Seasonal changes in pituitary function: amplification of midfollicular luteinizing hormone secretion during the dark season

Seasonal reproduction and gonadal function: A focus on humans starting from animal studies

Photoperiod impacts reproduction in many species of mammals. Mating occurs at specific seasons to achieve reproductive advantages, such as optimization of offspring survival. Light is the main regulator of these changes during the photoperiod. Seasonally breeding mammals detect and transduce light signals through extraocular photoreceptor, regulating downstream melatonin-dependent peripheral circadian events. In rodents, hormonal reduction and gonadal atrophy occur quickly, and consensually with short-day periods. It remains unclear whether photoperiod influences human reproduction. Seasonal fluctuations of sex hormones have been described in humans, although they seem to not imply adaptative seasonal pattern in human gonads. This review discusses current knowledge about seasonal changes in the gonadal function of vertebrates, including humans. The photoperiod-dependent regulation of hypothalamic-pituitary-gonadal axis, as well as morphological and functional changes of the gonads are evaluated herein. Endocrine and morphological variations of reproductive functions, in response to photoperiod, are of interest as they may reflect the nature of past population selection for adaptative mechanisms that occurred during evolution.

The use of saliva for assessment of cortisol pulsatile secretion by deconvolution analysis

Cortisol is the key effector molecule of the HPA axis and is secreted in a pulsatile manner in all species studied. In order to understand cortisol signalling in health and disease, detailed analysis of hormone pulsatility is necessary. To dissect cortisol pulsatility in plasma deconvolution techniques have been applied. Blood sampling is a labour-intensive, expensive and invasive technique that causes stress and alters HPA axis activity. Therefore saliva has been extensively investigated as an alternative sample to measure cortisol. Here we use state of the art deconvolution algorithms to investigate cortisol pulsatility in saliva. Blood and saliva samples were obtained at 15-min intervals over an 8h period in 18 healthy men to analyse their diurnal cortisol levels. A multiparameter deconvolution technique was used to generate statistically significant models of cortisol secretion and elimination in plasma and saliva. The models consisted of estimates of the number, amplitude, duration and frequency of secretory bursts as well as the elimination half-life (t1/2) in a subject specific manner. No significant differences were noted between plasma and saliva with regard to the observed secretory bursts (7.8±1.5 vs. 7.0±1.4) and the interpeak interval (59.6±10.5 min vs. 61.0±11.5 min). Moreover a strong positive correlation between the numbers of peaks in both fluids was observed (r=0.83, P<0.0001). Monte Carlo simulations revealed an 84% temporal concordance between plasma and saliva peaks in all donors (P<0.05) with a mean of 1.3±0.8 plasma peaks unmatched in saliva. The percentage concordance increased to 90% when concording only the morning cortisol peaks in plasma and saliva up to 11:00 h. The deconvolution of the most distinct component of cortisol diurnal rhythm-cortisol awakening response (CAR), revealed an average 2.5±1.1 peaks based on the individual time for cortisol to return to baseline levels. In conclusion, deconvolution analysis of plasma and salivary cortisol concentration time series showed a close correlation and similar pulsatile characteristics between saliva and plasma cortisol. Similarly, Monte Carlo simulations revealed a high concordance between the peaks in these coupled time series suggesting that saliva is a suitable medium for subsequent deconvolution analysis yielding accurate and reliable models of cortisol secretion in particular during the morning hours.

Seasonal variability in the fertilization rate of women undergoing assisted reproduction treatments

The objective of this study was to evaluate whether seasonality affects human-assisted reproduction treatment outcomes. For this, 1932 patients undergoing intracytoplasmic sperm injection (ICSI) were assigned to a season group according to the day of oocyte retrieval: winter (n = 435), spring (n = 444), summer (n = 469) or autumn (n = 584). Analysis of variance was used to compare the ICSI outcomes. The fertilization rate was increased during the spring (winter: 67.9%, spring: 73.5%, summer: 68.7% and autumn: 69.0%; p < 0.01). In fact, a nearly 50% increase in the fertilization rate during the spring was observed (odds ratio 1.45, confidence interval 1.20-1.75; p < 0.01). The oestradiol concentration per number of oocytes was significantly higher during the spring (winter: 235.8 pg/mL, spring: 282.1 pg/mL, summer: 226.1 pg/mL and autumn: 228.7 pg/mL; p = 0.030). This study demonstrates a seasonal variability in fertilization after ICSI, where fertilization is higher during the spring than at any other time.

Menstrual cycles are influenced by sunshine

INTRODUCTION

The study determined the effect of seasons and meteorological variables on ovarian-menstrual function.

METHODS

Women (N=129) living in Novosibirsk (55°N), Russia, provided data on normal menstrual cycles for over 1 year between 1999 and 2008. Of these, 18 together with 20 other healthy women were investigated once in winter and once in summer in 2006-2009. The investigated variables included serum levels of follicle-stimulating hormone (FSH), luteinising hormone (LH) and prolactin on day ∼ 7 of the menstrual cycle, ovary follicle size (by ultrasound) on day ∼ 12 and ovulation occurrence on subsequent days.

RESULTS

In summer vs. winter, there was a trend towards increased FSH secretion, significantly larger ovarian follicle size, higher frequency of ovulation (97% vs. 71%) and a shorter menstrual cycle (by 0.9 days). LH and prolactin levels did not change. In all seasons combined, increased sunshine (data derived from local meteorological records) 2-3 days before the presumed ovulation day (calculated from the mean menstrual cycle) led to a shorter cycle length. Air/perceived temperature, atmospheric pressure, moon phase/light were not significant predictors.

CONCLUSIONS

Ovarian activity is greater in summer vs. winter in women living in a continental climate at temperate latitudes; sunshine is a factor that influences menstrual cycle.

Weak evidence of bright light effects on human LH and FSH

Background

Most mammals are seasonal breeders whose gonads grow to anticipate reproduction in the spring and summer. As day length increases, secretion increases for two gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH). This response is largely controlled by light. Light effects on gonadotropins are mediated through effects on the suprachiasmatic nucleus and responses of the circadian system. There is some evidence that seasonal breeding in humans is regulated by similar mechanisms, and that light stimulates LH secretion, but primate responses seem complex.

Methods

To gain further information on effects of bright light on LH and FSH secretion in humans, we analyzed urine samples collected in three experiments conducted for other goals. First, volunteers ages 18-30 years and 60-75 commenced an ultra-short 90-min sleep-wake cycle, during which they were exposed to 3000 lux light for 3 hours at balanced times of day, repeated for 3 days. Urine samples were assayed to explore any LH phase response curve. Second, depressed participants 60-79 years of age were treated with bright light or dim placebo light for 28 days, with measurements of urinary LH and FSH before and after treatment. Third, women of ages 20-45 years with premenstrual dysphoric disorder (PMDD) were treated to one 3-hour exposure of morning light, measuring LH and FSH in urine before and after the treatments.

Results

Two of the three studies showed significant increases in LH after light treatment, and FSH also tended to increase, but there were no significant contrasts with parallel placebo treatments and no significant time-of-day treatment effects.

Conclusions

These results gave some support for the hypothesis that bright light may augment LH secretion. Longer-duration studies may be needed to clarify the effects of light on human LH and FSH.

Season of birth and risk for adult onset glioma

Adult onset glioma is a rare cancer which occurs more frequently in Caucasians than African Americans, and in men than women. The etiology of this disease is largely unknown. Exposure to ionizing radiation is the only well established environmental risk factor, and this factor explains only a small percentage of cases. Several recent studies have reported an association between season of birth and glioma risk. This paper reviews the plausibility of evidence focusing on the seasonal interrelation of farming, allergies, viruses, vitamin D, diet, birth weight, and handedness. To date, a convincing explanation for the occurrence of adult gliomas decades after a seasonal exposure at birth remains elusive.

Stimulatory effect of morning bright light on reproductive hormones and ovulation: results of a controlled crossover trial

Objectives:

Studies have shown a shortening of the menstrual cycle following light exposure in women with abnormally long menstrual cycles or with winter depression, suggesting that artificial light can influence reproductive hormones and ovulation. The study was designed to investigate this possibility.

Design:

Placebo-controlled, crossover, counterbalanced order.

Setting:

Medical centres and participants' homes in Novosibirsk (55°N), Russia.

Participants:

Twenty-two women, aged 19–37 years, with baseline menstrual cycle length 28.1–37.8 d and no clinically evident endocrine abnormalities completed the study. The study lasted for two menstrual cycles separated by at least one off-protocol cycle.

Interventions:

During one experimental cycle, bright light was administered at home for 1 wk with a light box emitting white light at 4,300 lux at 41 cm for 45 min shortly after awakening. During the other experimental cycle, dim light was <100 lux at 41 cm with a one-tube fluorescent source.

Outcome Measures:

Blood samples and ultrasound scans were obtained in the afternoon before and after the week of light exposure, on day ∼7 and 14 after menstruation onset. Further ultrasound scans after day 14 documented ovulation. Serum was assayed for thyroid-stimulating hormone (TSH), prolactin (PRL), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol (E2).

Results:

Concentrations of PRL, LH, and FSH were significantly increased with bright versus dim light exposure, as was follicle size (ANOVA, intervention × day, p = 0.0043, 0.014, 0.049, and 0.042, respectively). The number of ovulatory cycles increased after exposure to bright compared to dim light (12 versus 6 cycles, Wilcoxon tied p = 0.034).

Conclusions:

Morning exposure to bright light in the follicular phase of the menstrual cycle stimulates the secretion of hypophyseal reproductive hormones, promotes ovary follicle growth, and increases ovulation rates in women with slightly lengthened menstrual cycles. This might be a promising method to overcome infertility.

Background: It is not clear whether light plays any role in determining menstrual cycles or ovulation in women. However, light is used as a treatment for some medical conditions related to rhythm, most notably seasonal affective disorder. In this study, the researchers wanted to examine the role of light in influencing the menstrual cycle. In the trial reported here, 22 women with lengthened menstrual cycles were provided with a light box that emitted either bright light or dim light, and the women were asked to use the light box for a defined period each day for one menstrual cycle. The study had a crossover design, where women would receive either bright or dim light for one cycle, then another cycle without the light box, and finally a cycle with either bright or dim light, whichever they did not receive first. Outcomes assessed in the trial included measurements of the blood levels of certain hormones. Specifically, the researchers looked at three hormones that determine the reproductive cycle (lutenizing hormone [LH], follicle stimulating hormone [FSH], and prolactin); these are produced by a region of the brain that is controlled by the hypothalamus, a gland that is directly responsive to light. Additionally, ultrasound scans were used to check for ovulation during each cycle. The trial was carried out in winter in Novosibirsk, a Russian city.

What the trial shows: When the researchers compared hormone levels between the “bright light” and “dim light” phases of the study, they found statistically significant increases in levels of LH, FSH, and prolactin in the blood. Ovulation was more likely in the “bright light” phase of the study as compared to the “dim light” phase. However, levels of two other hormones, thyroid stimulating hormone, and estradiol, were not significantly different when comparing the “bright” and “dim” cycles.

Strengths and limitations: In this trial the use of a crossover design enabled each woman to act as her own control, thereby reducing the number of participants that were needed in the trial. A further strength in this study was the use of ultrasound scans to allow the researchers to pinpoint ovulation in the participants; similar studies have not tried to examine the effects of light both on reproductive hormones and ovulation. A weakness of the design is that participants were assigned to receive either dim light first or bright light first using alternation, not true randomization. Therefore blinding was not possible and the researchers recruiting participants would have known in advance what intervention each participant would receive first. Other weaknesses include the limited number of participants in this study, and the nature of the participant population, all of whom had lengthened menstrual cycles and were living at fairly northerly latitude.

Contribution to the evidence: This study adds data suggesting that in women with lengthened menstrual cycles, ovulation can be stimulated by bright light. However, this finding would need to be replicated in a larger sample of women and it is not yet clear whether bright light will have the same effect on ovulation in women outside northerly latitudes and with average-length menstrual cycles.

Circannual rhythm in the incidence of cryptorchidism in Finland

Conflicting data on circannual variation in birth rates of urogenital malformations have been reported previously. To assess risk factors of cryptorchidism we studied the seasonal variation of cryptorchidism in Finland. We performed a prospective cryptorchidism study in Turku, Finland, from 1997 to 2001 to evaluate the incidence of cryptorchidism. Clinical examinations were performed at birth and at 3 months. Of 9511 liveborn boys (1471 preterm boys) 216 (53 preterm boys) were cryptorchid at birth and 106 (19 preterm boys) at 3 months. The incidence of cryptorchidism was significantly higher in spring (February-April) (3.0%) than in summer (May-July) (1.7%) (OR 1.79; 95% CI: 1.23-2.63). This seasonal difference was observed both among preterm and term boys. We conclude that a circannual fluctuation in the incidence of cryptorchidism exists, which indicates an influence by environmental factors. The underlying reason for cyclicity affects similarly both preterm and term boys.

Seasonal trends in the birth of sinistrals

This study examined the proposition that hand preference may change with season of birth in a group of 523 students born in southern Australia. Hand preference and performance measures revealed a higher incidence of sinistrality or weak dextrality for individuals born in winter and autumn compared to summer and spring. These seasonal effects tended to be more pronounced for females compared to males. Similar seasonal patterns have been observed in the northern hemisphere. Previous research has accounted for seasonal changes in hand preference in terms of changes in the frequency of viral infections. It is proposed that seasonal variations in hand preference can also be accounted for by seasonal variations in hormone levels. Higher levels of testosterone in spring compared to autumn have been reported in females. Exposure to higher levels of testosterone during the first trimester of foetal development is thought to promote the development of the right hemisphere. Individuals born in winter would have been exposed to the high testosterone levels associated with spring during the first critical trimester of foetal brain development. The lack of seasonal effect observed for males may be related to endocrinological differences between the male and female foetus.

In vitro modulation of steroidogenesis and gene expression by melatonin: a study with porcine antral follicles

The effects of melatonin on steroidogenesis and gene expression of CYP 11A, CYP 17, and CYP 19 were investigated using a porcine antral follicle culture model. Follicles were cultured with melatonin at doses of 10, 50, and 100 ng/mL in the presence and absence of an optimum dose of luteinizing hormone (LH) (100 ng/mL) for a period of 30 hours. It was found that melatonin stimulated progesterone production both in the presence and absence of LH. Androstenedione production was stimulated by melatonin at the highest dose of 100 ng/mL but melatonin had an inhibitory effect in the presence of LH. Estradiol production was not affected by melatonin alone, while in the presence of LH it showed a bimodal effect. Expression of genes for steroidogenic enzymes specific for the production of progesterone, androstenedione and estradiol (CYP 11A, CYP 17, and CYP 19, respectively) were also analyzed in the theca of follicles cultured with and without LH. Results showed an inhibition of CYP 11A and CYP 17 expression both in the presence and absence of LH. However, the expression of CYP 19 was not affected. Our results indicate that melatonin modulates ovarian theca cell steroidogenesis at the molecular level and this modulation may be mediated by its effects on the transcriptional activity of the steroidogenic enzymes.

Melatonin in relation to physiology in adult humans

The role exerted by melatonin in human physiology has not been completely ascertained. Melatonin levels have been measured in different physiopathological conditions, but the effects induced by melatonin administration or withdrawal have been tested only recently. Some effects have been clearly documented. Melatonin has hypothermic properties, and its nocturnal secretion generates about 40% of the amplitude of the circadian body temperature rhythm. Melatonin has sleep inducing properties, and exerts important activities in the regulation of circadian rhythms. Melatonin is capable of phase shifting human circadian rhythms, of entraining free-running circadian rhythms, and of antagonizing phase shifts induced by nighttime exposure to light. Its effect on human reproduction is not completely clear, but stimulatory effects on gonadotropin secretion have been reported in the follicular phase of the menstrual cycle. Direct actions on ovarian cells and spermatozoa have been also documented. Beside these, new important actions for melatonin may be proved. Melatonin may exert protective effects on the cardiovascular system, by reducing the risk of atherosclerosis and hypertension, and may influence immune responses. Finally, by acting as an antioxidant, melatonin could be important in slowing the processes of ageing.