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Biomedical subjects

R F Walker

Publications and source records attributed to R F Walker.

At least 91 records · Page 5Linked to original sources
PubMed1984

Longitudinal studies of luteal function by salivary progesterone determinations.

A 'normal range' for salivary progesterone concentrations has been established using data derived from women who were menstruating regularly and in whom dating of the cycle by accepted criteria was possible. Since these values are in agreement with those in the first 9 days of conception cycles and with those in cycles in which ovulation was confirmed by ultrasonography, they provide a reliable index of progesterone output compatible with fertility. Measurement of daily salivary progesterone values in subfertile women for time spans exceeding 3 months allowed accurate assessment of base-line ovarian activity and of the response to ovulation-induction therapy. Salivary sampling, by allowing collection of frequent samples with a minimum of time, stress and inconvenience, is ideally suited to longitudinal studies of ovarian activity. This sampling regimen is also applicable to the monitoring of progesterone output throughout pregnancy.

Adolescent↗
PubMed1984

Hormone rhythms and breast cancer chronoepidemiology: salivary progesterone concentrations in pre- and post-menarchal girls and in normal premenopausal women.

Circadian and circatrigintan time series of salivary progesterone levels in premenarchal and adolescent girls and healthy mature premenopausal women have been investigated as a possible determinant for breast cancer risk. Circadian variations in progesterone appear to be more random than systematic and estimates of total daily progesterone output are better represented by samples pooled from several 2-hr specimens. Different patterns of circatrigintan progesterone secretion in girls are recognised and relate to those experienced in infertile and fertile women, though their relation to chronological or menarchal age is as yet uncertain. These data suggest that the measurement of salivary progesterone at premenarche, adolescence and maturity is a feasible, though statistically difficult, study for prospective identification of individuals at risk for breast cancer.

Adolescent↗
PubMed1983

A modified enzymatic-isotopic microassay for serotonin (5HT) using 5HT-N-acetyltransferase partially purified from Drosophila.

Serotonin-N-acetyltransferase (EC 2.3.1.5), partially purified from Drosophila melanogaster (DNAT) was substituted for rat liver enzyme (RNAT) in a previously published radioenzymatic assay for serotonin (5HT). The purpose was to determine if this modification would increase the sensitivity and reliability of the original assay. Compared with RNAT, DNAT is 3-4 times more active; it lacks secondary 5HTP decarboxylase activity; and it is more stable. Under conditions of the modified assay, the only radioactive product formed from hypothalamic tissue extracts is 3H-melatonin; which can be measured from as little as 15 pg of serotonin substrate. Thus, substitution of DNAT for RNAT improves the original radioenzymatic assay allowing measurement of endogenous 5HT in hypothalamic nuclei from individual animals.

Acetyltransferases↗
PubMed1983

Salivary steroid assays for assessing variation in endocrine activity.

Salivary sampling regimens are non-invasive, and therefore facilitate dynamic tests of hormone function and assessment of biological rhythms. Concentrations of neutral steroids in saliva are independent of flow rate and appear to reflect the non-protein-bound, 'free' fraction. Comparison of replicate determinations of quality control pools with determinations of samples collected at 2 min intervals allows the significance of short-term fluctuations in cortisol and testosterone secretory activity to be estimated. Samples collected at 15 min intervals provide a convenient way to estimate circadian rhythms, particularly in young children. Determination of salivary progesterone concentrations in samples collected by women daily, over extended periods of time, provides a valuable means of assessing ovarian function. Such assays may be used to monitor ovulation-induction therapy.

Adult↗
PubMed1982

Salivary cortisol assays for assessing pituitary-adrenal reserve.

Cortisol concentrations were determined in matched samples of plasma and saliva from patients and healthy volunteers throughout the course of standard tests of pituitary and adrenal reserve. During insulin tolerance tests the percentage incremental changes in cortisol concentrations in saliva were strictly comparable with those in plasma and showed less inter-subject variance. The clinical decision taken with regard to the integrity of the pituitary-adrenal axis was the same whether plasma or salivary cortisol was measured. In the short tetracosactrin test changes in salivary cortisol reflected those in plasma and patients with loss of adrenal responsiveness would have been diagnosed as such using either measurement. In normal subjects, the circadian rhythm in salivary cortisol concentrations exactly paralleled that in plasma. Absence of the circadian rhythm in cases of hypercortisolism was seen as well in saliva as in plasma. Assays for salivary cortisol therefore provide information which is as clinically useful as that of plasma determinations. Since salivary cortisol concentrations were shown to reflect the free, biologically active fraction in plasma, salivary assay may, in selected cases, provide results of greater diagnostic significance than plasma total concentrations.

Adult↗
PubMed1982

Melatonin:serotonin interaction during termination of the LH surge in rats.

This study determined whether melatonin's ability to block phasic secretion of LH is a positive timing factor in the reproductive cycle of the female rat. When melatonin synthesis was delayed by extending the photophase on proestrus, serum LH levels were significantly elevated at 2200h. However, melatonin given at 1900h depressed these levels to control values by 2200h despite the extended photophase. This suggests that melatonin helps terminate the LH surge. Since the effect was blocked by pretreatment with quipazine, a serotonin receptor agonist, melatonin may help terminate the LH surge by blocking serotonin neurotransmission. Furthermore, the effects of melatonin and methiothepin, a serotonin receptor antagonist, on hypothalamic serotonin metabolism were comparable, and opposite from quipazine. Temporal patterns of the LH surge changed two months after pinealectomy. These findings suggest that melatonin contributes to termination of the LH surge by an antiserotonin mechanism. The rising levels of melatonin after dark help terminate serotonin signals, and provide a definitive end point for the LH surge, thus helping entrain the gonadotropin rhythm to the light:dark cycle.

Animals↗
PubMed1981

The role of salivary progesterone in studies of infertile women.

Fifteen women with normal menstrual cycles, dated by accepted criteria, had salivary progesterone concentrations during the luteal phase of the cycle which were significantly higher than those in the follicular phase. Progesterone concentrations in matched samples of plasma and saliva showed excellent correlation in both normal and infertile women. Salivary progesterone profiles derived from daily sampling of 20 infertile patients not only allowed accurate assessment of ovarian dysfunction but also indicated more effectively than conventional techniques the change in hormonal status following ovulation induction therapy with clomiphene citrate or bromocriptine.

Adolescent↗