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PubMed1993

Accelerated rejection of murine cardiac allografts by murine cytomegalovirus-infected recipients. Lack of haplotype specificity.

Clinical studies have revealed a correlation between cytomegalovirus (CMV) infection and acute allograft rejection. Likewise, for a murine model we observed that C3H (H-2k) recipients infected with murine CMV (MCMV) rejected BALB/c (H-2d) cardiac allografts earlier than uninfected recipients (6.9 +/- 0.1 d compared with 8.1 +/- 0.6 d; P < 0.001). It has been hypothesized that MCMV epitopes crossreact with alloantigens and in this manner induce rejection. However, we also demonstrated that MCMV caused accelerated rejection in the reverse combination (C3H heart engrafted to BALB/c recipient; 7.2 +/- 0.3 and 9.4 +/- 0.4 d for infected and control animals, respectively; P < 0.001) and accelerated rejection of grafts of a third, unrelated haplotype (C57Bl/6; H-2b; 8.0 +/- 0.7 d compared with 10.1 +/- 0.6 for infected and control C3H recipients, respectively; P < 0.03). Ultraviolet (UV) inactivation of MCMV before administration to the graft recipient abrogated the ability to induce rapid rejection. Activated T lymphocytes were present in grafts from infected recipients 2 d before control recipients (P < 0.02) and, at the time of graft rejection, were almost exclusively CD8+ for both infected and control recipients. Thus, MCMV accelerated rejection appears not to result from crossreaction between MCMV epitopes and MHC products. The failure of UV-inactivated virus to accelerate rejection and the high proportion of CD8+ T cells recovered from all rejected grafts suggest that the class I pathway of antigen presentation may be important in the induction of early rejection.

Animals↗

PubMed1993

Glucocorticoids accelerate fetal maturation of the epidermal permeability barrier in the rat.

The cutaneous permeability barrier to systemic water loss is mediated by hydrophobic lipids forming membrane bilayers within the intercellular domains of the stratum corneum (SC). The barrier emerges during day 20 of gestation in the fetal rat and is correlated with increasing SC thickness and increasing SC lipid content, the appearance of well-formed lamellar bodies in the epidermis, and the presence of lamellar unit structures throughout the SC. Because glucocorticoids accelerate lung lamellar body and surfactant maturation in man and experimental animals, these studies were undertaken to determine whether maternal glucocorticoid treatment accelerates maturation of the epidermal lamellar body secretory system. Maternal rats were injected with betamethasone or saline (control) on days 16-18, and pups were delivered prematurely on day 19. Whereas control pups exhibited immature barriers to transepidermal water loss (8.16 +/- 0.52 mg/cm2 per h), glucocorticoid-treated pups exhibited competent barriers (0.74 +/- 0.14 mg/cm2 per h; P < 0.001). Glucocorticoid treatment also: (a) accelerated maturation of lamellar body and SC membrane ultrastructure; (b) increased SC total lipid content twofold; and (c) increased cholesterol and polar ceramide content three- to sixfold. Thus, glucocorticoids accelerate the functional, morphological, and lipid biochemical maturation of the permeability barrier in the fetal rat.

Animals↗

PubMed1996

Imbalance towards Th1 predominance is associated with acceleration of lupus-like autoimmune syndrome in MRL mice.

To investigate the respective roles of Th1 and Th2 cells in the pathogenesis of lupus-like autoimmune disease, we have analyzed the spontaneous and antigen-induced productions of IgG1 vs IgG2a and IgG3 subclasses in relation to the mRNA expression of INF-gamma (Th1 cytokine promoting IgG2a and IgG3 production), IL-4 (Th2 cytokine promoting IgG1 production), and IL-10 (Th2 cytokine) in CD4+ T cells from lupus-prone MRL mice. For this purpose, two paired sets of MRL mice were chosen for the comparison of these parameters: (a) MRL-lpr/lpr (lpr for lymphoproliferation) and its recently described substrain with a prolonged survival, termed MRL-lpr/lpr.ll (ll for long lived) and (b) MRL male mice bearing the Yaa (Y-linked autoimmune acceleration) gene (MRL.Yaa) with an accelerated disease and their male counterparts lacking the Yaa gene. We demonstrate herein that the accelerated development of lupus-like autoimmune disease in MRL-lpr/lpr and MRL.Yaa mice, as compared with MRL-lpr/lpr.ll and MRL-+/+ mice, respectively, was correlated with an enhanced expression of IFN-gamma vs IL-4 and IL-10 mRNA in CD4+ T cells, which paralleled with an increase of spontaneous and foreign T cell-dependent antigen-induced productions of IgG2a and IgG3 vs IgG1 antibodies. These data suggest that an imbalance towards Th1 predominance may play a significant role in the acceleration of lupus-like autoimmune disease in MRL mice.

Animals↗

PubMed1996

Hormonal basis for the gender difference in epidermal barrier formation in the fetal rat. Acceleration by estrogen and delay by testosterone.

Previous studies have shown that ontogeny of the epidermal permeability barrier and lung occur in parallel in the fetal rat, and that pharmacologic agents, such as glucocorticoids and thyroid hormone, accelerate maturation at comparable developmental time points. Gender also influences lung maturation, i.e., males exhibit delayed development. Sex steroid hormones exert opposite effects on lung maturation, with estrogens accelerating and androgens inhibiting. In this study, we demonstrate that cutaneous barrier formation, measured as transepidermal water loss, is delayed in male fetal rats. Administration of estrogen to pregnant mothers accelerates fetal barrier development both morphologically and functionally. Competent barriers also form sooner in skin explants incubated in estrogen-supplemented media in vitro. In contrast, administration of dihydrotestosterone delays barrier formation both in vivo and in vitro. Finally, treatment of pregnant rats with the androgen antagonist flutamide eliminates the gender difference in barrier formation. These studies indicate that (a) estrogen accelerates and testosterone delays cutaneous barrier formation, (b) these hormones exert their effects directly on the skin, and (c) sex differences in rates of barrier development in vivo may be mediated by testosterone.

Animals↗

PubMed2006

Low-intensity pulsed ultrasound accelerates bone-tendon junction healing: a partial patellectomy model in rabbits.

BACKGROUND: Low-intensity pulsed ultrasound has been demonstrated to be beneficial for accelerating fracture healing, delayed union, nonunion, and soft tissue repair. HYPOTHESIS: Low-intensity pulsed ultrasound accelerates healing of bone-to-tendon junction repair by promoting osteogenesis and tissue remodeling at the healing junction. STUDY DESIGN: Controlled laboratory study. METHODS: Standard partial patellectomy was conducted in forty-eight 18-week-old rabbits divided into an ultrasound treatment and control group. Daily ultrasound was delivered 3 days after surgery onto the patellar tendon-patella healing junction and continuously up to weeks 2, 4, 8, and 16 postoperatively, when the patella-patellar tendon complexes were harvested for radiographic, histologic, and biomechanical evaluations. RESULTS: Radiographic measurements showed significantly more newly formed bone at the patellar tendon-patella healing junction in the ultrasound group compared with the controls at week 8 (4.91 +/- 2.74 mm(2) vs 2.50 +/- 1.83 mm(2), P < .05) and week 16 (7.22 +/- 2.34 mm(2) vs 4.61 +/- 2.22 mm(2), P < .05) after partial patellectomy. Histologically, the ultrasound group at weeks 8 and 16 showed improved tissue integration, characterized by trabecular bone expansion from the remaining patella and regeneration of fibrocartilage layer at the patellar tendon-patella healing junction. Fluorescence microscopy revealed earlier bone formation in the ultrasound group when compared with the controls at week 8 (1.78 +/- 0.32 vs 1.23 +/- 0.43, P < .01) and week 16 (2.10 +/- 0.67 vs 1.29 +/- 0.35, P < .01). Mechanical testing showed significantly higher failure load and ultimate strength in the ultrasound group (300.2 +/- 61.7 N and 7.10 +/- 1.29 MPa, respectively) as compared with controls (222.3 +/- 65.1 N and 5.26 +/- 1.36 MPa, respectively) at week 16 (P < .05 for both). CONCLUSION: Low-intensity pulsed ultrasound was able to accelerate bone-to-tendon junction repair. CLINICAL RELEVANCE: These results may help establish treatment efficacy for accelerating bone-to-tendon junction repair and facilitating earlier rehabilitation.

Analysis of Variance↗

PubMed2001

Low ambient temperature accelerates short-day responses in Siberian hamsters by altering responsiveness to melatonin.

Exposure to low ambient temperatures (Ta) accelerates appearance of the winter phenotype in Siberian hamsters transferred from long to short day lengths. Because melatonin transduces the effects of day length on the neuroendocrine axis, the authors assessed whether low Ta promotes the transition to winterlike traits by accelerating the onset of increased nocturnal melatonin secretion or by enhancing responsiveness to melatonin in short day lengths. Male hamsters were transferred from 16L (16 h light/day) to 8L (8 h light/day) photoperiods and held at 5 degrees C or 22 degrees C. Locomotor activity was recorded continuously, and body mass, testis size, and pelage color were determined biweekly for 8 weeks. The duration of nocturnal locomotion (alpha), a reliable indicator of the duration of nocturnal melatonin secretion, lengthened significantly earlier in hamsters exposed to a Ta of 5 degrees C than 22 degrees C. Cold exposure increased the proportion of hamsters that were photoresponsive: gonadal regression in short days increased from 44% at 22 degrees C to 81% at 5 degrees C (p < 0.05); low Ta did not, however, accelerate testicular regression in animals that were photoresponsive. Nonphotoresponsive animals at 5 degrees C temporarily had longer alphas during the first 4 weeks in short days and significant decreases in body mass and testicular size that were reversed during the ensuing weeks when alpha decreased. In a 2nd experiment, pinealectomized male hamsters infused for 10 h/day with melatonin for 2 weeks had significantly lower body and testes masses when maintained at 5 degrees C but not 22 degrees C. Low-ambient temperature appears to accelerate the appearance of the winter phenotype primarily by increasing target tissue responsiveness to melatonin and to a lesser extent by augmenting the rate at which the duration of nocturnal melatonin secretion increases in short day lengths.

Analysis of Variance↗

PubMed1996

Chemical and behavioral stimulation from females accelerates recrudescence in male Syrian hamsters exposed to short days.

Interaction with female hamsters maintained under long photoperiods (LP) accelerates behavioral recrudescence in short photoperiod (SP) males. In this experiment, the authors investigated the effects of various types of female sociosexual cues on different measures of reproductive recrudescence in the male. Five groups of SP males were exposed to different female cues for 3 weeks (Weeks 12 to 15). At Week 16, males were allowed to interact with estrus females; behavioral, physiological, and fecundity measures were monitored. The results show that all measures responded in a pseudo-dose-dependent manner to the different female cues presented. SP males not exposed to any female cues and those exposed to distal visual, auditory, and volatile pheromonal cues from estrus females did not copulate, deposit sperm, or impregnate estrus females presented to them at Week 16. SP males allowed direct access to the bedding of estrus females showed marked improvements on these same reproductive measures by Week 16. However, SP males that interacted with LP females between Weeks 12 and 15 showed the greatest level of reproductive function at Week 16. These results show that the type of female sociosexual stimulation is important in accelerating reproductive recrudescence; whereas interaction with LP females may be important in accelerating behavioral recrudescence, both interaction with and exposure to the bedding of LP females may be important in accelerating physiological and reproductive success measures.

Animals↗

PubMed2003

Red light accelerates and melatonin retards metamorphosis of frog tadpoles.

BACKGROUND: Earlier studies from this laboratory reported that light and its spectra influence reproduction in the Indian skipper frog Rana cyanophlyctis through both ocular and extra ocular photoreception. During the course of our ongoing studies on chromotactic behaviour of the tadpoles, we noticed that tadpoles held in red light metamorphosed earlier than those held in white or other colours of light. The focus of the present study therefore was to examine the effect of red light on metamorphosis of the tadpoles. RESULTS: Tadpoles, both intact and blind (optectomised), held in red light metamorphosed earlier than those held in white light. Addition of melatonin to aquarium water (5 micrograms/litre) prevented the red light-induced acceleration of metamorphosis both in intact and blinded tadpoles. CONCLUSION: Both ocular and extra-ocular perception of light is involved in red light-induced precocious metamorphosis. Melatonin inhibits the red light-induced acceleration of metamorphosis. The mechanism by which red light accelerates metamorphosis is not yet known. Melatonin counteracts red-light induced acceleration of metamorphosis in this tadpole.

Animals↗

PubMed2006

Systemic hypothermia increases PAI-1 expression and accelerates microvascular thrombus formation in endotoxemic mice.

INTRODUCTION: Hypothermia during sepsis significantly impairs patient outcome in clinical practice. Severe sepsis is closely linked to activation of the coagulation system, resulting in microthrombosis and subsequent organ failure. Herein, we studied whether systemic hypothermia accelerates microvascular thrombus formation during lipopolysacharide (LPS)-induced endotoxemia in vivo, and characterized the low temperature-induced endothelial and platelet dysfunctions. METHODS: Ferric-chloride induced microvascular thrombus formation was analyzed in cremaster muscles of hypothermic endotoxemic mice. Flow cytometry, ELISA and immunohistochemistry were used to evaluate the effect of hypothermia on endothelial and platelet function. RESULTS: Control animals at 37 degrees C revealed complete occlusion of arterioles and venules after 759 +/- 115 s and 744 +/- 112 s, respectively. Endotoxemia significantly (p < 0.05) accelerated arteriolar and venular occlusion in 37 degrees C animals (255 +/- 35 s and 238 +/- 58 s, respectively). This was associated with an increase of circulating endothelial activation markers, agonist-induced platelet reactivity, and endothelial P-selectin and plasminogen activator inhibitor (PAI)-1 expression. Systemic hypothermia of 34 degrees C revealed a slight but not significant reduction of arteriolar (224 +/- 35 s) and venular (183 +/- 35 s) occlusion times. Cooling of the endotoxemic animals to 31 degrees C core body temperature, however, resulted in a further acceleration of microvascular thrombus formation, in particular in arterioles (127 +/- 29 s, p < 0.05 versus 37 degrees C endotoxemic animals). Of interest, hypothermia did not affect endothelial receptor expression and platelet reactivity, but increased endothelial PAI-1 expression and, in particular, soluble PAI-1 antigen (sPAI-Ag) plasma levels. CONCLUSION: LPS-induced endotoxemia accelerates microvascular thrombus formation in vivo, most probably by generalized endothelial activation and increased platelet reactivity. Systemic hypothermia further enhances microthrombosis in endotoxemia. This effect is associated with increased endothelial PAI-1 expression and sPAI-Ag in the systemic circulation rather than further endothelial activation or modulation of platelet reactivity.

Animals↗

PubMed2026

Effects of different training modalities on lower-limb explosive power, acceleration, 20-m sprint performance, and change-of-direction ability in youth soccer players: a systematic review and network meta-analysis.

BACKGROUND: Youth soccer players repeatedly perform explosive actions, short accelerations, linear sprints, decelerations, and multidirectional movements. However, the comparative effects of different structured physical-conditioning programmes remain uncertain. METHODS: Seven databases were searched from inception to 3 July 2026 using a final expanded search strategy encompassing plyometric, strength or resistance, sprint, acceleration, speed, change-of-direction, neuromuscular, multicomponent, and combined training. Randomised controlled trials involving healthy youth soccer players were eligible. Intervention arms were classified using operational, content-based node definitions. Construct-restricted primary networks and expanded sensitivity networks were analysed using frequentist random-effects network meta-analysis. Hedges' adjusted g was preferentially calculated from post-intervention or final-follow-up means, standard deviations, and sample sizes. Estimates were presented so that positive values indicated better performance. P-scores were treated as descriptive ranking summaries. Risk of bias was assessed using an adapted study-level application of the five-domain RoB 2 framework, and confidence in the evidence was assessed using CINeMA. A post hoc strict-age sensitivity analysis excluded two age-boundary studies. RESULTS: Eighty-nine studies were included in the expanded quantitative analysis, of which 74 contributed to at least one construct-restricted primary network. The primary lower-limb explosive-power, acceleration, 20-m sprint, and planned change-of-direction networks included 55, 20, 25, and 38 studies, respectively. Compared with usual soccer training, plyometric training combined with sprint and/or change-of-direction training showed favourable estimates for lower-limb explosive power (SMD 0.79, 95% CI 0.55 to 1.03), acceleration (1.19, 0.90 to 1.49), 20-m sprint performance (0.80, 0.33 to 1.28), and planned change-of-direction ability (1.46, 1.13 to 1.80). Corresponding I² values were 34.6%, 21.8%, 65.0%, and 41.0%. Between-design inconsistency was detected in the 20-m sprint (P = 0.0036) and change-of-direction (P = 0.0007) networks. CINeMA confidence for these four comparisons was low, low, very low, and low, respectively. Expanded sensitivity networks showed substantially greater heterogeneity. The highest-ranked intervention differed across outcome domains but remained consistent within each outcome across the three analysis sets. Excluding the two age-boundary studies did not materially alter the principal estimates. CONCLUSIONS: Plyometric training combined with sprint and/or planned change-of-direction training produced favourable comparative estimates across the four performance outcomes. However, evidence for several nodes and active-versus-active comparisons was sparse, heterogeneity in programmes and outcomes was present, inconsistency was detected in some networks, and confidence in the evidence was low or very low. These limitations do not support a conclusion that any training category is universally superior. The findings should be interpreted as provisional category-level signals rather than definitive training prescriptions. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD420261347297, registered on 21 March 2026, https://www.crd.york.ac.uk/PROSPERO/view/CRD420261347297 .

Change-of-direction ability↗

PubMed1995

Granulocyte colony-stimulating factor accelerates neutrophil engraftment following peripheral-blood stem-cell transplantation: a prospective, randomized trial.

PURPOSE: It is well-established that the infusion of hematopoietic growth factors (HGF) accelerates neutrophil recovery in patients undergoing high-dose therapy followed by autologous bone marrow infusion. In addition, there is evidence that the infusion of autologous peripheral-blood stem cells (PBSC) accelerates engraftment in comparison to patients who receive bone marrow alone. However, few data are available regarding the ability of HGF to accelerate engraftment further in patients who receive PBSC following high-dose therapy. PATIENTS AND METHODS: Forty-one patients undergoing high-dose therapy followed by infusion of autologous PBSC with or without bone marrow were randomized to receive granulocyte colony-stimulating factor (G-CSF) 5 micrograms/kg/d beginning on day + 1 following transplant or standard posttransplant supportive care without HGF. RESULTS: The median time to a neutrophil count > or = 500/microL was 10.5 days in the G-CSF group versus 16 days in the control group (P = .0001). G-CSF was associated with statistically significant reductions in the time to neutrophil engraftment among patients who received PBSC alone (11 v 17 days, P = .0003) and in patients who received PBSC in conjunction with bone marrow (10 v 14 days, P = .02). The median duration of posttransplant hospitalization (18 v 24 days, P = .002) and the median number of days on nonprophylactic antibiotics (11 v 15, P = .03) were also significantly reduced. CONCLUSION: Administration of G-CSF in the posttransplant period accelerates the rate of neutrophil engraftment, shortens the duration of hospitalization, and reduces the number of days on nonprophylactic antibiotics in patients who receive autologous PBSC with or without autologous bone marrow following high-dose therapy.

Adult↗

PubMed2005

Epidermal growth factor receptor expression in pretreatment biopsies from head and neck squamous cell carcinoma as a predictive factor for a benefit from accelerated radiation therapy in a randomized controlled trial.

PURPOSE: Accelerated repopulation is a main reason for locoregional failure after fractionated radiotherapy for head and neck squamous cell carcinoma (HNSCC). Epidermal growth factor receptor (EGFR) is a key controller of cellular proliferation in HNSCC, which stimulated the current study to look for a direct link between EGFR status and a possible clinical advantage of accelerated radiotherapy. PATIENTS AND METHODS: Immunohistochemical staining for EGFR was performed in 304 patients with available pretreatment tumor biopsy material among 918 patients randomized to receive continuous hyperfractionated accelerated radiotherapy versus conventionally fractionated radiotherapy. The EGFR index was estimated as the proportion of tumor cells with EGFR membrane staining. RESULTS: Significant benefit in locoregional tumor control from continuous hyperfractionated accelerated radiotherapy was seen in patients with HNSCC with high EGFR expression (2P = .010) but not in those with low EGFR expression (2P = .85). EGFR status had no significant effect on survival or rate of distant metastases. The EGFR index was significantly associated with histologic grade and microvessel density. There was moderate support for an association between EGFR status and subsite within the head and neck region but no significant association with Ki-67 index, Ki-67 pattern, p53 index, p53 intensity, bcl-2 expression, or cyclin D1 index. CONCLUSION: This study indicates a key role for the EGFR receptor in determining the proliferative cellular response to fractionated radiotherapy in HNSCC. It also shows that we can select the dose-fractionation regime that has the greatest chance of benefiting the patient. These results also encourage further development of EGFR targeting combined with fractionated radiotherapy in HNSCC.

Adult↗

PubMed1999

A short term (accelerated release) approach to evaluate peptide release from PLGA depot-formulations.

An accelerated method to evaluate peptide release from poly(dl-lactide-co-glycolide) (PLGA) depot formulations in short time is described. Peptide-loaded microspheres were made from hydrophilic 50:50 PLGA by a dispersion-solvent extraction technique, and peptide release was studied at 37 degrees C and at higher temperatures in various media. For all accelerated conditions, release was faster at temperatures above the glass transition, Tg, of the host polymer. Complete release of peptide from 8600 MW PLGA was achieved in 35 hours at 50 degrees C in buffered and nonbuffered media containing 0.5% polyvinyl alcohol (PVA). Type of release media and concentration of PVA influenced the release profiles. A PVA concentration of 0.1 to 0.5% was found to prevent aggregation of microspheres at higher temperatures, with an increase in release at the higher PVA concentration. Peptide release was associated with a reduction of pH of the releasing media and increased mass loss. Complete peptide release at pH 4 from 8.6 kd and 28 kd PLGA at 50 and 60 degrees C occurred within 30-40 hours and correlated well with the real-time release at 37 degrees C and pH 7.0. At the higher molecular weight, a slightly longer accelerated release time and higher temperature were required to correlate with the real-time release. The data suggest that by optimization of release conditions such as temperature, surfactant concentration, buffer component, and pH, an accelerated study could be employed to evaluate depot formulations for a given polymer type.

Buffers↗

PubMed2003

Pubertal acceleration of pulsatile gonadotropin-releasing hormone release in male rats as revealed by microdialysis.

A microdialysis technique was used in male rats to directly assess the postulate that pubertal maturation is associated with accelerated GnRH pulsatility. Juvenile male rats, postnatal d 43 or 45 (n = 4) were stereotaxically fitted with guide cannulas directed toward the lateral median eminence, and repeated microdialysis experiments were conducted over 4-6 d. In each session, samples were collected continuously over 12 h (0900-2100 h) at 5-min intervals Results from individual peripubertal animals were pooled into two time bins for postnatal d 45-47 and 48-50, respectively, and GnRH characteristics were compared between the two epochs. The GnRH pulse frequency and mean GnRH concentration were significantly elevated at 48-50 d compared with 45-47 d. The GnRH pulsatility characteristics for 45-47 d vs. 48-50 d were as follows: pulse frequency, 0.74 +/- 0.16 vs. 1.79 +/- 0.19 pulses/h (P < 0.05); pulse amplitude, 254.1 +/- 22.3 vs. 347.2 +/- 15.8 deltapg/ml (difference in value from trough to peak); and mean release, 0.55 +/- 0.03 vs. 2.04 +/- 0.04 pg/5 min (P < 0.05). An additional two rats were dialyzed only once on postnatal d 50 to assess the effects of repeated sampling; the GnRH pulse characteristics in these animals were similar to those in rats sampled for a third or fourth time on postnatal d 48-50. To further assess the possible effects of repeated sampling on GnRH release profiles, a group of adult male rats (postnatal d 95-105; n = 3) was also dialyzed on four consecutive days. In these rats no significant alteration in GnRH pulse generator activity was observed over the four sessions. Moreover, the increase in GnRH pulse frequency observed in the peripubertal rats was found to be sustained in adult animals. To better understand the temporal relationship of GnRH pulse generator activity to reproductive maturation, groups of male rats were killed from postnatal d 45-56 along with an adult group at 95-105 d (n = 5/group) and examined for physiological signs of reproductive development. Gradual increases in serum levels of LH and testosterone and decreases in FSH and inhibin B were seen from postnatal d 45-56 to adulthood. Mature spermatozoa were found in the vas deferens by postnatal d 53. Our results demonstrate that in the late juvenile stage of male rat development, GnRH pulse generator activity is gradually accelerated over the course of consecutive days. This acceleration occurs over a period during which serum LH and testosterone are rising to adult levels, and it precedes the presence of mature spermatozoa in the vas deferens by 3 d. Our observations provide direct support for the hypothesis that an acceleration of GnRH pulsatility is the critical neural stimulus for the initiation of pubertal maturation in males. The peripheral and central cues that prompt the pubertal activation of the GnRH pulse generator remain to be characterized.

Aging↗

PubMed2004

Long-term in vivo administration of glucocorticoid hormones attenuates their capacity to accelerate in vitro proliferation of rat splenic T cells.

Previous work has shown that glucocorticoids accelerate splenic T cell proliferation in vitro. To test whether chronic exposure to high levels of glucocorticoids in vivo would affect this accelerating effect, we offered adrenalectomized rats a high dose of corticosterone (CORT; 150 microg/ml in saline), a physiological replacement dose of CORT (15 microg/ml in saline), or saline to drink. We also included a group of sham-adrenalectomized rats. After 1 wk of treatment, splenic lymphocytes of these animals were cultured in the presence or the absence of 1000 nm CORT. The central finding was that the CORT-evoked acceleration of the proliferative response in vitro was attenuated in splenic T cells from animals that had received the high-dose CORT treatment in vivo. This observation could not be explained by changes in IL-2 levels in culture supernatants, the cellular composition of the spleens, or an altered glucocorticoid receptor expression in T cells. As a candidate mechanism, we identified the abrogation of a CORT-evoked enhancement of IL-2 receptor expression. This finding underscores the pivotal role of the IL-2 receptor in the modulation of cellular immunity by glucocorticoids. We conclude that the attenuated acceleration of T cell proliferation after long-term exposure to elevated glucocorticoid levels may underlie the well-known impairment of immune function under chronic stress.

Adrenalectomy↗

PubMed1986

Effectiveness of different estrogen pulses in plasma for accelerating ovum transport and their relation to estradiol levels in the rat oviduct.

Elevations of circulating estradiol (E2) levels due to administration of exogenous E2 accelerate embryo transport through the genital tract in pregnant rats. This study relates oviductal embryo transport to tissue E2 levels associated with blood E2 oscillations of differing profiles. Plasma E2 pulses differing in rate of increase, amplitude, and duration were achieved through various schedules of iv and sc E2 administration. Rats on the first day of pregnancy received a total dose of 5 micrograms 17 beta-E2 by short (10-15 min) or long (200-300 min) term iv infusions. Some animals were used to monitor blood and tissue levels of E2 (oviduct and diaphragm). Others were killed 24 h after treatment to assess number of embryos recovered. Fast iv infusions caused brief, high amplitude (greater than 1000 pg/ml) E2 oscillations which were ineffective in eliciting accelerated embryo transport. The longer iv infusions produced lower but sustained elevations of circulating E2 levels comparable to those achieved by sc administration and were associated with accelerated embryo transport. The oviductal E2 concentration during and after a short iv infusion was never lower than that associated with a sc injection. The lack of response to a brief, high amplitude increase in circulating E2, therefore, could not be accounted for by decreased tissue content of the hormone. These results indicate that when the total mass of E2 administered is kept constant, the magnitude of embryo transport acceleration is positively correlated with the duration and negatively correlated with the amplitude and/or slope of increase in circulating estrogen. Since different tissue content of E2 does not account for the response or no response observed it follows that the geometry of E2 oscillations in plasma has a signal value for the target cells which acts independently from the bioavailability of the hormone.

Animals↗

PubMed2000

Systemically and topically administered leptin both accelerate wound healing in diabetic ob/ob mice.

Leptin is a 16 kD protein that is produced by adipocytes and induces weight loss in both normal and genetically obese ob/ob mice. ob/ob mice are obese, have multiple metabolic abnormalities, and exhibit impaired wound healing. Exogenous administration of leptin to these animals induces weight loss and corrects their metabolic defects. Leptin's effect on wound repair, however, has not been studied. Systemic administration of leptin at doses ranging from 0.1 to 10 mg/kg/day induced a highly significant acceleration in wound repair in ob/ob mice (p<0.0001), but not in db/db mice, indicating that leptin's effects on wound repair were mediated through the leptin receptor. We then investigated the possibility that leptin was acting directly at the wound site by administering leptin topically, and found that topical leptin also induced a dose dependent acceleration in wound repair (p<0.0001). In addition, we found that all forms of leptin receptor, including the signal transducing long form, were present in skin by RNase protection assay, and that leptin receptor localized to subcutaneous vessels of wounded skin by in situ hybridization. Finally, we investigated the possibility that leptin stimulated angiogenesis in wounds by analyzing wound hemoglobin and wound vessel density. Neither systemic nor topical leptin induced any significant changes in either parameter, suggesting that leptin accelerates wound repair by a mechanism other than stimulation of angiogenesis. In summary, both systemic and topical leptin accelerate wound repair in diabetic ob/ob mice, possibly via the direct interaction of leptin with its receptors in wounded skin, but do not appear to significantly stimulate wound angiogenesis. Further studies to better elucidate the mechanisms of leptin's effects on wound repair are warranted.

Administration, Topical↗

PubMed2003

Ectopic expression of kruppel like factor 4 (Klf4) accelerates formation of the epidermal permeability barrier.

Dysfunction of the epidermal permeability barrier can result in dehydration, electrolyte imbalance and poor thermoregulation. Immature skin is a portal of entry for infectious agents and potential toxins in topically applied substances. As the skin is one of the last organs to mature in utero, premature infants born before 34 weeks gestation are at great risk for complications. The transcription factor kruppel-like factor 4 (Klf4), has been shown by a targeted ablation, to have an essential function in barrier acquisition. We investigated whether Klf4 expression in utero is sufficient to establish the epidermal barrier. Specifically, we generated lines of mice that express Klf4 from a tetracycline inducible promoter when crossed with transgenic mice expressing the tetracycline transactivator tTA from the epidermal keratin 5 promoter. These mice exhibit acceleration in barrier acquisition as manifest by the exclusion of a dye solution one day earlier in development than controls. Underlying this dye impermeability are morphological changes, including an increased number of stratified layers, expression of terminal differentiation markers and assembly of cornified envelopes. By all criteria, Klf4 ectopic expression accelerates the normal process of terminal differentiation. Premature barrier acquisition in these mice follows the normal pattern rather than the pattern of the transgene promoter, indicating that there are fields of competence in which KLF4 acts. Although other transgenic mice have perturbed barrier acquisition, these mice are the first to accelerate the process of barrier establishment. These studies show that KLF4 regulates barrier acquisition and provides an animal model for studying how to accelerate the process of barrier acquisition for the premature infant.

Animals↗