Testosterone reaction after testicular biopsies--further investigation in the normogonad and cryptorchid rat model

From the follow-up of patients undergoing extensive testicular sperm extraction, the question of a consecutive decrease in testosterone levels arose. Further investigation was performed in the normogonad and cryptorchid Sprague-Dawley rat model. From groups A (n = 40 normogonad rats) and B (n = 40 cryptorchid rats), eight animals were taken and the following surgical interventions were performed: general anaesthesia (A-0, B-0), scrotal exploration (A-1, B-1), one testicular biopsy with a 2-mm tunica incision (A-2, B-2), two biopsies with a 4-mm incision (A-3, B-3), and four biopsies with a 2-mm incision (A-4, B-4). Standardised testosterone control was performed 1 day before as well as 1, 7 and 14 days after surgery. No specific testosterone reaction was found in A-0, an insignificant decrease in A-1 (3.8 nmol/l), a significant decrease in A-2 (6.27 nmol/l), in A-3 (12.96 nmol/l) and in A-4 (11.88 nmol/l). In the B rats, even in B-3 and B-4 no significant decrease was measured. The testosterone reaction correlated to the amount of tissue that was extracted, but not to the number of biopsies. The cryptorchid rats did not react in a more sensitive manner.

Novel selective hypotensive vasopressin peptides: cardiovascular and structure–activity-relationship studies

Recently, we discovered a series of peripheral acting selective hypotensive vasopressin peptides. Whether these peptides may interact with receptors outside the vasopressin receptor family and affect cardiac function could not be excluded. Accordingly, we tested the effects of these hypotensive vasopressin peptides on blood pressure and heart rate in intact rats and on the heart rate, ventricular contractile force and coronary flow of isolated perfused rat hearts. We found that the hypotensive vasopressin peptides did not modify cardiac function, either in vivo or in vitro. The vasodepressor potency was reduced when assayed in rats with vasopressin-maintained baseline blood pressure, suggesting that vasopressin and the hypotensive peptide compete for a common vasodilating vasopressin receptor in the vasculature. We have now synthesized more potent and radioiodinatable hypotensive peptides that could serve as lead compounds for the development of a radiomarker for the putative vasodilating vasopressin receptor.

Imprinting analysis in spermatozoa prepared for intracytoplasmic sperm injection (ICSI)

Genetic imprinting is a mechanism of gene regulation by which only one of the parental copies of a gene is expressed. This process is mediated by the methylation of DNA. As spermatozoa represent exclusively the paternal contribution to a future individual, they are expected to carry the paternal imprint only. For intracytoplasmic sperm injection (ICSI), spermatozoa mostly have to be selected from samples with pathological semen parameters. Correct establishment of the paternal imprint in these spermatozoa has not yet been demonstrated. In the present study, imprinting analysis was undertaken using DNA extracted from spermatozoa from men with normal semen analysis (group A: n=30 patients) and from men with an abnormal sperm count (B: n=30 patients with 5--20 million spermatozoa/mL and C: n=30 patients with < or =5 million spermatozoa/mL) from the ICSI program. It was performed using firstly a conventional methylation-specific polymerase-chain-reaction (M-PCR) and secondly a more sensitive modified hemi-nested M-PCR technique. In addition, a single cell PCR was performed on a total of 88 single spermatozoa (collected from nine males) and on 25 leucocytes (control group). With the conventional M-PCR, exclusively paternal imprints were found in all groups. Using the more sensitive hemi-nested M-PCR, additional maternal imprints were found in 63% of the samples in A, 57% in B and 60% in C. In the single cell PCR, exclusively paternal imprints were detected. Because of the very small amount of DNA (3 pg), a complete amplification failure occurred in 43% of spermatozoa. The correct paternal and maternal imprints were found in 56% of the analysed leucocytes (complete amplification failure in the other 44%). In conclusion, ejaculated spermatozoa from males with medium or high-grade semen pathology proved to have the same imprinting status as those from males with normal semen parameters. As the additional maternal imprints were never found at the single cell level, they were classified as contamination by diploid cells such as leucocytes or immature germ cells in the processed and purified semen samples, which can be detected by a more sensitive PCR method in contrast to the conventional standard PCR.

Round spermatids from infertile men exhibit decreased protamine-1 and -2 mRNA

During spermiogenesis, histone-to-protamine exchange causes chromatin condensation. Spermatozoa from infertile men are known to exhibit an increased protamine-1 (PRM1) to protamine-2 (PRM2) protein ratio. Since patients undergoing testicular sperm extraction (TESE) followed by intracytoplasmic sperm injection (ICSI) reveal low fertilization rates, whether the outcome of ICSI could be related to the percentage of round spermatids expressing PRM1-mRNA and PRM2-mRNA was investigated. Applying in-situ hybridization, 55 testicular biopsies from men undergoing TESE/ICSI were investigated. The percentage of PRM1-mRNA and PRM2-mRNA positive spermatids was significantly (P < 0.0001) decreased in men with at least qualitatively normal spermatogenesis (PRM1-mRNA: 58.4 +/- 13.8%; PRM2-mRNA: 56.4 +/- 11.3%) and impaired spermatogenesis (PRM1-mRNA: 32.6 +/- 10.8%; PRM2-mRNA: 31.7 +/- 11.1%) compared with men with obstructive azoospermia and quantitatively normal spermatogenesis (PRM1-mRNA: 79.9 +/- 4.6%; PRM2-mRNA: 78.1 +/- 5.7%). A positive correlation (r(PRM1) = 0.733; r(PRM2) = 0.784; P < 0.001) was demonstrated between the score and the percentage of PRM1-mRNA and PRM2-mRNA positive spermatids. While successful fertilization was neither related to the score, nor to the percentage of PRM1-mRNA and PRM2-mRNA positive spermatids, a significant (P < 0.05) relationship was demonstrated between successful fertilization and the PRM1-mRNA to PRM2-mRNA ratio. Therefore, the PRM1-mRNA to PRM2-mRNA ratio in round spermatids may serve as a possible predictive factor for the outcome of ICSI.

Study of DNA-methylation patterns at chromosome 15q11-q13 in children born after ICSI reveals no imprinting defects

The introduction of intracytoplasmic sperm injection (ICSI) has raised concern about safety in terms of a possible increase in the incidence of major congenital malformations, chromosomal aberrations or developmental problems. The possible influence of genetic imprinting on an ICSI procedure has not yet been investigated. We therefore studied the DNA-methylation status at a defined region in chromosome 15q11-q13 in 92 children born after an ICSI procedure. Imprinting defects in this region are associated with neurogenetic disorders, e.g. Angelman syndrome (AS) and Prader-Willi syndrome (PWS). Blood samples were taken directly after birth and stored at -80 degrees C. Genomic DNA purification was performed from 3-7 ml EDTA-blood. Sodium bisulphite treatment was carried out in order to distinguish methylated from unmethylated DNA by transferring the unmethylated nucleic acid cytosine into uracil and leaving the methylated cytosine unchanged. Subsequently, a methylation-specific polymerase chain reaction (M-PCR) was performed. In all 92 children (83 from ICSI with ejaculated spermatozoa and nine from ICSI with non-ejaculated spermatozoa), a regular DNA-methylation pattern was found in the PWS/AS region. In none of the children were clinical symptoms of PWS or AS present. In conclusion, the results of this study do not indicate a higher risk of DNA-methylation defects in children born after ICSI.

Using north carolina medicare data to assess excess prostate cancer mortality among african americans

PURPOSE: To investigate the basis for the higher prostate cancer mortality rate for African American (AA) men, which is twice the rate for White men.METHODS: 221 AA and 979 White men with a primary diagnosis code of prostate cancer ("patients") in the North Carolina Medicare Hospitalization claims from 1997 were compared with 1,326 AA and 5,874 White men of the same age with no cancer hospitalizations ("beneficiaries") selected from the NC Medicare Enrollment files. Mortality rates were calculated as the cumulative percent of deaths using the hospital discharge date as day 1. AA and White age distributions were similar.RESULTS: Cumulative mortality percentages at 6, 12, and 18 months were, respectively, 4.5, 7.7, 10.9 for AA patients; 2.8, 6.5, 9.2 for White patients; 2.3, 3.8, 7.4 for AA beneficiaries; and 1.8, 3.1, 6.1 for White beneficiaries.CONCLUSIONS: AA prostate cancer patients had higher overall mortality than did White prostate cancer patients during the first year, but by 12-months the White-Black survival advantage for prostate cancer patients was similar in magnitude to the White-Black survival advantage among the non-cancer Medicare beneficiaries. AAs' higher prostate cancer mortality may derive from higher short-term case fatality rates, which may reflect differences in treatment and access to quality medical care, co-morbidities, and tumor characteristics such as stage and grade at diagnosis, and in part from the survival disadvantage for AA in the general population.

Conserved aromatic residues in the transmembrane region VI of the V1a vasopressin receptor differentiate agonist vs. antagonist ligand binding

Despite their opposite effects on signal transduction, the nonapeptide hormone arginine-vasopressin (AVP) and its V1a receptor-selective cyclic peptide antagonist d(CH2)5[Tyr(Me)2]AVP display homologous primary structures, differing only at residues 1 and 2. These structural similarities led us to hypothesize that both ligands could interact with the same binding pocket in the V1a receptor. To determine receptor residues responsible for discriminating binding of agonist and antagonist ligands, we performed site-directed mutagenesis of conserved aromatic and hydrophilic residues as well as nonconserved residues, all located in the transmembrane binding pocket of the V1a receptor. Mutation of aromatic residues of transmembrane region VI (W304, F307, F308) reduced affinity for the d(CH2)5[Tyr(Me)2]AVP and markedly decreased affinity for the unrelated strongly hydrophobic V1a-selective nonpeptide antagonist SR 49059. Replacement of these aromatic residues had no effect on AVP binding, but increased AVP-induced coupling efficacy of the receptor for its G protein. Mutating hydrophilic residues Q108, K128 and Q185 in transmembrane regions II, III and IV, respectively, led to a decrease in affinity for both agonists and antagonists. Finally, the nonconserved residues T333 and A334 in transmembrane region VII, controlled the V1a/V2 binding selectivity for both nonpeptide and cyclic peptide antagonists. Thus, because conserved aromatic residues of the V1a receptor binding pocket seem essential for antagonists and do not contribute at all to the binding of agonists, we propose that these residues differentiate agonist vs. antagonist ligand binding.

Discovery and design of novel and selective vasopressin and oxytocin agonists and antagonists: the role of bioassays

Synthetic oxytocin and vasopressin agonists and antagonists have become important tools for research and were instrumental in the identification of the four known receptor subtypes, V1a, V2, V1b (V3) and oxytocin, of these peptide hormones. However, the relative lack of receptor selectivity, particularly of the antagonists, has limited their usefulness as experimental probes and their potential as therapeutic agents. We now present some findings from our continuing studies aimed at the design of more selective oxytocin and vasopressin agonists and antagonists and a structure-activity relationship update on our recently discovered novel hypotensive vasopressin peptides. Bioassays have been, and continue to be, of critical importance in leading to the discovery of the novel agonists, antagonists and hypotensive peptides reported here. This paper highlights three main aspects of these studies. (1) Replacement of the tyrosine2 and/or phenylalanine3 residues in the V2 agonist deamino,[Val4,D-Arg8]arginine-vasopressin (dVDAVP) by thienylalanine resulted in selective V2 agonists with strikingly high potencies. However, the peptide solutions were unstable and lost activity over time. These highly potent V2 agonists, which are devoid of vasopressor activity, are promising leads for improving drugs for treating diabetes insipidus, enuresis and coagulation disorders. (2) Diaminopropionic acid and diaminobutyric acid substitution at position-5 in oxytocin and in V1a antagonists yielded, respectively, the first specific antagonist for the oxytocin receptor, desGly-NH2,d(CH2)5[D-Trp2,Thr4,Dap5]OVT and the first specific antagonist for the vasopressin V1a receptor, d(CH2)5[Tyr(Me)2,Dab5]AVP. The availability of single receptor subtype-specific or selective antagonists will enhance our ability to delineate receptor functions. Utilising these new receptor specific probes, we were able to show that the uterotonic action of vasopressin is mediated principally by oxytocin and not by V1a receptors. (3) Replacement of the phenylalanine3 residue in the V1a/V2/oxytocin antagonist, d(CH2)5[D-Tyr(Et)2,Val4]AVP, with arginine3 yielded the novel, selective, hypotensive vasopressin peptide, d(CH2)5[D-Tyr(Et)2,Arg3,Val4]AVP (Peptide I). Bioassay characterisations of Peptide I show that its vasodepressor action is independent of the peripheral autonomic, bradykinin, nitric oxide and prostaglandin systems and is not mediated by the known classical oxytocin and vasopressin receptors. These findings suggest the existence of a new vasopressin receptor subtype that may be relevant to the vasodilating action of vasopressin in regional vascular beds. Iodinatable hypotensive peptides have been synthesised and could be developed as markers for the putative new receptor. Ongoing structure-activity relationship studies on Peptide I have led to more potent and selective hypotensive peptides for use as new research tools and as leads for the development of a new class of antihypertensive agents.

Radiobiological considerations in the design of fractionation strategies for intensity-modulated radiation therapy of head and neck cancers

PURPOSE

The dose distributions of intensity-modulated radiotherapy (IMRT) treatment plans can be shown to be significantly superior in terms of higher conformality if designed to simultaneously deliver high dose to the primary disease and lower dose to the subclinical disease or electively treated regions. We use the term "simultaneous integrated boost" (SIB) to define such a treatment. The purpose of this paper is to develop suitable fractionation strategies based on radiobiological principles for clinical trials and routine use of IMRT of head and neck (HN) cancers. The fractionation strategies are intended to allow escalation of tumor dose while adequately sparing normal tissues outside the target volume and considering the tolerances of normal tissues embedded within the primary target volume.

METHODS AND MATERIALS

IMRT fractionation regimens are specified in terms of "normalized total dose" (NTD), i.e., the biologically equivalent dose given in 2 Gy/fx. A linear-quadratic isoeffect formula is applied to convert NTDs into "nominal" prescription doses. Nominal prescription doses for a high dose to the primary disease, an intermediate dose to regional microscopic disease, and lower dose to electively treated nodes are used for optimizing IMRT plans. The resulting nominal dose distributions are converted back into NTD distributions for the evaluation of treatment plans. Similar calculations for critical normal tissues are also performed. Methods developed were applied for the intercomparison of several HN treatment regimens, including conventional regimens used currently and in the past, as well as SIB strategies. This was accomplished by comparing the biologically equivalent NTD values for the gross tumor and regional disease, and bone, muscle, and mucosa embedded in the gross tumor volume.

RESULTS

(1) A schematic HN example was used to demonstrate that dose distributions for SIB IMRT are more conformal compared to dose distributions when IMRT is divided into a large-field phase and a boost phase. Both were shown to be significantly superior compared to dose distributions obtained using conventional beams for the large-field phase followed by IMRT for the boost phase. (2) The relationship between NTD and nominal dose for HN tumors was found to be quite sensitive to the choice of tumor clonogen doubling time but relatively insensitive to other parameters. (3) For late effect normal tissues embedded in the tumor volume and assumed to receive the same dose as the tumor, the biologically equivalent NTD for the SIB IMRT may be significantly higher. (4) Normal tissues outside the target volume receive lower dose due to the higher conformality of the IMRT plans. The biologically equivalent NTDs are even lower due to the lower dose per fraction in the SIB strategy.

CONCLUSIONS

IMRT dose distributions are most conformal when designed to be delivered as SIB. Using isoeffect radiobiological relationships and published HN data, fractionation strategies can be designed in which the nominal dose levels to the primary, regional disease and electively treated volumes are appropriately adjusted, each receiving different dose/fx. Normal tissues outside the treated volumes are at reduced risk in such strategies since they receive lower total dose as well as lower dose/fx. However, the late effect toxicities of tissues embedded within the primary target volume and assumed to receive the same dose as the primary may pose a problem. The efficacy and safety of the proposed fractionation strategies will need to be evaluated with careful clinical trials.

The potential for sparing of parotids and escalation of biologically effective dose with intensity-modulated radiation treatments of head and neck cancers: a treatment design study

PURPOSE

Conventional radiotherapy for cancers of the head and neck (HN) can yield acceptable locoregional tumor control rates, but toxicity of many normal tissues limits our ability to escalate dose. Xerostomia represents one of the most common complications. The purpose of this study is to investigate the potential of intensity-modulated radiotherapy (IMRT) to achieve adequate sparing of parotids and to escalate nominal and/or biologically-effective dose to achieve higher tumor control without exceeding normal tissue tolerances.

METHODS AND MATERIALS

An IMRT optimization system, developed at our institution for research and clinical purposes, and coupled to a commercial radiation treatment planning system, has been applied to a number of cases of HN carcinomas. IMRT plans were designed using dose- and dose-volume-based criteria for 4 and 6 MV coplanar but non-collinear beams ranging in number from 5 to 15 placed at equi-angular steps. Detailed analysis of one of the cases is presented, while the results of the other cases are summarized. For the first case, the IMRT plans are compared with the standard 3D conformal radiation treatment (3DCRT) plan actually used to treat the patient, and with each other. The aim of the 3DCRT plan for this particular case was to deliver 73 Gy to the tumor volume in 5 fractions of 2 Gy and 28 fractions of 2.25 Gy/fx; and 46 Gy to the nodes in 2 Gy/fx while maintaining critical normal tissues to below specified tolerances. The IMRT plans were designed to be delivered as a "simultaneous integrated boost" (SIB) using the "sweeping window" technique with a dynamic MLC. The simultaneous integrated boost strategy was chosen, partly for reasons of efficiency in planning and delivery of IMRT treatments, and partly with the assumption that dose distributions in such treatments are more conformal and spare normal tissues to a greater extent than those with sequential boost strategy. Biologically equivalent dose normalized to 2 Gy/fx, termed here as normalized total dose (NTD), for this strategy was calculated using published head and neck fractionation data.

RESULTS

IMRT plans were more conformal than the 3DCRT plans. For equivalent coverage of the tumor and the nodes, and for the dose to the spinal cord and the brainstem maintained within tolerance limits, the dose to parotids was greatly reduced. For the detailed example presented, it was shown that the tumor and the nodes in the 3DCRT plan receive NTDs of 78 and 46 Gy, respectively. For the IMRT plan, a nominal dose of 70 Gy could be delivered to the tumor in 28 fractions of 2.5 Gy each, simultaneously with 50.4 Gy to nodes with 1.8 Gy/fx. The two are biologically equivalent to 82 and 46 Gy, respectively, if delivered in 2 Gy/fx. Similar computations were carried out for other cases as well. The quality of IMRT plans was found to improve with increasing number of beams, up to 9 beams. Dose-volume-based criteria led to a modest improvement in IMRT plans and required less trial and error.

CONCLUSION

IMRT has the potential to significantly improve radiotherapy of HN cancers by reducing normal tissue dose and simultaneously allowing escalation of dose. SIB strategy is not only more efficient and yields better dose distributions, but may also be biologically more effective. Dose-volume-based criteria is better than purely dose-based criteria. The quality of plans improves with number of beams, reaching a saturation level for a certain number of beams, which for the plans studied was found to be 9.

Synthesis and structure-activity investigation of novel vasopressin hypotensive peptide agonists

We report the solid phase synthesis and vasodepressor potencies of the novel hypotensive peptide [1(-beta-mercapto-beta,beta-pentamethylene propionic acid)-2-O-ethyl-D-tyrosine, 3-arginine, 4-valine] arginine vasopressin, d(CH2)5[D-Tyr(Et)2, Arg3, Val4]AVP (A), its related Lys3 (B), Tyr-NH(9)2 (C), [Lys3, Tyr-NH(9)2 (D) analogs and in a preliminary structure-activity study of positions 2-4 and 7-9, 24 analogs (1-24) of A-C. Peptides 1-6, 9-14 have the following single substituents at positions 2, 3, 4, 8 and 9 in (A): 1, D-Tyr(Me)2; 2, L-Tyr(Et)2; 3, Orn3; 4, N-Me-Arg3; 5, Glu3; 6, Arg4; 9, D-Arg8; 10, Eda9; 11, Arg-NH(9)2; 12, Ala-NH(9)2; 13, desGly9; 14, desGly-NH(9)2. Peptides 15 and 16 are analogs of B which possess the following single modifications: 15, Arg-NH(9)2; 16, desGly9. Peptides 7 and 8 are analogs of (C) with the following single modification: 7, Gln4; 8, Lys8. Peptides 17-24 are analogs of A possessing the following multiple modifications: 17, [Sar7, Eda9]; 18, [Arg7, Eda9]; 19, [Arg7, Eda9<--Tyr10]; 20, [Arg4, Arg-NH(9)2]; 21, [Ile4, desGly9]; 22, [Arg4, desGly9]l; 23, [Arg7, desGly9]; 24, [Arg7, Lys8, desGly9]. All 24 new peptides were evaluated for agonistic and antagonistic activities in in vivo antidiuretic (V2-receptor), vasopressor (V1a-receptor) and in in vitro (no Mg2+) oxytocic (OT-receptor) assays and like the parent peptides (A-D) (Chan et al. Br. J. Pharmacol. 1998; 125: 803-811) were found to exhibit no or negligible activities in these assays. Vasodepressor potencies were determined in anesthetized male rats with baseline mean arterial blood pressure maintained at 110-120 mmHg. The effective dose (ED), in microg 100 g(-1) i.v., required to produce a vasodepressor response of 5 cm2, area under the vasodepressor response curve (AUC) during the 5-min period following the injection of the test peptide, was determined. Therefore, the EDs measure the relative vasodepressor potencies of the hypotensive peptides. The following ED values were obtained for A-D and for peptides 1-24: A, 4.66; B, 5.75; C, 10.56; D, 11.60; 1, approximately 20; 2, approximately 30; 3, 6.78; 4, non-detectable (ND); 5, ND; 6, approximately 32; 7, ND; 8, 8.67; 9, ND; 10, 2.43; 11, 3.54; 12, 10.57; 13, 4.81; 14, ND; 15, 4.47; 16, 9.78; 17, 5.72; 18, 1.10; 19, 1.05; 20, 10.41; 21, 9.13; 22, approximately 33; 23, 3.01; 24, 1.71. A is clearly the most potent of the four original hypotensive peptides A-D. These data provide insights to which modification of A enhance, retain or abolish hypotensive potencies. Six of the new hypotensive peptides are significantly more potent than A. These are peptides 10, 11, 18, 19, 23 and 24. Peptide 19, a radioiodinatable ligand, is ten times more potent than C or D. The Gln4 modification of C and the N-Me-Arg3, Glu3, D-Arg8 and desGly-NH(9)2 modifications of A abolished hypotensive potency. By contrast, the Eda9, Arg-NH(9)2, [Sar7, Eda9], [Arg7, Eda9<- -Tyr10], [Arg7, desGly9], [Arg7, Lys8, desGly9] modifications of A all led to enhancements of hypotensive potency. This initial structure-activity exploration provides useful clues to the design of (a) more potent vasodepressor peptides and (b) high affinity radioiodinatable ligands for the putative AVP vasodilating receptor. Some of the peptides here may be of value as pharmacological tools for studies on the complex cardiovascular actions of AVP and may lead to the development of a new class of anti-hypertensive agents.

Use of the Amplatz thrombectomy device for severe deep venous thrombosis

Venous thromboembolism is a significant cause of morbidity in the United States. Thrombectomy devices are not currently the standard of treatment in deep venous thromboses. The Amplatz thrombectomy device is used for arterial occlusions and pulmonary emboli, but its regular use in venous thromboses has not been documented in the literature. We report a unique case of treatment of lower extremity deep venous thrombosis with the Amplatz thrombectomy device.

An investigation of position 3 in arginine vasopressin with aliphatic, aromatic, conformationally-restricted, polar and charged amino acids

We report the solid-phase synthesis and some pharmacological properties of 23 new analogs of arginine vasopressin (AVP) which have the Phe3 residue replaced by a broad variety of amino acids. Peptides 1-9 have at position 3: (1) the mixed aromatic/aliphatic amino acid thienylalanine (Thi) and the aliphatic amino acids; (2) cyclohexylalanine (Cha); (3) norleucine (Nle); (4) Leu; (5) norvaline (Nva); (6) Val; (7) alpha-aminobutyric acid (Abu); (8) Ala; (9) Gly. Peptides 10-23 have at position 3: the aromatic amino acids, (10) homophenylalanine (Hphe): (11) Tyr; (12) Trp; (13) 2-naphthylalanine (2-Nal); the conformationally-restricted amino acids (14) Pro; (15) 2-aminotetraline-2-carboxylic acid (Atc); the polar amino acids (16) Ser; (17) Thr; (18) Gln; and the charged amino acids (19) Asp; (20) Glu; (21) Arg; (22) Lys; (23) Orn. All 23 new peptides were evaluated for agonistic and, where appropriate, antagonistic activities in in vivo antidiuretic (V2-receptor) and vasopressor (V1a-receptor) assays and in in vitro (no Mg2+) oxytocic assays. The corresponding potencies (units/mg) in these assays for AVP are: 323+/-16; 369+/-6 and 13.9+/-0.5. Peptides 1-9 exhibit the following potencies (units/mg) in these three assays: (1) 379+/-14; 360+/-9; 36.2+/-1.9; (2) 294+/-21: 73.4+/-2.7; 0.33+/-0.02; (3) 249+/-28; 84.6+/-4.3; 4.72+/-0.16; (4) 229+19; 21.4+/-0.6; 2.1+/-0.2; (5) 134+/-5; 31.2+/-0.9; 28.4+/-0.2; (6) 114+/-9; 45.3+2.3; 11.3+/-1.6; (7) 86.7+/-2.5; 4.29+/-0.13; 0.45+/-0.03; (8) 15.5+/-1.5; 0.16+/-0.01; approximately 0.02: (9) 3.76+/-0.03; < 0.02; in vitro oxytocic agonism was not detected. These data show that the aliphatic amino acids Cha, Nle, Leu, Nva and Val are well-tolerated at position 3 in AVP with retention of surprisingly high levels of antidiuretic activity. Peptides 2-9 exhibit significant gains in both antidiuretic/vasopressor (A/P) and antidiuretic/oxytocic (A/O) selectivities relative to AVP. [Thi3]AVP appears to be a more potent antidiuretic and oxytocic agonist than AVP and is equipotent with AVP as a vasopressor agonist. The antidiuretic potencies of peptides 10-23 exhibit drastic losses relative to AVP. They range from a low of 0.018+/-0.001 units/mg for the Lys3 analog (peptide 22) to a high of 24.6+/-4.6 units,mg for the Hphe3 analog (peptide 10). Their vasopressor potencies are also drastically reduced. These range from a low of < 0.002 units/mg for peptide 22 to a high of 8.99+0.44 units/mg for the Atc3 analog (peptide 15). Peptides 10-23 exhibit negligible or undetectable in vitro oxytocic agonism. The findings on peptides 10-23 show that position 3 in AVP is highly intolerant of changes with aromatic, conformationally-restricted, polar and charged amino acids. Furthermore, these findings are in striking contrast to our recent discovery that position 3 in the potent V2/V1a/OT antagonist d(CH2)5D-Tyr(Et)2VAVP tolerates a broad latitude of structural change at position 3 with many of the same amino acids, to give excellent retention of antagonistic potencies. The data on peptides 1-4 offer promising clues to the design of more potent and selective AVP V2 agonists.

Discovery and design of novel vasopressin hypotensive peptide agonists

This presentation will trace the serendipitous discovery of novel vasopressin (VP) hypotensive agonists d(CH2)5[D-Tyr(Et)2,X3]VAVP (where X = Arg, Lys). These peptides were uncovered as part of an ongoing program aimed at the design of potent and selective VP antidiuretic (V2 receptor) antagonists. We will also present highlights of our subsequent preliminary studies seeking (i) to design high affinity radioiodinatable ligands for the localization and characterization of the putative VP vasodilatory (V1c?) receptor; (ii) to identify the structural features of selective and non-selective cyclic and linear VP and oxytocin (OT) antagonists of the V2 receptor, the vascular (V1a) receptor and of the uterine (OT) receptor required for hypotensive agonism and; (iii) to enhance hypotensive potency. These novel VP hypotensive agonists could serve as valuable research tools in studies on the roles of VP in blood pressure regulation and may also lead to the development of a new class of therapeutically useful antihypertensives.

Functional architecture of vasopressin/oxytocin receptors

Three-dimensional models of G protein-coupled receptors (GPCR) have been defined using most experimental data available and protein modeling techniques. The endogenous ligand binding sites have been qualitatively described and putative receptor activation mechanisms have been proposed. The model has been recently refined to take into account recent crystallographic data. Most experimental results published are in excellent qualitative agreement with the initial model. We have undertaken to study more systematically by site directed mutagenesis the vasopressin/oxytocin receptor binding domain as a prototype of neuropeptide receptors. The experimental results are in very good agreement with the models. The residues responsible for the neuropeptide binding have been identified and confirm the predicted localization of the neuromediator in the transmembrane domain of the receptors. The side chain of the 8th residue of vasopressin interacts with a non-conserved receptor residue located in the first extracellular loop. As predicted from the model, this interaction is completely responsible for the selectivity of the ligand-receptor interaction. Finally, aromatic residues which allow the modulation of the efficacy of agonists have been identified.

The D136A mutation of the V2 vasopressin receptor induces a constitutive activity which permits discrimination between antagonists with partial agonist and inverse agonist activities

The substitution, in the human V2 vasopressin receptor, of the aspartate at position 136 by alanine leads to agonist-independent activation of this mutant V2 receptor. Pharmacological studies of the D136A V2 receptor helped us in characterizing different V2 receptor antagonists. SR-121463A and OPC-31260, two non-peptide antagonists, behaved as inverse agonists, while two cyclic peptides d(CH2)5[D-Tyr(Et)2,-Val4,Tyr-NH(2)9]AVP and d(CH2)5[D-Ile2,Ile4,Tyr-NH(2)9]AVP known to be V2 antagonists, demonstrated clear partial agonist properties. The finding of a constitutively activated human V2 receptor represents a useful tool in characterizing V2 receptor antagonist ligands.

Identification of residues responsible for the selective binding of peptide antagonists and agonists in the V2 vasopressin receptor

To improve our understanding of the functional architecture of G protein-coupled receptors, we have taken advantage of differences among mammalian species in ligand binding to search for the rat versus human selectivity determinants of the V2 vasopressin receptor and of its peptide ligands. Our data indicate that residue 2 of species-selective peptide antagonists such as d(CH2)5-[D-Ile2,Ile4, Tyr-NH29]arginine vasopressin controls their rat versus human selectivity. For species-selective agonists such as desmopressin, residues 1 and 8 modulate the binding selectivity. Among residues different between rat and human V2 receptors, those localized in the upper part of the human V2 receptor have been substituted with their rat V2 homologs. Pharmacological analysis of mutant receptors revealed that residues 202 and 304 fully control the species selectivity of the discriminating antagonists in an independent and additive manner. A third residue (position 100) is necessary to observe an equivalent phenomenon for the discriminating agonists. The substitution of these three residues does not modify the affinity of the nonselective agonists and antagonists. In conclusion, extracellular loops and the top of the transmembrane domains of V2 vasopressin receptors may provide the molecular basis for peptide ligand-binding species selectivity. Very few residues in these regions may control the binding mode of both agonists and antagonists.