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Biomedical subjects

D McDonald

Publications and source records attributed to D McDonald.

At least 127 records · Page 7Linked to original sources
PubMed1982

Enzymic synthesis of steroid sulphates. XV. Structural domains of oestrogen sulphotransferase.

Pure preparations of oestrogen sulphotransferase (3'-phosphoadenylylsulphate:oestrone sulphotransferase, EC 2.8.2.4), exhibiting the normal four-isoenzyme pattern on gel electrophoresis, revealed limited proteolytic splits in the protein chain when examined by SDS-polyacrylamide gel electrophoresis. In addition to the normal 74000 molecular weight (74 kDa) protein band, an additional major band was seen at 36 kDa, often accompanied by band at 24kDa and 12kDa. Such preparations, either alone, or after reduction and S-carboxymethylation, showed an extremely strong resistance to dissociation, a concentration of 2% SDS being required for dissociation on Sephadex G-100 column chromatography. These lower molecular weight fragments, isolated by several techniques employing dissociative conditions, all showed a remarkable ability to reassociate to a species of approx. Mr 70000 when examined by SDS-polyacrylamide gel electrophoresis. In addition, the 12kDa fragment yielded dimeric, trimeric, tetrameric, pentameric and hexameric forms. Results of amino acid analyses and tryptic digestion fingerprints of the 36kDa, 24kDa and 12kDa fragments, in conjunction with N-terminal amino acid determinations, suggested in initial protease cleavage at a susceptible region midway in the chain. One, or both, of the resultant 36kDa lobes was then further attacked to yield the 12kDa and 24kDa species - the latter again being capable of cleavage to two 12kDa species. Tryptic maps indicated that the 12kDa, 36kDa and 72kDa species were discrete polypeptide chains and not composed of subunits of the 12kDa species. These data suggest that the enzyme contains a number of domains and that strong interaction occurs between them. If these domains possess oestrogen-binding properties this would explain the most unusual wave-like kinetics exhibited by the enzyme consistent with a rate equation of degree greater than 4. Such properties also provide evidence further to that previously reported which suggests that the enzyme may be genetically related to serum albumin.

Amino Acids↗
PubMed1982

The low affinity component of [3H]spiperone binding reflects association to a non-dopaminergic, neuroleptic site.

The pharmacological properties of a low affinity site labelled by [3H]spiperone in membranes prepared from the rat nucleus accumbens were examined by investigating the ability of dopaminergic agonists, antagonists and various other drugs to displace the binding of 2 nM [3H]spiperone. Neuroleptic drugs were the most potent displacers of binding, and dopaminergic agonists, except for bromocryptine and lergotrile, had inhibition constants greater than 1 microM. The majority of drugs studied exhibited a high selectivity for the high affinity site labelled by [3H]spiperone and low affinity sites probably represent a non-specific, non-dopaminergic site for neuroleptic drugs.

Animals↗
PubMed1982

[3H]Spiperone labels non-cyclase-linked dopamine receptors in the ventral tegmental area of rat brain.

The binding of [3H]spiperone, a neuroleptic/dopamine receptor ligand, to membranes of the ventral tegmental area of the rat was studied in vitro and found to be rapid, saturable, reversible, and of high affinity. Specific binding was displaced by the dopaminergic agonists dopamine, apomorphine, and 2-amino-6,7-dihydroxytetralin, and stereospecifically by the neuroleptic drugs butaclamol and flupenthixol. Bromocryptine and other ergots displaced the binding, as did the D-2 antagonists domperidone, molindone, metoclopramide, and sulpiride. Noradrenergic, histaminergic, and serotonergic components of the binding were not detected in displacement studies with various agonists and antagonists. These data are consistent with the hypothesis that [3H]spiperone labels dopamine receptors in the ventral tegmental area that are not linked to adenylate cyclase and are therefore likely to be of the D-2 type.

Adenylyl Cyclases↗
PubMed1982

Neurochemical studies of the mesolimbic dopaminergic pathway: [3H]spiperone labels two bindings sites in homogenates of the nucleus accumbens of rat brain.

The binding of [3H]spiperone to membranes of the nucleus accumbens of the rat brain was studied in vitro and found to be of high affinity, rapid, saturable, reversible and stereospecific. Dissociation and saturation experiments indicated the presence of two specific binding sites with apparent dissociation constants of 70 pM and greater than 1 nM. Specific binding with 25 pM [3H]spiperone represented greater than 90% of total binding and was displaced by dopaminergic agonists, neuroleptic drugs and ergot derivatives. The rank order of potency for the ergot derivatives was bromocryptine greater than pergolide greater than lergotrile, and that for D-2 antagonists was domperidone greater than sulpiride greater than molindone greater than metoclopramide. Noradrenergic, histaminergic and serotonergic components of the binding were not detected. [3H]Spiperone binds to high-affinity sites in homogenates of nucleus accumbens, which are likely to be D-2 receptors.

Animals↗
PubMed1981

Enzymic synthesis of steroid sulphates. XIV. Properties of human adrenal steroid alcohol sulphotransferase.

Pure steroid alcohol sulphotransferase (EC 2.8.2.-) has the property of sulphurylating hydroxyl groups on different positions of the steroid ring. It has now been established that although only monosulphates are formed from substrates such as 3,17-diols, the position of the sulphate group depends on the relative configuration of the hydroxyl groups. Androst-5-ene-3 beta,17 beta-diol, for example, is sulphurylated mainly at the 17-position. In addition, compounds such as epitestosterone and 17 alpha-estradiol are sulphurylated at much higher rates than their respective 17 beta-epimers. It is believed that the steroid can approach the sulphurylation site via (i) ring A with the beta-side upwards, and in this mode a 3 beta-hydroxyl is sulphurylated at a higher rate than a 3 alpha-hydroxyl, or (ii) ring D with the beta-side downwards, and in this mode a 17 alpha-hydroxyl group is oriented in an analogous fashion to the 3 beta-hydroxyl in (i). The enzyme exhibits non-Michaelis-Menten kinetics within physiological concentrations (0-2 micro M) of the substrate dehydroepiandrosterone and evidence was obtained for the presence of multiple interacting steroid-binding sites. A regulatory role for the enzyme in the secretion of dehydroepiandrosterone from the human adrenal gland is proposed.

Adrenal Glands↗
PubMed1981

Plasma prolactin and gonadotrophins in anorexia nervosa and amenorrhoea due to weight loss.

The role of prolactin in anorexia nervosa is controversial and both hyperprolactinaemia and normoprolactinaemia were reported in patients with anorexia nervosa. We have measured immunoreactive prolactin by radioimmunoassay in plasma samples from 14 consecutive patients with anorexia nervosa and found normoprolactinaemia in 13 patients and a borderline elevation of plasma prolactin in one patient. The mean plasma prolactin level in anorexia nervosa patients did not differ from an age-matched control group of patients with amenorrhoea due to simple weight loss. While we were unable to confirm reports on the common occurrence of hyperprolactinaemia in anorexia nervosa, the absence of hyperprolactinaemia suggests a different mechanism of amenorrhoea in patients with anorexia nervosa and due to simple dieting from that in idiopathic secondary amenorrhoea in which the frequency of hyperprolactinaemia is about 30%. The mean plasma follicle-stimulating hormone was abnormally low both in patients with anorexia nervosa and simple weight loss, while the mean plasma luteinizing hormone was depressed only in patients with anorexia nervosa. This difference is compatible with a more profound hypothalamic disorder in anorexia nervosa, which is not solely dependent on the weight loss, than in amenorrhoea due to simple dieting.

Adolescent↗
PubMed1980

Enzymic synthesis of steroid sulphates. XIII. Isolation and properties of dehydroepiandrosterone sulphotransferase from human foetal adrenals.

Human foetal adrenals have provided a rich source of steroid alcohol sulphotransferase (EC 2.8.2.-). The latter was isolated in pure form in one step by affinity chromatography on an (NH4)2SO4 cut derived from the cytosol fraction of the glands. The yield was 6-fold higher than that obtained from adult human adrenals. General properties of the enzyme are given and it appears to be identical to that obtained previously from adult human adrenals.

Adrenal Glands↗
PubMed1980

Substance P in human cord blood and its degradation by placenta in vitro.

Plasma immunoreactive substance P (iSP) was measured by radioimmunoassay in 12 paired samples of maternal and cord blood, and in placental extracts. The mean plasma iSP concentration in the cord vein was 42.5 pg/ml, as compared to 77.3 pg/ml in the maternal peripheral vein plasma. There was no difference in the mean iSP concentration in the cord vein and artery. Although no iSP was detected in placental tissue, the placenta could not be excluded as the source of iSP in cord blood in view of the rapid degradation of synthetic SP by the placental in vitro.

Female↗
PubMed1980

Clinical course and outcome of thirty-five pregnancies in infertile hyperprolactinemic women.

Thirty-five pregnancies occurred during a 21-month follow-up period in 68 women (51%) who presented with infertility and hyperprolactinemia. Bromocriptine was used in 33 patients, of whom 25 (76%) conceived. In the remaining 35 patients who did not receive bromocriptine, there were 10 pregnancies (28%). The presence or absence of menses and galactorrhea in infertile hyperprolactinemic women treated with bromocriptine did not affect significantly the pregnancy rate. No pituitary complication occurred during pregnancy in any hyperprolactinemic patient and there was no change in sellar x-ray appearance, even in two patients whom a plain skull x-ray showed a minor sellar abnormality. Of the 35 pregnancies, 25 occurred after bromocriptine therapy, 2 after thyroxine therapy, 2 after clomiphene therapy, and 6 without any treatment. Five pregnancies ended in first-trimester abortion, including four after bromocriptine treatment. It is concluded that hyperprolactinemia is a good prognostic factor in infertility and that the majority of patients become fertile after a course of bromocriptine. No congenital abnormalities were observed in the offspring of patients treated with bromocriptine, but the abortion rate was higher than average.

Abortion, Spontaneous↗