Search PubMed⌕ Search

Biomedical subjects

O Vakkuri

Publications and source records attributed to O Vakkuri.

52 records · Page 3Linked to original sources
PubMed1987

CNS-induced natriuresis is not mediated by the atrial natriuretic factor.

Studies were performed on anaesthetized Wistar-Kyoto rats to investigate whether the natriuretic response to stimulation of the cerebroventricular system with a hypertonic sodium solution is in part caused by increased plasma concentrations of atrial natriuretic factor (ANF). Through a cannula inserted into a lateral cerebral ventricle a solution with a normal (CSF, 152 mmol l-1) or high (NaCSF, 1,000 mmol l-1) sodium ion content was infused. In the stimulated animals which received NaCSF, the sodium excretion increased more than 13-fold, from 0.07 +/- 0.02 (mean +/- SEM) to 0.97 +/- 0.22 mumol min-1 g-1 kidney wt (P less than 0.01). Potassium excretion rose more than eight-fold, from 0.37 +/- 0.05 to 3.01 +/- 0.13 mumol min-1 g-1 kidney wt (P less than 0.001), and the urine flow rate more than seven-fold, from 1.35 +/- 0.11 to 9.74 +/- 1.23 microliters min-1 g-1 kidney wt (P less than 0.001). The mean arterial blood pressure increased from 100 +/- 3 to 129 +/- 7 mmHg (P less than 0.001). In the control animals which received CSF throughout the experiment there was no significant change in the above variables. The concentrations of ANF in plasma taken at the end of the experiments were determined by a radioimmunoassay. The mean plasma concentration of ANF in animals receiving CSF throughout the experiment was 175 +/- 36 pg ml-1. This was not significantly different from the corresponding value in animals which were given NaCSF (118 +/- 34 pg ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

A cyclic isomer of 2-hydroxymelatonin: a novel metabolite of melatonin.

A previously unknown melatonin metabolite was isolated by chloroform extraction and reverse phase HPLC from human and rat urine after administration of synthetic melatonin and characterized by mass spectroscopy and proton magnetic resonance spectroscopy to 1-acetyl-1,2,3,3a,8,8a-hexahydro-8a-hydroxy-5-methoxypyrrolo[2,3-b ]indole, a cyclic isomer of 2-hydroxymelatonin. This isolation was based on the fact that our melatonin antibody (a-MT-K1) cross-reacted against this novel metabolite at a level of 0.1% (melatonin 100%). In our HPLC program for indoles the cyclic 2-hydroxymelatonin eluted at 25 min, separately from synthetic indoles, between 6-hydroxymelatonin (19 min) and melatonin (35 min). In [3H] melatonin studies it was found to be present (at 25 min in our HPLC), accounting for 5% of the urinary metabolites of melatonin in the rat. Since beta-glucuronidase-arylsulfatase treatment of rat urine did not liberate the cyclic 2-hydroxymelatonin this would appear to be excreted into urine as the free form.

Adult↗
PubMed1987

Inverse seasonal relationship between melatonin and ovarian activity in humans in a region with a strong seasonal contrast in luminosity.

The effects of season on the activity of the pituitary-ovarian axis and the pineal gland were studied in 11 women by serum and urinary melatonin determinations and in 21 women by measurements of the serum concentrations of anterior pituitary and ovarian hormones during the dark and light seasons. A melatonin index was determined by integration of the area below the curve of serum melatonin concentrations during 24-h periods in both seasons. During the dark season, the daytime 12-h melatonin index and daytime urinary melatonin excretion were significantly higher than during the light season. In addition, the duration of the nocturnal melatonin pulse (serum melatonin levels, greater than 65 pmol/L) was lengthened during this season, whereas the mean serum estradiol concentration was significantly decreased at the time of ovulation and during the luteal phase of the cycle, indicating lowered ovarian activity. Luteal phase gonadotropin concentrations were increased during the dark season, which was also characterized by increased sex hormone-binding globulin (SHBG) and decreased free testosterone concentrations and free androgen indices (ratio of testosterone to SHBG X 700) throughout the menstrual cycle. The dark season was thus characterized by increased melatonin secretion and decreased ovarian and androgenic activities. In summary, we characterized two season-dependent hormonal phenomena. Although we did not prove any cause and effect association between melatonin and anterior pituitary-ovarian hormones, the inverse seasonal relationship in pineal gland and ovarian secretion suggests that melatonin is causally related to reproduction in humans.

Adult↗
PubMed1986

Effects of physical exercise on the serum concentration of melatonin in female runners.

The serum melatonin concentration was measured in 11 runners before and after a long-distance race, and during one menstrual cycle of another 11 runners who were performing a strenuous training programme, and in their 12 control subjects. The concentration of melatonin was significantly increased (p less than 0.05) after the competition, whereas during one menstrual cycle of female runners it did not differ from the corresponding concentrations of non-athletes. Training did not cause any chronic changes in melatonin secretion, and the serum melatonin increases following the physical exercise remained clearly below the nocturnal level. Hence, the antigonadotropic effect of endurance running activity is very likely not a melatonin-associated phenomenon.

Adult↗
PubMed1985

Oral administration and distribution of melatonin in human serum, saliva and urine.

In order to evaluate for future physiological and pharmacological studies the extent to which orally administered melatonin is found in human serum and saliva and excreted into urine we measured serum, saliva and urine concentrations of melatonin by radioimmunoassay after oral administration of 100 mg melatonin. Elevated melatonin concentrations were observed with peak values of 435 nmol/l in serum and 241 nmol/l in saliva at 60 min. Elimination was monophasic following first-order kinetics. The half-lives for serum and saliva melatonin were 41 and 38 min, respectively. The results suggest that melatonin is passively secreted into saliva which reflects closely the changes in serum melatonin. Saliva sampling is thus useful in studies on peripheral melatonin both in physiological and experimental conditions. Urinary excretion of melatonin was 0.01 % of the amount of melatonin ingested. In high-performance liquid chromatography urine extracts were found to contain also a minor unknown immunoreactive component which we suggest to be some unknown metabolite of melatonin.

Administration, Oral↗
PubMed1985

Presence of immunoreactive melatonin in different tissues of the pigeon (Columba livia).

The distribution of melatonin was studied at midday and midnight in pigeon plasma, pineal, hypothalamus, eyes, Harderian glands, and duodenum. Tissue samples were homogenized, extracted with chloroform, evaporated, and measured by our melatonin radioimmunoassay (RIA). All the extracts gave dilution curves parallel to that of synthetic melatonin and eluted in reverse-phase high-performance liquid chromatography (HPLC) as synthetic melatonin indicating that the immunoreactivity was due to endogenous melatonin in pigeon tissues. Melatonin was found to be present in pigeon plasma, pineal, hypothalamus, eyes, Harderian glands, and duodenum. In all tissues it had a clear diurnal variation with low levels at midday and high levels at midnight. The highest amounts of melatonin were found in the eyes, duodenum, and the pineal so that extrapineal melatonin exceeded pineal melatonin. Further studies are needed to evaluate the significance of extrapineal melatonin.

Animals↗
PubMed1985

Diurnal rhythm of melatonin in human saliva.

Human mixed saliva extracted with chloroform was found to contain immunoreactive melatonin which eluted in HPLC as synthetic melatonin. There was a clear diurnal rhythm in saliva melatonin with low day and high night levels. A similar rhythm was observed in serum. The high night levels in saliva were lower than the corresponding levels in serum. The calculated secretion rate of melatonin into saliva was less than 0.5-0.9 pmol X h-1 during the day and 1.0-2.4 pmol X h-1 during the night. Saliva sampling can be used as a simple and non-invasive way of studying melatonin secretion in human body.

Adult↗
PubMed1985

Circannual concentrations of melatonin, gonadotrophins, prolactin and gonadal steroids in males in a geographical area with a large annual variation in daylight.

This study was aimed at elucidating the possible effects of a large annual variation in photoperiodicity on the secretory activities of the pineal gland, pituitary and testes. Serum daytime melatonin, FSH, LH, prolactin (Prl), testosterone and oestradiol concentrations were determined monthly over a year in 24 healthy young adult men (except for melatonin which was analysed only in 11 subjects) in northern Finland, where the day length is 22 h in mid-summer and 3.5 h in mid-winter. Serum daytime melatonin levels showed two annual peak values, in December and May, and a nadir was observed in August. The absolute values of the other hormones measured did not show significant month to month variation over the observation period. When hormone levels were calculated as percentages of the individual annual means, several significant differences were found between monthly levels. The melatonin peak in May (133 +/- 20%, SE, of the annual mean) was associated with significant increases in LH (110 +/- 4%) and FSH (107 +/- 3%). Prl levels (115 +/- 9%) reached a maximum in January. The nadirs of melatonin and the pituitary hormones measured were seen in August. Oestradiol showed the highest values in April-June, but no significant variation was found in serum testosterone levels. Positive correlations were observed between FSH and LH (r = 0.41, P less than 0.01), and Prl and LH (r = 0.26, P less than 0.01), whereas Prl and testosterone (r = -0.17, P less than 0.01) were inversely correlated.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Plasma and tissue concentrations of melatonin after midnight light exposure and pinealectomy in the pigeon.

The effect of midnight light exposure and pinealectomy on plasma and tissue concentrations of immunoreactive melatonin was studied in the pigeon. Light exposure of 80 min reduced plasma melatonin by 85%. The melatonin concentration fell to 50% of the original value during 12 min. Pinealectomy reduced plasma melatonin so that at midnight about 36 h after the operations the melatonin concentration of pinealectomized pigeons was about 55% of that of sham-operated pigeons. Two weeks after the operations plasma melatonin of pinealectomized pigeons had increased to 64% of that of sham-operated birds. At midday, melatonin levels were unaffected by the operations. The light-dark rhythm of plasma melatonin was also observed in pinealectomized pigeons. In tissue determinations pinealectomy was found to reduce hypothalamic melatonin significantly, suggesting that the pineal is the main source of hypothalamic melatonin. In the Harderian glands a significant increase of melatonin concentrations was observed after pinealectomy. These glands may therefore be the compensatory organs, explaining the presence of circulating melatonin after pinealectomy.

Animals↗
PubMed1984

Iodinated melatonin: preparation and characterization of the molecular structure by mass and 1H NMR spectroscopy.

Synthetic melatonin was iodinated by treatment with potassium iodide in the presence of an oxidizing agent, Iodo-Gen. The iodination products of melatonin were extracted with chloroform and separated by HPLC. The fraction showing immunoreactivity with respect to melatonin antisera was characterized as iodomelatonin by mass spectrometry, so that the substitution of iodine had occurred at a ring carbon atom. 1H NMR spectra showed the iodine to be incorporated at the C-2 position of the indole moiety. The N-[2-(2-iodo-5-methoxy-1H-indol-3-yl)ethyl]acetamide (2-iodomelatonin) reported here is more useful than [3H]melatonin as a tracer in melatonin radioimmunoassay. This method offers also the possibility of preparing iodinated serotonin and other indoleamines for biological studies.

Binding Sites↗
PubMed1984

Development and validation of a melatonin radioimmunoassay using radioiodinated melatonin as tracer.

A new radioimmunoassay (RIA) using [125I]-melatonin as tracer for determination of melatonin in biological fluids has been developed. Melatonin antisera were raised in rabbits by immunization with bovine thyroglobulin conjugate of N-acetyl-5- methoxytryptophan . Two high-affinity and specific antisera were obtained. Unlike in previous studies melatonin was radioiodinated directly. Iodo-Gen was used as the oxidant. Radioiodinated melatonin was purified by TLC for use in RIA. Melatonin was extracted from plasma, serum and urine samples (1 ml) with chloroform. Using the extraction the sensitivity of the RIA method was 18 fmol/ml of original sample. Plasma, serum and urine extracts diluted parallelly with synthetic melatonin in RIA. HPLC analysis of plasma and serum extracts showed only one immunoreactive peak co-eluting with synthetic melatonin. Majority of urine immunoreactivity co-eluted with synthetic melatonin, but 7-23% contaminating immunoreactivity was also observed. Daytime values for rat plasma, human serum and urine melatonin were 30-60, 20-40 and 50-130 fmol/ml and the respective night values were 160-300, 180-370 and 230-470 fmol/ml. Thus a characteristic diurnal rhythm of melatonin was observed in all cases. The urinary excretion of immunoreactive melatonin during the day was 3-9 and during the night 11-28 pmol/h. Thus we have developed a specific and valid RIA method for the determination of plasma and serum melatonin. Despite the incomplete specificity of the RIA for urine determinations, a clear diurnal rhythm for urine melatonin was observed. The distinct advantage of the utilization of [125I]melatonin as tracer is that the costly and cumbersome scintillation counting can be avoided.

Animals↗
PubMed1984

Radioimmunoassay for MPV-295, a new antihypertensive drug.

A specific and simple radioimmunoassay for the determination of MPV-295, 4(5)-[2-(2,6-dimethylphenyl)-ethyl]imidazole, in human serum is described. The antibodies were produced in rabbits immunized with a conjugate of MPV-295 and bovine thyroglobulin prepared by diazo reaction. They were shown to be specific for MPV-295 tested against several synthetic analogues. MPV-295 was iodinated with the chloramine-T method and 125I-MPV-295 was purified in cation exchange chromatography for use as tracer. The sensitivity of the assay is 2-5 pmol/ml depending on the sample volume. Serum determinations were carried out directly with 20-50 microliter serum volumes. This assay has been used to monitor serum levels of MPV-295 in pharmacokinetic studies in healthy and hypertensive subjects.

Antibodies↗
PubMed1982

Photoperiod-induced changes in temperature-metabolism curve, shivering threshold and body temperature in the pigeon.

A short photophase combined with cold-acclimation changed the shivering threshold of the pigeon from 21 to 14 degrees C. The change of critical temperature was also found in the temperature-metabolism curve. A long photophase both alone and combined with warm-acclimation induced a reduction of body temperature to a lower level (about 2 degrees C) at all ambient temperature, ranging from 5 to 40 degrees C.

Acclimatization↗
PubMed1981

Development and validation of a radioimmunoassay for beta-endorphin-related peptides.

A radioimmunoassay method suitable for measuring levels of B-endorphin, B-lipotropin and proopiocortin in tissue and plasma extracts was developed and the method was evaluated by using 3 independently prepared antisera. Of the several variables tested the choice of assay buffer and test tubes and the purification of tracer were found to be the most critical in the successful performance of B-endorphin radioimmunoassay. The prevention of degradation of tracer during incubation was also necessary when crude tissue extracts or plasma were assay. The sensitivities of the assays obtained with the 3 antisera utilized (Bendo 2, K2 and RB 100) were 1, 2.8 and 4 fmol B-endorphin per tube. All the antisera crossreacted equimolarly with B-lipotropin. The method was employed to measure the levels of B-endorphin immunoreactivity in rat pituitary and plasma by separating the different immunoreactants by gel filtration. It was found that both pituitary and plasma contain significant amounts of proopiocortin, B-lipotropin and B-endorphin, the molar proportions being 10:33:57 in pituitary and 15:15:17 in plasma, respectively. Both anterior and posterior lobes of rat pituitary were found to contain all the three immunoreactants. However, anterior lobe contained mostly the larger molecules, while posterior lobe was rich in B-endorphin. No absolute levels of the immunoreactants could be obtained due to the heterologous system used. Moreover the elution pattern of the immunoreactivity was found to be dependent on the conditions used for elution in gel filtration: higher proportion of the immunoreactivity eluted like B-endorphin when the elution was done in dissociating conditions (6 M urea) compared to elution with ordinary buffers.

Animals↗