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Biomedical subjects

K Purvis

Publications and source records attributed to K Purvis.

At least 127 records · Page 7Linked to original sources
PubMed1977

hCG suppression of LH receptors and responsiveness of testicular tissue to hCG.

A single injection of 75 IU of human chorionic gonadotropin (hCG) into adult male rats caused a dramatic reduction in the concentration of membrane receptors for luteinizing hormone (LH) in the testis. The mean receptor level reached a nadir which was 5--10% of that in the control testes, 3 days after the injection, after which it gradually returned toward normal. This cannot be due to increased competition caused by the injected hCG since no decrease was observed at a time when the circulating levels of hCG were at a maximum (2--24 h after injection). Furthermore, at a time when receptor levels had been maximally reduced, circulating hCG was at or below the level of detection. Reduction in the number of LH binding sites in the testis was associated with a decreased responsiveness of the testicular tissue to hCG as measured by hCG-stimulated testosterone production in vitro. This inhibitory effect of large quantities of LH on its own receptor is suggested as a possible explantation for the previously observed low concentrations of LH receptor in the testis of the testicular feminized male (tfm) rat. This syndrome is characterized by high endogenous levels of plasma LH (Sherins et al., 1971).

Animals↗
PubMed1977

Androgen stimulation of prolactin receptors in rat prostate.

Specific receptors for iodine-labelled human prolactin ([125I]hPrl) are present in membrane preparations of the rat ventral prostate. The binding is saturable with an apparent association constant (Ka) of 2.2 X 10(9) M-1 and a binding capacity of about 1 pmol/100mg prostatic tissue. The binding of [125I]hPrl is inhibited by hPrl, ovine Prl (otprl) and human growth hormone, but not by ovine FSH or LH. Serum from rats having Prl-producing pituitary tumors caused a displacement of the [125I]hPrl from the receptors, and the displacement curve was parallel with that of the hPrl standard. Treatment of immature rats with varying doses of dihydrotestosterone propionate (10-5000 microng) causes a dose-dependent stimulation of Prl receptors calculated both as binding sites per mg of membrane protein and as binding sites per prostate. Androgen stimulation of prostatic Prl receptors increases the tissue sensitivity for circulating Prl and may be one reason for the known increases in endogenous cAMP levels in prostatic tissue after androgen treatment in vivo.

Animals↗
PubMed1977

Prolactin binding in rat testis: specific receptors in interstitial cells.

Specific receptors for [125I]hPrl (human prolactin) are present in membrane preparations of rat testis. The receptors are specific for lactogenic hormones (prolactin and human growth hormone) but do not bind gonadotropins. The prolactin receptors are localized exclusively in the interstitial cell tissue, and are not present in membrane preparations from isolated seminiferous tubules. The localization of prolactin receptors interstitial tissue suggests that the effect of prolactin on LH/hCG-stimulated testosterone production is due to a direct effect of prolactin of Leydig cells.

Animals↗
PubMed1976

Steroid conjugates in human seminal plasma.

A technique for the measurement of five conjugated steroids (dehydroepiandrosterone sulphate, pregnenolone sulphate, testosterone sulphate, dihydrotestosterone sulphate and testosterone glucuronide) in human seminal plasma is described. The steroid sulphates and testosterone glucuronide were measured by radioimmunoassay after solvolysis and enzyme hydrolysis, respectively. In all cases the recognized criteria of assay reliability were fulfilled. In a group of men with established fertility, dehydroepiandrosterone sulphate had the highest concentration and testosterone sulphate had the lowest (mean levels of 1-04 mumoles/1 and 1-52 nmoles/1, respectively). The levels of pregnenolone sulphate, dihydrotestosterone sulphate and testosterone glucuronide were 30-3, 4-37 and 38-8 nmoles/1, respectively. In all cases the levels of conjugated steroid exceeded the levels of the corresponding unconjugated compound.

Adult↗
PubMed1976

Endocrine effects of vasectomy.

In order to provide information on the endocrine effects of vasectomy, unconjugated pregnenolone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone, oestrone and oestradiol were analysed in the blood plasma of twenty Mexican men on two occasions before and 1, 3, 6 and 12 months after vasectomy. Vasectomy appeared to be associated with a significant decrease in the plasma levels of pregnenolone, dehydroepiandrosterone and androstenedione and a significant increase in the levels of dihydrotestosterone and oestrone. A probably significant increase in oestradiol levels took place 12 months after vasectomy but not before. No consistent changes were found in testosterone (up to 12 months) or in FSH and LH levels (up to 6 months) after vasectomy. The unconjugated steroids indicated above, except oestrone, were also estimated, whenever possible, in seminal plasma specimens obtained from thirty-nine subjects (including the twenty indicated above) on the same occasions. Vasectomy was associated with a highly significant decrease of seminal plasma dihydrotestosterone levels on all occasions and a significant decrease in androstenedione levels after 6 and 12 months. After 12 months there was a decrease in dehydroepiandrosterone and an increase in oestradiol; these changes were both probably significant. In another preliminary study, the levels of pregnenolone sulphate, dehydroepiandrosterone sulphate, testosterone glucuronide, testosterone sulphate and dihydrotestosterone sulphate were estimated before and 1 month after vasectomy in the seminal plasma of fourteen to seventeen subjects. Testosterone glucuronide fell, probably significantly, but other conjugates were unchanged. The data indicate that vasectomy may be associated with significant changes in the circulating and in seminal plasma levels of several steroids. The gradual nature of some of the changes observed suggests the necessity of conducting in several centres large-scale, long-term studies on vasectomized subjects and on a carefully matched control group. During the last decade vasectomy has been widely practised in several parts of the world as a method of fertility control. However, information on the endocrine effects of this intervention appears to be scanty. In most of the human studies reported, a small number of individuals were investigated and the studies have been confined to the assessment of the short-term effects of the operation. Moreover, the hormonal indices assessed by the various investigators have been limited, in most cases, to gonadotrophins and testosterone in blood. The present study was designed to assess in the same subjects the levels of a number of unconjugated steroids, FSH and LH on two occasions before and 1, 3, 6 and 12 months after vasectomy. The studies were extended to include steroid analyses in seminal plasma in the hope that such assays might yield information as to the effects of vasectomy on the distribution of steroids in the fluids of the male reproductive tract.

Adult↗
PubMed1976

Plasma concentrations of testosterone in the developing ram in different social environments.

Plasma testosterone profiles were determined by taking frequent blood samples at intervals from birth to 21 months of age from rams reared in isolation, in an all-male group and in a mixed-sex group. The testosterone pattern was not modified by these different social environments. The ability of the ram to copulate when first exposed to an oestrous ewe, apparently a maturational process, was also independent of social rearing. At birth plasma testosterone levels were detectable but low, they were higher at 10 and 16 weeks of age and showed a marked rise by 26 weeks, coincident with the time of puberty. Depressive effects of season on testosterone profiles occurred during the 2nd year of life but not the 1st year.

Age Factors↗
PubMed1976

Endocrine effects of masturbation in men.

The levels of pregnenolone, dehydroepiandrosterone (DHA), androstenedione, testosterone, dihydrotestosterone (DHT), oestrone, oestradiol, cortisol and luteinizing hormone (LH) were measured in the peripheral plasma of a group of young, apparently healthy males before and after masturbation. The same steroids were also determined in a control study, in which the psychological antipation of masturbation was encouraged, but the physical act was not carried out. The plasma levels of all steroids were significantly increased after masturbation, whereas steroid levels remained unchanged in the control study. The most marked changes after masturbation were observed in pregnenolone and DHA levels. No alterations were observed in the plasma levels of LH. Both before and after masturbation plasma levels of testosterone were significantly correlated to those of DHT and oestradiol, but not to those of the other steroids studied. On the other hand, cortisol levels were significantly correlated to those of pregnenolone, DHA, androstenedione and oestrone. In the same subjects, the levels of pregnenolone, DHA, androstenedione, testosterone and DHT, androstenedione and oestrone. In the same subjects, the levels of pregnenolone, DHA, androstenedione, testosterone and DHT in seminal plasma were also estimated; they were all significantly correlated to the levels of the corresponding steroid in the systemic blood withdrawn both before and after masturbation. As a practical consequence, the results indicate that whenever both blood and semen are analysed, blood sampling must precede semen collection.

Adolescent↗
PubMed1976

Importance of controlled liquefaction periods for valid steroid assays in human seminal plasma.

Incubation of seminal plasma for different periods up to 24 hours at room temperature resulted in a marked gradual increase in the levels of unconjugated pregnenolone, dehydroepiandrosterone, and testosterone, whereas no alterations were detected in unconjugated dihydrotestosterone and estradiol. No significant difference was observed in the levels of the most sensitive indicators of artifactual changes, pregnenolone and dehydroepiandrosterone, when seminal plasma was frozen immediately or within 30 minutes of ejaculation. It is suggested that, at least when steroid analyses in seminal plasma are contemplated, the samples of ejaculate should be provided by masturbation on hospital premises so that the necessary liquefaction period can be kept short, approximately 30 minutes.

Adolescent↗
PubMed1975

Indices of gonadal function in the human male. I. Plasma levels of unconjugated steroids and gonadotrophins under normal and pathological conditions.

A radioimmunoassay technique for the simultaneous measurement of eight unconjugated steroids (progesterone, pregnenolone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone, oestrone and oestradiol) in the peripheral plasma of human males is described. Determinations of these steroids and of immunoreactive FSH and LH were carried out on the plasma of twenty-one normal individuals and the levels were compared to those of eleven and ten males exhibiting oligospermia and azoospermia, respectively. Mean values and tolerance limits for each hormone, based on a lognormal distribution of individual values, are presented for all groups. Oligospermia was associated with a significant reduction in plasma dihydrotestosterone and testosterone levels. Azoospermic subjects also exhibited decreased dihydrotestosterone levels but a normal range of testosterone concentrations. Mean peripheral plasma levels of FSH were significantly elevated in both pathological groups and this was paralleled in the azoospermic men by increased concentrations of plasma LH.

Adult↗
PubMed1975

Indices of gonadal function in the human male. II. Seminal plasma levels of steroids in normal and pathological conditions.

A radioimmunoassay method developed previously for the measurement of unconjugated pregnenolone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone and oestradiol in peripheral plasma was applied to the assay of these steroids in seminal plasma of normal, oligospermic and azoospermic males. It was not possible to use the plasma assay method for the determination of progesterone and oestrone in seminal plasma, because some of the reliability criteria were not fulfilled. A detailed analysis of these steroids in the peripheral plasma of the same subjects has been described previously. The levels of all steroids in seminal plasma were significantly lower than the corresponding blood levels. The ratios of blood plasma/seminal plasma levels of the various steroids varied from 37 (testosterone) to 1.7 (dihydrotestosterone). There was a positive correlation between the testosterone and dihydrotestosterone levels of the seminal plasma of normal and azoospermic subjects. The concentrations of dihydrotestosterone, pregnenolone and oestradiol were significantly lower in azoospermic subjects than in normals. The only pathological finding in the seminal plasma of oligospermic subjects was a diminished level of dihydrotestosterone. Enzymic hydrolysis of a seminal plasma pool resulted in a 3- to 8-fold increase in the concentration of pregnenolone, dehydroepiandrosterone, testosterone, dihydrotestosterone and oestradiol, indicating that human seminal plasma contains large amounts of steroid conjugates. It is suggested that the analysis of steroids in the seminal plasma in combination with determinations in peripheral plasma may be a valuable aid to the assessment of testicular function.

Adult↗