Clonidine pretreatment modifies the growth hormone secretory pattern induced by shortterm continuous GRF infusion in normal man

OBJECTIVE: The aim of this study was to investigate the effect of a single dose of clonidine on the pattern of GH release in response to a 10-hour continuous GRF infusion in normal man. DESIGN: Plasma GH was analysed in samples withdrawn at 20-minute intervals, from 0900 to 1900 h, according to the following protocols: in a control study, a placebo was given at 1000 h; in other experiments, clonidine (300 micrograms, orally) was given at 1000 h, alone or together with a continuous intravenous infusion of GRF 1-29 (0.3 micrograms/kg/h) starting at this time. In another experiment, the continuous infusion of GRF 1-29 was preceded by placebo administration at 1000 h. PATIENTS: Eight normal volunteers (four women and four men), aged 19-24 years were studied. MEASUREMENTS: Plasma GH levels were measured by RIA. Analysis of the pattern of GH secretion was performed using cluster analysis. RESULTS: Clonidine induced a slight but significant increase in plasma GH values, peaking 60 to 120 minutes later; however, no significant changes were observed in indices of total and pulsatile GH release for the whole sampling period in this study. Continuous GRF administration led to increased episodic GH secretion, by augmenting GH peak amplitude, although peak frequency was not modified. An increase in interpulse GH values was also observed during GRF infusion. Pretreatment with clonidine clearly changed the pattern of GH release during GRF infusion: the amount of GH secreted was significantly higher, the number of GH peaks significantly increased, and almost all the GH was secreted within them. CONCLUSIONS: These data concord with our previous demonstration that clonidine disrupts the hypothalamic-somatotroph rhythm by inhibiting the hypothalamic release of somatostatin. Given that clonidine pretreatment induced a more physiological episodic pattern of GRF-induced GH release, the possibility of combining clonidine and GRF therapy for short stature in children is envisaged.     

Effect of elevated prolactin levels on the synthesis and release of catecholamines from the adrenal medulla in female rats

Recent evidence suggests that increased plasma prolactin (PRL) levels could be modifying the synthesis and release of catecholamines (CA) from the adrenal medulla. In order to study this possibility, female rats bearing an anterior pituitary gland, from a litter-mate donor, under the right kidney capsule since day 30 of life and their sham-operated controls were sacrificed by decapitation 45 days after the transplant operation. Plasma PRL and CA levels and CA content in the adrenal medulla were analyzed. A significant increase in plasma PRL levels was shown in grafted (22 +/- 2 micrograms/l) when compared to control rats (6 +/- 0.3 micrograms/l), together with a significant increase in plasma norepinephrine (NE) (4.2 +/- 1.1 micrograms/l vs. 1.7 +/- 0.7 micrograms/l) and epinephrine (E) (2.9 +/- 0.6 micrograms/l vs. 1.6 +/- 0.2 micrograms/l). Similar plasma dopamine (DA) levels were found in both groups (0.6 +/- 0.2 micrograms/l vs. 0.8 +/- 0.3 micrograms/l). An increase in adrenal DA content (29.1 +/- 6.8 ng/mg protein), together with a decrease in NE (33.3 +/- 6.8 ng/mg protein) and E content (65.9 +/- 11.8 ng/mg protein) was detected in grafted as compared to control rats (DA: 12.0 +/- 3.6 ng/mg protein; NE: 79.3 +/- 22.1 ng/mg protein; E: 184.2 +/- 39.2 ng/mg protein). We can conclude from these data that the elevation of circulating PRL levels induced by a pituitary graft is able to increase the synthesis and release of CA from the adrenal medulla in female rats.     

Same molecule but different expression: aging and sepsis trigger NLRP3 inflammasome activation,a target of melatonin

The connection between the innate immune system, clock genes, and mitochondrial bioenergetics was analyzed during aging and sepsis in mouse heart. Our results suggest that the sole NF‐κB activation does not explain the inflammatory process underlying aging; the former also triggers the NLRP3 inflammasome that enhances caspase‐1‐dependent maturation of IL‐1β. In this way, aged mice enter into a vicious cycle as IL‐1β further activates the NF‐κB/NLRP3 inflammasome link. The origin of NF‐κB activation was related to the age‐dependent Bmal1/Clock/RORα/Rev‐Erbα loop disruption, which lowers NAD⁺ levels, reducing the SIRT1 deacetylase ability to inactivate NF‐κB. Consequently, NF‐κB binding to DNA increases, raising the formation of proinflammatory mediators and inducing mitochondrial impairment. The cycle is then closed with the subsequent NLRP3 inflammasome activation. This paired contribution of the innate immune pathways serves as a catalyst to magnify the response to sepsis in aged compared with young mice. Melatonin administration blunted the septic response, reducing inflammation and oxidative stress, and enhancing mitochondrial function at the levels of nonseptic aged mice, but it did not counteract the age‐related inflammation. Together, our results suggest that, although with different strengths, chronoinflammaging constitutes the biochemical substrate of aging and sepsis, and identifies the NLRP3 inflammasome as a new molecular target for melatonin, providing a rationale for its use in NLRP3‐dependent diseases.     

Reduced apurinic/apyrimidinic endonuclease 1 activity and increased DNA damage in mitochondria are related to enhanced apoptosis and inflammation in the brain of senescence- accelerated P8 mice (SAMP8)

The senescence- accelerated mouse prone 8 (SAMP8) is a well- characterized animal model of senescence that shows early age- related neurodegeneration with impairment in learning and memory skills when compared with control senescence- resistant mice (SAMR1). In the current study, we investigated whether such impairment could be partly due to changes in mitochondrial DNA (mtDNA) repair capacity and mitochondrial DNA damage in the brain of SAMP8 mice. Besides we studied whether these potential changes were related to modifications in two major processes likely involved in aging and neurodegeneration: apoptosis and inflammation. We observed that the specific activity of one of the main mtDNA repair enzymes, the mitochondrial APE1, showed an age- related reduction in SAMP8 animals, while in SAMR1 mice mitochondrial APE1 increased with age. The reduction in mtAPE1 activity in SAMP8 animals was associated with increased levels of the DNA oxidative damage marker 8oxodG in mtDNA. Our results also indicate that these changes were related to a premature increase in apoptotic events and inflammation in the brain of SAMP8 mice when compared to SAMR1 counterparts. We suggest that the premature neurodegenerative phenotype observed in SAMP8 animals might be due, at least in part, to changes in the processing of mtDNA oxidative damage, which would lead to enhancement of apoptotic and inflammatory processes.     

Depending on the time of administration, dexamethasone potentiates or blocks growth hormone-releasing hormone-induced growth hormone release in man

In humans, corticoids suppress growth hormone (GH) secretion elicited by a variety of stimuli, while in vitro they potentiate GH release. To further study this problem, the effect of two doses of dexamethasone on GH secretion elicited by GH-releasing hormone (GHRH) in 6 normal volunteers was studied. Each subject underwent three tests, on 3 separate days with GHRH 1-29 (1 microgram/kg i.v. at 12.00 h). On the control day, only GHRH was given, on the second day dexamethasone 4 mg i.v. was administered at 09.00 h (3 h before GHRH) and on the third day dexamethasone 8 mg p.o. was given 12 h before GHRH (at 00.00 h). The GHRH-induced GH peak was 9.9 +/- 2.0 ng/ml, while 4 mg dexamethasone significantly (p less than 0.05) potentiated GH secretion elicited by GHRH (29.2 +/- 5.7 ng/ml). When dexamethasone 8 mg was given 12 h before, GHRH-induced GH secretion was completely blocked (3.0 +/- 1.1 ng/ml) (p less than 0.05). These results indicate that corticoids have two different actions: an acute potentiating activity on GHRH, and a delayed blocking action on GHRH-induced GH secretion.     

Circadian urinary 6-sulphatoxymelatonin, cortisol excretion and locomotor activity in airline pilots during transmeridian flights

Airline pilots divided into two groups of age (over and under 50 years) were studied before, during and after westbound (Madrid-Mexico City-Madrid, n = 12) and eastbound (Madrid-Tokyo-Madrid, n = 21) flights. A group of 10 age-matched people staying in Madrid were submitted to the same tests and served as a control group. Changes in urinary 6-sulphatoxymelatonin (6-aMTs) and free cortisol excretion (determined in 6-hr intervals) were measured by radioimmunoassay. Using wrist actigraphy, the circadian locomotor activity rhythm (LAR) was also monitored. Maximal baseline excretion of 6-aMTs occurred between 00:00 and 12:00 hr and maximal excretion of cortisol took place between 6:00 and 12:00 hr in the control group. Analysed globally, older pilots exhibited significantly lower values of 6-aMTs than younger ones. In both flight directions, pilots maintained the pattern of excretion of 6-aMTs, corresponding to baseline. The return flight to Madrid from Mexico and Tokyo coincided with a maximum in 6-aMTs excretion. Pilots kept the cortisol pattern found in the control group, with those over 50 years of age exhibiting significantly lower cortisol values than the younger ones. A 7-hr delay in acrophase of LAR after 2 days in Mexico City was found after cosinor analysis, and similar pre-flight values were found after returning to Madrid. An 8-9-hr acrophase advance of LAR was observed after arriving in Tokyo, with acrophase on the post-return flight day still being advanced 3 4 hr as compared to pre-flight values. Decreases in the amplitude of LAR in older pilots were found at Mexico City, as well as at Tokyo stopover and on post-flight day. Data confirm the occurrence of internal desynchronization in airline crewmembers after transmeridian flights.     

Effects of Local Melatonin Application on Implant Osseointegration

Purpose: The aim of this study was to assess the effect of local melatonin administration on bone osseointegration around implants in rabbit tibiae. Material and Methods: Ten female, 6‐month‐old New Zealand rabbits were randomly divided into two groups: the experimental group, where five rabbits were treated with local application of melatonin (3 mg) to implant sites when placed into the rabbit tibia, and the control group, those who where without additive materials. Four weeks later, animals were sacrificed; tibiae were dissected from soft tissues and fixed in buffered formaldehyde, and then included in methacrylate. Histological sections were performed to be studied under light microscopy and analyzed morphometrically to evaluate the amount of bone to implant contact (BIC), trabecular area density, and cortical area density. One‐way analysis of variance test was used for statistical evaluation. p < .05 was considered to be significant. Results: Histological evaluation showed more trabecular reaction in the melatonin group. Morphometrical analysis showed a statistically significant increase in trabecular BIC in the melatonin group when compared with the control group (24.61% ± 2.87 vs 13.62% ± 1.44; p < .01). Cortical BIC was decreased in the melatonin group, without statistical significance (71.08 ± 3.63 vs 76.28 ± 2.57; p = 0.31). Trabecular area density was increased significantly in the melatonin group (8.68 ± 1.61 vs 4.02 ± 0.36; p < .05). Cortical area density was decreased significantly in the melatonin group (91.31 ± 1.6 vs 95.7 ± 0.5; p < .05). Conclusion: Within the limitation of this animal study, local melatonin application at the time of implant placement might induce more trabecular bone at implant contact and higher trabecular area density.