Biomedical subjects

Michael J Wheeler

Publications and source records attributed to Michael J Wheeler.

8 recordsLinked to original sources

PubMed2006

Self-incompatibility in Papaver targets soluble inorganic pyrophosphatases in pollen.

In higher plants, sexual reproduction involves interactions between pollen and pistil. A key mechanism to prevent inbreeding is self-incompatibility through rejection of incompatible ('self') pollen. In Papaver rhoeas, S proteins encoded by the stigma interact with incompatible pollen, triggering a Ca2+-dependent signalling network resulting in pollen tube inhibition and programmed cell death. The cytosolic phosphoprotein p26.1, which has been identified in incompatible pollen, shows rapid, self-incompatibility-induced Ca2+-dependent hyperphosphorylation in vivo. Here we show that p26.1 comprises two proteins, Pr-p26.1a and Pr-p26.1b, which are soluble inorganic pyrophosphatases (sPPases). These proteins have classic Mg2+-dependent sPPase activity, which is inhibited by Ca2+, and unexpectedly can be phosphorylated in vitro. We show that phosphorylation inhibits sPPase activity, establishing a previously unknown mechanism for regulating eukaryotic sPPases. Reduced sPPase activity is predicted to result in the inhibition of many biosynthetic pathways, suggesting that there may be additional mechanisms of self-incompatibility-mediated pollen tube inhibition. We provide evidence that sPPases are required for growth and that self-incompatibility results in an increase in inorganic pyrophosphate, implying a functional role for Pr-p26.1.

Inbreeding↗

PubMed2006

Immunoassay techniques.

No other development has had such a major impact on the measurement of hormones as immunoassay. Reagents and assay kits can now be bought commercially but not for the more esoteric or new hormones. This chapter explains the basics of the immunoassay reaction and gives simple methods for immunoassays and immunometric assays and for the production of reagents for both antigenic and hapten hormones. Alternative methods are given for the preparation of labeled hormones as well as several possible separation procedures. The methods described here have been previously used in a wide range of assays and have stood the test of time. They will allow the production of usable immunoassays in a relatively short period of time.

Animals↗

PubMed2006

Assays for LH, FSH, and prolactin.

In the clinical laboratory the reproductive hormones are probably the most commonly measured hormones after the thyroid hormones. More than 300 laboratories participate in the UK National External Quality Control Scheme. In addition, investigations into reproduction and fertility in humans and animals remains a major area of research. Illustrative methods are described for the three reproductive hormones (leutinizing hormone, follicle-stimulating hormone, prolactin). Radioimmunoassay, immunoradiometric assay, and enzyme assays are described to give a wide choice of assay formats. There are many commercial assays available and illustrative ones are described. Possible interferences are discussed and procedures for investigating their presence and removal are given.

Animals↗

PubMed2006

Measurement of androgens.

Testosterone is the major androgen measured in clinical and research investigations of both men and women. Nevertheless, many other androgens have an important role in the investigation of andrenal and gonadal physiology and pathology. Commercial assays are generally used in clinical laboratories but these have poor precision at low concentrations and poor sensitivity. Extraction assays, described in this chapter, can be much more sensitive and precise. There is interest in measuring free steriods and a steady-state gel filtration method used in the author's laboratory is described. Methods are also provided for the measurement of steroids in saliva and hair.

Androgens↗

PubMed2005

Bone mineral density and its relationship to prolactin levels in patients taking antipsychotic treatment.

Antipsychotic treatment is frequently associated with elevated prolactin levels. Raised prolactin levels have been linked with osteoporosis. The objective of this study is to determine whether patients taking antipsychotics show reduced bone mineral density (BMD), and whether this is associated with prolactin levels. BMD (standardized as z scores) was compared using dual x-ray absorptiometry of the lumbar spine and hip in patients taking antipsychotics (n = 102, mean age: 46.0, SD: 13.1, 47% male, median treatment duration: 3.0 years) to matched reference controls. Levels of prolactin, markers of bone metabolism, and risk factors for osteoporosis were measured. Mean BMD was not significantly reduced, other than the total spine score for black males (mean z score: -0.88, P = 0.00001). BMD was correlated with body mass index but there was no correlation with prolactin. BMD was not correlated with prolactin levels and showed no clinically significant reduction. The low BMD in black males warrants further investigation.

Adult↗

PubMed2004

Effects of oral administration of androstenedione on plasma androgens in young women using hormonal contraception.

Androstenedione as a dietary supplement has been targeted at the sporting community, but there are limited data regarding its effects on plasma androgens in young women. A double-blind, cross-over study was undertaken involving 10 women (20-32 yr) using hormonal contraception. Because contamination of supplements has been reported, an in-house oral formulation was prepared containing purified androstenedione, the control being lactose only. After oral administration of a single dose of androstenedione (100 mg), blood was collected frequently up to 8 h and at 24 h. Maximum plasma androgen concentrations observed between volunteers were well above the upper limit of reference ranges for women, being 121-346 nmol/liter for androstenedione, 14-54 nmol/liter for testosterone (T), 11-32 nmol/liter for 5alpha-dihydrotestosterone, and 23-90 nmol/liter for 3alpha-androstanediol glucuronide. The free androgen index and T concentration changed in a similar manner. The mean change in area under the plasma concentration-time curve (0-24 h), compared with control data were: androstenedione approximately 7-fold, T approximately 16-fold, 5alpha-dihydrotestosterone approximately 9-fold, and 3alpha-androstanediol glucuronide approximately 5-fold; the mean conversion ratio of androstenedione to T was 12.5% (range 7.8-21.6%). Increases in T area under the plasma concentration-time curve were correlated with SHBG concentration (r = 0.80; P = 0.005). Formulation characteristics and SHBG levels appear to be important factors when considering plasma androgen increases after acute androstenedione administration.

Administration, Oral↗

PubMed2002

The effects of antipsychotic-induced hyperprolactinaemia on the hypothalamic-pituitary-gonadal axis.

Hyperprolactinaemia is commonly induced by antipsychotic medications that have dopamine-blockade as their main mechanism of action. The purpose of this study was to assess the effect of antipsychotic-induced hyperprolactinaemia on hypothalamic-pituitary-gonadal axis (HPG) function.HPG axis function was assessed in 67 consecutive outpatients who were diagnosed with schizophrenia and stabilized for a period of not less than 2 years on typical antipsychotic medication, by means of clinical history, relevant questionnaires and measurement of plasma prolactin, estradiol, progesterone, testosterone, LH, FSH, sex hormone binding globulin, and TSH levels. Normative laboratory data were used to assess whether hormone levels fell within the reference range for a normal population. There was a significant correlation between dose of medication and plasma prolactin levels for the total group (P<0.001). Prolactin levels were significantly negatively associated with sex hormone levels in females (P<0.05). Males taking antipsychotic medication had a mean prolactin level of 404.1m/IU and mean gonadotrophin and sex hormone levels that fell within normal limits. The results of this study indicate that neuroleptic-induced prolactin secretion is a dose-related side effect and, in females, the level of hyperprolactinaemia is correlated with the degree of suppression of the HPG axis. Women taking long-term prolactin-raising antipsychotic medications are likely to be hyperprolactinaemic and have an associated hypogonadal state. In males, prolactin levels remain within normal limits, but at the upper end, with no apparent disturbance of reproductive hormones.

Adult↗

PubMed2002

Free cortisol index as a surrogate marker for serum free cortisol.

BACKGROUND: The biologically active component of a hormone is the unbound or free fraction. Changes in cortisol-binding protein could give misleading results if only total cortisol is measured for the interpretation of dynamic function tests. METHODS: This study aimed to measure serum free cortisol using a steady-state gel-filtration method and then to evaluate the correlation between the serum free cortisol and the free cortisol index (FCI), defined as serum total cortisol/cortisol-binding globulin (CBG). RESULTS: Forty-eight serum samples from healthy volunteers undergoing a short Synacthen test were analysed for total cortisol, free cortisol and CBG. The FCI correlated well with a previously established, but more complex, calculation of serum free cortisol (R = 0.98, P <0.001) and with measured serum free cortisol (R = 0.90, P < 0.001). CONCLUSION: Free cortisol index is a reliable and user-friendly measure of serum free cortisol.

Adult↗