [1-beta-mercapto-beta,beta-cyclopenta-methylenepropionic acid), 4-threonine]oxytocin [2, d(CH2)5TOT], [1-deaminopenicillamine,2-O-methyltyrosine]oxytocin [3, dPTyr(Me)OT], and [1-deaminopenicillamine,2-O-methyltyrosine,4-threonine]oxytocin [4, dPTyr(Me)TOT]. The required protected intermediates were synthesized by a combination of solid-phase peptide synthesis and by individual 8 + 1 couplings in solution. All four analogues antagonize the actions of oxytocin on the rat uterus (a) in the absence of Mg2+, (b) in the presence of 0.5 mM Mg2+, and (c) in situ. They exhibit, respectively, the following pA2 values in each of the assay systems a-c: (1) (a) 7.72 +/- 0.11, (b) 7.36 +/- 0.09, (c) 6.47 +/- 0.11; (2) (a) 7.91 +/- 0.13, (b) 7.81 +/- 0.09, (c) 6.94 +/- 0.11; (3) (a) 7.76 +/- 0.12, (b) 7.80 +/- 0.12, (c) 6.86 +/- 0.12; (4) (a) 7.64 +/- 0.14, (b) 7.79 +/- 0.09, (c) 6.84 +/- 0.10. They have the following antivasopressor pA2 values: (1) 6.30 +/- 0.13; (2) 5.86 +/- 0.03; (3) 7.59 +/- 0.05; (4) 7.32 +/- 0.04. Compounds 2-4 are among the most potent in vivo antagonists of oxytocin reported to date.

Characterization of an antiserum used in a radioimmunoassay for arginine-vasopressin: implications for reference standards

The region of the arginine-vasopressin (AVP) molecule critical for binding to the effective antibodies in a RIA has been localized to the vicinity of the Phe3 position by using the cross-reaction in the assay between AVP and a number of its structural analogs. Binding seems to be almost independent of any direct contributions from components of the tripeptide tail of AVP. Using this RIA it was found that disequilibrium conditions of incubation produce a 5-fold increase in assay sensitivity over equilibrium conditions. Amino acid analysis revealed that three synthetic peptide preparations used as reference standards comprised only 70-80% of their weight as peptide and this finding points up the need to correct such reference standards for their peptide content. The ratio of rat vasopressor activity to RIA activity of these three preparations as well as of a natural AVP preparation, however, approximated unity. Results obtained comparing measurements of AVP in rat neural lobes by RIA and rat vasopressor assay show a correlation between RIA and bioassay of 0.9406, a slope of 1.086, and an intercept of 20 mU, suggesting good agreement for AVP determined by these two assay systems.

Design of potent antagonists of the vasopressor response to arginine-vasopressin

As part of a program in which we are attempting to design and synthesize antagonists of the vasopressor response to arginine-vasopressin (AVP), [1-deaminopenicillamine]arginine-vasopressin (dPAVP), [2-O-methyl)tyrosine]-arginine-vasopressin [Tyr(Me)AVP], and [1-deaminopenicillamine,2-(O-methyl)tyrosine]arginine-vasopressin [dPTyr(Me)AVP] were synthesized by the solid-phase method and assayed for vasopressor, antidiuretic, and oxytocic activities. Tyr(Me)AVP has a vasopressor potency of 9.7 +/- 0.5 units/mg and an antidiuretic potency of 386 +/- 36 units/mg. These values are 2.5 and 120%, respectively, of the corresponding potencies of AVP. The analogue is an antagonist of the in vitro response to oxytocin (pA2 = 7.44 +/- 0.12). dPAVP has an antivasopressor pA2 of 7.45 +/- 0.11. Its antidiuretic potency is 42.2 +/- 2 units/mg, 2.5% that of its parent, 1-[deamino]arginine-vasopressin (dAVP). It is an antagonist of the in vitro response to oxytocin (pA2 value = 6.93 +/- 0.10). dPTyr(Me)AVP has an antivasopressor pA2 of 7.96 +/- 0.05 and an antidiuretic potency of 3.5 +/- 0.5 units/mg. It is also an antagonist of the in vitro oxytocic response to oxytocin (pA2 value = 7.61 +/- 0.14). It is thus one of the most potent vasopressor antagonists reported to date.

[1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),4-valine,-8-D-arginine]vasopressin, a potent and selective inhibitor of the vasopressor response to arginine-vasopressin

As part of a program in which we are attempting the design and synthesis of an antagonist of the antidiuretic response to arginine-vasopressin (AVP) [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),4-valine,8-D-arginine]vasopressin [d(CH2)5VDAVP] was synthesized and assayed for antidiuretic, vasopressor, and oxytocic activities. The required protected intermediate was synthesized by a combination of solid-phase synthesis and an [8 + 1] coupling in solution. d(CH2)5VDAVP has an antidiuretic potency of 0.10 +/- 0.02 unit/mg, less than 1/10000 that of its parent [deamino,4-valine,8-D-arginine]vasopressin (dVDAVP). d(CH2)5VDAVP is a specific antagonist of the vasopressor responses to AVP. It has an antivasopressor pA2 value of 7.68 +/- 0.05 when tested against AVP. It is also an antagonist of the in vitro oxytocic response to oxytocin (pA2 value = 6.62 +/- 0.07). With its negligible antidiuretic activity, absence of oxytocic activity, and its potent and specific ability to antagonize the vasopressor effects of AVP, d(CH2)5VDAVP is one of the most potent and selective vasopressor antagonists reported to date. It should thus be a useful tool with which to probe the possible role(s) that AVP may play in cardiovascular regulation under normal and pathological conditions.

[1-Deaminopenicillamine,4-threonine]oxytocin, a potent inhibitor of oxytocin

[1-Deaminopenicillamine,4-threonine]oxytocin was prepared in duplicate from S-benzyl-3-mercapto-3,3-dimethylpropanoyl-Tyr(Bzl)-Ile-Thr(Bzl)-Asn-Cys(Bzl)-Pro-Leu-Gly-NH2 (I) by removal of the Bzl-protecting groups with Na-NH3, followed by cyclization of the resulting disulfhydryl compound with K3Fo(CN)6. The analogue was purified by desalting on Sephadex G-15 in 50% acetic acid and gel filtration of Sephadex G-15. The protected peptide I was synthesized (a) by the solid-phase method and (b) by a combination of solid-phase synthesis and an [8 + 1] coupling in solution. The analogue has no detectable agonist activity in rat vasopressor or isolated rat uterus assays. It has an antivasopressor pA2 of 6.67 +/- 0.09. It is a potent inhibitor of the in vitro oxytocic response to oxytocin and has a pA2 value of 7.46 +/- 0.04. (Material from the repeat synthesis has a pA2 value of 7.59 +/- 0.08.) Thus the substitution of threonine for glutamine in the antagonist [1-deaminopenicilliamine]oxytocin (pA2, 7.14 +/- 0.05) has effected a twofold increase in inhibitory potency. [1-deaminopenicillamine,4-threonine]oxytocin is one of the most potent inhibitors of oxytocin known to date.

[1-deaminopenicillamine,4-valine]-8-D-arginine-vasopressin, a highly potent inhibitor of the vasopressor response to arginine-vasopressin

In attempting to design an antagonist of the antidiuretic response to arginine-vasopressin (AVP) [1-deaminopenicillamine,4-valine,8-D-arginine]vasopressin (dPVDAVP) was synthesized by the solid-phase method and assayed for antidiuretic, vasopressor, and oxytocic activities. dPVDAVP has an antidiuretic potency of 123 +/- 22 units/mg, one-tenth that of its parent [deamino,4-valine,8-D-arginine]vasopressin (dVDAVP). Like dVDAVP its antidiuretic effect in conscious diabetes insipidus rats is greatly prolonged when compared to AVP. dPVDAVP causes a prolonged inhibition of vasopressor responses to AVP but not to norepinephrine or angiotensin II. It has an antivasopressor pA2 value of 7.82 +/- 0.05 when tested against AVP. Thus the penicillamine substitution at position 1 in dVDAVP increased its antivasopressor activity sixfold (dVDAVP has a pA2 value of 7.03 +/- 0.11). dPVDAVP is thus the most potent vasopressor antagonist yet reported. dPVDAVP was also found to be a potent inhibitor of the in vitro oxytocic response to oxytocin (pA2 value = 7.23 +/- 0.04). dPVDAVP with its potent and specific ability to antagonize the vasopressor effects of AVP should be a useful pharmacological tool with which to explore the possible participation of AVP's potent vasoconstrictor properties in cardiovascular regulation in physiological and pathological states.

[1-(L-2-hydroxy-3-mercaptopropanoic acid)] analogues of arginine-vasopressin, [8-D-arginine]vasopressin, and [4-valine,8-D-arginine]vasopressin

[1-(L-2-Hdroxy-3-mercaptopropanic acid)]arginine-vasopressin (hydroxy-AVP), [1-(L-2-hydroxy-3-mercaptopropanoic acid),8-D-arginine]vasopressin (hydroxy-DAVP), and [1-(L-2-hydroxy-3-mercaptopropanoic acid),4-valine,8-D-arginine]vasopressin (hydroxy-VDAVP) were synthesized by a combination of the solid-phase and solution methods of peptide synthesis. Protected octapeptides synthesized by the solid-phase method were further acylated by 1 + 8 couplings in solution to furnish the key intermediates. Hydroxy-AVP has antidiuretic potency of 470 units/mg and activity in the rat vasopressor assay of 550 units/mg, representing a small enhancement of activity over that of arginine-vasopressin (AVP) in each case. Hydroxy-DAVP and hydroxy-VDAVP have essentially the same high antidiuretic activity (900 units/mg) and very low vasopressor potencies (0.9 and less than 0.02 units/mg, respectively). Hydroxy-AVP, hydroxy-DAVP, and hydroxy-VDAVP thus have antidiuretic-pressor selectivity (A/P) of 1, 1000, and greater than 45 000, respectively. These data are compared with those of other vasopressin analogues. Hydroxy-VDAVP is a highly specific antidiuretic peptids and may be useful in pharmacological studies of antidiuresis.

Design of neurohypophyseal peptides that exhibit selective agonistic and antagonistic properties

Within the spectrum of the characteristic pharmacological activities (oxytocic (O), milk-ejecting (ME), antidiuretic (A), pressor (P) associated with the known natural and synthetic analogs of oxytocin and vasopressin it is possible to discern patterns of selectivity of these types: 1) interpeptide-like (a) O/A, (b) O/P; 2) intraoxytocin-like (a) O/ME; (b) ME/O; 3) intravasopressinlike (a) A/P, (b) P/A. Consideration of structural modifications of oxytocin or vasopressin, which individually or in combination give rise to peptides possessing enhanced selectivity of a given type, can in some cases provide a rational basis for the design of peptides with even greater selectivity. [1-Deamino-4-valine-8-D-arginine]vasopressin, the most highly specific antidiuretic peptide known to date, was designed in this fashion. By contrast, intraoxytocin-like selectivity, is manifested to only a minor degree in all peptides studied to date. Enhanced interpeptide-like selectivity of the type 1a (O/A; O/P) is readily attainable by specific single substitutions at positions 4 or 7 in oxtocin. Substitution of threonine in the 4 position of the oxytocic antagonist [1-deaminopenicillamine]oxytocin brought about a threefold enhancement in oxytocic inhibitory activity. Thus [1-deaminopenicillamine-4-threonine]oxytocin (dPTOT) is the most potent antagonist of the in vitro oxytocic response to oxytocin known to date. Thus analysis of the pharmacological data from over 300 analogs of oxytocin and vasopressin allows the delineation of those structural modifications that can optimize selectivities. The potential and limitations of this approach for the design of peptides possessing desired agonistic or antagonistic selectivity for potential clinical use and for studies on oxytocin and vasopressin receptors is discussed.

Synthesis and some pharmacological properties of [4-threonine, 7-glycine]oxytocin, [1-(L-2-hydroxy-3-mercaptopropanoic acid), 4-threonine, 7-glycine]oxytocin (hydroxy[Thr4, Gly7]oxytocin), and [7-Glycine]oxytocin, peptides with high oxytocic-antidiuretic selectivity

[4-Threonine, 7-glycine]oxytocin and [1-(L-2-hydroxy-3-mercaptopropanoic acid), 4-threonine, 7-glycine]oxytocin (hydroxy[Thr4, Gly7]oxytocin) were synthesized by a combination of solid-phase and classical methods of peptide synthesis. A protected octapeptide was synthesized by the solid-phase method and following ammonolysis and purification 1 + 8 couplings in solution were employed to furnish the required key nonapeptide and acyl octapeptide intermediates, respectively. [7-Glycine]oxytocin was prepared from a sample of the protected nonapeptide intermediate used in the original synthesis of this peptide. [7-Glycine]oxytocin has an oxytocic potency (O) of 93 +/- 4 units/mg and an antidiuretic potency (A) of 0.0056 +/- 0.0003 units/mg. It has an O/A ratio of 16 000. [4-Threonine, 7-glycine]oxytocin has an oxytocic potency of 166 +/- 4 units/mg and an antidiuretic potency of 0.002 +/- 0.0004 units/mg. Its O/A ratio is 83 000. Threonine substitution has thus brought about a substantial enhancement in oxytocic activity and a fivefold enhancement in O/A selectivity. Hydroxy [Thr4, Gly7]oxytocin has an oxytocic potency of 218 +/- 8 units/mg and antidiuretic potency of 0.0040 +/- 0.0005 units/mg. Its O/A ratio is thus 54 500. All three 7-glycine-substituted analogues exhibit a marked sensitivity to Mg2+ on the rat uterus assay ststem and in the presence of 0.5 mM Mg2+ had oxytocic potencies in the range of 900-1000 units/mg. Should these peptides exhibit enhanced oxytocic selectivity in humans, they might offer a greater margin of safety than oxytocin in those clinical stiuations in which the latter is currently employed.

Synthesis and some pharmacological properties of deamino(4-threonine,8-D-arginine)vasopressin and deamino(8-D-arginine)vasopressin, highly potent and specific antidiuretic peptides, and (8-D-arginine)vasopressin and deamino-arginine-vasopressin

Deamino[4-threonine,8-D-arginine]vasopressin (dTDAVP), deamino[8-D-arginine]vasopressin (dDAVP), [8-D-arginine[vasopressin (DAVP), and deamino-arginine-vasopressin (dAVP) were synthesized by the solid-phase method and tested for their biological activities. dTDAVP has an antidiuretic potency of 793+/-95 units/mg and undetectable vasporessor activity, less than 0.02unit/mg. The antidiuretic-pressor (A/P) ratio of dTDAVP is greater than 39 000. dDAVP has an antidiuretic potency of 1200+/-126 units/mg and a vasopressor potency of 0.39+/-0.02; its A/P ratio is thus 3000. DAVP has an antidiuretic potency of 253+/-44 units/mg, a vasopressor potency of 1.1+/-0.04 units/mg, and an A/P ratio of 240. The A/P ratios of dDAVP and DAVP are much higher than those originally reported. dAVP has an antidiuretic potency of 1745+/-385 units/mg, a vasopressor potency of 346+/-13, and an A/P ratio of 5; values are in general agreement with those in the literature. Threonine subsitution has thus brought about a significant enhancement in antidiuretic specificity, a finding entirely consistent with earlier observations that enhancement of lipophilicity at position 4 alone or in combination in arginine-vasopressin can lead to enhanced antidiuretic specificity.

Synthesis and some pharmacological properties of [1-(L-2-hydroxy-3-mercaptopropanoic acid), 4-threonine]oxytocin (hydroxy [4-thr]oxytocin), a peptide with strikingly high oxytocic potency and of [1-(L-2-hydroxy-3-mercaptopropanoic acid)]oxytocin (hydroxy-oxytocin)

[1-(L-2-Hydroxy-3-mercaptopropanoic acid), 4-threonine]oxytocin (hydroxy[4-Thr]oxytocin) and [1-(l-2-hydroxy-3-mercaptopropanoic acid)]oxytocin (hydroxy-oxytocin) were synthesized by a combination of solid phase and classical methods of peptide synthesis. Protected octapeptides were synthesized by the solid-phase method and 1 + 8 couplings in solution were then employed to furnish the required key protected intermediates. Hydroxy[4-Thr]oxytocin has oxytocic potency as measured in the rat uterus suspended in a Mg2+-free solution, of about 4200 units/mg, eight times the potency of oxytocin, while its antidiuretic potency is approximately equal to that of oxytocin. It thus exhibits a significantly favorable oxytocic-antidiuretic sleectivity. Hydroxy-oxytocin has an oxytocic potency of approximatels 1300 units/mt, 2.5 times that of oxytocin. Threonine substitution in hydroxy-oxytocin has thus caused a significant enhancement in both oxytocic potency and selectivity. The enhancement in oxytocic potency of these two peptides relative to oxytocin and [4-Thr]oxytocin appears to correlate with their lipophilic characteristics, suggesting a significant role of lipophilicity in the interplay of oxytocin-like peptides with oxytocic receptors.

Independent release of oxytocin and vasopressin during parturition in the rabbit

1. Oxytocin and vasopressin were assayed in samples of blood collected from seven conscious rabbits during parturition.2. Oxytocin was detected in the blood in ten out of fourteen samples collected during the expulsion of one or more foetuses. Four samples contained 6-100 muu./ml., three 100-200 muu./ml. and three 200-500 muu./ml.3. Vasopressin was detected in six blood samples collected during the delivery of foetuses but in only one experiment did the amount exceed that found in the corresponding control sample collected before or after delivery.4. When both hormones were detected in the same blood sample, the ratio of oxytocin to vasopressin varied from 5:1 to at least 26:1.5. It is concluded that, while oxytocin may not be essential for parturition in the rabbit, stretching of the birth canal during the expulsion of foetuses normally acts as a stimulus for the reflex release of oxytocin from the neurohypophysis and that oxytocin is released independently of vasopressin.

Blood levels of oxytocin and vasopressin during suckling in the rabbit and the problem of their independent release

1. Oxytocin and vasopressin were assayed in samples of blood collected from conscious rabbits during suckling. The milk yields were determined from the weight gain of the litters.2. With normal milk yields (35-155 g), relatively high concentrations (31-375 muu./ml.) of oxytocin were present in the blood but vasopressin was detected in only one out of eight samples. It is concluded that the release of oxytocin by the milk-ejection reflex is essential for normal milk removal in the rabbit and that this hormone is released independently of vasopressin.3. When the milk yield did not exceed 15 g, an amount which could be removed by passive withdrawal from the mammary gland, vasopressin was detected in four out of five blood samples but none contained a detectable concentration of oxytocin. This result can be explained by the intervention of emotional stress which is known to block the milk-ejection reflex but which acts as a stimulus for the release of vasopressin.4. Emotional stress could inhibit the milk-ejection reflex either centrally by blocking the release of oxytocin, or peripherally by blocking the response of the mammary gland to circulating oxytocin. The absence of the hormone in blood during ineffectual suckling suggests that the block is central.

The assay of milk-ejecting activity in the lactating rat

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