An exploration of the effects of L- and D-tetrahydroisoquinoline-3-carboxylic acid substitutions at positions 2, 3 and 7 in cyclic and linear antagonists of vasopressin and oxytocin and at position 3 in arginine vasopressin

We have investigated the effects of mono-substitutions with the conformationally restricted amino acid, 1,2,3,4 tetrahydroisoquinoline-3-carboxylic acid (Tic) at position 3 in arginine vasopressin (AVP), at positions 2, 3 and 7 in potent non-selective cyclic AVP V2/V1a antagonists, in potent and selective cyclic and linear AVP V1a antagonists, in a potent and selective oxytocin antagonist and in a new potent linear oxytocin antagonist Phaa-D-Tyr(Me)-Ile-Val-Asn-Orn-Pro-Orn-NH2 (10). We report here the solid-phase synthesis of peptide 10 together with the following Tic-substituted peptides: 1. [Tic3]AVP: 2. dICH2)5[D-TIc2]VAVP: 3, d(CH2)5[D-Tyr(Et)2Tic3]VAVP: 4, d(CH2)5[Tic2Ala-NH2(9)]AVP: 5. d(CH2)5[Tyr]Me)2.Tic3,Ala-NH2(9)]AVP: 6. d(CH2)5 [Tyr(Me)2,Tic7]AVP: 7, Phaa-D-Tyr(Me)-Phe-Gln-Asn-Lys-Tic-Arg-NH2: 8, desGly-NH2,d[CH2]5[Tic2,Thr4]OVT: 9. desGly-NH2d(CH2)5[Tyr(Me)2Thr4, Tic7[OVT; 11, Phaa-D-Tic-Ile-Val-Asn-Orn-Pro-Orn-NH2, using previously described methods. The protected precursors were synthesized by the solid-phase method, cleaved, purified and deblocked with sodium in liquid ammonia to give the free peptides 1-11 which were purified by methods previously described. Peptides 1-11 were examined for agonistic and antagonistic potency in oxytocic (in vitro, without Mg2+) and AVP antidiuretic (V2-receptor) and vasopressor (V1a-receptor) assays. Tic3 substitution in AVP led to drastic losses of V2, V1a and oxytocic agonistic activities in peptide 1, L- and D-Tic2 substitutions led to drastic losses of anti-V2/anti-V1a and anti-oxytocic potencies in peptides 2, 4, 8 and 11 (peptide 2 retained substantial anti-oxytocic potency; pA2 = 7.25 +/- 0.025). Whereas Tic3 substitution in the selective V1a antagonist d(CH2)5[Tyr(Me)2,Ala-NH2(9)]AVP(C) led to a drastic reduction in anti-V1a potency (from anti-V1a pA2 8.75 to 6.37 for peptide 5, remarkably, Tic3 substitution in the V2/V1a antagonist d(CH2)5(D-Tyr(Et)2]VAVP(B) led to full retention of anti-V2 potency and a 95% reduction in anti-V1a potency. With an anti-V2 pA2 = 7.69 +/- 0.05 and anti-V1a pA2 = 6.95 +/- 0.03. d(CH2)5[D-Tyr(Et)2, Tic3]VAVP exhibits a 13-fold gain in anti-V2/anti-V1a selectivity compared to (B). Tic7 substitutions are very well tolerated in peptides 6, 7 and 9 with excellent retention of the characteristic potencies of the parent peptides. The findings on the effects of Tic3 substitutions reported here may provide promising leads to the design of more selective and possibly orally active V2 antagonists for use as pharmacological tools and as therapeutic clinical agents for the treatment of the syndrome of the inappropriate secretion of antidiuretic hormone (SIADH).

Postoperative myositis in a neonatal foal: a case report

A foal with azotemia, acidemia, and electrolyte abnormalities was diagnosed with uroperitoneum. The foal was anesthetized with isoflurane, and throughout the 4 hours of anesthesia and abdominal surgery, its mean arterial pressure ranged between 45 and 65 mm Hg. The foal developed a myopathy postoperatively and died 24 hours after surgery.

Agonist and antagonist specificities of decidual prostaglandin-releasing oxytocin receptors and myometrial uterotonic oxytocin receptors in pregnant rats

This paper describes further pharmacological characterization of the decidual prostaglandin-releasing oxytocin receptors and the myometrial uterotonic oxytocin receptors in the uterus of the pregnant rat. The effects of oxytocin, arginine-vasopressin and their related agonists and antagonists on the release of PGF2 alpha were studied in vitro on isolated uteri from rats on day 19-20 of pregnancy that had been incubated in Krebs buffer, pH 7.4, at 37 degrees C. The concentration of PGF2 alpha in the media was measured using specific radioimmunoassays. It was found that the decidual and myometrial oxytocin receptors exhibit different ligand specificities. Of the agonists tested, oxytocin and arginine-vasopressin stimulated PGF2 alpha release in a dose-dependent manner. Arginine-vasopressin has only 3% of the uterotonic potency of oxytocin, but was found to have 16% of its PGF2 alpha-releasing activity. [4-Threonine, 7-glycine]oxytocin, a highly potent and selective uterotonic oxytocin analogue, had no detectable prostaglandin-releasing activity at a dosage 30 times higher than oxytocin. However, 1-deamino-[8-D-arginine]vasopressin, a highly potent and selective antidiuretic arginine-vasopressin analogue, which has only 10% of the uterotonic activity of arginine-vasopressin, was as potent as arginine-vasopressin in prostaglandin-releasing activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin-binding sites in the pig pituitary gland: competition by novel vasopressin antagonists suggests the existence of an unusual receptor subtype in the anterior lobe

Arginine vasopressin (AVP) acts in the pituitary gland, in synergy with corticotrophin-releasing factor, to induce ACTH release in response to stressful stimuli. Pituitary AVP receptors in the rat are coupled to phospholipase C, as are the so-called V1-type AVP receptors. The present study examined [3H]AVP binding in membranes prepared from the anterior lobe of the pituitary gland of the pig. [3H]AVP, alone or in competition with analogues, bound to sites in the pig anterior lobe which are pharmacologically similar to those described previously by others in the rat pituitary gland. For comparison, the same competition studies were performed on membrane preparations from the rat liver which contain the classic V1-type AVP receptor. Pituitary and liver AVP-binding sites were dissimilar; both cyclic and linear V1 antagonists had, in general, a much lower affinity for pituitary AVP-binding sites than for those in the liver. Thus, Phaa-D-Tyr(Et)-Phe-Gln-Asn-Lys-Pro-Arg-NH2 (Phaa = phenylacetyl) has a 2500-fold greater affinity for the latter (negative logarithm of inhibition constant (pKi) = 9.64) than for the former (pKi = 6.22). One linear antagonist, Pa-D-Tyr-Phe-Val-Asn-Arg-Pro-Arg-Arg-NH2 (Pa = propionyl) had about equal affinities for liver and pituitary membranes (pKi = 6.39 and 6.53 respectively). Another compound, Phaa-D-Tyr-Phe-Val-Asn-Arg-Pro-Arg-Arg-NH2 had the highest affinity found to date for binding to AVP sites in the pituitary (pKi = 7.43). These findings suggest some ideas for the design of more potent and/or selective AVP analogues acting in the pituitary gland.

Nutrition, genital tract infection, hematologic values, and premature rupture of membranes among African American Women

Using a prospective comparative design, African American gravidae with and without genital tract infection were assessed with respect to dietary intakes, serum nutrient values, hematologic values, and pregnancy outcomes. Intakes of ascorbic acid, vitamin A, protein, and iron were the dietary variables while levels of ascorbic acid, protein, albumin, globulin, and ferritin were the variables measured in serum. The hematologic variables included hemoglobin, hematocrit, and red and white blood cell counts. Pregnancy outcome was defined on the basis of premature rupture of the membranes (PROM), and infant birth weight, birth length, gestational age, and head circumference. The sample consisted of 335 nulliparous women who were between 16-35 years of age, 96 of whom had genital tract infection based on laboratory reports. Findings indicated no significant differences between the mean dietary intakes as well as serum values of the infected and non-infected women, and no difference in the incidence of PROM. However, non-infected women had a better mean hematologic profile than the infected gravidae during pregnancy. Also, for the non-infected group, there were significant relationships between head circumference and protein consumption (P = .015) and serum ferritin (P = .05). For the infected women, the relationship between the hemoglobin and hematocrit measurements obtained at the first prenatal visit and infant birth weight, birth length and head circumference were statistically significant.

Biochemical profile of African American women during three trimesters of pregnancy and at delivery

The data presented are the results from a prospective observational study which was conducted to investigate the effects of nutrition and other related factors on the outcome of pregnancy in nulliparous African American women 16-35 years old. Fasting blood samples were collected from the women during the first, second and third trimesters of pregnancy. At delivery, both maternal and cord samples were collected. Biochemical variables such as, serum folate, vitamin B12, ascorbic acid, vitamin E, ferritin, selected minerals as well as complete blood count (CBC) and red cell folate were analyzed in the blood samples. The concentrations of hematocrit, hemoglobin, white blood cells, red blood cells and vitamin B12 were below the reference non-pregnant ranges throughout gestation. Maternal concentrations of folate and vitamin E increased sequentially with increased gestational age. Serum ferritin, during the third trimester, declined to 58% of the first trimester concentration. Maternal levels of ferritin at delivery were one third of the values found in the infant (cord) sample. Cord levels of folate, ascorbic acid and vitamin B12 were higher than the concentrations in the maternal delivery samples. The data suggest that among this group of pregnant women, major physiological changes, such as plasma volume expansion which alters blood chemistry and maternal to fetal transfer of nutrients, were similar to the findings of other investigators. In this population however, the findings for serum and whole blood folate are contrary to those reported by other researchers, and the sequential increase in the maternal concentration of the vitamin during pregnancy could be attributed to the use of vitamin supplements.

Maternal low level lead and pregnancy outcomes

We examined the relationship between the concentrations of blood lead and pregnancy outcomes in a subset of 349 African American women who enrolled in the program project, "Nutrition, Other Factors, and the Outcome of Pregnancy." Vitamin-mineral supplement users had significantly higher serum levels of ascorbic acid and vitamin E. Also, in supplement users, there were significantly lower mean concentrations of maternal blood lead. Inverse correlations were found between maternal levels of lead and the antioxidant vitamins, vitamin E and ascorbic acid. In addition, significant Pearson's correlations were observed between maternal blood lead levels and the following variables: positive correlations with calcium, phosphorus, mean corpuscular volume; inverse correlations with gestational age, Ponderal Index, infant orientation, and hematologic values. In the total subset, the three trimester sample means for maternal blood lead concentrations were not significantly different for mothers of infants who weighed less than 2500 g (low birth weight) and those who were delivered infants who weighed 2500 g or more. Clinically, nutrition may play a role in the reduction of potentially adverse effects from lead during pregnancy, i.e. protection of the fetus against lead toxicity and/or free radical damage through the antioxidant actions of vitamin E and ascorbic acid. Even when maternal blood lead levels are within the so-called "safe" range, maternal/use of a vitamin supplement supplying vitamin E and ascorbic acid during pregnancy may offer protection.

Ureteral stone. Treatment using the Modulith SL 20 and Lithostar plus

The treatment of ureteric calculi by extra-corporeal shock waves was found to have an 80% success rate by Mannheim authors, regardless of the site of the calculus. The authors compared two 3rd generation apparatuses: 1--the Siemens Lithostar Plus, in which waves are produced by a electromagnetic cylinder and focussed by a parabolic electromagnetic cylinder and focussed by a parabolic reflector: 2--the Storz Medical Modulith SL 10, in which waves produced by an electromagnetic coil are focussed by acoustic lenses. Both apparatuses are based upon image-intensification and ultrasonography concepts. No difference in efficacy was found between the two apparatuses. A second shock wave session was necessary in 16% of cases and some other type of additional treatment in 7% of cases.

Synthesis of paraxanthine analogs (1,7-disubstituted xanthines) and other xanthines unsubstituted at the 3-position: structure-activity relationships at adenosine receptors

Synthetic procedures for the preparation of various 3-unsubstituted xanthines, including paraxanthine analogs (1,7-disubstituted xanthines) and 1,8-disubstituted xanthines, were developed. Silylation of 1-substituted xanthines followed by alkylation at the 7-position provides a facile route to paraxanthine analogs. Regioselective alkylation of tris(trimethylsilyl)-6-aminouracil provides 3-substituted 6-aminouracils, which are converted to 1,8-disubstituted xanthines by standard procedures. The ring closure of 3-substituted 5-cyclopentanecarboxamido- and 5-(benzoylamino)-6-aminouracils requires drastic reaction conditions. Affinity for brain A1 and A2 adenosine receptors was determined in binding assays for these and other xanthines with substituents in 1-, 3-, 7-, 8-, and 9-positions. Substitution at the 1-position was necessary for high affinity at adenosine receptors. 1,3-Disubstituted xanthines generally had higher affinity than 1,7-disubstituted xanthines. 1,8-Disubstituted xanthines had high affinity for adenosine receptors; some were highly selective for A1 receptors.

Effect of trifluoromethyl and other substituents on activity of xanthines at adenosine receptors

An aryl p-(trifluoromethyl) substituent increases the affinity of 1,3-disubstituted 8-phenylxanthines at A2a-adenosine receptors, while having little effect on affinity at A1-adenosine receptors. In contrast, an aryl p-(trifluoromethyl) substituent has little effect on affinity of 3,7-disubstituted and 1,3,7-trisubstituted 8-phenylxanthines. An aryl p-sulfo substituent reduces affinity of all 8-phenylxanthines at A1- and A2a-adenosine receptors. An 8-(trifluoromethyl) substituent markedly reduces affinity of 1,3-dialkylxanthines at both A1- and A2a-adenosine receptors. In contrast, 8-(trifluoromethyl)caffeine retains affinity for A2a-adenosine receptors, but does lose affinity for A1-adenosine receptors. 8-Bromo-, 8-acryl-, and 8-pent-1-enylcaffeines are also selective for A2-adenosine receptors, while 8-cyclobutylcaffeine is nonselective. 8-[trans-2-(tert-butyloxycarbonyl)vinylcaffeine is 20-fold selective for Aza vs A1 receptors.

Oxytocin receptor subtypes in the pregnant rat myometrium and decidua: pharmacological differentiations

Oxytocin (OT) has a dual action in the uterus: a uterotonic action on myometrial cells and a prostaglandin (PG)-releasing action on endometrial/decidual cells. It had not been determined whether the OT-binding sites or receptors on the myometrial and the endometrial/decidual membranes are of the same type or may represent two subtypes. Our studies presented in this paper show that isolated day 19-22 pregnant rat uterine horns and myometrial tissues (uterine horns with decidual tissues removed) incubated in Kreb's buffer at 37 C released PGF2 alpha in sustained quantities into the bathing medium. OT stimulated PG release over the basal release rate in a dose-dependent manner in the whole uterine horn but not in the myometrial tissue. Two OT antagonists, P[Phe(Me)2,Thr4]ornithine vasotocin (antagonist A) and desGly-NH2(9),d(CH2)5(1)[Tyr(Me)2,Thr4]ornithine vasotocin (antagonist B) were found to have different effects on the PG-releasing action of OT. At antiuterotonic doses, antagonist A had no antagonism of the PG-releasing action of OT. On the contrary, antagonist A was found to stimulate uterine PG release. Antagonist B was a full OT antagonist. At equivalent antiuterotonic doses, antagonist B inhibited both the uterotonic action and the PG-releasing action of OT. These findings suggest that OT-sensitive PGs are synthesized/released principally in the endometrium/decidua. The myometrial uterotonic OT receptors and the endometrial/decidual PG-releasing OT receptors are two distinct subtypes and can be differentiated. The existence of two OT receptor subtypes in the uterus has important implications in the clinical application of OT antagonists as tocolytics for preterm labor. To be efficacious, OT antagonist therapy needs to block both the uterotonic and the PG-releasing action of OT.

A general correspondence approach to apparent motion

A general framework is considered for how different features of image parts determine the perceived direction of apparent motion between these parts as a function of their internalized feature weights. It is shown how the compatibility and constraints between pairwise part correspondences also play important roles in the types of perceived motion between parts; this process is modelled via a multivariate constraint-satisfaction procedure.

Design, synthesis and some uses of receptor-specific agonists and antagonists of vasopressin and oxytocin

Selective agonists and antagonists are powerful tools for studies on AVP and OT receptors and on the physiological and pathophysiological roles of AVP and OT. Here we show how some of these peptides and their radiolabelled derivatives were designed. We also present examples of the currently available cyclic and linear OT and AVP agonists and antagonists from our laboratories.

Extracorporeal shock wave lithotripsy of ureteric stones with the Modulith SL 20

A series of 138 patients with ureteric calculi was treated by in situ extracorporeal shock wave lithotripsy (ESWL) during the clinical introduction of the Modulith SL 20. This machine represents a newly developed lithotriptor with an electromagnetic cylinder as shock wave source and a dual localisation system consisting of in-line ultrasound and an integrated fluoroscope C-arm. During the first 2 months, 12 patients (phase 1) were treated under ultrasound localisation alone; during the next 5 months, 37 patients (phase 2) were treated using dual imaging modalities with reduced peak pressure (max. 18 kV = 800 bar); during the final 7 months, 89 patients (phase 3) were treated under ultrasonic and fluoroscopic localisation combined with an increased maximal shock wave pressure (20 kV = 1024 bar). The introduction of fluoroscopic targeting (phases 2 and 3) resulted in satisfactory localisation of calculi in the mid-ureter, previously limited by use of only coaxial ultrasound. The extension of stone localisation to the whole length of the ureter was associated with a marked decrease in treatment time, reflecting the easy handling of the dual localisation system. The rise in generator voltage (phase 3) improved the disintegration rate from 81% (phase 2) to 85%, whereas the number of impulses remained unchanged. However, the rate of auxiliary procedures following ESWL (adjuvant and curative) was reduced from 33% (phase 2) to 24.5%. Thus the Modulith SL 20 in its final design enables in situ ESWL to be the treatment of choice for all ureteric calculi, rendering special positioning techniques or multiple treatment unnecessary.

Potent V2/V1a vasopressin antagonists with C-terminal ethylenediamine-linked retro-amino acids

We report the solid-phase synthesis and antagonistic potencies of 25 analogues (1-25) of [1-(beta-mercapto-beta,beta-pentamethylenepropionic acid),2-O-ethyl-D-tyrosine,4-valine]arginine-vasopressin (d(CH2)5D-Tyr(Et)2-VAVP) (A) and of the related Ile4 (D) and [D-Phe2,Ile4] (E) analogues, potent antagonists of the antidiuretic (V2-receptor) and of the vasopressor (V1a-receptor) responses to arginine-vasopressin (AVP). Six of these peptides (1, 13, 17, 19, 21, and 23) have the Pro-Arg-Gly-NH2 tripeptide side chain fully or partially replaced or extended by ethylenediamine (Eda). The remaining 19 peptides have L- or D-amino acids retrolinked to these six C-terminal Eda peptides. Peptides 1, 13, 17, and 19 all have the ring structure of (A). Their side-chain structures are as follows: 1, Eda; 13, Pro-Eda; 17, Pro-Arg-Eda; 19, Arg-Gly-Eda. Peptide 21 is the Pro-Arg-Eda analogue of D; peptide 23 is the Pro-Arg-Gly-Eda analogue of E. Peptide 2 is the retro-Arg analogue of 1. Its side-chain structure is Eda<--Arg. Peptides 3-6 are analogues of 2 which have the D-Tyr-(Et)2 residue replaced by L-Tyr(Et)2 (3), D-Phe2 (4), D-Ile2 (5), or D-Leu2 (6), respectively. Peptides 7-12 are analogues of 2 which have the C-terminal retro-Arg replaced in retrofashion by D-Arg (7), Gly (8), Orn (9), D-Orn (10), D-Lys (11), or Arg-Arg (12). Peptides 14-16 have D-Orn (14), D-Lys (15), and D-Arg (16) retrosubstituted to peptide 13. Peptides 18, 20, and 22 are the retro-Arg-substituted analogues of 17, 19, and 21, respectively. Peptides 24 and 25 have Val and D-Val in retrolinkage with 23, respectively. All 25 peptides were examined for agonistic and antagonistic potencies in AVP V2/V1a assays. With the exception of peptides 5 and 6, all exhibit potent anti-V1a antagonism, with anti-V1a pA2 values in the range 7.64-8.33.(ABSTRACT TRUNCATED AT 400 WORDS)

Novel approach to the design of synthetic radioiodinated linear V1A receptor antagonists of vasopressin

We report the solid phase synthesis of six analogs of the potent and selective linear AVP vasopressor (V1a receptor) antagonist: Phaa1-D-Tyr(Et)2-Phe3-Gln4-Asn5-Lys6-Pro7-Arg-NH(8)2(A) (where Phaa = phenylacetyl) in which the Phaa1 residue is replaced by hydroxyphenylacetyl (HO-Phaa), hydroxyphenylpropionyl (HO-Phpa) and phenylpropionyl (Phpa) and the D-Tyr(Et)2 and Lys6 residues by D-Tyr(Me)2 and Arg6 substituents. The phenolic-containing peptides were synthesized to test the feasibility of using this approach for the design of high affinity selective ligands for AVP V1a receptors. The following analogs of A were synthesized: 11 [(HO)Phaa1]; 2. [(HO)Phaa1,D-Tyr(Me)2]; 3. [(HO)Phaa1,D-Tyr(Me)2, Arg6]; 4. [(HO)Phaa1,Arg6]; 5. [Phpa1]; 6. [(HO)Phpa1]. All six peptides were examined for agonistic and antagonistic potencies in vasopressor (V1a-receptor) and antidiuretic (V2-receptor) and in vitro oxytocic assays in rats. The affinities of the phenolic-containing peptides for hepatic V1a and uterine receptors were also determined. The phenolic-containing peptides all exhibit potent V1a antagonism. Their anti-V1a pA2 values range from 8.23 to 8.63 (the anti-V1a pA2 value of A = 8.69). Their inhibition constants (Ki in nM) range 0.4 to 1.0. They are weak antidiuretic agonists with activities ranging from 0.022 U/mg to 0.13 U/mg (A = 0.033 U/mg). They all exhibit OT antagonism in vitro. Their anti-OT pA2 values range from 7.28 to 7.71 (A = 7.62). All five phenolic compounds were iodinated using iodine chloride and tested in the same in vivo and in vitro assay system.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and some pharmacological properties of potent and selective antagonists of the vasopressor (V1-receptor) response to arginine-vasopressin

We report the solid-phase synthesis of eight position-9-modified analogues of the potent V1-receptor antagonist of arginine-vasopressin, [1-(beta-mercapto-beta,beta-pentamethylenepropionic acid),2-O-methyltyrosine]arginine-vasopressin (d(CH2)5Tyr(Me)AVP) (1-8) and five position-9-modified analogues of the closely related beta,beta-dimethyl less potent V1 antagonist, [1-deaminopenicillamine,2-O-methyltyrosine]arginine-vasopressin (dPTyr(Me)AVP) (9-13). In d(CH2)5Tyr(Me)AVP the C-terminal Gly-NH2 was replaced by (1) ethylenediamine (Eda), (2) methylamine (NHMe), (3) Ala-NH2, (4) Val-NH2, (5) Arg-NH2, (6) Thr-NH2, (7) Gly-Eda, (8) Gly-N-butylamide (Gly-NH-Bu); in dPTyr(Me)AVP the C-terminal Gly-NH2 was replaced by (9) Ala-NH2, (10) Val-NH2, (11) Thr-NH2, (12) Arg-NH2, and (13) Tyr-NH2. All 13 analogues were tested for agonistic and antagonistic activities in in vivo rat vasopressor (V1-receptor) and rat antidiuretic (V2-receptor) assays. They exhibit no evident vasopressor agonism. All modifications in both antagonists were well-tolerated with excellent retention of V1 antagonism and striking enhancements in anti-V1/anti-V2 selectivity. With anti-V1 pA2 values of 8.75, 8.73, 8.86, and 8.78, four of the analogues of d-(CH2)5Tyr(Me)AVP (1-3 and 6) are equipotent with d(CH2)5Tyr(Me)AVP (anti-V1 pA2 = 8.62) but retain virtually none of the V2 agonism of d(CH2)5Tyr(Me)AVP. They are in fact weak V2 antagonists and strong V1 antagonists with greatly enhanced selectivity for V1 receptors relative to that of d(CH2)5Tyr(Me)AVP. With anti-V1 pA2 values respectively of 8.16, 8.05, 8.04, 8.52, and 8.25, all five analogues (9-13) of dPTyr(Me)AVP are at least as potent V1 antagonists as dPTyr(Me)AVP (pA2 = 7.96) and three of these (9, 12, 13) actually show enhanced V1 antagonism over that of dPTyr(Me)AVP. In fact, the Arg-NH2(9) analogue (12) is almost equipotent with d(CH2)5Tyr(Me)AVP. These new V1 antagonists are potentially useful as pharmacological tools for studies on the cardiovascular roles of AVP. Furthermore the analogues of dPTyr(Me)AVP may be useful in studies on the role(s) of AVP in the V1b-receptor-mediated release of ACTH from corticotrophs.

A radioiodinated linear vasopressin antagonist: a ligand with high affinity and specificity for V1a receptors

A linear vasopressin antagonist, Phaa-D-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-Tyr-NH2 (Linear AVP Antag) (Phaa = Phenylacetyl), was monoiodinated at the phenyl moiety of the tyrosylamide residue at position 9. This antagonist appeared to be a highly potent anti-vasopressor peptide with a pA2 value in vivo of 8.94. It was demonstrated to bind to rat liver membrane preparations with a very high affinity (Kd = 0.06 nM). The affinity for the rat uterus oxytocin receptor was lower (Ki = 2.1 nM), and affinities for the rat kidney- and adenohypophysis-vasopressin receptors were much lower (Ki = 47 nM and 92 nM, respectively), resulting in a highly specific vasopressin V1a receptor ligand. Autoradiographical studies using rat brain slices showed that this ligand is a good tool for studies on vasopressin receptor localization and characterization.