The pluripotency factor LIN28 in monkey and human testes: a marker for spermatogonial stem cells?

Mammalian spermatogenesis is maintained by spermatogonial stem cells (SSCs). However, since evidentiary assays and unequivocal markers are still missing in non-human primates (NHPs) and man, the identity of primate SSCs is unknown. In contrast, in mice, germ cell transplantation studies have functionally demonstrated the presence of SSCs. LIN28 is an RNA-binding pluripotent stem cell factor, which is also strongly expressed in undifferentiated mouse spermatogonia. By contrast, two recent reports indicated that LIN28 is completely absent from adult human testes. Here, we analyzed LIN28 expression in marmoset monkey (Callithrix jacchus) and human testes during development and adulthood and compared it with that in mice. In the marmoset, LIN28 was strongly expressed in migratory primordial germ cells and gonocytes. Strikingly, we found a rare LIN28-positive subpopulation of spermatogonia also in adult marmoset testis. This was corroborated by western blotting and quantitative RT–PCR. Importantly, in contrast to previous publications, we found LIN28-positive spermatogonia also in normal adult human and additional adult NHP testes. Some seasonal breeders exhibit a degenerated (involuted) germinal epithelium consisting only of Sertoli cells and SSCs during their non-breeding season. The latter re-initiate spermatogenesis prior to the next breeding-season. Fully involuted testes from a seasonal hamster and NHP (Lemur catta) exhibited numerous LIN28-positive spermatogonia, indicating an SSC identity of the labeled cells. We conclude that LIN28 is differentially expressed in mouse and NHP spermatogonia and might be a marker for a rare SSC population in NHPs and man. Further characterization of the LIN28-positive population is required.

Type II iodothyronine 5'-deiodinase in mouse brown adipose tissue is stimulated by a single injection of isoproterenol in an oil/water emulsion

A single subcutaneous morning injection of the beta-adrenergic agonist isoproterenol (ISO) (10 mg/kg body weight) in an oil/water emulsion (70/30; v/v) caused a marked increase in the activity of the enzyme type II iodothyronine 5'-deiodinase (5'-D II) in the interscapular brown adipose tissue of BDF-1 mice. After a delay of 4 hours, the 5'-D II activity began to rise in an almost linear fashion and was increased 3-fold after 8 hours, when compared to the control values. The results indicate that this method of ISO administration may be a valid tool for artificial stimulation of brown adipose tissue in animals by beta-adrenergic agonists.

Characteristics of pulsatile and circadian prolactin release and its variability in men

In order to investigate the intra- and interindividual variability of spontaneous prolactin (PRL) secretion, 24 h blood sampling at 10 min intervals was performed in ten healthy young men (age 19 to 25 yrs) on three occasions (intervals 2 weeks and 3 months). Plasma PRL concentrations were determined in duplicate by immunoradiometric assay. Peak detection was carried out with the PULSAR program. The circadian rhythm was analyzed by a complex cosinor method combining fundamental (24 h), 1st harmonic (12 h), and 2nd harmonic (6 h) frequencies. The original data was well represented by this calculation as shown by mean (+/- SD) correlation coefficients of 0.84 +/- 0.08. Mean and integrated PRL concentrations showed the lowest intraindividual variability (range 2.8 to 19.6%) of all parameters tested. For the number of peaks per 24 h, a median intraindividual variability of 24.2% (range 6.9 to 50%) was seen. In general, intraindividual variability of parameters of pulsatile PRL release was lower than the variability between subjects. The complex cosinor analysis revealed a bimodal pattern of PRL secretion in most profiles. Acrophases (times of highest PRL levels) were found between 0040 and 1000 h, nadirs between 0030 and 2300 h. The amplitude of the circadian rhythm (Max-Min) ranged from 3.8 to 16.9 ng/ml. The time lag between onset of sleep and acrophase was variable (1.75 to 7.38 hrs). Variability of nadir, minimal and maximal PRL, amplitude, and minimal PRL as percent of the mesor was significantly lower within individuals than between subjects (p < 0.02). During sleep, peak heights and peak amplitudes were significantly higher than during waking periods (p < 0.004). No statistically significant differences were found in the distribution of relative frequencies of peak number, peak amplitudes and peak heights between the three series of profiles. The distribution of peak heights was compatible with a normal distribution. In conclusion, it was shown that the circadian rhythm of PRL secretion in normal men can be analysed accurately and reliably with the complex cosinor method, which is relatively easy to perform and yields results comparable to those obtained by much more complicated programs.(ABSTRACT TRUNCATED AT 400 WORDS)

Clockwork blue: on the evolution of non-image-forming retinal photoreceptors in marine and terrestrial vertebrates

This paper presents a hypothesis that could explain why blue light appears to dominate non-image-forming (NIF) ocular photoreception in marine as well as terrestrial vertebrates. Indeed, there is more and more evidence suggesting that 'novel' retinal photoreceptors, which are sensitive to blue light and were only discovered in the 1990s, could be a feature shared by all vertebrates. In our view, blue light photoreception evolved and persisted as NIF photoreception because it has been useful in the colonisation of extensive photo-dependent oceanic habitats and facilitated the move of vertebrates from an aquatic to a terrestrial environment. Because the available scattered evidence is compatible with the validity of our hypothesis, we hope that our rationale will be followed up. Indeed, it (1) involves testable predictions, (2) provides plausible explanations for previous observations, (3) unites phenomena not previously considered related to one another and (4) suggests tests that have not been carried out before. Overall, our approach not only embraces cross-disciplinary links; it, moreover, serves as a reminder of an all-embracing evolutionary history, especially with regard to a ubiquitous photoreceptive 'clockwork-blue' in marine and terrestrial vertebrates.

Exposure set-ups for in vivo experiments using radial waveguides

Radial waveguide set-ups are introduced as exposure devices for long-term experiments with large numbers of non-restrained animals exposed simultaneously. Methods are presented to ensure well-defined exposure conditions even for potentially overmoded waveguides and for the exposure of large groups of animals per cage. The proposed methods are applied for a four-generation study being performed on up to 2500 mice exposed to a generic UMTS test signal at prescribed averaged whole body specific absorption rates (SARs). The variation of the whole body SAR due to the movement of the mice inside the cage is calculated by using the finite-difference time-domain method and detailed animal models for selected configurations of the mice inside the cage for all stages of the study.

Potentiation of antiproliferative effects of tamoxifen and ethanol on mouse hepatoma cells by melatonin: possible involvement of mitogen-activated protein kinase and induction of apoptosis

Melatonin, the major secretory product of the pineal gland, is in focus of many research areas because of its ability to scavenge free oxygen radicals and thereby protect cells and tissues from radical damage. Some studies suggest melatonin may be a possible therapeutic agent with potential clinical applications against pathological states due to reactive oxygen species. Here, we investigated the effects of melatonin on the mouse hepatoma cell line HEPA 1-6, coincubated with ethanol, and tamoxifen, respectively. Cell proliferation rates were detected by the 3-[4,5 dimethylthiazol-2-y1]-2,5-diphenyltetrazolium bromide (MTT) proliferation assay. A dose-dependent inhibition of the proliferative activity by melatonin was observed from 640 microM to 3 mM, which was significantly higher (P < 0.01) than with the solvent (ethanol) alone. Concentrations of 320 microM and less had no effect on cell proliferation. This antiproliferative effect might be because of the prolonged activation of mitogen-activated protein kinase which was activated by phosphorylation 15 min after the induction with melatonin. Furthermore, apoptosis was found to be enhanced by melatonin (75% more than with the solvent alone, P < 0.001). Finally, we show that the inhibitory effect of tamoxifen (25 microM) is markedly enhanced by the coincubation with melatonin (1.3 mM) up to 75% (P < 0.001). These data show that the antiproliferative effects of tamoxifen and ethanol, respectively, on mouse hepatoma cell line HEPA 1-6 are enhanced by melatonin. Although at the conditions described here the antiproliferative effects of melatonin occur at supraphysiological concentrations, these data may help to support clinical studies where melatonin is given simultaneously with tamoxifen or other standard chemotherapeutica.

Clearance of melatonin and 6-sulfatoxymelatonin by hemodialysis in patients with end-stage renal disease

Patients with end-stage renal disease (ESRD) suffer from a number of related disorders. These include endocrine abnormalities, sleep disturbances, and depression. Melatonin is involved in the synchronization of exogenous zeitgebers with the endogenous rhythms, and it has effects on various psychological factors. As the concentrations of melatonin and the effects of dialysis have only occasionally been investigated in ESRD, we performed a study involving 35 patients, measuring the serum concentrations of melatonin, and of its major metabolite 6-sulfatoxymelatonin (aMT6s), before and after hemodialysis. Serum samples taken during morning hours from a control group (n=11) with intact kidneys served as controls. Patients were dialyzed for approximately 4 hr between 07:00 and 13:00 hr (S1), between 13:00 and 20:00 hr (S2), or between 18:30 and 22:30 hr (S3). Mean melatonin concentrations before hemodialysis were highly elevated when compared with the controls (40.6 vs. 6.7 pg/mL; P<0.001). Although melatonin levels were decreased to 20.3 pg/mL after dialysis, they were still well above the control levels. Likewise, aMT6s concentrations before dialysis were highly elevated in ESRD patients before dialysis when compared with controls (39.5 vs. 2.0 pg/mL; P<0.001), and also decreased by dialysis to levels still well above control levels (25.3 pg/mL). Clearance efficacy was better for melatonin (48.9%) than for aMT6s (36.6%; P<0.05). In ESRD patients, a diurnal rhythm for melatonin was observed (S1, 45.1 pg/mL; S2, 31.5 pg/mL; S3, 48.7 pg/mL; P<0.05), indicating that the normal synthesis rhythm is maintained. None of the following secondary disorders were correlated with melatonin concentrations: insomnia, delayed sleep onset, night-time arousals, and restless-leg syndrome. The reason for this observation is probably the melatonin concentrations, which were so high that no sub-classification could be identified. It is concluded that in ESRD patients, hemodialysis is unable to decrease elevated levels of melatonin and aMT6s to normal values. It is speculated that some of the secondary disorders in ESRD are caused by supraphysiological concentrations of melatonin.

Is inhibin B a pharmacodynamic parameter for FSH in normal men?

OBJECTIVE

This study aims to investigate the pharmacodynamic effect of FSH on inhibin B serum levels in normal men in order to elucidate the physiological regulation of inhibin B secretion in more detail.

DESIGN AND METHODS

Injections of 3000 IU recombinant, human FSH (rhFSH) were followed by single-blinded injections of placebo, 1000 and 2000 IU rhFSH spaced by at least 28 days between injections.

RESULTS

After injection of 3000 IU rhFSH, inhibin B values were significantly elevated above baseline for 24, 96 and 120 h (maximal increase after 96 h, mean +/- s.e.m. 303+/-18 pg/ml). Injection of 2000 IU rhFSH led to a significant increase in inhibin B (maximum mean +/- s.e.m. 318+/-20 pg/ml) from 24 to 120 h. Injection of 1000 IU rhFSH led to a significant increase in inhibin B after 96 h (maximum mean +/- s.e.m. 300+/-16 pg/ml). The inhibin B areas under the curve after injection of 2000 and 3000 IU rhFSH were significantly higher than those following the placebo and 1000 IU rhFSH. In the 12 fertile men investigated, at baseline a strong diurnal rhythm of inhibin B parallel to that of testosterone was observed.

CONCLUSIONS

Serum inhibin B can be considered only a partial pharmacodynamic parameter of FSH in vivo, since the integrity of the spermatogenic process appears to be a second fundamental component in the regulation of its secretion from the testis.

Direct suppressive effects of weak magnetic fields (50 Hz and 16 2/3 Hz) on melatonin synthesis in the pineal gland of Djungarian hamsters (Phodopus sungorus)

In many investigations performed thus far on rodents, a suppression of melatonin synthesis was observed when animals were exposed to weak magnetic fields. However, among the several issues not yet resolved is the question of whether the observed changes are caused by direct effects on the pineal gland or by indirect effects, e.g., at the level of the eyes. We, therefore, performed a series of experiments in which direct effects of weak magnetic fields were studied in isolated pineal glands of Djungarian hamsters (Phodopus sungorus). After sacrifice of animals during morning hours, pineal glands were removed and placed individually into glass chambers that were perfused with oxygenated buffer. Experiments (n = 8) lasted for 8 hr. Magnetic fields (1,623 or 50 Hz at 86 microTesla) were generated by Helmholtz coils, and were present during the entire period. In each experiment, 12 exposed, and 12 sham-exposed, pineal glands were placed individually in glass chambers, which were surrounded by identical coils. Because of the design of the coils (bifilament), and the experimental setup (black box), the experimentator was not aware which coil was activated until the results were obtained. After 3.25 hr of adaptation, melatonin production was stimulated by isoproterenol (10(-7) M) for 30 min. Eluted fractions were collected, and melatonin concentrations were measured by radioimmunoassay. Maximum melatonin production was achieved after 5-7 hr. In all experiments, maximum melatonin concentrations were lower in the exposed groups compared with the sham-exposed controls. Statistical analyses for each frequency showed significant suppressive effects at 16(2/3) Hz (P < 0.01), and 50 Hz (P < 0.00). It is concluded that the suppressive effects of magnetic fields on the synthesis of melatonin are a result of primary mechanisms at the level of the pineal gland.

Estradiol and high-dose dihydrotestosterone treatment causes changes in cynomolgus monkey prostate volume and histology identical to those caused by testosterone alone

To evaluate the effects of testosterone (T), dihydrotestosterone (DHT), and estradiol (E2) on the regulation of prostate growth and tissue composition, the following study was conducted in a nonhuman primate model. Fifteen adult, long-term castrated cynomolgus monkeys were randomly assigned to receive implants filled with T (0.19 +/- 0.01 g), DHT alone (0.21 +/- 0.01 g), or (99%) DHT + (1%) E2 (0.21 +/- 0.01 g). Prior to and at 4-week intervals during the treatment phase of 252 days, prostate volumes (PV), body weight, ejaculate weight, hormone levels (of T, DHT, and E2), and red blood cell count were measured. Five adult, intact monkeys served as controls for prostate volume and histology. At the end of the study, histological analysis of an ultrasound-guided prostate biopsy was performed. T levels increased significantly in the T group compared with baseline (P < 0.01) and with the DHT and DHT + E2 groups (P < 0.05). Both groups receiving DHT showed higher DHT levels than did animals in the T group (P < 0.001). E2 levels in all groups increased over time (P < 0.05), although significant differences (P < 0.01) could only be detected between the DHT + E2 and the DHT group. Prostate volume in all groups increased (at baseline: T = 1.03 +/- 0.12 ml, DHT = 1.08 +/- 0.15 ml, DHT + E2 = 1.13 +/- 0.09; at day 252: T = 5.83 +/- 1.00, DHT = 4.72 +/- 0.9, DHT + E2 = 5.05 +/- 0.62) over time (P < 0.001), whereas no differences could be detected between the groups. Prostate biopsy could be performed successfully in 15 out of 20 monkeys. Prostate tissue evaluation between the treatment groups and the evaluated intact monkeys revealed no differences in the status of secretory epithelia, nuclear chromatin, excretory vacuoles, interstitial stroma, smooth muscles, and total functional status, whereas the prostate of a long-term castrated monkey showed severe atrophy. Thus, both androgens fully restored prostate volume and ejaculatory function. Highly supraphysiological DHT serum levels are not associated with abnormal volumetric or histological changes of the prostate. Comparing the DHT group with the DHT + E2 group, an additional stimulatory effect of normal or slightly elevated estrogens on the prostate cannot be found in the presence of highly supraphysiological DHT levels.

Sex ratios at birth and environmental temperatures

The relationship between average monthly air temperature and sex ratios at birth (SRB) was analyzed for children born in Germany during the period 1946-1995. Both the absolute temperature and--more markedly--the monthly temperature deviations from the overall mean were significantly positively correlated with the SRB (P < 0.01) when temperatures were time-lagged against the SRB data by -10 or -11 months. It is concluded that the sex of the offspring is partially determined by environmental temperatures prior to conception.

Isolation method of Leydig cells from mature male Djungarian hamsters (Phodopus sungorus) and their steroidogenic activity in vitro

For studies addressing the functions of Leydig cells, isolated cells are often better suited than intact animals. Here, the isolation procedure of Leydig cells from adult male Djungarian hamsters (Phodopus sungorus) is described. Cells were isolated using a procedure involving enzymatic dissociation and Percoll-gradient centrifugation. For each experiment, approximately 4.4 x 10(6) Leydig cells from six animals were obtained. The cells showed high steroidogenic responsiveness to physiological (ovine luteinizing hormone (oLH) and human chorionic gonadotropin (hCG)) and nonphysiological (forskolin) stimuli in vitro. Approximately 98% of cells were viable as assessed by trypan blue exclusion, and the purity varied from 80 to 95% as tested by 3 beta-hydroxysteroid dehydrogenase activity. Leydig cells were also identified by a bright yellow halo under phase-contrast microscopy. They contained numerous lipid droplets and showed round nuclei and prominent nucleoli. The cells responded to oLH, hCG and forskolin with an increased testosterone production in a dose-dependent manner. Dose-response curves in these studies suggest that Leydig cells of Djungarian hamsters undergo desensitization, probably due to down regulation of their LH/CG receptors.

Melatonin in epilepsy: first results of replacement therapy and first clinical results

At a single evening dose of 5-10 mg, melatonin (MLT), the pineal gland hormone, can exert a positive effect on the frequency of epileptic attacks in children with sleep disturbances of various etiologies. We have shown that the sleep behavior can be normalized and an existing epilepsy can be favorably influenced. Pretherapeutic MLT secretion profiles can provide new information concerning the origin and treatment of these disturbances. In vitro experiments suggest that this effect might be the result of the interaction between MLT and MLT-specific receptors in the neocortex. Due to its favorable safety profile, MLT can be liberally administered in the specified doses and be considered as a useful antiepileptic drug.

Expression of the gene for the retinal protein peripherin in the pineal gland of humans and Djungarian hamsters (Phodopus sungorus)

This study investigated whether the gene for peripherin, a protein previously considered to play only a role in the retina, may also be expressed in the pineal gland of both Djungarian hamsters (Phodopus sungorus) and humans. After extraction of mRNA from pooled pineal glands of hamsters and from one human pineal gland, mRNA was transcribed into cDNA followed by PCR amplification with specific primers. Clear signals were obtained at the expected sizes of the PCR products. An additional experiment in hamsters revealed that the peripherin gene is expressed throughout the entire 24-h period. Since peripherin is an important protein in the retina stabilizing the photoreceptor discs it is speculated that this protein might also play a structural role in the pineal gland.

Changes in the seasonality of mortality in Germany from 1946 to 1995: the role of temperature

Based on records from the Federal Bureau for Statistics of Germany, the seasonality of mortality was investigated for the period 1946-1995. Lowest mortality rates were found during summer (August or September) while highest values were found in winter (January through March). Non-linear regression of all monthly mortality data with the average monthly temperatures in Germany revealed a significant negative relationship (r = -0.739; n = 600; P < 0.0001). The fact that the differences between the long-range monthly temperatures and the individual monthly temperatures also showed a distinct relationship to the mortality rates speaks against a mere coincidence of both parameters. The amplitude of this seasonal rhythm declined steadily within the observation period. It is concluded that low temperatures cause an increase in mortality rates and that this effect has become less important during recent decades due to the increased use of central heating and because of improvements in the public health system.

The effects of pulsing magnetic fields on pineal melatonin synthesis in a teleost fish (brook trout, Salvelinus fontinalis)

Based on findings in various mammalian species, where exposure to electromagnetic fields decreased the nocturnal synthesis of the pineal secretory product melatonin, we investigated the effects of magnetic field (MF) exposure in a teleost fish, the brook trout (Salvelinus fontinalis). Fields were generated by Helmholtz coils (maximum flux density 40 microT, frequency 1 Hz, 200 ms on, 800 ms off). Melatonin concentrations were estimated by a specific radioimmunoassay. MF exposure significantly increased night-time pineal (P < 0.001) and serum (P < 0.01) melatonin levels, as compared with the controls. It is suggested that either the pineal glands are directly affected, i.e. by an increased Ca2+-influx into pineal photoreceptors, or that the responses are indirect since induced currents, caused by the rapid rise and decay of the generated MF, may have disturbed the sensory system for electric fields.

Exposure of female rats to a 100-microT 50 Hz magnetic field does not induce consistent changes in nocturnal levels of melatonin

The hypothesis whereby alternating (50 or 60 Hz) magnetic fields such as those produced by electric power reduce the nocturnal production of melatonin in the pineal gland and thereby indirectly enhance development and growth of breast cancer has attracted a great deal of interest. In view of the potential importance of this hypothesis that there is a link between electric power and breast cancer, which is also known as the "melatonin hypothesis", we undertook various experiments in female Sprague-Dawley rats to evaluate whether 100-microT 50 Hz magnetic-field exposure, i.e. a flux density shown recently to exert a tumor (co)promoting effect in the 7,12-dimethylbenz[a]anthracene (DMBA) model of breast cancer in Sprague-Dawley rats, consistently reduces melatonin levels and, if not, which factors may be involved in the inconsistent effects of magnetic-field exposure on production of melatonin. Long-term exposure of female Sprague-Dawley rats to magnetic fields for 13 weeks did not alter the nocturnal levels of melatonin in the pineal gland or serum (determined 5 h after the onset of darkness) significantly, irrespective of whether rats were treated with DMBA or not. In one experiment, when blood was sampled 3, 5 and 6 h after the onset of darkness after 2 weeks of magnetic-field or sham exposure, a significant decrease in melatonin was seen in magnetic-field-exposed rats at 6 h. However, the results could not be reproduced in two subsequent experiments in other groups of rats. Shorter (1 day, 1 week) or longer (4, 8, 13 weeks) exposure periods also did not result in any significant effects of the magnetic field on melatonin levels when blood sampling was performed either 5 or 6 h after onset of the dark phase. Various potential sources of variation in melatonin levels or in magnetic-field effects on melatonin levels were evaluated, but the reason(s) for the inconsistent effect of magnetic-field exposure remains unclear. Thus the present study failed to demonstrate a consistent effect of 100-microT 50 Hz magnetic-field exposure on melatonin levels in Sprague-Dawley rats.

Urinary 6-sulfatoxymelatonin profiles in male Djungarian hamsters (Phodopus sungorus) responding and not responding to short-day photoperiods: possible role of elevated daytime levels

The lack of endocrine and physiological responses of some Djungarian hamsters (Phodopus sungorus) to the transition from long to short photoperiods (L:D 16:8 --> L:D 8:16) has been known for a long time but is not yet understood. We investigated the role of melatonin synthesis in this context because melatonin, as part of the circadian system, may play a role in non-responsiveness. In ten responding and ten non-responding male hamsters, the urinary 24 hr 6-sulfatoxymelatonin (aMT6s) profiles under L:D 8:16 and L:D 16:8 were measured. Both short day responding and non-responding hamsters showed diurnal aMT6s excretion rhythms. Whereas responders reacted to the transition L:D 16:8 --> L:D 8:16 with a marked elevation of aMT6s excretion, in non-responders no adjustment of the melatonin rhythm to the change of the photoperiod was seen. Furthermore, under L:D 16:8 the daytime levels of aMT6s were significantly (P<0.001) lower in responders compared to non-responders whereas under L:D 8:16 these levels were higher (P<0.01). It is speculated that high daytime levels of aMT6s under long-day photoperiods in non-responders result in down-regulation of melatonin receptors of the nucleus suprachiasmaticus, the pacemaker for the pineal gland, leading to a lack of response to the transition to short-day photoperiods.

Seasonality of sex ratio in Germany

It was investigated whether there is a seasonal variation in sex ratio at birth in Germany. The analysis was based on records from the German Bureau for Statistics, covering the period from 1946 to 1995. A highly significant (P < or = 0.001), albeit low-amplitude rhythm was found with two peaks in May and December, and two nadirs in March and October. No correlations were found between sex ratios and seasonal birth rates during this period.

Acceleration of mammary tumorigenesis by exposure of 7,12-dimethylbenz[a]anthracene-treated female rats in a 50-Hz, 100-microT magnetic field: replication study

In view of the methodological problems of epidemiological studies on associations between residential and occupational exposures to 50/60-Hz magnetic fields (MF) and increased incidence of cancers, laboratory studies are necessary to determine if 50/60-Hz MF can affect cancer development or growth. Recently, it was reported that alternating (50-Hz) MF of low flux density (100 microT) increase tumor growth and progression in a model of breast cancer in female rats in which mammary tumors were induced by the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA). The objective of the present study was to determine if a replicate experiment carried out in the same laboratory under the same experimental conditions yields a significant increase in tumor development and growth of similar magnitude. For the MF experiment, a group of 99 female Sprague-Dawley rats was exposed to a homogeneous horizontally polarized MF for 24 h/d (minus time for weighing, tumor palpation, cage cleaning, cage rotation), 7 d/wk; another group of 99 rats was sham exposed. DMBA was administered intragastrically at a dose of 5 mg/rat at the first day of exposure and at weekly intervals thereafter up to a total dose of 20 mg/rat. Duration of MF or sham exposure was 91 d. In both MF-exposed and sham-exposed rats, the first tumors could be recorded 6 wk after the initial DMBA application. At 9 wk after DMBA application, the group of MF-exposed rats exhibited significantly more animals with tumors than the sham-exposed group. This significant difference in the rate of tumor development was observed throughout the subsequent period of exposure. After autopsy, the incidence of macroscopically visible mammary tumors was 62% in controls, but 83% in MF-exposed rats, with the 35% difference between groups being statistically significant. Data substantiate that long-term exposure of DMBA-treated female Sprague-Dawley rats in an alternating MF of low flux density promotes the development and growth of mammary tumors, thus indicating that MF exposure exerts tumor-promoting and/or copromoting effects. Furthermore, the data show that the effects of MF exposure in the DMBA breast cancer model are reproducible if the same experiment is repeated in the same laboratory.

Initial expression of the common alpha-chain in hypophyseal pars tuberalis-specific cells in spontaneous recrudescent hamsters

When exposed to short-day conditions, hamsters and other long-day breeders undergo gonadal regression. With chronic exposure to short days, however, the animals become photorefractory and gonadal recrudescence occurs. The underlying mechanism for this insensitivity is still unknown. There is growing evidence, however, that specific cells of the pituitary pars tuberalis (PT) mediate these photoperiod/nonphotoperiod-dependent changes as a direct or indirect "Zeitgeber" for the endocrine system. We investigated messenger RNA (mRNA)/protein formation for several hypophyseal hormones (beta-TSH, beta-LH, PRL, common alpha-chain) in the pars distalis (PD) and PT of female Djungarian hamsters in long photoperiod (LP) and after 18, 28, and 38 weeks of short photoperiod (SP). As indicated by gonadal and body weight, the hamsters displayed gonadal regression after 18 and 28 weeks of SP; after 38 weeks of SP, all animals showed recrudescence. At 18 and 28 weeks of SP, only PRL mRNA and protein levels were significantly reduced in the PD and returned to LP values after 38 weeks of SP. The expression of hypothalamic tyrosine hydroxylase in the arcuate nucleus that was determined by immunocytochemistry and by in situ hybridization was also down-regulated in SP18 and SP28 with increasing levels at SP38. Urinary 6-sulfatoxymelatonin levels were elevated in SP with highest levels in the SP18 group. In the PT, beta-TSH mRNA and protein were not detectable in all SP groups compared with the moderate signal intensity in LP. The common alpha-chain mRNA and protein, however, which were also reduced in the animals of the SP18 group, were already elevated after 28 weeks of SP and nearly reached LP-levels after 38 weeks of SP. These results show that, in contrast to LH and TSH, PRL expression in the PD is a sensitive indicator for photoperiod dependent changes of the endocrine system and seems to be tyrosine hydroxylase independent. The increase of common alpha-chain expression in PT-specific cells depending upon duration of SP that precedes the hormonal changes in the PD leads us to speculate that PT-specific cells initiate spontaneous recrudescence via a PT-PD pathway.

In vitro fertilizing capacity of sperm from FSH-treated photoinhibited Djungarian hamsters (Phodopus sungorus)

In hypogonadal male Djungarian hamsters FSH alone can induce normal spermatogenesis. However, for the induction of mating behavior, supplementation with testosterone is necessary. We have here investigated, by in vitro fertilization, whether sperm produced by photoinhibited hamsters treated with FSH alone can fertilize without testosterone. Photoinhibited hypogonadal male Djungarian hamsters were injected daily with human FSH (10 IU; Fertinorm) for 5-7 weeks. The hormone stimulated regrowth of the testes. Neither body weight nor the weights of the androgen-dependent organs-epididymides, prostates, accessory glands-showed significant differences from photoinhibited controls; furthermore FSH treatment did not raise intratesticular or serum testosterone levels. In eleven out of the twelve FSH-treated photoinhibited hamsters, elongated spermatids were found in the testes; in five out of nine epididymides, sperm was found by histological examination. In two out of the twelve FSH-treated hamsters, the amount of sperm in the caudal part of the epididymis was sufficient for in vitro fertilization with oocytes collected from superstimulated females. These spermatozoa fertilized 16-29% of the oocytes. Spermatozoa from photostimulated controls produced similar levels of fertilization.

Relationship between sleep-related erections and testosterone levels in men

In order to identify a possible threshold for a serum testosterone level below which sleep-related erections are impaired and to compare this threshold with the normal laboratory range of testosterone serum levels, we studied 201 men, including hypogonadal and eugonadal subjects. The protocol included nocturnal penile tumescence and rigidity monitoring and the assay of basal testosterone, prolactin, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) serum levels. The subjects were assigned to eight groups according to their testosterone serum levels. Group 1 had testosterone between 0 ng/dl and 99 ng/dl; the following seven groups had testosterone levels increased by 100 ng/dl per group. The groups of subjects with higher testosterone serum levels showed almost constantly higher values for the erectile parameters we studied than the subjects with serum testosterone < or = 99 ng/dl. On the contrary, subjects with higher testosterone serum levels showed higher values for only some erectile parameters compared to the subjects with serum testosterone between 100 and 199 ng/dl, without any significant difference among the groups with testosterone serum levels in the normal range. Our data suggest that the serum testosterone threshold for sleep-related erections is lower than the low end of the normal laboratory male range and is about 200 ng/dl. Further efforts are needed to find the precise serum testosterone ranges related to normal sleep-related erections and to normal sexual behavior, the testosterone ranges of which will probably not coincide.

Growth retardation, testicular stimulation, and increased melatonin synthesis by weak magnetic fields (50 Hz) in Djungarian hamsters, Phodopus sungorus

Male Djungarian hamsters (Phodopus sungorus; 45 animals per group) were either sham-exposed or exposed to a sinusoidal magnetic field for 56 days (Experiment 1: 50 Hz, 450 microTesla peak; max. dB/dt = 140 mTesla s(-1); 24 hrs day(-1)). Except for day 7, no effects were observed with respect to body weights during exposure. However, testicular cell numbers were significantly increased by exposure (tetraploid (4C): p=0.022; diploid (2C): p=0.039). Rectangular magnetic fields (Experiment 2: 360 microTesla; max. dB/dt = 2.5 Tesla s(-1)) caused a significant (p<0.001) but transient suppressing effect on body weights. Significant increases were also observed in testicular cell numbers (4C: p=0.034; haploid (1C): p=0.014) and in serum melatonin (p=0.001). It is concluded that weak magnetic fields may affect reproductive and physiological functions in the mammalian species tested and that the degree of these effects depends upon the fields' gradients.

Episodic variations of prolactin, thyroid-stimulating hormone, luteinizing hormone, melatonin and cortisol in infertile women with subclinical hypothyroidism

Preliminary data have suggested that female infertility due to corpus luteum insufficiency may be caused by subclinical hypothyroidism [exaggerated thyroid-stimulating hormone (TSH) response to thyrotrophin-releasing hormone (TRH) stimulation]. L-Thyroxine supplementation has been recommended to achieve pregnancies in subclinical hypothyroid women. This controlled study was carried out in order to investigate the biochemical diagnosis of subclinical hypothyroidism as a possible infertility factor. Five infertile patients (aged 25-36 years) with subclinical hypothyroidism (n = 4, stimulated TSH >20 microU/ml) or primary hypothyroidism (n = 1) and five healthy controls (aged 22-39 years) with normal thyroid function (stimulated TSH <15 microU/ml), regular cycles and no history of infertility were studied in the early follicular phase. In the pre-study evaluation, eight of 23 volunteers (34.8%) had to be excluded because of subclinical hypothyroidism with stimulated TSH values (TSHs) >15 microU/ml. Cycle function of patients and controls was compared by the method of LH pulse pattern analysis. Therefore blood samples were drawn every 10 min during a 24 h period. Sleep was recorded from midnight to 7 a.m. Repetition of the TRH tests at the end of the 24 h blood sampling period confirmed the difference in stimulated TSH values of the two study groups. Pulse analysis for luteinizing hormone (LH), TSH and prolactin showed no differences between patients and controls for pulse frequency, amplitude, height, length, area under curve (AUC) and the 24 h mean. Even the hypothyroid patient had a normal LH pulse pattern. Additional measurement of melatonin in pooled sera every 30 min gave the well-documented diurnal profiles during day and night for both groups. Patients had significantly higher melatonin values at seven time points during the night. Peaks for LH, TSH, prolactin and cortisol were correlated with the sleep stages wake, rapid eye movement, 1 + 2 and 3 + 4. We concluded that corpus luteum insufficiency in female infertility cannot be explained by subclinical hypothyroidism and thus should not be treated with L-thyroxine for fertility reasons.

Afternoon injections of melatonin in the Djungarian hamster Phodopus sungorus: long lasting sex-specific effects and influence of acute treatment on the endogenous pineal melatonin rhythm

The effects of exogenous melatonin on gonadal function and on the endogenous melatonin profiles of male and female Djungarian hamsters were investigated. Daily afternoon subcutaneous injections of melatonin (50 micrograms) in hamsters kept in long photoperiods (LD 16:8) led to gonadal inhibition in all the treated females (n = 13) but in only 2 of 13 males within the treatment period of 8 weeks (uteri: 244 +/- 11 mg in controls vs. 79 +/- 4 mg in treated hamsters, P < 0.001; ovaries: 13.6 +/- 0.6 mg in controls vs. 7.9 +/- 0.7 mg in treated hamsters, P < 0.001; testes: 1,021 +/- 54 mg in controls vs. 732 +/- 100 mg in treated hamsters, P < 0.05; and accessory glands: 641 +/- 38 mg in controls vs. 548 +/- 70 mg in treated hamsters, P > 0.05). These results indicate that there are some circumstances under which the gonadal responses of the reproductive organs of male and female Djungarian hamsters differ. Interestingly, pineal concentrations of melatonin were found to be significantly higher in males (P < 0.01), possibly indicating a more robust endogenous supply with the hormone, whereas serum melatonin levels were not significantly different between males and females. However, the subcutaneous injection of melatonin (5, 25, and 125 micrograms) exerted no acute effect on the endogenous, circadian melatonin-profile, independent of dosage and sex.

Study on pineal function and DMBA-induced breast cancer formation in rats during exposure to a 100-mG, 50 Hz magnetic field

Reduction of circulating melatonin levels by pinealectomy or constant light has previously been shown to enhance the development and growth of mammary cancers induced by the polyaromatic hydrocarbon 7,12-dimethylbenz[a]anthracene (DMBA) in female rats. Since pineal melatonin production can also be disturbed by electromagnetic field exposure, we studied whether there is an association between melatonin depression by magnetic field (MF) exposure and DMBA-induced breast cancer growth in female rats. In the present experiments, 216 female Sprague-Dawley rats were divided into 4 groups. Two of the groups (with 99 animals each) received oral applications of DMBA and were either sham-exposed or exposed in a 50-Hz, 100-mG (10 microT) MF for 24 h/d, 7 d/wk, for a period of 91 d. The other two groups (nine animals each) were either sham-exposed or MF-exposed without DMBA treatment. The exposure chambers and all other environmental factors were identical for MF-exposed and sham-exposed animals. The animals were palpated once weekly to assess the development of mammary tumors. At the end of the exposure period, all animals were sacrificed for autopsy and determination of nocturnal melatonin levels in pineal and serum. In controls, DMBA induced palpable tumors in about 55% of the animals within 3 mo after first application. There was a tendency to an enhanced tumor incidence in MF-exposed rats throughout the period of exposure, which, however, was not statistically significant. At autopsy, 60.6% of the sham-exposed and 66.6% of the MF-exposed rats had developed macroscopically visible mammary tumors. Tumor size and tumor burden were similar in both groups. Compared to the groups without DMBA treatment, DMBA-treated rats had significantly lower nocturnal pineal melatonin levels without difference in terms of MF exposure. MF-exposed rats, however, had significantly lower nocturnal melatonin levels in serum than sham-exposed animals. The data demonstrate that although exposure of female rats to a 50-Hz, 100-mG MF significantly decreases circulating melatonin, this is not associated with a significant effect on development or growth of DMBA-induced mammary tumors. In view of the fact that, by using the same model, we recently demonstrated a tumor-copromoting effect of MF exposure at a 10 times higher flux density, the effects of MF exposure on DMBA-induced mammary carcinogenesis appear to be dose dependent.

Exposure of DMBA-treated female rats in a 50-Hz, 50 microTesla magnetic field: effects on mammary tumor growth, melatonin levels, and T lymphocyte activation

There is growing public concern about the possible health risks, particularly increased cancer risks of exposure to magnetic fields (MF) associated with power distribution systems. Recently, we have started a series of animal studies to investigate this issue, using the DMBA (7,12-dimethylbenz[a]anthracene) model of breast cancer in female rats. In the present study, female rats were chronically exposed to a 50-Hz, 50 microTesla (microT) MF with or without DMBA treatment. Because alterations in circulating levels of the pineal hormone melatonin and impaired immune system functions have been involved in breast cancer growth, and both melatonin and immune system are thought to be targets for MF-effects, serum melatonin and the proliferative capacity of splenic lymphocytes were determined in MF-exposed and sham-exposed rats. For this purpose, 216 female Sprague-Dawley rats were divided into four groups. Two of the groups (with 99 animals each) received oral applications of DMBA and were either sham-exposed or exposed in a 50-Hz, 50 microT MF for 24 h/day 7 days/week for a period of 91 days. The other two groups (9 animals each) were either sham-exposed or MF-exposed without DMBA treatment. The exposure chambers and all other environmental factors were identical for MF-exposed and sham-exposed animals. The DMBA-treated animals were palpated once weekly to assess the development of mammary tumors. At the end of the three-month period of MF exposure, the number and size of mammary tumors was determined by autopsy. In controls, DMBA induced tumors in approximately 55% of the animals within the 3 month period of sham-exposure. Already 8 weeks after DMBA application, the MF-exposed group exhibited significantly more tumors than sham-exposed animals. At time of autopsy, significantly more MF-exposed DMBA-treated rats exhibited macroscopically visible mammary tumors than DMBA-treated controls, thus indicating that MF exposure enhances the development and growth of cancers in this model. Comparison of the data from 50 microT with recent data from other flux densities indicated that long-term MF exposure of DMBA-treated rats increases the incidence of palpable and/or macroscopically visible mammary tumors in a highly dose-related fashion. Determination of nocturnal serum melatonin after 9 and 12 weeks of exposure at 50 microT did not yield significant differences between MF-exposed rats and sham-exposed controls, whereas a marked suppression of T cell proliferative capacity was seen in MF exposed rats. The data add further evidence to the hypothesis that hormone-dependent tissues such as breast might be particularly sensitive to MF-effects and indicate that immune system depression is involved in the increased breast cancer growth observed in MF exposed rats.

Direct effects of the pineal hormone melatonin on testosterone synthesis of Leydig cells in Djungarian hamsters (Phodopus sungorus) in vitro

Leydig cells of adult Djungarian hamsters, stimulated with luteinizing hormone (LH), were co-incubated with melatonin at various concentrations in a primary culture system. Testosterone secretion was only affected by melatonin when cells were stimulated with LH. Maximal suppression was observed at low doses of LH (0.5 ng/ml). These effects are at least partially mediated through the adenylate cyclase system, since melatonin was able to reduce forskolin-stimulated testosterone secretion. These results indicate that the time between pulses of LH can be considered to be most highly effective for tonic melatonin actions.

Sustained response of pineal melatonin synthesis to a single one-minute light pulse during night in Djungarian hamsters (Phodopus sungorus)

Previous experiments have demonstrated that short light pulses during the night suppress pineal melatonin formation almost completely for the remainder of the night. Here, the effects of a single 1 min light pulse during the night on melatonin synthesis during the following night was investigated in Djungarian hamsters (Phodopus sungorus). It is shown that the melatonin pattern during the consecutive night is suppressed to a greater extent than that caused by acute light exposure, indicating a very effective light memory of the melatonin-generating neuronal network, possibly a key to understanding the reliability of the photoperiod-measuring system.

Diurnal variations of serum and testicular testosterone and dihydrotestosterone (DHT) in Djungarian hamsters (Phodopus sungorus): testes are the main source for circulating DHT

Testes and sera of adult Djungarian hamsters kept in a light:dark cycle of 16L:8D were collected every 1.5-3 hr for 24 hr. The concentrations of testosterone (T) and its metabolite 5 alpha-dihydrotestosterone (DHT) were estimated by HPLC separation of the steroids followed by radioimmunoassay. Both testicular and serum concentrations of T and DHT exhibited strong diurnal variations (P < 0.001) with highest levels at the end of the light phase, while both hormones declined drastically during the dark period. The ratios of DHT/T, as an indicator of the activity of the enzyme 5 alpha-reductase, were on average 0.39 in the testes and 0.29 in serum. Comparisons of individual data revealed highly significant correlations between testicular and serum concentrations of the hormones (T:r = 0.87; P < 0.0001; DHT:r = 0.69, P < 0.0001). Likewise, the individual values of testicular and serum DHT/T ratios correlated highly significantly (r = 0.60; P < 0.001). The results indicate that in Djungarian hamsters the main source of DHT is the testes, while the peripheral conversion of T to DHT seems to be negligible.

Breeding of Djungarian hamsters (Phodopus sungorus): influence of parity and litter size on weaning success and offspring sex ratio

The reproduction of 368 breeding pairs of Djungarian hamsters (Phodopus sungorus) has been recorded and evaluated during 5 consecutive years. Three-hundred-and-eight pairs (= 83.7%) were successful breeders giving birth to 2113 litters (up to 13 per dam) with a total of 12,591 offspring (mean: 6.0 +/- 2.2 [+/- SD] per litter). One-hundred-and-fifty dams delivered within 25 days after pairing, indicating a breeding success in the first oestrous cycle of 40.8% of all pairs (95% confidence interval: 35.7%-46.0%). The average number of offspring was higher in the 2nd than in the first litter, reaching a maximum in the 3rd (6.8 +/- 2.0), and decreasing thereafter. The loss of offspring (mean: 24.2%) was higher in older parents and influenced by the number of offspring per litter, indicating that experience and stress contribute to breeding success. A small, but significantly higher number of females was recorded only when no loss of offspring occurred until weaning (females: 2.36 +/- 1.75; males: 2.16 +/- 1.63, P < 0.001). There was no indication of a shift of the offspring sex ratio towards favouring females with increased litter numbers, in contrast to the predictions of the Trivers-Willard hypothesis, at least with respect to the species and the breeding conditions as described in this report. Since all breeders were kept under long-day type photoperiods (16L:8D), no signs of seasonality in breeding outcome were noted.

Circadian and ultradian variations of pituitary and pineal hormones in normal men: evidence for a link between melatonin, gonadotropin, and prolactin secretion

The study was performed to investigate the physiological relationship between the pineal hormone melatonin and pituitary functions in normal men. Series of blood samples were obtained at 10-min intervals for 24-hr periods from 10 male volunteers (age 19-25 years). Samplings were repeated after 2 weeks and 3 months. Serum levels of melatonin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), and testosterone (T) were estimated by immunoassay methods (LH, PRL, every sample; melatonin, every 30 min; T, every 4 hrs; FSH once for each session). Diurnal characteristics of PRL and melatonin profiles were estimated by complex cosinor analysis, while short-term pulsatility of LH and PRL secretion was analyzed by the PULSAR algorithm. Data were correlated by linear regression analysis. The combined information of all three sampling sessions revealed significant negative correlations between the following parameters (N = 10): Amplitude (Ampl) melatonin and Ampl PRL: r = -0.727, P < 0.02; Ampl melatonin and maximal (Max) PRL values: r = -0.73, P < 0.02; Max melatonin and Max PRL: r = -0.725, P < 0.02; area under the curve (AUC) melatonin and Ampl PRL: r = -0.637, P < 0.05; AUC melatonin and Max PRL: r = -0.640; P < 0.05; duration (Dur) of melatonin synthesis and Ampl PRL: r = -0.685, P < 0.03; Dur melatonin and Max PRL: r = -0.676, P < 0.04; Dur melatonin and FSH levels: r = -0.663, P < 0.04; AUC melatonin and LH mean concentration: r = -0.732, P < 0.02; Max melatonin and LH mean concentration: r = -0.657, P < 0.04.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoperiodic responses in Djungarian hamsters (Phodopus sungorus): importance of light history for pineal and serum melatonin profiles

Male Djungarian hamsters with previous light experience of long photoperiods of 16 h of light per day (16L:8D) or short photoperiods (8L:16D) were transferred either to the opposite photoperiods or to intermediate photoperiods (14L:10D). It was demonstrated that the same intermediate photoperiod could exert inhibitory or stimulatory effects on coat color, body weight, and the reproductive system, dependent on the previous light history. The response was graduated in accordance with the degree of change in day length. Despite opposite responses to the same photoperiod, diurnal patterns of melatonin in the pineal glands were identical. However, the circadian melatonin pattern in serum of photoinhibited hamsters had a more pronounced nighttime elevation than that found in the serum of photostimulated animals. In hamsters nonresponsive to short photoperiods, no proper short-day pattern was found. Melatonin production is a highly dynamic process, causing concentration shifts in the pineal gland and changes in the serum amplitude during prolonged exposure to short photoperiods. The different reactions to identical photoperiods are associated with different serum melatonin patterns, as shown here for the first time.

The adult human cerebellum is a target of the neuroendocrine system involved in the circadian timing

In an investigation aimed at comprehensive mapping of the adult human brain with respect to receptor sites for the pineal hormone melatonin, we consistently observed specific binding in the cerebellum. Autoradiography and in vitro binding analysis with 125I-labeled melatonin were used to examine the location and the properties of these binding sites. In all cerebellar lobes, highest-density specific binding was localized to the external zone of the molecular layer. The binding was rapid, saturable, displaceable, specific and of high affinity. Physiological concentrations of NaCl decreased the affinity, while presence of calcium ions promoted it. The non-hydrolyzable GTP analog, GTP gamma S, inhibited binding in a dose-dependent manner and provoked a shift towards low affinity. The results strongly suggest that these binding sites may be functional melatonin receptors, and indicate that the adult human cerebellum is a target of melatonin, the pineal hormone involved in the control of the circadian timing.

Increased oxidation of pineal serotonin as a possible explanation for reduced melatonin synthesis in the aging Djungarian hamster (Phodopus sungorus)

Groups of young adult (1.7 months) and old adult (9.7 months) female Djungarian hamsters were exposed to short-day photo-periods (SD; 8L:16D) or long-day photoperiods (LD; 16L:8D) for 6 weeks. Pineal and serum melatonin rhythms were dampened in old SD animals when compared with young SD animals. The melatonin precursor serotonin showed diurnal variations with opposite phases to melatonin synthesis. However, pineal serotonin levels were even lower in old SD animals than in young SD animals, contrary to the expected accumulation of the precursor. The synthesis of a metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA), was significantly lower in younger hamsters, under both photoperiods. These results indicate that the age-associated decline in the production of melatonin is a consequence of an increased oxidation of its precursors.

Effects of weak alternating magnetic fields on nocturnal melatonin production and mammary carcinogenesis in rats

Since extremely low frequency (i.e., 50- or 60-Hz) magnetic fields (MFs) from overhead power lines and other electromagnetic sources are ubiquitous in modern societies, the possible carcinogenic effect of such fields recently suggested by epidemiological studies has engendered much concern. However, in view of various unknown and uncontrolled variables which may bias epidemiological studies on MF interactions, a causal relationship between MFs and tumorigenesis can only be determined precisely in animal experiments. The goal of the study reported here was to determine if low frequency MFs at the low flux densities which are relevant for human populations induce tumor-promoting or copromoting effects in a model of breast cancer. Furthermore, since reduction in pineal production of melatonin has been implicated as a cause of tumor promotion by electromagnetic fields, determinations of nocturnal melatonin peak levels in serum were performed during MF exposure. Mammary tumors were induced by intragastric administration of 20 mg (5 mg/week) 7,12-dimethylbenz(a)anthracene (DMBA) in female Sprague-Dawley rats. Groups of 36 rats were either sham-exposed or exposed for 91 days at a 50-Hz gradient MF of 0.3-1 microT, which is a relevant range for elevated domestic MF exposure as arising from neighboring power lines. Nocturnal melatonin levels were significantly reduced by exposure to this weak alternating MF. However, histopathological evaluation of mammary lesions did not disclose any significant difference between MF- and sham-exposed animals. Incidence of mammary tumors was 61% in controls versus 67% in MF-exposed rats. The predominant tumor type was the invasive adenocarcinoma, which was found in 21 rats of both groups. Examination of tumor size did not indicate significant differences in tumor burden between both groups. Furthermore, the incidence of preneoplastic lesions was not altered by MF exposure. Thus, the data of this study indicate that alternating MF do not exert significant tumor promoting or copromoting effects at environmentally relevant flux densities in the rat mammary cancer system.

Reliable analysis of individual human melatonin profiles by complex cosinor analysis

The analysis of diurnal secretion patterns of the pineal hormone melatonin should provide information about magnitude of peak concentration, time of peak (acrophase), and duration of elevated hormone levels. We report here on a method for analysis of human melatonin secretory rhythms which fulfills these requirements with considerable precision. Blood samples were obtained from 10 healthy male volunteers at 30 min intervals throughout a 24 hr period, three times (the initial blood sampling was repeated after 2 weeks and 3 months). These sets of 48 plasma samples per volunteer were analyzed for melatonin by radioimmunoassay. The mean intra-assay variation was 10.3%, and inter-assay variations were 15.8% at 21 pg/ml, 11% at 28 pg/ml, and 9.4% at 48.6 pg/ml. Data were subjected to single cosinor analysis (SCA) or analyzed by a complex cosinor analysis (CCA) with the fundamental and the first harmonic as parameters. Both methods provided essentially the same information about the acrophases, whereas the CCA had a clear advantage in terms of better regression coefficients between the original data points and the calculated curve (CCA: r = 0.952 +/- 0.018; SCA: r = 0.867 +/- 0.039 [means +/- SD]; P < 0.001). As a consequence, maximum and minimum values and the times of onset and cessation of melatonin production could be estimated easily and reliably without the need for rough and/or subjective measures. By comparing the three sampling sessions, the secretory rhythm of each individual was clearly reproducible (mean coefficient of variation 8.4%), thus confirming earlier work. Interindividual differences, however, were quite pronounced, especially with respect to amplitudes (more than 25% coefficient of variation).(ABSTRACT TRUNCATED AT 250 WORDS)