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Biomedical subjects

V C Stevens

Publications and source records attributed to V C Stevens.

At least 37 records · Page 2Linked to original sources
PubMed1986

The identification of peptide sequences of human chorionic gonadotropin containing a conformational epitope.

A series of overlapping peptides were synthesized representing the entire amino acid sequence of the beta-subunit of human chorionic gonadotropin (hCG) and these were reacted with a monoclonal antibody shown to be specific for hCG. One linear peptide (residues 40-52 of the sequence) reacted significantly with the monoclonal antibody but a conjugate of this peptide to diphtheria toxoid (DT) failed to elicit significant levels of antibodies reactive to hCG in rabbits. The subsequent preparation of an extended peptide (residues 38-57) in which the two cysteines were oxidized to form a loop peptide yielded a highly immunogenic antigen when conjugated to DT. Antibody levels reactive with hCG from loop peptide immunizations of rabbits exceeded those found after immunization with a 37 residue peptide representing the carboxyl terminus of the beta-hCG subunit. The antisera did not react with pituitary glycoprotein hormones with similar sequences.

Amino Acid Sequence↗
PubMed1985

Antibody reactivity against trophoblast and trophoblast products.

Sensitive immunoassays have been applied to WHO reference bank sera from fertile and infertile women in order to assess any naturally occurring antibody reactive with isolated human placental trophoblast membranes or two separate trophoblast protein products (hCG and SP1). A very low incidence of antibody reactive with solubilised trophoblast membrane was detected, and no significant antibody to either hCG or SP1 could be detected. Infertile states represented within this serum bank appear unlikely to involve adverse immune reactions to trophoblast.

Antibodies↗
PubMed1985

Non-cross-reactive monoclonal antibodies to human chorionic gonadotropin generated after immunization with a synthetic peptide.

Noncross-reactive monoclonal antibodies specific for human chorionic gonadotropin (hCG) were obtained after pre-selection for submolecular specificity with a synthetic peptide immunogen. Mice were immunized with a synthetic peptide representing a segment unique to the beta-subunit of hCG (amino acid residues 109-145), conjugated to diphtheria toxoid. We then derived nine different hybridomas that secreted monoclonal antibodies reactive with both native hCG and isolated C-terminal peptide, after somatic cell hybridization of immune spleen cells with a nonsecretory myeloma cell line. None of the nine monoclonal antibodies, termed beta-hCG-CTPa1----a9, reacted with hLH, hFSH, or hTSH, although these pituitary hormones display extensive amino acid sequence homology with hCG. The noncross-reactive anti-beta-hCG monoclonal antibodies show apparent association constants on the order of 10(9) to 10(10) M-1. A sandwich-type enzyme-linked immunosorbent assay was set up with cut-off values of around 5 mIU/ml. These antibodies might have important implications for: a) improving the diagnosis and clinical management of pregnancy; b) monitoring the course of development of carcinomas which secrete the hormone, through in vitro assays or in vivo radioimmunodetection; c) evaluating the antibodies' therapeutic potential against such carcinomas; d) studying the biologic functions of the C-terminal segment of beta-hCG; and e) addressing the anti-fertility effect of antibodies raised against that segment.

Animals↗
PubMed1984

Levels of adrenal and gonadal hormones in rhesus monkeys during chronic hypokinesia.

The purpose of this study was to evaluate the effect of chronic immobilization on the hypophysial-adrenal and hypophysial-gonadal axes of adult male rhesus monkeys and the effect such manipulation has on the ability of these axes to respond to exogenous corticotropin, gonadotropin, and GnRH administration. A comparison was also made of the effects of immobilization on testosterone secretion at periods of low (April) and high (November) gonadal activity in this animal. Adult male rhesus monkeys were immobilized in a horizontal position for periods of up to 20 days during March/April. The function of the hypophysial-adrenal and hypophysial-gonadal axes was studied by monitoring plasma levels of cortisol, 17-hydroxylated precursors, 11 deoxycortisol, and testosterone during the period of restraint. Groups of immobilized and control animals also received iv injections of ACTH, FSH, and LH or LHRH on day 18 of the experiment. An additional group of animals was immobilized for 20 days, but did not receive exogenous hormone treatment. This group was used for comparison of seasonal differences in testosterone secretion with another group of animals subjected to the same treatment in November. During the first 3 h of immobilization, levels of cortisol, 17-hydroxylated precursors, and 11-deoxycortisol increased markedly from initial levels. Cortisol levels remained elevated for 3 days, whereas levels of the other three adrenal hormones declined to near-initial levels within 24 h. Testosterone levels declined steadily during the first 6 h of immobilization in males studied at a time of high testicular activity (November), while an increase during the first hour of restraint followed by a decline during the next 3 days were observed in males studied during a period of low testicular activity (April). Animals injected with ACTH on day 18 of immobilization had cortisol levels similar to those of control animals, but other groups of animals restrained for a similar period exhibited a lower level of plasma testosterone than controls after the injection of FSH and LH or LHRH. These data suggest that adaptation to stress results in a reduced demand for corticosteroid production and that the adrenals of chronically stressed animals are capable of responding to exogenous corticotropin, or alternatively, the immobilization imposed was stressful for only a limited time, and after a few days, animals no longer reacted as in response to stress. Also, secretion of testosterone in male monkeys is markedly influenced by the functional state of the gonads at the time of stress initiation.

17-alpha-Hydroxypregnenolone↗
PubMed1983

Studies of the human chorionic gonadotrophin-like substance of human pituitary glands and its significance.

Radioimmunoassays utilizing antisera specific for the carboxyl-terminal portion of human chorionic gonadotrophin (hCG) beta-subunit were used to measure the concentration in human pituitary extracts of an immunoactive hCG factor (hCG') which was different from human LH (hLH). The content of hCG' from different human pituitary pools collected between 1966 and 1979 was relatively constant at 0.5-1.1 microgram per gland. The hCG' concentrations observed in acetone-dried powder of individual human pituitary glands (0.4-26 ng/mg) were close to those reported for full-term placental powder. After separation and partial purification of human pituitary glycoprotein hormones, pituitary hCG' was found mainly in the crude human FSH (hFSH) fraction. It was separated from hFSH by diethylaminoethyl-cellulose chromatography at pH 7 and by gel filtration on Sephadex G-100. On gel filtration its molecular size was larger than that of hLH or hFSH and it was strongly bound to Concanavalin A-Sepharose. The most active preparations of pituitary hCG' obtained by these procedures were approximately 5 per cent as potent by specific radioimmunoassay as hCG purified from pregnancy urine. Although the hCG' content in individual pituitary glands was more variable than the hLH content, on average pituitary hCG' was estimated to be around 25- to 50-fold less than the content of hLH, hFSH or human TSH in the human pituitary gland.

Chorionic Gonadotropin↗
PubMed1982

Circular dichroic and immunological properties of human choriogonadotropin- beta carboxyl terminal peptides.

Circular dichroic spectra have been obtained in aqueous solution and in trifluoro-ethanol for several synthetic (non-glycosylated) human choriogonadotropin carboxyl terminal peptides of the beta-subunit ranging in size from 10 residues to 40 residues. These was no evidence for formation of alpha-helicity or beta-structure, but the spectra in 90% (v/v) trifluoroethanol were consistent with the occurrence of beta-turns. The Chou-fasman predictive rules also suggest a high probability of beta-turns in these peptides which could result in the occurrence of repeating kinks. Disulfide-linked dimers were also investigated by circular dichroism, and there was evidence of stabilization of particular skewness of the disulfide dihedral angle depending upon the location of the disulfide bond. The single phenylalanyl residue at position 115 in the beta-subunit also contributed to the circular dichroic spectra above 250 nm. Antibodies raised to a peptide consisting of residues 111-145 have been shown to contain two immunological determinants, but the sum of antibodies raised to separate determinant sequences do not equal those raised to the full length peptide. These data could reflect the existence of a conformation-related determinant on the 111-145 peptide or stearic hindrance of immunoglobulin binding of two antibodies to the same peptide.

Chorionic Gonadotropin↗
PubMed1981

Reduction of fertility in female baboons immunized with lactate dehydrogenase C4.

Immunization of female rabbits and mice with the sperm-specific isozyme of lactate dehydrogenase, LDH-C4, significantly reduced their fertility. Similar studies have been extended to nonhuman primates. Two female baboons, immunized with human LDH-C4, produced low antibody titers. These titers were markedly enhanced by booster injections of murine LDH-C4. An additional seven female baboons responded with relatively high antibody titers after receiving murine LDH-C4 as both priming and booster dosages. All nine females received injections of murine LDH-C4 at varying times determined by serum titer levels during fertility studies. These antisera reacted with human, mouse, and baboon LDH-C4. In a series of breeding experiments, 22 of 30 matings, or 73%, were infertile as compared with 28% in control matings. This contraceptive effect of the vaccine containing LDH-C4 was related to antibody titer and was reversible. Normal pregnancies ensued in animals in which the titer declined after termination of booster injections of vaccine.

Animals↗
PubMed1981

Antifertility effects of immunization of female baboons with C-terminal peptides of the beta-subunit of human chorionic gonadotropin.

Fifteen adult female baboons were immunized with a conjugate of tetanus toxoid coupled with a synthetic carboxy-terminal peptide of the beta-subunit of human chorionic gonadotropin and another 15 were immunized with tetanus toxoid. Freund's complete adjuvant was used in all immunizations. All females were placed with males of proven fertility during the third menstrual cycle after the primary immunization and those not sustaining pregnancy were mated in two additional consecutive cycles. Four pregnancies occurred following 42 matings in the conjugate-immunized group and 15 pregnancies resulted from 21 matings in the tetanus toxoid-immunized animals. Low levels of antibodies reactive to baboon chorionic gonadotropin were found in the pregnant animals in the conjugate-immunized group.

Animals↗
PubMed1981

Suppression of luteal and placental function in pregnant baboons with agonist analogs of luteinizing hormone-releasing hormones.

Implantation of pelleted agonistic analogs of luteinizing hormone-releasing hormone (LH-RH) into six pregnant baboons, ranging between 14 and 21 days after mating in individual animals, resulted in two abortions: one at 39 and the other at 67 days after mating. Plasma progesterone levels were low in treated animals through the 23rd day after mating, in spite of rising levels of plasma chorionic gonadotropin. Plasma levels of progesterone then rose rapidly to normal in five of six animals. Plasma estradiol levels were low from treatment on in the late-aborting animal but were normal until 5 days before delivery in the early abortant. The profile of circulating chorionic gonadotropin was truncated in treated animals, which may be the first indication of a paradoxical effect of LH-RH agonist on the trophoblast.

Abortion, Spontaneous↗
PubMed1980

Affinity, cross-reactivity and biological effectiveness of rabbit antibodies against a synthetic 37 amino acid C-terminal peptide of human chorionic gonadotrophin.

As a part of a programme to develop a fertility regulating vaccine, antibodies specific for human chorionic gonadotrophin were raised by immunizing rabbits with a synthetic 37 amino acid C-terminal peptide of beta hCG conjugated to tetanus toxoid as carrier, and using Bordetella pertussis or Freund's complete adjuvant as adjuvants. Lack of cross-reactivity of the antibodies with human luteinizing hormone was determined by direct binding in a radioimmunoassay and by immunofluorescence on adult human pituitary sections. Not only did the antibodies bind to native hormone in a radioimmunoassay but they also neutralized the biological activity of hCG as measured by an in vivo bioassay. Rabbits which had been injected with the conjugate with B. pertussis as adjuvant made antibodies of comparable affinity to those animals which had been immunized with the antigen in Freund's complete adjuvant, though the latter group did produce more antibodies.

Agglutination Tests↗
PubMed1978

Immunological control of fertility: measurement of affinity of antibodies to human chorionic gonadotrophin.

Four baboons were primed with diazotized beta human chorionic gonadotrophin and boosted with diazotized C-terminal beta human chorionic gonadotrophin peptide, and the changes in antibody amount and affinity determined using a double isotope modified Farr assay, using labelled human chorionic gonadotrophin as the antigen. The degree of cross-reaction with human luteinizing hormone was also determined. Although appreciable reactivity with luteinizing hormone was observed soon after immunization, this declined rapidly during the response. At the time intervals studied, there was a progressive increase in affinity of antibodies to human chorionic gonadotrophin until day 248 after priming. At day 313, in two of the animals, there was a decrease in affinity from 1.04 X 10(11) to 6.80 X 10(10) and 1.05 X 10(11) to 4.93 X 10(10) l/mol, whereas in the other two baboons there was a further increase in antibody affinity. At corresponding time intervals, there was a steady decrease in values of total antibody binding sites. To determine the overall effect of the maturation of affinity with a decrease in antibody amount on biological efficacy, the theoretical amount of chorionic gonadotrophin that would be neutralized was calculated. We computed that in all instances, over 99% of a peak concentration of chorionic gonadotrophin that could be in circulation in a pregnant baboon would be neutralized. This was in excellent agreement with results of mating experiments in these baboons. In over forty cycles studied, none of the matings resulted in a sustained pregnancy.

Animals↗
PubMed1978

Radioimmunological study of rat uterine extract.

A radioassay was used to demonstrate the high affinitiy of a crude rat uterine extract for tritiated estradiol-17B. Although no other chemical procedures were employed to further characterize the extract, it may contain the estrogen binding protein isolated by others. The isolate was antigenic in rabbits and administration of immune serum to female rats significantly lowered the in vitro retention of tritiated estradiol-17B in the rat uterus. It is thought that this immune serum could be successfully used to study the estrogen binding activity of rat uterus.

Animals↗