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Biomedical subjects

T Loughlin

Publications and source records attributed to T Loughlin.

At least 19 recordsLinked to original sources
PubMed1996

Drug substance manufacture process control: application of flow injection analysis and HPLC for monitoring an enantiospecific synthesis.

Effective process control can only be achieved through an understanding of the operating issues of the reaction. The development and use of effective and rugged analytical methods is necessary to monitor these parameters. The intent of this paper is to present some key analytical issues encountered in the synthesis of MK-0679, an LTD4 antagonist. In a key step of the compound's synthesis, a prochiral diester intermediate undergoes an enantioselective enzymatic hydrolysis (in the presence of Triton X-100) leading to the (S)-ester acid. Subsequent processing transforms the ester acid into the final product. The residual amount of the detergent in the final product, the rapid determination of the enzymatic activity and the optical purity of the final product emerged as key issues in the control of the reaction. As a solution, two techniques were utilized and are presented: flow injection analysis and HPLC.

Chromatography, High Pressure Liquid↗
PubMed1991

Daily cortisol production rate in man determined by stable isotope dilution/mass spectrometry.

Growth retardation as well as the development of Cushingoid features in adrenally insufficient patients treated with the currently accepted replacement dose of cortisol (33-41 mumol/day.m2; 12-15 mg/m2.day) prompted us to reevaluate the cortisol production rate (FPR) in normal subjects and patients with Cushing's syndrome, using a recently developed thermospray liquid chromatography-mass spectrometry method. The stable isotope [9,12,12-2H3]cortisol was infused continuously for 31 h at about 5% of the anticipated FPR. Blood samples were obtained at 20-min intervals for 24 h, spun, and pooled in 4-h groups. Tracer dilution in plasma was determined by liquid chromatography/mass spectrometry. The method was validated with controlled infusions in 6 patients with adrenal insufficiency. Results from 12 normal volunteers revealed a FPR of 27.3 +/- 7.5 mumol/day (9.9 +/- 2.7 mg/day) or 15.7 mumol/day.m2; 5.7 mg/m2. day). A previously unreported circadian variation in FPR was observed. Patients with Cushing's syndrome demonstrated unequivocal elevation of FPR and cortisol concentration correlated during each sample period in normal volunteers, indicating that cortisol secretion, rather than metabolism, is mainly responsible for changes in plasma cortisol. Our data suggest that the FPR in normal subjects may be lower than previously believed.

Chromatography, Liquid↗
PubMed1989

Mild familial goitrous hypothyroidism associated with prolonged 131-iodine retention: possible defect in thyroglobulin synthesis.

Four male siblings presented with goitrous hypothyroidism which had been present from the first few years of life. Serum total thyroxine (T4), free T4 index and free T4 levels were low or in the low-normal range while TSH levels were elevated; triiodothyronine (T3) levels were normal. The 131-I-uptake was elevated at 4 and 24 h, 76-93% and 69-82% respectively (normal less than 50%), and remained elevated 96 h after the administration of radioiodine. Administration of potassium perchlorate did not cause a reduction in thyroidal radioiodine. These findings, therefore, were not consistent with defects affecting iodine trapping, iodine organification or iodotyrosine deiodinase. If a coupling defect was the cause of the disorder, iodotyrosines would have to cycle between the thyroid cell and thyroglobulin in the follicular lumen undergoing deiodination, and reorganification continually. To examine this possibility carbimazole, which inhibits organification of iodine was taken orally following administration of 131-I; potassium perchlorate was given to discharge any accumulating nonorganified radioiodine. 131-I uptake changed only from 50 to 48% and from 68 to 71% in the 2 subjects studied. These findings do not support a coupling defect. The possibility of abnormal thyroglobulin synthesis was supported by the finding of inappropriately low serum thyroglobulin levels. A specimen of thyroid tissue demonstrated a 40-fold reduction in normal thyroglobulin content. These findings suggest that our sibship have a rare partial defect in thyroglobulin synthesis and that iodine is incorporated into an alternative complex which is resistant to mobilization.

Goiter↗
PubMed1989

The effect of pulsatile human corticotropin-releasing hormone administration on the adrenal insufficiency that follows cure of Cushing's disease.

Successful transsphenoidal surgery for Cushing's disease leads to secondary adrenal insufficiency in most patients. This form of transient adrenal insufficiency is thought to result from hypothalamic and pituitary suppression due to the preceding hypercortisolism. Whether the rate-limiting step in the recovery of adrenal function in this setting is the hypothalamic CRH neuron or the pituitary corticotroph cell, however, is not known. We studied this question by examining the response to ovine CRH (oCRH) before, during, and after prolonged pulsatile administration of human CRH (hCRH) beginning 1-2 weeks after curative microadenomectomy for Cushing's disease. Five patients cured of Cushing's disease received eight hCRH injections (1 microgram/kg) daily for 7 days. This CRH regimen was found previously to normalize plasma ACTH and cortisol patterns in patients with secondary adrenal insufficiency who had normal ACTH responses to a single injection of oCRH (hypothalamic adrenal insufficiency). The plasma ACTH and cortisol responses to oCRH (1 microgram/kg at 2000 h) were assessed immediately before, 2.5 h after, and 7 days after the end of pulsatile hCRH administration. To control for time-related improvement in the hormonal response to ovine CRH, an additional five patients cured of Cushing's disease underwent oCRH tests 1-2 and 3-4 weeks after transsphenoidal surgery, but did not receive hCRH. There was no significant difference in basal or oCRH-stimulated plasma ACTH and cortisol levels among any of the three oCRH tests in the patients who received hCRH. The baseline and oCRH-stimulated plasma ACTH and cortisol levels 1-2 and 3-4 weeks after surgery in the patients who did not receive pulsatile hCRH were similar to the values at those times in the patients who received pulsatile hCRH. Compared to normal subjects, however, both the hCRH-treated and non-hCRH-treated patients had significantly decreased peak and time-integrated plasma ACTH and cortisol responses to oCRH. We conclude that an impaired pituitary response to CRH contributes to the postoperative hypocortisolism of patients recently cured of Cushing's disease, and that this impaired pituitary response to CRH is not reversible by 1 week of pulsatile hCRH administration.

Adolescent↗
PubMed1988

Stable isotope dilution method using thermospray liquid chromatography/mass spectrometry for quantification of daily cortisol production in humans.

A thermospray high-performance liquid chromatography/mass spectrometry method for the separation and quantification of cortisol in human serum has been developed. The technique does not require derivatization, allows for both qualitative and quantitative determinations, provides increased specificity not available from conventional high-performance liquid chromatography, and has a detection limit of 5 pmol on-column. This isotope dilution mass spectrometry method, using d3-cortisol as an internal standard, allows precise determinations even at low isotopic ratios (2%-5 mole%). Evidence that this technique can be applied to the quantification of serum cortisol and to the determination of daily cortisol production in humans is presented.

Chromatography, High Pressure Liquid↗
PubMed1988

Plasma pro-opiomelanocortin fragments and adrenal steroids following administration of metyrapone to normal and hirsute women.

The present study was undertaken to characterize further the adrenal abnormalities in the polycystic ovary syndrome (PCOS) and idiopathic hirsutism (IH). We have previously reported the close association of elevated estrone levels with amenorrhea in hyperandrogenemic patients. In addition we have suggested that high estrone levels in PCOS occur as a consequence of the provision of excess substrate, androstenedione, for conversion to estrone. In the present study plasma estrone levels rose following endogenous adrenal stimulation induced using metyrapone; the highest plasma estrone levels achieved were seen in patients with PCOS and occurred later than peak androstenedione levels. These findings are consistent with the hypothesis that elevated estrone levels occurring in PCOS may arise as a consequence of increased adrenal androgen secretion. In addition, we have examined ACTH and other pro-opiomelanocortin (POMC) fragments in an attempt to identify a factor responsible for the excessive adrenal androgen secretion occurring in hirsute patients. Plasma levels of ACTH, and of immunoreactive beta-endorphin and h-lipotropin were not elevated when androgen levels were raised prior to therapy, although these POMC fragments, and also the 16K fragment, rose in response to metyrapone treatment as did androgen levels. Following treatment with dexamethasone there was more profound suppression of the 16K, beta-endorphin and h-lipotropin responses to metyrapone stimulation, than of the ACTH response, as indicated by decreased POMC-fragment/ACTH ratios; this parallels the dissociation of cortisol from androgens in hirsute patients under similar conditions. However, we have not identified a POMC fragment which consistently parallels changes in androgen levels in patients with idiopathic hirsutism or PCOS.

Administration, Oral↗
PubMed1988

Macronodular adrenal hyperplasia in Cushing disease.

Computed tomographic (CT) scans of the adrenal glands were obtained in nine patients with Cushing disease as a result of an adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma and macronodular hyperplasia of the adrenal glands. The findings were compared retrospectively with those in six patients with Cushing syndrome as a result of an autonomous adrenal adenoma and 16 with Cushing syndrome as a result of ectopic ACTH production. Seven of nine patients with macronodular adrenal hyperplasia had hyperplastic adrenal glands in addition to single or multiple focal adrenal nodules. The six patients with hypercortisolism caused by an autonomous adrenal adenoma showed atrophic (four patients) or normal (two patients) ipsilateral and contralateral adrenal glands. Fourteen of 16 patients with the ectopic ACTH syndrome had hyperplasia of the adrenal glands without nodularity, and only two had focal nodules.

ACTH Syndrome, Ectopic↗
PubMed1987

Identification of ACTH-producing intrathoracic tumors by measuring ACTH levels in aspirated specimens.

Three patients with Cushing syndrome secondary to ectopic adrenocorticotropic hormone (ACTH) production underwent direct 22-gauge needle aspiration of bronchial (two cases) and mediastinal (one case) carcinoid tumors. High levels of ACTH were measured in all three tumors. This technique permits absolute identification of an ectopic source of ACTH before surgery.

ACTH Syndrome, Ectopic↗
PubMed1986

Evaluation of an aldosterone radioimmunoassay: the renin-angiotensin-aldosterone axis as a function of sex and age.

A highly specific radioimmunoassay for aldosterone in plasma has been developed utilising extraction from plasma into dichloromethane, an antiserum raised to aldosterone-3-carboxy-methyloxime-BSA and a radio-iodinated derivative of aldosterone. The plasma values obtained after only extraction correlated very well with the results following chromatography over celite. The within- and between-batch variations for plasma pools ranged between 5 and 15%. The range obtained, 100-1806 pmol/L for 96 random upright subjects, was comparable to others reported. Measurement of plasma aldosterone and plasma renin activity in these subjects showed that both these parameters are higher in subjects under 40 years of age than in those over 40. In addition, plasma aldosterone levels are higher in women than in men even though their plasma renin activity levels are similar. The plasma aldosterone/renin activity ratios which provide an index of adrenal sensitivity to stimulation, are lower in men than in women. The findings in this study suggest that higher aldosterone levels in younger subjects are associated with greater stimulation of the adrenals than in older subjects and that the adrenal is more sensitive in women than in men.

Age Factors↗
PubMed1986

Adrenal abnormalities in polycystic ovary syndrome.

This study was undertaken to examine the role of adrenal androgen excess in the pathogenesis of polycystic ovary syndrome (PCOS) and, if such was present, to assess its reversibility using dexamethasone given in physiological dosage at night. Mean plasma testosterone (T), T/sex-hormone binding globulin (T/SHBG) ratio, androstenedione, and 17-OH-progesterone levels were elevated in the 19 patients studied. Plasma estrone values were elevated, whereas estradiol levels were normal. Plasma FSH was decreased and LH responsiveness to LHRH was exaggerated. Metyrapone, an 11-hydroxylase inhibitor, was administered at 2400 h to induce hypocortisolemia and compensatory ACTH secretion so that adrenal androgen and glucocorticoid responsiveness to endogenous stimulation could be examined. Plasma T, androstenedione, and 11-deoxycortisol responses to metyrapone were excessive in PCOS patients, thus indicating a specific adrenal abnormality. After 3 months treatment with dexamethasone, 0.5 mg at night, mean plasma T/SHBG and androstenedione declined to normal, and mean plasma dehydroepiandrosterone and dehydroepiandrosterone sulfate declined to below normal. The mean estrone value was slightly lower during dexamethasone. Plasma LH responsiveness to LHRH was no longer significantly different from normal, but FSH was suppressed. During treatment androgen responsiveness to metyrapone stimulation was normal, whereas 11-deoxycortisol responsiveness was suppressed. Fifteen patients completed 3 months of treatment with dexamethasone. Of these, 10 resumed regular menstruation. The latter group had suppression of plasma T, T/SHBG, androstenedione, dehydroepiandrosterone, and dehydroepiandrosterone sulfate. Only plasma androstenedione fell significantly in the remainder. These observations support the hypothesis that, in at least some patients, PCOS develops in response to abnormal gonadotropin secretion induced by hyperestronemia occurring as a consequence of excessive adrenal androgen secretion.

17-alpha-Hydroxyprogesterone↗
PubMed1985

Altered androstenedione and estrone dynamics associated with abnormal hormonal profiles in amenorrheic subjects with weight loss or obesity.

The present study was designed for exploration of hormonal disturbances underlying common forms of amenorrhea. Polycystic ovary syndrome (PCO) patients and obese amenorrheic subjects had significantly elevated estrone (E1) levels, elevated luteinizing hormone/follicle-stimulating hormone ratios, and an exaggerated luteinizing hormone response to luteinizing hormone-releasing hormone. However, androstenedione (delta 4A), the precursor of E1, was elevated only in PCO. Thus, the E1/delta 4A ratio, which provides an indirect index of aromatase activity in extraglandular sites, was raised in obese subjects as a group but not in PCO subjects. These findings suggest that elevated E1 levels, which give rise to abnormal gonadotropin secretion, arise from increased available androgens in PCO but from an increased effect of aromatase (present in adipose tissue) in obese subjects. Measurement of androgens and the E1/delta 4A ratio provides insights into the relative contributions of hyperandrogenemia and enhanced aromatase activity to the genesis of amenorrhea in these groups. In patients with suppressed estradiol levels associated with hyperprolactinemia or weight loss, follicle-stimulating hormone levels were suppressed, while luteinizing hormone was not elevated. Prolactin excess explains these findings in hyperprolactinemia. Plasma E1 levels and the E1/delta 4A ratio were suppressed in patients with weight loss, possibly as a consequence of reduced adiposity. This finding suggests that hypothesis that a minimum level of E1, dependent upon adequate adiposity, is critical for the normal mature function of the hypothalamic-pituitary-ovarian axis. Abnormal E1/delta 4A ratios, high in obesity-associated amenorrhea and suppressed in weight loss-associated amenorrhea, may provide specific markers for these groups of patients.

Adolescent↗
PubMed1985

The adrenal cortex and virilization.

The physiological control of adrenal androgen secretion has not been definitively established. However, there is evidence to suggest that a dexamethasone-suppressible factor other than ACTH may have a specific role to play. The majority of patients with idiopathic hirsutism (hirsutism associated with regular menstruation) have findings suggestive of adrenal androgen excess, including enhanced androgen responsiveness following administration of metyrapone, and respond to treatment with dexamethasone, 0.5 mg given each night. Patients with idiopathic hirsutism have elevated androgens but normal oestrogen and gonadotrophin levels. In contrast, while patients with polycystic ovary syndrome (PCOS) also demonstrate evidence of adrenal androgen excess, these patients have elevated oestrone levels and gonadotrophin secretion is abnormal. Approximately 50% of patients with PCOS treated with dexamethasone resume regular menstruation. Oestrone excess appears to be primary to the abnormal gonadotrophin secretion and to the development of PCOS. In non-obese patients with PCOS elevated oestrone appears to occur as a consequence of the availability of the excessive amounts of its immediate precursor, androstenedione, an androgen mainly of adrenal origin. Androstenedione is converted to oestrone in fat. Obese amenorrhoeic subjects have normal androstenedione values but elevated oestrone levels with abnormal gonadotrophin secretion as seen in PCOS. These findings indicate that abnormal gonadotrophin secretion is associated with elevated oestrone levels whether these occur as a consequence of excessive adrenal androgen secretion, or the excessive conversion of normal amounts of available androstenedione. Patients with idiopathic hirsutism and elevated androstenedione levels but normal oestrone values appeared to be protected against the development of PCOS by relatively poor conversion of androstenedione to oestrone. It is likely, therefore, that if patients with idiopathic hirsutism gain additional adipose tissue, elevated oestrone levels will result and PCOS will develop. These observations explain the frequent association of PCOS and obesity. There is a close clinical association between elevated androgen levels and hirsutism and between elevated oestrone levels and menstrual disturbances. However, some patients with amenorrhoea but without hirsutism may demonstrate marked elevations of androgens and oestrone, the correction of which leads to the resumption of regular ovulation. This presentation, 'amenorrhoea with cryptic hyperandrogenaemia', is probably explained by diminished sensitivity of androgen receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

17-alpha-Hydroxyprogesterone↗
PubMed1985

The relationship between sex steroids and sex-hormone-binding globulin in plasma in physiological and pathological conditions.

Physiological and many pathological changes in plasma sex-hormone-binding globulin (SHBG) levels have been attributed to the opposing effects of androgens which lower, and oestrogens which elevate, levels. We examined four clinical situations in which changes in SHBG levels may not be explained by sex steroid alterations. (1) Dexamethasone caused an increase in SHBG levels in hyperandrogenaemic hirsute women whether or not androgens were suppressed. (2) In male patients with untreated isolated gonadotrophin deficiency there was a highly significant correlation between SHBG levels and age, but there was no relationship between the levels of SHBG and those of plasma testosterone, androstenedione or DHEAS. (3) Two 46-XY siblings, phenotypic female subjects with complete androgen insensitivity, demonstrated a marked decline in SHBG levels between the ages of 9-13 and 12-16 years. (4) SHBG was suppressed in obese oligomenorrhoeic women while plasma concentrations of testosterone, androstenedione and oestradiol were normal and that of oestrone was elevated; however, the testosterone:SHBG ratio, an index of free testosterone, was elevated. These observations indicate that the decline in SHBG levels which normally occurs in men during the second decade of life is independent of androgen activity and is under the influence of as yet unidentified factors. Glucocorticoids in small doses under the influence of as yet unidentified factors. Glucocorticoids in small doses increase SHBG levels independently of sex steroid alterations while elevated free testosterone concentration may contribute to suppression of SHBG in obesity.

Adolescent↗
PubMed1984

Variable clinical and hormonal manifestations of hyperandrogenemia.

This study was undertaken to contrast the hormonal profiles in patients with various hyperandrogenemic states in an attempt to correlate clinical manifestations with specific hormonal abnormalities. Patients with idiopathic hirsutism, polycystic ovaries, and a syndrome recently described by us, amenorrhea with cryptic hyperandrogenemia, ie, without hirsutism, participated. Total testosterone, the testosterone: sex-hormone-binding globulin (SHBG) ratio, and androstenedione levels were elevated in each group of patients. SHBG levels were suppressed in patients with idiopathic hirsutism and in patients with polycystic ovaries. In patients with polycystic ovaries or cryptic hyperandrogenemia, plasma estrone levels were elevated and the luteinizing hormone (LH) responses to luteinizing-hormone-releasing hormone (LH-RH) were exaggerated. Estrone is derived from androstenedione under the influence of the enzyme, aromatase. While elevated androstenedione occurred in both patients with polycystic ovaries or idiopathic hirsutism, estrone levels were only elevated in patients with polycystic ovaries. Reduced aromatase activity may have protected patients with idiopathic hirsutism from elevated estrone values and, thereby, from menstrual disturbances. The hormonal profiles in polycystic ovary syndrome and in patients with amenorrhea with cryptic hyperandrogenemia were very similar, with the exception that SHBG levels were high normal in three of five patients with cryptic hyperandrogenemia while estrone values were markedly elevated in these patients. Elevated estrone levels may explain the normal SHBG values, which are usually suppressed in hyperandrogenemic states. While each of the hyperandrogenemic disorders studied has a characteristic hormonal profile, the various clinical manifestations cannot be accounted for solely by abnormalities in circulating hormonal levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Plasma sex hormone-binding globulin levels decrease during the second decade of life irrespective of pubertal status.

The plasma concentrations of sex hormone-binding globulin (SHBG) and sex steroids determine the nonprotein bound or free steroid fraction, which probably exerts the biological activity of sex steroids. Androgens lower and estrogens raise SHBG levels. The established pubertal fall in SHBG levels occurring in men has been attributed to rising androgen levels. In this study we examined the relationship between plasma SHBG and androgens in four men with untreated isolated gonadotropin deficiency and in two siblings with complete androgen insensitivity. In patients with untreated isolated gonadotropin deficiency there was a highly significant inverse correlation between SHBG levels and age (r = -0.9, P less than 0.001), although testosterone levels did not rise and there was no relationship between SHBG levels and testosterone, androstenedione, or dehydroepiandrosterone-sulfate. Two 46 XY siblings, who were phenotypic females, with complete androgen insensitivity had a marked decline in SHBG levels from 28.0 ng/ml at 9 yr to 17.1 ng/ml at 13 yr and from 15.2 ng/ml at 12 yr to 8.1 ng/ml at 16 yr, respectively. These observations indicate that the fall in SHBG levels during the second decade of life occurs irrespective of androgen activity and is under the control of other unidentified influences.

Adolescent↗