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Biomedical subjects

O Vakkuri

Publications and source records attributed to O Vakkuri.

At least 37 records · Page 2Linked to original sources
PubMed1993

Cardiopulmonary and behavioral responses to computer-driven infusion of detomidine in standing horses.

Cardiopulmonary and behavioral responses to detomidine, a potent alpha 2-adrenergic agonist, were determined at 4 plasma concentrations in standing horses. After instrumentation and baseline measurements in 7 horses (mean +/- SD for age and body weight, 6 +/- 2 years, and 531 +/- 48.5 kg, respectively), detomidine was infused to maintain 4 plasma concentrations: 2.1 +/- 0.5 (infusion 1), 7.2 +/- 3.5 (infusion 2), 19.1 +/- 5.1. (infusion 3), and 42.9 +/- 10 (infusion 4) ng/ml, by use of a computer-controlled infusion system. Detomidine caused concentration-dependent sedation and somnolence. These effects were profound during infusions 3 and 4, in which marked head ptosis developed and all horses leaned heavily on the bars of the restraining stocks. Heart rate and cardiac index decreased from baseline measurements (42 +/- 7 beats/min, 65 +/- 11 ml.kg of body weight-1.min-1) in linear relationship with the logarithm of plasma detomidine concentration (ie, heart rate = -4.7 [loge detomidine concentration] + 44.3, P < 0.01; cardiac index = -10.5 [loge detomidine concentration] + 73.6, P < 0.01). Second-degree atrioventricular block developed in 5 of 7 horses during infusion 3, and in 6 of 7 horses during infusion 4. Mean arterial blood pressure increased significantly from 118 +/- 11 mm of Hg at baseline to 146 +/- 27 mm of Hg at infusion 4. Similar responses were observed for mean pulmonary artery and right atrial pressures. Systemic vascular resistance (baseline, 182 +/- 28 mm of Hg.ml-1.min-1.kg-1) increased significantly during infusions 3 and 4 (to 294 +/- 79 and 380 +/- 58, respectively). (ABSTRACT TRUNCATED AT 250 WORDS)

Analgesics↗
PubMed1992

Noradrenergic inhibition and alpha 2-adrenergic stimulation of melatonin secretion in the pigeon.

Adrenergic regulatory mechanisms of melatonin synthesis and secretion were studied in the pigeon in vivo. Late-afternoon intraperitoneal injection of noradrenaline (NA; 1 mg/kg) resulted in a significant decrease in plasma melatonin levels in 3 h. The same effect was seen after phenylephrine treatment (1 mg/kg i.p.), indicating that an alpha 1-adrenergic mechanism may mediate the inhibition. Propranolol treatment had no effect on plasma melatonin levels, supporting this concept. Detomidine (1 mg/kg i.p.), an alpha 2-adrenergic agonist, increased melatonin levels. This stimulatory effect was blocked by yohimbine, an alpha 2-adrenergic antagonist. However, yohimbine alone had no effect on the plasma melatonin levels, suggesting that alpha 2-adrenergic transmission is not primarily responsible for the nocturnal stimulation of melatonin synthesis and secretion in the pigeon.

Animals↗
PubMed1992

Pineal muscarinic phosphoinositide responses: age-associated sensitization, agonist-induced desensitization and increase in melatonin release from cultured pineal glands.

Regulation of phosphoinositide (PI) signaling through the muscarinic cholinergic receptors (mAChRs) and their possible role were explored in the rat pineal gland. A sensitization of the PI signaling pathway was seen with advancing age. Binding of the mAChR ligand [N-methyl-3H]scopolamine to pineal sections, as detected by autoradiography, significantly decreased with advancing age and thus negatively correlated with the gland's ability to respond to cholinergic stimulus. The cholinergic agonist carbachol induced a time-dependent desensitization of the muscarinic PI signaling after 2 h of pretreatment in vitro (43 and 61% dampening of the PI response after 2 and 11 h pretreatment, respectively). This homologous desensitization was not mimicked by forskolin or phorbol esters, suggesting that proteins kinases A and C were not involved. Carbachol stimulation of the pineal glands in vitro increased melatonin release 2-fold, an effect quantitatively similar to that seen after adenylyl cyclase activation. Carbachol failed, however, to affect pineal cAMP levels. These results suggest that the PI signaling through pineal mAChRs is desensitized in young rats, possibly due to higher exposure to endogenous acetylcholine. Thus acetylcholine might play a prominent role in the developing gland. Moreover, acetylcholine could modulate melatonin release from the adult pineal gland in vivo.

Aging↗
PubMed1992

Seasonal and daily patterns in melatonin secretion in female reindeer and their calves.

Daily patterns of pineal function were studied in different seasons in 10 adult semidomesticated female reindeer and 5 prepubertal calves living in a natural arctic environment at latitude 69 degrees 10'N. Serum samples for melatonin RIA were collected every 4 h for 24 h in October (10 h of light, 14 h of darkness and 8 h of light, 16 h of darkness), December (24 h of darkness), March (13 h of light, 11 h of darkness), and June (24 h of light). A significant daily variation in serum melatonin levels was observed in the adult reindeer, with peak values (20-50 ng/liter) occurring during the night in autumn, winter, and spring, but not summer. The daytime values at 13 h (5-10 ng/liter) were constant throughout the year. Total daily amounts of melatonin, the duration of peak levels, and maximal concentrations were significantly lower in spring and summer than before the rut in autumn. The exposure of adult animals to artificial darkness from bright sunlight on August 1 and September 21 resulted in an immediate increase in serum melatonin concentrations. The 2-week-old calves had detectable serum melatonin levels, but no daily rhythm in the spring, whereas a rhythm was detectable by the first autumn, only to disappear unexpectedly during the first winter and return in the spring. At the age of 16 months, the calves had serum melatonin concentrations similar to those in the adults. Our present results show that the continuous illumination experienced during the summer abolished the normal daily melatonin rhythm. This does not seem to be related to organic changes in the pineal gland, since exposure to darkness during the summer increased melatonin levels. The highest melatonin secretion occurred in the autumn and was evidently associated with the rut. Similarly, the daily melatonin rhythm of an adult type observed in the calves at the age of 16 months may be related to the observation that most calves were in rut. Thus, a high rhythmical melatonin secretion appears to relate to puberty and the initiation of heat in female reindeer.

Animals↗
PubMed1992

Differential regulation of the rat melatonin receptors: selective age-associated decline and lack of melatonin-induced changes.

To gain some understanding of the factors regulating high affinity melatonin (MT) receptors in the rat, we conducted a series of studies using quantitative autoradiography of [2-125I]iodo-MT binding in vitro with validated assay conditions. MT receptor status and the relative protein content of the autoradiographic sections were assessed in the anterior pituitary gland, the area postrema, the caudal (tail) artery (CA), the anterior cerebral artery (ACA), and the suprachiasmatic nuclei (SCN) of 9-, 96-, and 306-day-old Wistar rats. When age-associated changes in protein content were taken into account, MT receptor expression in the area postrema and the SCN remained relatively constant between 9-306 days of age. On the contrary, a dramatic loss of MT receptors was observed in the arteries of 306-day-old rats (98% and 89% loss compared to the 9-day-old rats in the ACA and CA, respectively). In the anterior pituitary gland, MT receptors were expressed only in the 9-day-old rats. The above changes reflected major changes in binding capacity and minor changes in binding affinity. Neither removal of endogenous circulating MT (acute light exposure for 24 h, pinealectomy, or superior cervical ganglionectomy) nor MT injections (1 mg/kg for 10 days 6 h after lights on) affected MT receptor status in the ACA, CA, area postrema, or SCN. Our data suggest that MT receptor expression is differentially regulated during development and that permanent alterations in MT levels do not affect rat MT receptor status.

Age Factors↗
PubMed1990

Moclobemide, an inhibitor of MAO-A, does not increase daytime plasma melatonin levels in normal humans.

1. Plasma melatonin concentrations were determined after administration of single oral doses (100, 200 and 300 mg) of moclobemide, a reversible inhibitor of monoamine oxidase (MAO) with predominant effects on the A-type of the enzyme, to eight young, healthy male volunteers in a double-blind, random-order, placebo-controlled study. The investigation was later continued in an open fashion by giving a single 10 mg dose of the MAO-B inhibitor deprenyl to the same subjects. 2. Neither drug had any effects on plasma melatonin levels, in spite of very marked MAO-A inhibition after moclobemide (as evidenced by up to 79% average decreases in the plasma concentrations of 3,4-dihydroxyphenylglycol, a deaminated metabolite of noradrenaline) and over 90% inhibition of MAO-B activity in blood platelets after deprenyl. 3. It is concluded that daytime human plasma melatonin levels do not accurately reflect MAO-A inhibition in acute drug studies.

Adult↗
PubMed1990

Melatonin in infants and mothers at delivery and in infants during the first week of life.

To evaluate the possible effect of the extreme and permanent changes in the hormonal milieu and in the lighting conditions at birth on the pineal hormone, melatonin (MT), we measured maternal vein and umbilical artery concentrations of MT in 19 parturients, post-partum urinary concentrations of MT in 14 mothers and their infants, and daytime (0800-2000 h) and night-time (2000-0800 h) urinary concentrations of MT and 6-sulphatoxymelatonin in 22 infants during the first 8 days of life. The mean MT concentrations in maternal venous blood and umbilical arterial blood did not differ significantly from each other and there was a positive correlation between them. The same was true for postpartum urinary MT of the mothers and their infants. There was no diurnal rhythm of MT during the first week of life. MT excretion in neonates was 2-5 pmol/12 h (only 1-5% in comparison with adults) and that of 6-sulphatoxymelatonin 150-300 pmol/12 h. In reverse phase high pressure liquid chromatography (HPLC) studies, 84-100% of total MT immunoreactivity was eluted at the same position as synthetic MT, and a small amount of hydrophobic MT-like immunoreactive material was also detected in five of the 10 urine extracts studied. This material (perhaps a novel neonatal metabolite of MT) may be indicative of immaturity of neonatal metabolism of MT although 6-hydroxylation is also functional in neonates. Although infant MT immediately after delivery at least partly reflects maternal MT secretion, our results show that the pineal gland is capable of producing MT at this time.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Circadian and seasonal variation in human preovulatory follicular fluid melatonin concentration.

The concentrations of melatonin in 112 preovulatory follicular fluid (FF) samples obtained from 60 women undergoing in vitro fertilization and 27 patients at laparotomy during a spontaneous cycle were measured by RIA and compared with those in peripheral serum. The circadian and seasonal variations in FF melatonin were also analyzed. The FF melatonin concentrations in stimulated (mean +/- SEM, 61.9 +/- 6.4 pmol/L) and spontaneous cycles (98.1 +/- 8.9 pmol/L) were significantly higher (P less than 0.005) than those in peripheral serum (25.4 +/- 1.2 and 38.6 +/- 1.8 pmol/L, respectively), and in the stimulated cycles there was a positive correlation between them. The FF melatonin concentration in the morning (58.9 +/- 3.8 pmol/L) was significantly higher (P less than 0.005) than that in the daytime (23.2 +/- 0.8 pmol/L), but the morning concentrations did not differ between the light and the dark seasons of the year, whereas the daytime values were higher (P less than 0.005) during the dark season (27.1 +/- 2.1 pmol/L) than during the light season (21.1 +/- 2.1 pmol/L). The FF melatonin concentration did not correlate with follicular volume, and FF and serum melatonin concentrations showed no significant correlation with the serum concentrations of estradiol, progesterone, testosterone, or PRL. There were also no differences between FF melatonin concentrations in aspirates with or without an ovum. In summary, significant circadian and circannual variations in high FF melatonin concentrations were found, which suggest that melatonin could potentially interfere with the regulation of reproduction in humans at the follicular level.

Chromatography, High Pressure Liquid↗
PubMed1989

Single-dose pharmacokinetics of detomidine in the horse and cow.

The pharmacokinetics of detomidine, a novel analgesic sedative, was studied in the major target species after high (80 micrograms/kg) i.v. and i.m. doses. In addition, drug residues in some organs were determined. Concentrations were measured using a sensitive, detomidine-specific radio-immunoassay method. Rapid absorption following i.m. dosing occurred. Absorption half-lives were 0.15 h (horse) and 0.08 h (cattle). The mean peak concentration in the horse (51.3 ng/ml) was achieved in 0.5 h and in the cow (65.8 ng/ml) in 0.26 h. The areas under the concentration curve after i.m. dosing were 66% (horse) and 85% (cow) of the corresponding i.v. values. Distribution was rapid with half-lives of 0.15 h (horse, i.v.) and 0.24 h (cow, i.v.). The apparent volume of distribution was higher after the i.m. dosing (horse 1.56 l/kg, cow 1.89 l/kg) than after i.v. dosing (horse 0.74 l/kg, cow 0.73 l/kg). Elimination half-lives were 1.19 h (horse) and 1.32 h (cow) for the i.v. dose and 1.78 h (horse) and 2.56 h (cow) for the i.m. dose. Total clearances ranged from 6.7 (horse, i.v.) to 12.3 (cow, i.m.) ml/min/kg. Renal clearances were less than 1% of the total clearances showing negligible excretion of the drug in urine and suggesting elimination by metabolism. A cross-reacting metabolite in urine corresponded to less than 1.5% of the detomidine dose's immunoreactivity. High-dose detomidine increased urine flow significantly. Excretion of detomidine in milk in cattle was extremely low. No detectable amounts were present 23 h after dosing.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1989

Pressor hormones regulate atrial-stretch-induced release of atrial natriuretic peptide in the pithed rat.

Atrial wall stretching is a known stimulus for atrial natriuretic peptide (ANP) secretion. The effects of the stimulation of autonomic nervous system, hemodynamic factors, and humoral factors (epinephrine, angiotensin, vasopressin, and brain extracts) on the release of ANP under basal conditions and during increased atrial pressure produced by acute volume loading in pithed rats were examined. In conscious rats, acute volume expansion by 0.9% of saline (4 ml) increased the plasma immunoreactive ANP (IR-ANP) concentrations by a factor of 4 (140 +/- 30 pg/ml vs. 521 +/- 140 pg/ml, p less than 0.001, n = 8), whereas volume-induced ANP release was blocked in pithed rats (75 +/- 9 pg/ml vs. 99 +/- 13 pg/ml, NS, n = 7). The ANP versus right atrial pressure curve shifted to the right, indicating that much smaller amounts of IR-ANP were released in pithed than in conscious rats for each given increase in right atrial pressure. Electrical vagal and sympathetic nerve stimulation or changes in heart rate had no effect on plasma IR-ANP concentrations and failed to restore the volume-load-induced release of ANP in pithed rats. When extracts of anterior pituitary lobe, brain cortex, or hypothalamus were infused, no effect on volume-expansion-induced plasma IR-ANP levels was seen. In contrast, acute volume expansion caused a fourfold increase in levels of circulating IR-ANP in pithed rats that received posterior pituitary extracts, and the ANP versus right atrial pressure curve shifted markedly to the left. Infusion of a V1 antagonist blocked the volume-expansion-induced ANP release produced by the posterior pituitary extract. When [Arg8]-vasopressin (0.025 or 0.05 micrograms/kg/min) was infused to pithed rats, mean arterial pressure increased but basal plasma IR-ANP did not change significantly. However, acute volume expansion in the presence of vasopressin infusion (0.05 micrograms/kg/min) increased the amount of circulating IR-ANP by a factor of 4 (113 +/- 14 pg/ml vs. 414 +/- 43 pg/ml, p less than 0.001, n = 8). Thus, for a given increase in right atrial pressure, a similar amount of IR-ANP was released in the pithed rat during the vasopressin infusion as in the normal conscious animal. V1 antagonist blocked the increase in mean aterial pressure as well as the increase of plasma IR-ANP produced by [Arg8]-vasopressin. In addition, volume expansion during intravenous epinephrine (1.75 micrograms/kg/min) and angiotensin (1.0 micrograms/kg/min) doubled plasma IR-ANP levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Diurnal rhythm of melatonin binding in the rat suprachiasmatic nucleus.

We used quantitative in vitro autoradiography to localize and characterize 2-125I-melatonin binding sites in the rat suprachiasmatic nuclei in relation to pineal melatonin production. In a light:dark cycle of 12:12 h, binding density exhibited significant diurnal variation with a peak at the dark-light transition and a trough 12 hours later. Saturation studies suggested that the decreased binding at light-dark transition might be due to a shift of the putative melatonin receptor to a low affinity state.

Animals↗
PubMed1989

Serum and amniotic fluid melatonin during human labor.

The serum and amniotic fluid concentrations of melatonin (MT) were measured by RIA during human labor in different conditions related to the type of delivery and the time of the day of delivery. Serum MT concentrations displayed a normal diurnal rhythm, resembling that of nongravid women; the mean concentration [163.8 +/- 149.6 (+/- SD) pmol/L] at night was significantly (P less than 0.001) higher than that during the day (31.4 +/- 16.3 pmol/L). The amniotic fluid MT concentration, which showed a significant positive correlation to the serum MT concentration (r = 0.625; P less than 0.01), also showed an obvious diurnal rhythm; the mean MT concentration was significantly (P less than 0.01) higher during the night [99.3 +/- 59.3 (+/- SD) pmol/L] than during the day (58.9 +/- 33.5 pmol/L). Reverse phase high pressure liquid chromatography confirmed that the amniotic fluid MT immunoreactivity eluated as synthetic MT. During the night the mean amniotic fluid MT concentration [99.3 +/- 59.3 (+/- SD) pmol/L] was significantly (P less than 0.01) lower than that in serum (178.9 +/- 189.6 pmol/L). The progress of delivery, estimated by cervical dilatation, did not affect serum MT concentrations. Induction of delivery by amniotomy and/or oxytocin, and operative delivery by cesarean section had no effect on serum MT concentrations. Human MT secretion does not seem to be influenced by the physical stress of labor or endocrine changes associated with parturition. The single factor regulating MT secretion during human delivery appears to be the time of day.

Adult↗
PubMed1989

Some endocrine responses to sauna, shower and ice water immersion.

Nine winter swimmer men were exposed to: (A) sauna and ice water immersion; (B) sauna and 15 degrees C shower; (C) sauna and room temperature; (D) head-out ice-water immersion and room temperature. The exposures were repeated and ended with a recumbent recovery. The initial, post-exposure and post-recovery concentrations of plasma ACTH, serum cortisol, serum melatonin, plasma norepinephrine and plasma epinephrine were determined. ACTH and cortisol indicated a slightly increased post-exposure level. Melatonin concentration did not change. Post-exposure norepinephrine levels increased (P less than 0.05) from the initial. Post-exposure epinephrine indicated a tendency to elevated levels with a nearly doubled (P less than 0.05) concentration in experiment A. The tendency toward enhanced ACTH and cortisol secretion and sympathetic activity shown by increased catecholamine secretion suggest that the winter swimming practice may raise the pain threshold and develop a potential for improved cold tolerance, possibly by nonshivering thermogenesis.

Adult↗
PubMed1988

Atrial natriuretic peptide (ANP) in rat gastrointestinal tract.

Acid extracts of rat stomach and small intestine contained 8.6 +/- 3.7 and 39 +/- 15 ng/g of immunoreactive atrial natriuretic peptide (ANP). When studied by gel filtration and reverse-phase high-performance liquid chromatography, the stomach immunoreactivity consisted of multiple components, whereas the small intestine contained mostly proANP and ANP 1-28-like material. These findings indicate that ANP may have a role in the physiology of the gastrointestinal tract, e.g. in the regulation of water and electrolyte absorption.

Animals↗
PubMed1988

The concentration of atrial natriuretic peptide (ANP) is decreased in plasma but not in atria in hypophysectomised rats.

To study the role of the pituitary gland in the release of Atrial Natriuretic Peptide (ANP) plasma and atrial concentrations were measured both in intact and in hypophysectomized rats. The plasma concentration of ANP (pg/ml) was significantly (p less than 0.01) decreased from 143 +/- 35 to 82 +/- 29 (mean +/- SD, n) while the tissue concentration (ng/wet tissue mg) remained unchanged, 192 +/- 46 and 194 +/- 39, respectively. The total atrial amount of ANP (ug) was, however, significantly (p less than 0.01) decreased from 29.7 +/- 7.8 to 17.0 +/- 3.3 after hypophysectomy. In intact animals, a volume load (1.1ml/100 body weight g 0.9% NaCl) resulted in 2-fold (p less than 0.001) increase in the plasma ANP levels whereas similar load had no effects on plasma ANP levels in hypophysectomized animals. In both groups, the right atrial pressure was increased from about 2 to about 6 mmHg. We conclude that in the absence of pituitary gland the right atrial pressure and the atrial ANP concentration do not change but plasma ANP levels and the response to volume stimulus are attenuated.

Animals↗
PubMed1988

Seasonal, menstrual and circadian secretions of melatonin, gonadotropins and prolactin in women.

In order to evaluate the role of the pineal gland in human reproduction, day- and night-time concentrations of serum melatonin, FSH, LH and prolactin were measured by radioimmunoassays on various days of the menstrual cycle during summer (average daylight 22 h) and winter (daylight 5 h) in healthy females (n = 12) from northern Finland (65 degrees N). A multifactorial analysis of variance showed that, in addition to the well-established increases of gonadotropins at midcycle and melatonin and prolactin at night, there was a significant effect of season on the serum levels of melatonin and LH. Night-time serum melatonin levels on cycle days 2 and 10 were 27% and 49% (P less than 0.05 and less than 0.01) higher in winter than in summer. Night-time serum LH levels at midcycle were 76% (P less than 0.05) higher in summer than in winter. There were no significant effects of season on the serum levels of FSH, prolactin, day-time melatonin or LH outside the mid-cycle. Neither were there any significant effects of the day of the menstrual cycle on the serum melatonin levels. It is possible that in winter the high levels of melatonin in the follicular phase have an inhibitory effect on the serum LH levels. In summer the melatonin levels are lower and perhaps less inhibitory on the secretion of LH, resulting in the stimulation of the reproductive competence in human females.

Adult↗
PubMed1987

Radioimmunoassay of detomidine, a new benzylimidazole drug with analgesic sedation properties.

A sensitive and specific radioimmunoassay was developed for detomidine, 4(5)-(2,3-dimethylbenzyl)imidazole. The antibodies were raised in rabbits against a conjugate of detomidine and bovine thyroglobulin prepared by diazo reaction. Detomidine was iodinated with chloramine-T and immunoreactive tracer was purified in cation exchange chromatography. The sensitivity of the RIA was 1.6 fmol/tube allowing direct detomidine measurements from minute serum and urine samples (0.1-0.2 microliter) as well as tissue homogenates (10 microliters). For concentrations below 16 pmol/ml chloroform extraction was used to extend the measurement range to 0.3 pmol/ml. Detomidine (80 micrograms/kg iv and im) was given to one horse and two calves and blood samples were taken and urine collected for 24 h whereafter the horse was slaughtered and tissue samples taken for RIA analyses. Serially diluted serum, urine and tissue samples produced a linear displacement curve parallel to synthetic detomidine in RIA. HPLC studies showed that serum and tissue immunoreactivity was unchanged detomidine whereas most immunoreactivity in the urine was due to an unknown metabolite.

Animals↗