The prognostic value of reduced global longitudinal strain (GLS) on cardiac outcomes in patients on peritoneal dialysis: a prospective study

Funding Acknowledgements

Type of funding sources: None.

Introduction

This study aims to evaluate the capacity of left ventricular global longitudinal strain (GLS) in end stage renal failure patients on peritoneal dialysis (PD) to predict cardiovascular mortality and major adverse cardiac events (MACE). GLS has been an established parameter in detecting subclinical left ventricular systolic dysfunction in the setting of preserved ejection fraction (EF > = 50%). We hypothesized that reductions of GLS (i.e. less negative value) are associated with adverse cardiovascular outcome.

Methods

We prospectively recruited a total of 60 PD patients from a single dialysis center in a tertiary hospital. GLS was determined by two-dimensional speckle-tracking echocardiography, under Philips QLab system. A less negative value reflects underlying subclinical LV dysfunction. The primary outcome was 4-point MACE, which was a composite of cardiovascular death, non-fatal myocardial infarction, non-fatal stroke and hospitalization for heart failure. Surrogate markers of inflammation (C-reactive protein [CRP], tumor necrosis factor [TNF]-alpha), nutrition (serum albumin), arterial stiffness (pulse wave velocity [PWV]), and serum N-terminal pro-brain natriuretic peptide (NT-proBNP) were also measured.

Results

16 (26.7%) and 34 (56.7%) PD patients had reduced GLS (≥ -18.3%) and left ventricular hypertrophy (LVH) respectively. In 12-month follow up, 4-point MACE occurred in 13.6% and 59.8% of normal and compromised GLS patients respectively (log-rank, P = 0.004), as illustrated by Kaplan-Meier curves (Fig 1). Patients with reduced GLS had higher proportion of uncontrolled blood pressure and higher prevalence of coronary artery disease. Their EF were significantly lower (53.6 ± 7.4% vs. 61.3 ± 4.1%, P= 0.001) compared with patients with normal GLS. In addition, GLS correlated with EF (r = -0.57, P <0.0001) and PWV (r= 0.33, P = 0.01). There was a trend towards an association between GLS and ln(CRP) (r= 0.25, P = 0.057), and ln(NT-proBNP) (r = 0.22, P= 0.09), respectively.

Conclusions

Subclinical LV systolic dysfunction was present in one-fourth of peritoneal dialysis patients despite having preserved EF. Reduced GLS (less negative than 18.3%, illustrated in Fig 2) is a strong predictor of poor cardiovascular prognosis among PD population. Abstract Figure 1  Abstract Figure 2

0090 Stage-Specific Sleep Disruption and its Effect on Spatial Navigational Memory

Introduction

The mechanisms by which sleep disruption impact memory may depend on sleep stage, as rapid eye movement (REM) and slow wave sleep (SWS) differ in several significant ways, including degree of neuronal synchrony and frequency of cortical local field potential oscillations. Here we sought to examine the relationship between stage-specific disruption of sleep and its effect on spatial navigational memory.

Methods

9 healthy adult subjects participated in this study which involved 3 in-lab polysomnograms (normal, REM-disruption, and SWS-disruption) accompanied by pre- and post-sleep functional neuroimaging of brain during a spatial navigational memory task. Graded auditory stimuli consisting of 0.5 second bursts of high-frequency tones (300-3000Hz) were used to disrupt sleep (REM/SWS) in real time. Primary metrics to ascertain the effect of these auditory tones on sleep were time in sleep stage (REM/SWS) as a % of total sleep time (TST), bout length. The primary metric for spatial navigational memory was %change in overnight completion time on a first-person-experience 3D maze task.

Results

Sleep macrostructure was normal during the normal night (TST:379.9±56.6 min; SWS:19.5±7.6%; REM:19.4±5.3%; mean±std). Stage-specific disruption of sleep was achieved using auditory tones during a) SWS-disruption condition (TST:388.9±47.4 mins; SWS:6.6±4.8%; REM:18.7±5.2%) and b) REM-disruption condition (TST:365.3±69.8 mins; SWS:17.1±7.7%; REM:12.1±6.6%). SWS-disruption reduced mean bout length of SWS as compared to no disruption (1.3±0.8 mins vs. 10.3±8.2 mins; p<0.01) and REM-disruption reduced mean bout length of REM as compared to no disruption (2.2±1.7 vs. 10.6±5.2 mins; p<0.01). When sleep was not disrupted, subjects achieved overnight improvements in performance (25.3±17%) which remained unchanged during REM-disruption (18.8±29.6%, p=0.5) and during SWS-disruption (38.8±24.4%; p=0.2). Morning psychomotor vigilance was also unaffected by condition.

Conclusion

Stage specific disruption of sleep can be achieved using graded auditory tones. While performance on a virtual 3D maze remain unchanged with stage specific sleep disruption, lower sample size may have limited our ability to detect the change. Activation patterns from functional neuroimaging that were acquired during the spatial navigation task may elucidate the interaction between stage-specific sleep disruption and performance.

Support

NIH R21AG059179

0418 Effect of Acute Administration of DORA-12 on Sleep Impairment in the Aged PS19 Mouse Model of Tauopathy

Introduction

Aged PS19 mice (MAPT P301S), a mouse model of tauopathy and neurodegeneration, display reduced NREM and REM sleep starting around 8-9 months before death around 12 months. Here, we tested the acute effect of a dual orexin receptor antagonist (DORA-12) on sleep in 11 mice (5 male, 6 female) at 10.3±1.8 months.

Methods

Two consecutive 24-hour recordings (12/12hr L:D cycle) were scored semi-automatically for non-REM sleep, REM sleep, and wake in mice implanted with EEG/EMG. Mice were treated with either vehicle (day 1) or 100mg/kg of DORA-12 (day 2) by oral gavage at both ZT0 and ZT9.

Results

After the first dose at ZT0, both latency to the first NREM sleep episode (paired t-test p=0.002) and to the first REM sleep episode (paired t-test p=0.005) was significantly shorter with DORA-12 (NREM: 20.8±17.8 min.; REM: 23.5±21.2 min.) compared to vehicle (NREM: 49.2±22.3 min.; REM: 127.0±93.3 min.). There was no difference in NREM or REM sleep latency observed after the second dose at ZT9. DORA-12 treatment increased NREM duration across the 24hr period (DORA-12: 664±52 min.; Veh: 601±54 min., paired t-test p=0.007) and also after the 2nd dose (DORA-12: 311±65 min.; Veh: 263±84 min., paired t-test p=0.009). DORA-12 treatment also increased REM duration across 24hrs (DORA-12: 61±30 min.; Veh: 48±29 min., paired t-test p=0.014) but not after the 2nd dose alone (DORA-12: 22±14 min.; Veh: 20±15 min., paired t-test p=0.388). Notably in both vehicle and DORA-12 conditions, we observed apparent dream enactment behavior including mastication, paw grasp, and fore limb extension during REM in 3 of 11 PS19 mice (all male), not typically observed in younger PS19 or age-matched non-transgenic mice, suggestive of a possible REM behavior disorder (RBD) phenotype. Wake-like behaviors occurred during theta-dominant EEG but with an EMG amplitude >4SD the preceding NREM sleep baseline for at least > 1sec.

Conclusion

In aged PS19 mice, DORA-12 was found to decrease the latency to NREM and REM after the first dose while also increasing NREM and REM duration across the entire 24hr recording period. We also capture a heretofore undescribed RBD-like phenotype in aged PS19 tauopathy mice.

Support

Merck MISP

0838 Sex Specific Changes in Sleep Macro-Structure With Obstructive Sleep Apnea in a Large Clinical Population of Older Adults

Introduction

Sleep architecture is influenced by age and sex and is disrupted by obstructive sleep apnea (OSA) and periodic limb movements (PLM) of sleep. Although increasing OSA severity is thought to decrease both REM and slow wave sleep (SWS), it may do so in non-linear ways. Here, we aim to 1) compare sleep macrostructure between older men and women, 2) compare metrics of total and REM-specific OSA severity between older men and women, and 3) examine associations between metrics of OSA severity and REM sleep and SWS in a clinical sample.

Methods

Clinical in-lab diagnostic polysomnography (PSG) in adults ≥64 years of age from the greater New York area recorded between 2006- 2016 were collated including demographic and traditional sleep scoring metrics. Studies where TST < 4 hours were removed. Demographic, sleep macrostructure, OSA (AHI4% & AHI3A criteria), pulse oximetry (SpO2) nadir and PLM measures were compared according to sex.

Results

PSGs from 1282 older adults (average age 70 years in both sexes, 41% female) were included in the analyses. Women had a significantly greater SWS% (14.5 vs 7.9, p<0.001) and less N1% (18.2 vs 24.4, p<0.001), without significant differences in TST, N2%, REM%, sleep efficiency or SpO2 nadir. Men had significantly higher all-sleep OSA (median AHI4% 8.8 vs 11.1, p=0.0004; median AHI3A 24.4 vs 27.9, p=0.003) and PLM’s (4.0 vs 7.6/hour, p=0.008) but women had significantly more OSA during REM sleep (median REM AHI4% 16.7 vs 14.0, p=0.01; median REM AHI3A 32.6 vs 27.4, p=0.0002). Inverse non-linear associations were observed between OSA severity and %SWS and %REM with a unique pattern for each sleep stage. The pattern between men and women within each stage appeared similar.

Conclusion

In this clinical sample of older adults, women exhibit a greater proportion of SWS and worse REM-related OSA then men. Increasing OSA severity is associated with non-linear reductions in %SWS and %REM, and we plan to further investigate these relationships and sexual dimorphism by using quantitative analysis of PSG signals for more precise measures of slow wave activity and breathing physiology than traditional sleep scoring metrics.

Support

R01AG056682

1150 Obstructive Sleep Apnea-dependent Racial/ethnic And Sex-specific Mechanisms Underlying Alzheimer’s Disease Risk: A Retrospective Cohort Analysis Of In-lab PSG Sleep Study Data

Introduction

We examined race and sex-specific biologic mechanisms of the relationship between obstructive sleep apnea (OSA) and incident AD.

Methods

Retrospective cohort analysis utilizing in-lab PSG sleep study data conducted among older adults between 2001 and 2005. OSA was defined using AHI4%. Participants had no history of cognitive decline or AD at baseline and included 663 (284 Non-Hispanic White (NHW), 207 Black/African-American (AA) and 172 Hispanic) OSA-patients matched on age, sex, race, BMI, 1:1 ratio to 663 (unexposed cohort I from sleep clinic) and 1:4 ratio to 2652 (unexposed cohort II from non-sleep clinics) non-OSA individuals. Incident AD was assessed annually from 2001-2013 with ICD-9-CM code 331.0. Adjusted cox proportional hazard regression models examined race and sex-specific biologic mechanisms including hypoxia, fragmentation and duration measures of OSA and AD risk.

Results

Of the 3,978 participants, 2,148 (54%) were women. Mean age at baseline was 72.6 (7.3) years. Over a mean follow-up time of 8.6 (1.4) years, 358 (9%) individuals (212 female) developed AD (119 NHW, 134 AAs, and 105 Hispanics). Relative to non-OSA individuals, OSA-patients had a higher risk of incident AD, with AAs and females showing stronger risk estimates (aHR: 2.24, 1.83, and 1.73, P <.001 for all, for AAs, Hispanics and NHW respectively; and aHR: 2.38, and 1.37, P <.001 for all, for female and male respectively). Measures of hypoxia, sleep fragmentation and sleep duration were associated with increase AD risk (P <.01 for all). Relative to NHW, AAs and Hispanics demonstrated up to 20% stronger effects/estimates on hypoxia and sleep duration measures. Relative to males, females demonstrated up to 25% stronger effects/estimates on sleep fragmentation measures, and 15% weaker effects/estimates on hypoxia measures (P <.01 for all).

Conclusion

Among OSA-patients, mechanisms related to hypoxia, sleep fragmentation and duration measures increase AD risk and may underlie race/ethnicity and sex disparities in AD.

Support

NIH/NIA/NHLBI (L30-AG064670, CIRAD P30AG059303 Pilot, T32HL129953, R01HL118624, R21AG049348, R21AG055002, R01AG056031, R01AG022374, R21AG059179, R01AG056682, R01AG056531, K07AG05268503, K23HL125939)

1153 Association Of Nocturnal Sleep Disturbance And Prospective Cognitive Decline In Cognitive Normal Elderly: Findings From The National Alzheimer’s Coordinating Center Uniform Dataset

Introduction

We determined whether nocturnal sleep disturbance (NSD) is associated with prospective cognitive decline in clinically normal older adults

Methods

Prospective longitudinal study utilizing data from the National Alzheimer’s Coordinating Center (NACC) Uniform Data set (UDS). NSD data, as characterized by the Neuropsychiatric Inventory Questionnaire (NPI-Q), were derived from 10,600 participants at baseline, with at least one UDS follow-up visit, from 32 National Institute of Aging Alzheimer’s Disease Research Centers (ADRC). Prospective cognitive decline was characterized as incident mild cognitive impairment (MCI) diagnosis during UDS follow-up. Logistic mixed-effects model with random intercept and slope examined associations between the NSD and longitudinal cognitive decline. All models included age at baseline, sex, years of education, APOE ε4 status and their interactions with time. Time was operationalized as years from baseline for each participant.

Results

Of the 10,600 cognitively normal participants at baseline, 1,017 (8.6%) had NSD. The proportion of males versus females with sleep problems was 10.1% vs. 9.3% respectively. For participants with NSD and no NSD, the mean (SD) age was 71 (7.3) and 70 (5.7) years and average follow-up time was 5.2 (2.6) and 4.9 (2.7) years, respectively. Participants with NSD were significantly more likely to develop incident MCI during UDS follow-up (OR: 1.42, p =.003). The interaction of NSD with time was significant (p< .001) suggesting an increase in the likelihood of conversion to MCI increased over time. Furthermore, there were significant differences in mean conversion rates to MCI in the NSD group when the previous time-point was compared to the next (p<01), with a time dependent dose response in the risk of conversion to MCI observed.

Conclusion

In elderly cognitive-normal individuals, nocturnal sleep disturbance is associated with a time-dependent progression risk to MCI. These findings are consistent with the role of disturbed sleep in the development of Alzheimer’s Disease.

Support

NIH/NIA/NHLBI (L30-AG064670, CIRAD P30AG059303 Pilot, T32HL129953, R01HL118624, R21AG049348, R21AG055002, R01AG056031, R01AG022374, R21AG059179, R01AG056682, R01AG056531, K07AG05268503, K23HL125939)

0144 Relationship Between Sleep EEG K-Complex Slow Wave Coupling and Next-Day Thalamic Activity During Psychomotor Vigilance Test in Obstructive Sleep Apnea

Introduction

There is large inter-individual variability in the relationship between obstructive sleep apnea (OSA) severity and lapses in vigilance as measured using psychomotor vigilance test (PVT). We have previously shown that overnight sleep EEG K-complex slow wave coupling (∆SWAK) exhibits a dose-responsive relationship with next-day lapses in vigilance in OSA on and off treatment. We hypothesized that a variable thalamic dysfunction in OSA explains difference in lapses in vigilance and alterations in ∆SWAK across individuals.

Methods

Five newly diagnosed severe OSA subjects (mean apnea-hypopnea index [AHI4%=57.1±22.8/hr.]) with excessive daytime sleepiness (Epworth Sleepiness Scale=11±3.4) underwent nocturnal polysomnography followed by PVT testing within a 3T SKYRA MRI scanner. The PVT task inside the scanner (PVT-fMRI) was adapted to match the gold standard PVT-192 device. Each fMRI scanning session consisted of 2 10-min PVT runs interleaved with 2 control conditions wherein the subject pressed the response button at random intervals absent of a visual stimulus. fMRI data was analyzed in 2-step procedure (individual time-series followed by group analysis) using Analysis of Functional Neuroimages (AFNI) software package. To estimate thalamic activity during PVT-fMRI, parameter estimates of the %change in blood-oxygen-level-dependent (BOLD) signal using the contrast PVT-Control were used as the primary metric. The region of interest was limited to the bilateral thalamus using the Eickhoff-Zilles macro labels from the MNI N27 template.

Results

In a preliminary test, PVT performance for the subjects inside the scanner was not significantly different from that outside the scanner (PVTLapsesfMRI=7.3±2.1 vs. PVTLapsesPVT192=6.4±3.6 mean±std; PVTLapses=reaction time > 500 ms.). Within subjects, a trend toward lower thalamic recruitment was observed during PVT-fMRI (-0.17±0.2%; p=0.1). Further, lower thalamic activity during PVT-fMRI also showed a trend to lower overnight ∆SWAK (mean -1.2±1.4) values (r = 0.61, p = 0.17).

Conclusion

In severe OSA subjects with excessive daytime sleepiness, we observed a trend to reduced thalamic activity during daytime PVT. Overnight EEG K-complex slow wave coupling showed a similar trend with next-day thalamic activity during PVT, however the small sample size may have limited our ability to detect this association with statistical significance.

Support

AASM Foundation 199-FP-18; NIH K24HL109156

Echocardiography update for primary care physicians: a review

Echocardiography is a key evaluation tool for the diagnosis, prognosis, and guidance of interventional management of numerous cardiovascular conditions, including ischaemia, heart failure, and structural heart diseases. Recent technological advancements have also seen the exploration of artificial intelligence, intracardiac vortex imaging, and three-dimensional printing in echocardiography. With cardiovascular diseases increasing in prevalence worldwide, it is important for clinicians including general practitioners to have updated knowledge of appropriate use of echocardiography. As such, this article reviews the current literature and summarises the latest developments and the general clinical usage of echocardiography.

Identification of novel genes expressed during spermatogenesis in stage-synchronized rat testes by differential display

The molecular mechanism regulating spermatogenesis at different developmental stages remains largely unknown. In a vitamin A-deficiency (VAD) rat model, five distinct histologically defined, stage-synchronized testes: (i) resting spermatogonia and preleptotene spermatocytes at Day 0 of post-vitamin A treatment (PVA); (ii) early pachytene spermatocytes at Day 7 PVA; (iii) late pachytene at Day 15 PVA; (iv) round spermatids at Day 25 PVA; and (v) elongated spermatids at Day 35 PVA were used to study gene expression profiles by mRNA differential display. Twenty-four differentially expressed cDNA fragments were identified and cloned; oligonucleotide sequence analyses indicated that there are 12 novel gene sequences, half of which share no apparent match in current GenBank/EMBL databases. Other 12 VAD clones share sequence homology to membrane channel and transport, transcription and translation, cell cycle and morphogenesis, inducer and transducer, surface or secreted glycoproteins or enzymes, and other miscellaneous molecules. Semi-quantitative RT-PCR analyses against different stages of VAD testes demonstrated: (i) restricted expression of VAD1.2 and 1.3 (novel) on Day 25 PVA when round spermatids form; (ii) escalating pattern of VAD12 (Cx43) in Sertoli cells; and (iii) relative constant levels of VAD4 (A5D3), VAD26.1 (ribonuclease), and VAD27 (GRP8) in spermatogenesis.

Progesterone together with estrogen attenuates homologous upregulation of gonadotropin-releasing hormone receptor mRNA in primary cultured rat pituitary cells

In a previous study, we clearly demonstrated that an application of gonadotropin-releasing hormone (GnRH) to cultured rat pituitary cells increased the expression of GnRH receptor (GnRH-R) mRNA through transcriptional activation of GnRH-R gene rather than suppression of the turnover rate of GnRH-R mRNA. Along with GnRH, gonadal steroids seem to be an important regulator for GnRH-R expression in the pituitary gland. Recent in vivo studies reported that an application of gonadal steroids to gonadectomized animals modulated GnRH-R mRNA expression in the pituitary gland. However, it has not been clearly understood whether steroids may act directly at the pituitary or indirectly via modulation of hypothalamic GnRH release. Therefore, we assessed the effects of estrogen and progesterone on GnRH-R mRNA expression in primary cultured female rat pituitary cells. Neither estradiol nor progesterone modulates the basal expression of GnRH-R mRNA in primary cultured pituitary cells. When cultured pituitary cells were exposed to different doses of estradiol in combination with GnRH (0.2 nM), the GnRH-stimulated increment of GnRH-R mRNA expression was not significantly changed by estradiol at any given doses. However, when different doses of progesterone were added to primary cultured pituitary cells in combination with GnRH (0.2 nM), GnRH-induced increases in GnRH-R mRNA levels were reduced in a dose-related manner, showing a significant reduction at 100 nM progesterone. Furthermore, the addition of estradiol reinforced the suppressive effect of progesterone on the homologous upregulation of GnRH-R mRNA expression. Collectively, our results clearly demonstrated that progesterone directly attenuates the homologous upregulation of GnRH-R mRNA expression at the pituitary level, and that estradiol potentiates the effect of progesterone.

Regulation of gonadotropin releasing hormone receptor mRNA expression in cultured rat granulosa cells

The homologous regulation of pituitary Gonadotropin Releasing Hormone Receptor (GnRH-R) mRNA expression by GnRH has been well demonstrated. However, the regulation of the ovarian GnRH-R is poorly understood. The present study was performed to demonstrate the presence of GnRH transcripts in addition to GnRH-R mRNA and the regulation of GnRH-R mRNA expression in the granulosa cells isolated from small antral follicles. The GnRH and GnRH-R mRNA levels were determined by a competitive reverse transcription-polymerase chain reaction (RT-PCR). The granulosa cells were obtained from immature rats implanted with diethylstilbestrol for 3 days. When GnRH transcript expression was examined in isolated granulosa cells by RT-PCR, the PCR products showed two bands. The larger band contained intronic sequences and the smaller band was a fully processed GnRH gene transcript identical to hypothalamic GnRH. This suggests that authentic GnRH gene transcripts are expressed in ovarian granulosa cells and may act on the granulosa cells in a paracrine or autocrine manner. Since GnRH action in the granulosa cells is mediated by specific GnRH-R, it is of interest to examine whether GnRH-R is synthesized in the granulosa cells. When the granulosa cells were cultured in media only, GnRH-R mRNA levels increased abruptly within 3 h and gradually decreased thereafter during the 24 h culture period. However, GnRH itself did not alter the GnRH-R mRNA expression levels in cultured granulosa cells. Interestingly, treatment with FSH decreased the GnRH-R mRNA levels in a dose-dependent manner. A time-course analysis revealed that the GnRH-R mRNA levels were significantly lower up to 9 h after FSH treatment, and returned to the basal level between 12 h-24 h. Activation of adenylate cyclase with forskolin also decreased the GnRH-R mRNA levels. It is therefore concluded that in the granulosa cells of the small antral follicles GnRH-R mRNA expression was not homologously regulated by GnRH, while FSH may negatively regulate GnRH-R mRNA expression in the granulosa cells possibly through a cAMP-protein kinase A pathway.

Progesterone together with estrogen attenuates homologous upregulation of gonadotropin-releasing hormone receptor mRNA in primary cultured rat pituitary cells

In a previous study, we clearly demonstrated that an application of gonadotropin-releasing hormone (GnRH) to cultured rat pituitary cells increased the expression of GnRH receptor (GnRH-R) mRNA through transcriptional activation of GnRH-R gene rather than suppression of the turnover rate of GnRH-R mRNA. Along with GnRH, gonadal steroids seem to be an important regulator for GnRH-R expression in the pituitary gland. Recent in vivo studies reported that an application of gonadal steroids to gonadectomized animals modulated GnRH-R mRNA expression in the pituitary gland. However, it has not been clearly understood whether steroids may act directly at the pituitary or indirectly via modulation of hypothalamic GnRH release. Therefore, we assessed the effects of estrogen and progesterone on GnRH-R mRNA expression in primary cultured female rat pituitary cells. Neither estradiol nor progesterone modulates the basal expression of GnRH-R mRNA in primary cultured pituitary cells. When cultured pituitary cells were exposed to different doses of estradiol in combination with GnRH (0.2 nM), the GnRH-stimulated increment of GnRH-R mRNA expression was not significantly changed by estradiol at any given doses. However, when different doses of progesterone were added to primary cultured pituitary cells in combination with GnRH (0.2 nM), GnRH-induced increases in GnRH-R mRNA levels were reduced in a dose-related manner, showing a significant reduction at 100 nM progesterone. Furthermore, the addition of estradiol reinforced the suppressive effect of progesterone on the homologous upregulation of GnRH-R mRNA expression. Collectively, our results clearly demonstrated that progesterone directly attenuates the homologous upregulation of GnRH-R mRNA expression at the pituitary level, and that estradiol potentiates the effect of progesterone.

Homologous upregulation of gonadotropin-releasing hormone receptor mRNA occurs through transcriptional activation rather than modulation of mRNA stability

In a previous study, we showed that even continuous application of gonadotropin-releasing hormone (GnRH) could increase the steady-state levels of GnRH receptor (GnRH-R) mRNA if treated for a relatively short period (6 h). Therefore, in the present study we examined whether GnRH-induced increment of GnRH-R mRNA is owing to stabilization of the preexisting GnRH-R mRNA or new synthesis of GnRH-R mRNA or both. Initially, to examine the effect on new RNA synthesis, the transcription inhibitor, actinomycin D (2 microM), was added to primary cultured rat anterior pituitary cells. In the presence of transcription inhibitor, GnRH-induced augmentation of GnRH-R mRNA levels was completely abolished. This result indicates that homologous upregulation of GnRH-R mRNA expression occurs at least through new RNA synthesis of GnRH-R gene. We further assessed the effects of GnRH on the turnover rate of GnRH-R mRNA using actinomycin D (2 microM). The basal half-life of GnRH-R mRNA was estimated to be approx 21 h. The application of GnRH tended to slightly suppress the basal turnover rate of GnRH; however, there was no statistically significant difference, compared with the group treated with actinomycin D alone. Collectively, our results suggest that the homologous upregulation of GnRH-R mRNA may occur through transcriptional activation of GnRH-R gene rather than enhancement of GnRH-R mRNA stability, although we did not examine the transcription rate of GnRH-R gene.

Effects of immobilization stress on estrogen-induced surges of luteinizing hormone and prolactin in ovariectomized rats

Reproductive function has been known to be impaired by various kinds of physical and emotional stress, but the mechanism by which stress impairs the reproductive axis has not been clearly understood. In the present study, the effects of immobilization stress were studied on the surges of luteinizing hormone (LH) and prolactin (PRL) induced by 17beta-estradiol (E2) in ovariectomized rats. Two weeks after bilateral ovariectomy, animals were implanted with the capsule containing E2 or vehicle at 1000 h (designated as d 0). Immobilization was started at 1000 h and continued to 2100 h on d 2. Blood samples were collected according to the time schedule by a jugular vein catheter procedure. Immobilization stress inhibited basal release of LH and abolished E2-induced LH and PRL surges in ovariectomized (OVX) rats. Daily repeated immobilization (from 1200 h to 1800 h, 6 h/d) for 3 d also abolished LH and PRL surges when examined at 1800 h on d 2. Although daily repeated immobilization stress reduced E2-induced PRL mRNA levels, this stress failed to change LHbeta mRNA levels in the anterior pituitary as determined by Northern blot analysis. Gonadotropin-releasing hormone (GnRH) receptor mRNA levels in the anterior pituitary were lowered by immobilization stress in the OVX, E2-treated group. Dopamine D2 receptor mRNA levels in the anterior pituitary of OVX, E2-treated rats were significantly decreased at 1800 h, compared with those at 1000 h. However, immobilization prevented a decrease in dopamine D2 receptor mRNA levels at 1800 h. GnRH content was increased in the mediobasal hypothalamus by immobilization in the OVX, E2-treated group, suggesting that GnRH release was inhibited. Interestingly, GnRH mRNA levels in the preoptic area-anterior hypothalamic area were suppressed by immobilization stress in OVX, E2-treated rats when determined at 1800 h. Therefore, we concluded that immobilization stress blocks E2-induced LH surge possibly by inhibiting synthesis and release of GnRH at the hypothalamic level, and an increase of dopaminergic activity via D2 receptor at the pituitary level might be involved in the stress blockage of E2-induced PRL surge.

Differential regulation of gonadotropin-releasing hormone (GnRH) receptor expression in the posterior mediobasal hypothalamus by steroid hormones: implication of GnRH neuronal activity

The present study is designed to evaluate the relationship between gonadotropin-releasing hormone (GnRH) and GnRH receptor (GnRHR) gene expression during the steroid-induced LH surge. One week after ovariectomy (OVX), a capsule containing 17beta-estradiol (E) or vehicle (V) was implanted into OVX rats, and 2 days later a single injection of progesterone (P) or V was administered s.c. at 10:00 h. Poly(A)-rich RNA samples were isolated from the micropunches of the preoptic area (POA) and the posterior mediobasal hypothalamus (pMBH) from both sides of individual brain slices. Using competitive reverse transcription-polymerase chain reaction (RT-PCR) procedures, three parameters (POA GnRH, pMBH GnRHR) and pituitary GnRHR mRNA levels were simultaneously determined in each individual animal. POA GnRH mRNA and pituitary GnRHR mRNA levels were decreased by treatment with E, but increased by a combination of E and P. In contrast, pMBH GnRHR mRNA levels were clearly augmented by treatment with E, and decreased by the combination of E and P. Temporal changes in such parameters were determined in OVX+E+V- and OVX+E+P-treated rats. P augmented POA GnRH mRNA levels at the time of the LH surge (17:00 h) and the increased GnRH mRNA levels were remained until 22:00 h, while E alone failed to alter POA GnRH mRNA levels. In the pMBH micropunch samples, P substantially decreased E-induced increase in GnRHR mRNA levels at 17:00 h and further lowered those until 22:00 h. Antisense oligonucleotides of GnRHR mRNA administered into the lateral ventricle of OVX+E-treated rats blocked the E-induced increase in pMBH GnRHR mRNA levels. The antisense oligonucleotides also prevented the LH surge as well as the increase in pituitary GnRHR mRNA levels in the OVX+E+P-treated group. However, administration of this antisense oligonucleotides failed to alter POA GnRH mRNA levels. In conclusion, the present study demonstrated that there is an inverse relationship between POA GnRH mRNA levels and pMBH GnRHR mRNA levels in response to E and/or P, and that the blockade of the E-induced increase in pMBH GnRHR mRNA levels effectively nullified the P-induced LH surge. These results indicate that pMBH GnRHR gene expression is involved in synchronizing the GnRH neuronal activity, which is crucial for the generation of the LH surge.