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Biomedical subjects

R F Walker

Publications and source records attributed to R F Walker.

At least 109 records · Page 6Linked to original sources
PubMed1980

Assessment of testicular function by the radioimmunoassay of testosterone in saliva.

A sensitive RIA (500 fg/tube) has been developed for assay of testosterone in male saliva and extensively validated. In normal male saliva samples, morning concentrations (368 +/- 167 pmol/l) were significantly higher than evening samples (212 +/- 132 pmol/l). The circadian rhythm was confirmed by COSINOR analysis. Levels of testosterone in saliva, in response to HCG stimulation, accurately reflected the increase observed in matched plasma samples. Synacthen administration, although increasing circulating cortisol levels, caused no significant change in plasma and salivary testosterone concentrations. Prostatic cancer patients on diethylstilboestrol therapy had low salivary (47--122 pmol/l) and plasma (1.0--2.8 nmol/l) testosterone concentrations. Correct assessment of testicular function following stimulation and treatment regimens requires multiple sampling. Since saliva samples are easily collected by non-invasive techniques they represent an attractive alternative to plasma for evaluation of androgenicity.

Adolescent↗
PubMed1980

Salivary steroid assays for screening endocrine function.

Current assessment of endocrine function requires multiple sampling regimens. Salivary studies have the advantage of collection by non-invasive techniques, ease of repetition and findings which accurately reflect circulating steroid concentrations. Since hormone concentrations in saliva are low, these investigations require development of highly sensitive, specific immunoassay techniques. Salivary studies may prove useful in assessing the influence of endocrine factors in depression and sexual dysfunction. Clinical and research applications are being rapidly developed.

Adolescent↗
PubMed1979

Age-related changes in reproductive hormones and in Leydig cell responsivity in the male Fischer 344 rat.

Age-related changes in testicular responsiveness to pituitary hormone stimulation were measured in Fischer rats. Suspensions of dispersed Leydig cells were prepared from the testes of groups which were 5, 12 and 29 months old. The suspended cells were challenged with 250, 750 and 2000ng Monkey-LH (LER 1909-2) for two hours and the medium subsequently assayed for testosterone. Concentrations of the hormone were determined per million cells in suspension. Besides measurement of testosterone production by each age group, pituitary and plasma LH, FSH and prolactin, and plasma testosterone were also assayed by radioimmuno-technique. Total testis weight increased in the oldest animals as the result of a high incidence of gonadal pathology. If tumorous tissue was excluded, however, testis weight fell for this group. Also, significant decreases in Leydig cell number were apparent in 12 and 29-month-old rats. Basal testosterone production, on a per million cell basis, however, was not significantly differnet in young and middle-aged rats, nor was the change in the amount of steroid produced by LH stimulation of the isolated Leydig cells. Seminal vesicle weight, prostate weight and serum testosterone decreased with age. Similarly, pituitary LH and FSH concentration decreased, but pituitary prolactin increased. Histological changes and pituitary hypertrophy reflected this increase in prolactin concentration. It is proposed that decreased testicular function in old age may not totally be the result of a decrement in Leydig cell steroid producing capacity, but that it may also occur due to Leydig cell loss, possibly as the result of age associated changes in the brain and pituitary.

Aging↗
PubMed1979

Induced ovulation in aged female rats by L-dopa implants into the medial preoptic area.

Direct placement of L-dopa into the medial preoptic area (MPOA) of aged pseudopregnant or constant vaginal estrous female rats resulted in a reinitiation of vaginal cycles and ovulation. Similar treatment with L-dopa in the dorsomedial septum or cortex was ineffective. Direct placement of leucine into any of the three brain regions did not have an effect on ovarian function. Intermittent treatment with L-dopa to MPOA was found to reinstate and maintain vaginal cycles in constant estrous females only when administered on the day of vaginal estrus of successive cycles. These findings support the hypothesis that age-dependent disturbances in ovarian function may be initiated by changes in neurotransmitter metabolism within the central nervous system.

Age Factors↗
PubMed1979

Radioimmunoassay of 17 alpha-hydroxyprogesterone in saliva, parotid fluid, and plasma of congenital adrenal hyperplasia patients.

We report a radioimmunoassay sensitive enough to determine 17 alpha-hydroxyprogesterone concentrations in 200 microliter of parotid fluid or mixed whole saliva. Because the correlation of concentrations in matched samples of parotid fluid and saliva was excellent (r = 0.98), we exclusively used saliva, which is easier to collect, in later studies. The assay is specific; saliva samples assayed with and without thin-layer chromatographic purification showed no significant difference. The assay is also precise, and has a lower limit of sensitivity of 4 pg per assay tube. In 14 patients having congenital adrenal hyperplasia from a C21-hydroxylase enzyme deficiency, all of whom were receiving cortisol replacement therapy, the range in 17 alpha-hydroxyprogesterone concentrations observed in saliva (67-26,300 pmol/L) was about 20-fold that seen in 32 healthy children (90-1520 pmol/L). The close correlation (r = 0.91) between 17 alpha-hydroxyprogesterone concentrations in matched samples of saliva and plasma from these patients indicates that determination of steroids in saliva could well replace determination in plasma. This concept is supported by 17 alpha-hydroxyprogesterone concentrations monitored throughout 24 h from one patient and following stimulation with synthetic corticotropin in another patient.

Adolescent↗
PubMed1979

Radioimmunoassay of progesterone in saliva: application to the assessment of ovarian function.

We report a specific radioimmunoassay that has the required sensitivity (7 pg per assay tube) for determining progesterone concentrations in 400 microL of mixed saliva collected from normal women. The assay is precise: intra and inter-assay variation (CV) never exceeded 11.0 and 8.0%, respectively. The assay was used to determine progesterone in saliva samples collected daily for not less than 28 days by normal women and by patients having abnormal ovarian function. Four normal women provided matched saliva and plasma samples for accurate dating of the menstrual cycle by plasma progesterone, estradiol, lutropin, and follitropin. Nine further subjects collected saliva samples only, and from these data a provisional "normal range" was established. Progesterone concentrations in saliva during the follicular phase of the cycle were low (less than 100 pmol/L) but rose beginning on day 12 to reach peak values of 230-550 pmol/L on day 21. Thereafter, progesterone concentrations in saliva declined to values generally less than 170 pmol/L at the commencement of menses. Saliva samples from three patients attending an infertility clinic were also studied to assess ovarian function.

Adult↗
PubMed1978

Influence of the thyroid gland on ovarian function in the aging rat.

The effects of underfeeding and manipulation of the thyroid axis on ovarian function were determined in young and old rats. The depressant effect of reduced food intake on ovarian cycling in young females was potentiated by chemical thyroidectomy, while young anestrous, underfed rats cycled when their diet was supplemented with thyroid extract. These observations iindicate that cycling aberrations in underfed rats may occur secondarily to an altered thyroid state. To determine if thyroid state influences ovarian function in old animals, constant estrous (CE) rats were underfed or chemically thyroidectomized. All underfed rats eventually cycled, while the response to chemical thyroidectomy alone, though still effective, was less dramatic. Realimented CE animals eventually returned to a pattern of constant vaginal cornification. Underfeeding had no effect on ovarian function in old recurrently pseudopregnant females however, these rats responded to thyroid treatment with renewed cycling. 4-6 (YC) 10-12 (PEP) month old females entered a persistent vaginal estrous condition when fed low doses of thyroid extract with their ad libitum diet. When the thyroid supplemented diet was discontinued, YC females resumed regular cycling, whereas the vaginal smear in 40% of the PEP rats remained cornified. Cycling could be restored in YC-thyroid induced CE rats by electrochemical stimulation of the medial preoptic area. These date suggest that senile deviations from normal cycling in the aging reproductive system may be affected by alterations in the thyroid state.

Aging↗
PubMed1978

Adrenal status assessed by direct radioimmunoassay of cortisol in whole saliva or parotid saliva.

We describe a direct radioimmunoassay for cortisol in 10-microliter volumes of parotid saliva or whole saliva. Binding proteins are absent from these fluids, as demonstrated by the excellent correlation between results for samples assayed directly and by a comparison procedure involving extraction with 1,2-dichloroethane. The direct assay is specific, precise, and had a lower limit of sensitivity of 4 pg per assay tube. Comparison of cortisol concentrations in plasma, parotid saliva, and whole saliva in persons undergoing investigations for assessing adrenal function, including stimulation with cosyntropin (Synacthen) and suppression with dexamethasone, indicated that changes in plasma cortisol concentration were accurately and immediately reflected in saliva from either the parotidgland or whole saliva. A marked circadian rhythm has also been demonstrated for cortisol in parotid-gland saliva and whole saliva. We had to modify the 1,2-dichloroethane extraction procedure for accurate determination of cortisol in parotid saliva and whole saliva of patients undergoing treatment with metyrapone.

Adrenal Glands↗