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P C Sizonenko

Publications and source records attributed to P C Sizonenko.

At least 91 records · Page 5Linked to original sources
PubMed1983

Solubilization of pituitary GnRH binding sites by means of a zwitterionic detergent.

Solubilization in an active form of the pituitary plasma membrane protein carrying binding sites for gonadotropin-releasing hormone (GnRH) was possible by using as detergent CHAPS (3[(3-cholamidopropyl)dimethylammonio]-1-propane sulphonate), which is a zwitterionic derivative of cholic acid. In contrast, the use of the non-ionic detergent Triton X-100 resulted in the loss of GnRH binding sites. CHAPS at a concentration of 5-10 mM allowed the solubilization of up to 80% of available sites, and remaining non-solubilized sites retained unaltered binding properties. Characterization of solubilized binding sites of GnRH was achieved by using as radioactive ligand and standard a stable GnRH analog. [D-Trp6,(NEt)Pro9,desGly10]-GnRH. Maximum binding of GnRH to solubilized binding sites was possible in the presence of a very low amount of CHAPS in the incubation medium. Scatchard analysis of classical saturation experiments indicated the presence of a single class of high affinity, low capacity binding sites. The mean value for the affinity constant KA was 0.36 +/- 0.07 X 10(10) M -1 (n = 5) for solubilized GnRH binding sites, when analysed in the presence of 2 mM CHAPS; when solubilized GnRH binding sites were analysed in the absence of CHAPS, significantly higher KA values were observed, ranging from 1.2 to 5.9 X 10(10) M -1. Parallel analysis of the plasma membranes prior to solubilization indicated a mean KA value of 0.53 +/- 0.13 X 10(10) M -1 (n = 5). The binding specificity of the pituitary GnRH binding sites as seen by evaluating cross-reactions with a panel of agonists and antagonists of GnRH was not altered by solubilization. Gel filtration on Sephadex G-25 of solubilized binding sites preincubated with radioiodinated GnRH analog demonstrated the presence of a large molecular weight complex. In conclusion, CHAPS appears to be quite suitable for the solubilization of the binding site moiety of the pituitary GnRH receptor with good retention of the binding characteristics, thus offering a new possibility for the purification and characterization of the GnRH receptor protein.

Animals↗
PubMed1983

Circulating levels of pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotrophin (hCG) in intrauterine and extrauterine pregnancies.

Pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotrophin (hCG) have been measured in the plasma of pregnant and non-pregnant women attending the outpatient clinic for suspicion of pregnancy. The plasma concentrations obtained were grouped into intrauterine or extrauterine pregnancies and compared with values obtained in non-pregnant patients with similar periods of amenorrhoea. Patients with ectopic pregnancies had slightly lower PAPP-A levels and significantly lower hCG concentrations than those in women with normal intrauterine pregnancies. Non-pregnant women had very low hCG and PAPP-A levels compared with those in pregnant patients. These data suggest that in patients with extrauterine pregnancies the poorly sustained ectopic trophoblast is unable to produce normal concentrations of hCG and probably PAPP-A and that the slightly diminished levels of PAPP-A in ectopic pregnancies might be derived from a decidual production.

Chorionic Gonadotropin↗
PubMed1983

Influence of exogenous melatonin on melatonin secretion and the neuroendocrine reproductive axis of intact male rats during sexual maturation.

The influence of daily sc administration of melatonin (5-100 micrograms/day) on sexual development of prepubertal and pubertal male rats was studied in vivo. Adult animals were also studied. When melatonin was injected daily into young animals starting at day 20 of age, dose-dependent reductions in plasma testosterone, testis and seminal vesicles weights, plasma FSH and LH levels, and pituitary GnRH receptor number were observed at day 40 or 45 of age when animals were killed. In contrast, prepubertal animals (5-20 days old) showed no significant responses to similar treatment with melatonin, whereas in adult animals (70-90 days old), melatonin elicited only a small decrease in plasma testosterone concentration. Melatonin analogs such as N-acetyl-serotonin and 5-hydroxytryptophol administered daily from 20-45 days of age did not produce any effect. Chronic melatonin administration from 20-50 days of life did not alter the occurrence of the nocturnal rise of circulating plasma melatonin, but did enhance its amplitude. Our results demonstrate that exogenous melatonin can inhibit or delay sexual maturation in the male rat if administered between 20 and 40 days of age and suggest that this inhibitory action is exerted at the hypothalamic and/or pituitary level.

Animals↗
PubMed1983

Human seminal plasma contains a protein that shares physicochemical, immunochemical, and immunosuppressive properties with pregnancy-associated plasma protein-A.

Pregnancy-associated plasma protein-A (PAPP-A) was detected by RIA in human seminal plasma. This was not due to interference with proteases or binding to seminal plasma proteins, since immunoreactivity was not affected by treatment with protease inhibitors, and the elution of [125I]PAPP-A was not altered by preincubation with seminal plasma. The major component of the seminal plasma PAPP-A coeluted with pure PAPP-A or plasma PAPP-A from pregnant and nonpregnant women. In the RIA, serial dilutions of seminal plasma gave parallel displacement curves to pregnancy plasma. Removing PAPP-A-like material from seminal plasma by adsorbtion to heparin-Sepharose reduced the inhibitory effect of seminal plasma on phytohemagglutinin-induced lymphocyte transformation. The source of seminal plasma PAPP-A-like immunoreactive material remains to be elucidated, but it is unlikely to be the testis, since PAPP-A levels in semen of vasectomized men were similar to those in nonvasectomized men.

Female↗
PubMed1983

Circulating levels of pregnancy proteins and depression of lymphoblastogenesis during pregnancy.

Plasma was obtained from 287 normal pregnant women at different times of gestation. Alpha-foetoprotein (AFP), human chorionic gonadotrophin (hCG), human placental lactogen (hPL) and pregnancy associated plasma protein-A (PAPP-A) were measured by radioimmunoassay. The capacity of those plasmas to inhibit phytohaemagglutinin (PHA) induced lymphocyte transformation was also tested. Between the 7th and the 12th week, pregnancy plasma has a relatively small inhibitory effect on lymphoblastogenesis. Plasmas taken between the 13th week and term pregnancy inhibit much more lymphocyte transformation. The factor which increases this inhibition is unknown. None of the proteins measured were significantly correlated with the inhibitory effect. Two explanations are proposed: either AFP, hCG, hPL and PAPP-A are not responsible for the in vitro inhibition of lymphoblastogenesis or else these factors exert a combined effect so that the concentration of each protein taken separately cannot account for the overall inhibitory effect observed with pregnancy plasma.

Female↗
PubMed1983

Prepubertal gynecomastia following topical inunction of estrogen containing ointment.

A six and a half-year-old boy was investigated for prepubertal gynecomastia and hyperpigmentation of the skin. The biological, clinical and radiological work-up did not reveal any endocrinological or tumoral cause. It was incidentally noticed that the patient's sister presented with similar clinical signs which could be related to an estrogen containing ointment. Long-term follow-up of the boy showed complete but delayed regression of the gynecomastia and persistence of hyperpigmentation. His sister developed later on a normal puberty.

Breast↗
PubMed1982

Follicle-stimulating hormone. IV. Study of the histology of pubertal cryptorchid and scrotal testes in relation to the secretion of gonadotropins.

The morphologic characteristics of 85 cryptorchid and 63 contralateral (scrotal) testes showing histologic changes of puberty were studied. Spermatogenesis was not only delayed on the cryptorchid side but also hypocellular in all cases. The scrotal testes appeared hypocellular in 82.5% of the cases. Repetitive biopsies, performed in 12 patients, showed no improvement of cellularity after orchidopexy but progress in pubertal maturation. In the 22 boys submitted to luteinizing hormone-releasing hormone (LH-RH) stimulation, luteinizing hormone (LH) baseline values did not change significantly whereas follicle-stimulating hormone (FSH) baseline levels increased with advancing age and histologic stage of maturation. LH responses increased with the stage of maturation (without statistical significance); however, LH responses were significantly higher in the group without germ cells. FSH responses to LH-RH stimulation were consistently and significantly higher with advancing stages of maturation and in the group without cells.

Adolescent↗
PubMed1982

Tissue and plasma concentrations of pregnancy-associated plasma protein-A (PAPP-A): comparison with other fetoplacental products.

Human placental lactogen (hPL), alpha fetoprotein (AFP), prolactin (PRL) and pregnancy-associated plasma protein-A (PAPP-A) were measured by radioimmunoassay in plasma, in homogenates of trophoblast, decidua, chorion, amnion and in amniotic fluid from 10 patients after non-complicated term delivery. Plasma samples and homogenates of trophoblast and decidua were also collected from 10 patients undergoing surgical termination of pregnancy between 7 and 12 weeks gestation. In addition, plasma and endometrial samples from 10 patients undergoing hysterectomy for other indications than malignancy were analysed for comparison. The highest tissue concentrations of hPL, AFP and PRL corresponded in each case to the known site of synthesis. For PAPP-A the highest concentration was found in maternal plasma at term [238.8 +/- 75.6 (SEM) micrograms/ml]. The highest tissue concentration was found at term in the decidua (57.0 +/- 2.0 micrograms/g), more than three times higher than that in the trophoblast (16.9 +/- 5.4 micrograms/g). The concentrations of PAPP-A in endometrial samples from non-pregnant women (1.9 +/- 0.6 micrograms/g) was 40 times higher than that in the corresponding plasma samples (0.05 +/- 0.02 microgram/ml). These observations point to the decidua as a possible source of PAPP-A.

Amniotic Fluid↗
PubMed1982

Amniotic fluid and plasma concentrations of pregnancy-associated plasma protein-A (PAPP-A) throughout pregnancy: comparison with other fetoplacental products.

The development of a sensitive radioimmunoassay has enabled measurements of pregnancy-associated plasma protein-A (PAPP-A) to be performed from early pregnancy. The present paper compares the plasma concentrations of PAPP-A with the levels of two trophoblastic proteins, human placental lactogen (hPL) and the beta-subunit of human chorionic gonadotrophin (beta-hCG), with a steroid of fetoplacental origin, total oestriol (total E3), and with a fetal protein, alpha-fetoprotein (AFP). PAPP-A was also measured in amniotic fluid and in maternal urine. In contrast with the secretion of the other substances studied, which either reach a plateau or even decrease during the last 4 weeks of pregnancy, PAPP-A steadily increased in the maternal circulation from 7 to 40 weeks gestation. It is proposed that PAPP-A production is either not related to placental mass or that PAPP-A is not of trophoblastic origin. The increase of PAPP-A in amniotic fluids parallels the increase in maternal blood; virtually no PAPP-A is excreted in urine.

Amniotic Fluid↗
PubMed1982

Endometrial and plasma concentrations of pregnancy-associated plasma protein-A (PAPP-A).

Pregnancy-associated plasma protein-A (PAPP-A), oestradiol and progesterone levels have been measured by radioimmunoassay in plasma and in endometrial homogenates of 20 women undergoing hysterectomy. Results were grouped according to the histological stages of the endometrium. In plasma, oestradiol and progesterone concentrations changed from proliferative to secretory stages in the well-established pattern of the menstrual cycle, but PAPP-A levels did not change. In endometrium, oestradiol levels were high during the proliferative stage and low in inactive and secretory endometrium. Endometrial PAPP-A and progesterone concentrations increased from inactive to secretory stages, but only the increase in PAPP-A was statistically significant. A positive correlation observed between endometrial PAPP-A concentrations and plasma oestradiol/progesterone ratio suggests a possible hormonal control for the presence of PAPP-A in the uterus.

Adult↗
PubMed1982

Pituitary receptor sites for gonadotropin-releasing hormone: effect of castration and substitutive therapy with sex steroids in the male rat.

To examine the role of pituitary gonadotropin-releasing hormone (GnRH) receptors (pit GnRH-R) in the regulation of gonadotropin secretion, male rats were orchidectomized and then selectively received substitutive therapy with sex steroids. Pituitary content of GnRH-R was determined by saturation analysis, using radioiodinated [D-Trp6,(N-Et)Pro5,des-Gly10]GnRH as tracer. Castration produced a rapid and sustained increase of the number of GnRH-R, which doubled after 2 days, and after 10 days the pituitary content of GnRH-R was 258 +/- 23 fmol/pituitary compared to 103 +/- 12 fmol/pituitary for sham-operated control animals. No change of the affinity constant (Ka) was observed (Ka = 1.13 +/- 0.08 X 10(10) M-1; n = 14). Plasma LH increased 5- to 10-fold and FSH-2- to 3-fold after castration, and hypothalamic GnRH content was depleted by 30-60%. Immediate substitution of castrated rats with testosterone propionate (250 micrograms daily) prevented the increases of both plasma gonadotropins and of GnRH-R. Treatment of acutely castrated rats for 7 days with testosterone propionate (50-200 micrograms), 5 alpha-dihydrotestosterone propionate (25-400 micrograms), or estradiol benzoate (2 micrograms) prevented the rise in pit GnRH-R in a dose-related manner and normalized the other parameters studied except that plasma FSH remained slightly elevated. In contrast, when substitutive therapy was started 8 days after castration or later, the 7-day treatment with sex steroids reduced plasma gonadotropins, but pit GnRH-R remained elevated, and hypothalamic GnRH content remained depleted. These results indicate that the marked increase of gonadotropin secretion after castration is mediated at least in part, by an increase in the number of pit GnRH-R. Sex steroids were able to reverse all castration-induced endocrine changes in acutely castrated rats, but in long term castrated animals their action at higher centers to normalize hypothalamic GnRH content, and indirectly, to reduce pit GnRH-R content, was either delayed or ineffective. Thus, the rapid feedback action of sex steroids in long term castrated rats may be predominantly exerted at the pituitary level.

Animals↗
PubMed1982

[Neuroendocrinology of puberty. Role of melatonin in man].

A general scheme of the presently known neuroendocrine events occurring with the onset of puberty has been described. Indirect experiments, both in the animal and the human, suggest that the arcuate nucleus located in the medio-basal hypothalamus secretes GnRH by pulses (with increasing amplitude, and probably frequency). GnRH stimulates the secretion of gonadotropins (LH and FSH) with maturation of the ovary and the testis, ripening of the follicle or spermatogenesis and secretion of oestradiol or of testosterone. The theory of the decrease of the sensitivity of the hypothalamus to the sex steroids which was thought to explain the pubertal increase of gonadotropins may not be valid. The increase of the pulsatile secretion of GnRH may be sufficient to explain the pubertal development. However, the response of the gonadotropins is modified by the feed-back mechanism from sex steroids. One of the factor that may influence the pubertal development is the pineal gland. Its main secretory product, melatonin, inhibits the sexual maturation of the rat and of the hamster. Present studies on night and day plasma concentrations and urinary excretions of melatonin do not attribute a role to this indolamine during human pubertal development.

Adolescent↗
PubMed1981

Pregnancy-associated plasma protein-A (PAPP-A) and hCG in early pregnancy.

Pregnancy-associated plasma protein-A (PAPP-A) is a recently described glycoprotein of unknown biological function. The development of a radioimmunoassay enabled us to measure plasma levels of PAPP-A and human chorionic gonadotrophin (hCG) in 12 non-pregnant volunteers and in 159 women in early pregnancy attending the outpatient clinic for legal abortion. PAPP-A but not hCG was measurable in all non-pregnant women. In pregnant patients (with 36 to 86 days of amenorrhea) hCG reached a peak value (163.1-197.6 ng/ml) between the 9th and the 13th week whereas PAPP-A steadily increased throughout this period of pregnancy. Between the 6th and the 13th week after the last menstrual period, levels of PAPP-A increased proportionally more than hCG. This work provides the first evidence of a PAPP-A production in non-pregnant subjects and the very early marked increase of PAPP-A secretion during pregnancy.

Adolescent↗
PubMed1981

Radioimmunological determination of urinary melatonin in humans: correlation with plasma levels and typical 24-hour rhythmicity.

To study melatonin secretion by a gentle noninvasive method, a simple and quick RIA procedure to analyze melatonin in small urine volumes has been developed. Urinary extracts were prepurified by alkaline washes, and melatonin content was determined by RIA. The specificity of urinary melatonin determinations was confirmed by both thin layer chromatography and by gas chromatography-mass spectrometry. In the present study, we compared the amount of melatonin excreted in urine with plasma levels in 140 specimens from 13 adult volunteers. Comparisons showed a very good correlation between plasma levels at midnight and nocturnal excretion of urine, indicating the biological relevance of melatonin determination in urine. Our studies show further that urinary melatonin excretion displays the characteristic circadian rhythm usually observed in plasma. On the average, melatonin excretion is greatest between 2300--0300 h. The total 24-h excretion of melatonin varies considerably among different individuals.

Adult↗