Changes in ectonucleotidase activities in rat Sertoli cells during sexual maturation

Sertoli cell maturation is a complex process involving both morphological and biochemical changes. These cells have previously been shown to be targets for extracellular purine structures such as ATP and adenosine. These compounds evoke responses in rat Sertoli cells through the purinoceptor families, P₂X and P₂Y and PA₁. The signals to purinoceptors are usually terminated by the action of ectonucleotidases. In a previous work, we demonstrated that rat Sertoli cells have ecto-ATPdiphosphohydrolase (EC 3.6.1.5), ecto-5-nucleotidase (EC 3.1.3.5) and ecto-adenosine deaminase (ecto-ADA) (EC 3.5.4.4) activities. Here we investigated whether some changes occur during rat Sertoli cell maturation in these activities. Rat Sertoli cells obtained from rats of different ages representing the pre pubertal, mid pubertal and young adult (10-, 18- and 35-day-old, respectively) were cultured and used for different assays. The nucleotide hydrolysis was estimated by measuring the Pi released using a colorimetric method and by HPLC analysis. ATP and ADP hydrolysis was increased 3-fold during sexual maturation. AMP hydrolysis increased 4-fold in 10- to 35-day-old Sertoli cells. Similar results were obtained when we used other substrates to measure the extracellular hydrolysis of nucleotides (GTP, GDP, GMP and IMP). The ecto-ADA activity showed a 2-fold increase in the specific activity (18- to 35-day-old Sertoli cells). The termination of the purine cascade by adenosine degradation was faster in the 35- than in 18-day-old Sertoli cells. Follicle Stimulating Hormone (FSH) influences on the ectonucleotidase activities were investigated in 10- and 18-day-old Sertoli cells and a significant increase in the ATP and ADP hydrolysis was observed. Our results show an increase in the extracellular purine cascade during the Sertoli cell development, indicating a rise in the purine communication inside the seminiferous tubules with rat sexual maturation.     

Effects of 6-month daily supplementation with oral beta-carotene in combination or not with benzo[a]pyrene on cell-cycle markers in the lung of ferrets

Epidemiological studies have demonstrated that people who eat more fruits and vegetables (rich in carotenoids) and people who have higher serum beta-carotene (BC) levels have a lower risk of cancer, particularly lung cancer. However, the two main human intervention studies of BC supplementation (the ATBC and the CARET trials) revealed an increased risk of lung cancer among smokers and asbestos workers. Previous studies carried out in the ferret have reported that BC effects are related to dose. Here, we treated ferrets with two concentrations of oral BC (0.8 and 3.2 mg/kg body weight per day) for 6 months, using BC in a formulation also containing dl-alpha-tocopherol and ascorbyl palmitate. The effect of the smoke-derived carcinogenic agent benzo[a]pyrene (BP), with or without low-dose BC, was also analysed. We determined the protein levels and mRNA expression levels of activator protein 1 (c-Jun and c-Fos), c-Myc, cyclin D1, proliferating cellular nuclear antigen and retinoic acid receptor beta. We did not find higher levels of cell proliferation markers in the lung of ferrets treated with BC or signals of squamous metaplasia lesions either. On the other hand, although no evident signals of pulmonary carcinogenesis were observed in animals exposed to BP, BC supplementation in these animals may prevent against excess cell proliferation, since this reestablishes Jun protein and cyclin D1 mRNA levels in the lung of BP-exposed animals. In summary, these results show that the combination of BC with alpha-tocopherol and ascorbyl palmitate does not induce pro-oxidant effects in the lung of ferrets.     

Effects of brain ischemia on intermediate filaments of rat hippocampus

Neurofilaments subunits (NF-H, NF-M, NF-L) and glial fibrillary acidic protein (GFAP) were investigated in the hippocampus of rats after distinct periods of reperfusion (1 to 15 days) following 20 min of transient global forebrain ischemia in the rat. In vitro [¹⁴Ca]leucine incorporation was not altered until 48 h after the ischemic insult, however concentration of intermediate filament subunits significantly decreased in this period. Three days after the insult, leucine incorporation significantly increased while the concentration NF-H, NF-M, and NF-L were still diminished after 15 days of reperfusion. In vitro incorporation of³²P into NF-M and NF-L suffered immediately after ischemia, but returned to control values after two days of reperfusion. GFAP levels decreased immediately after ischemia but quickly recovered and significantly peaked from 7 to 10 days after the insult. These results suggest that transient ischemia followed by reperfusion causes proteolysis of intermediate filaments in the hippocampus, and that proteolysis could be facilitated by diminished phosphorylation levels of NF-M and NF-L.     

Parturition in horses is dominated by parasympathetic activity of the autonomous nervous system

External and internal stressors prolong parturition in different species. At parturition, sympathoadrenal activation should be avoided because an increased sympathetic tone may cause uterine atonia via β₂-receptors. We hypothesized that at physiological parturition, horses are under parasympathetic dominance, and stress-response mechanisms are not activated during delivery of the foal. To evaluate stress responses, heart rate, heart rate variability, catecholamines, and cortisol were analyzed in mares (n = 17) throughout foaling. Heart rate decreased from 2 hours before (51 ± 1 beats/minute) to 2 hours after delivery (41 ± 2 beats/minute; P < 0.05). Heart rate variability variables, standard deviation of the beat-to-beat interval, and root mean square of successive beat-to-beat differences, changed over time (P < 0.05) with the highest values within 15 minutes after delivery. The number of mares with atrioventricular blocks and the number of atrioventricular blocks per mare increased over time (P < 0.01) and were significantly elevated from 15 minutes before to 45 minutes after birth of the foal. Salivary cortisol concentrations increased to a maximum at 30 minutes after delivery (25.0 ± 3.4 ng/mL; P < 0.01). Plasma epinephrine and norepinephrine concentrations showed significant fluctuations from rupture of the allantochorion to expulsion of the fetal membranes (P < 0.01) but were not markedly elevated at any time. In conclusion, mares give birth under high parasympathetic tone. Cortisol release during and after foaling is most likely part of the endocrine pathways regulating parturition and not a labor-associated stress response.     

Effects of progesterone and estradiol on the proliferation of phytohemagglutinin-stimulated human lymphocytes

In this paper we report on a study to elucidate whether the response of human lymphocytes to mitogenic stimulation was modified by physiological changes which occur during the menstrual cycle. Experiments with untreated cultures showed intra-individual variation to mitogen stimulation in female lymphocyte cultures, but a significant correlation between the menstrual cycle and the proliferation kinetics of lymphocytes was not found. Consequently, we performed experiments in which two of the hormones that regulate the menstrual cycle in women, estradiol and progesterone, were added to cultured human lymphocytes obtained from both men and women. The results indicate that both hormones at physiological concentrations have the capacity to modify the proliferation of PHA-stimulated human lymphocytes. Therefore, both hormones could play a role in the induction of the intra-individual variation observed in the untreated female cultures. However, in vivo other factors could also modify the proliferation kinetics of human lymphocytes preventing the demonstration of the effects of a single factor, such as the hormonal changes occurring during the menstrual cycle.     

Soil-vegetation relationships in cerrado (Brazilian savanna) and semideciduous forest, Southeastern Brazil

Several studies pointed out soil properties as the prime determinant ofcerrado (the Brazilian savanna) physiognomies, and a gradient from campocerrado (a shrub savanna) to cerradão (a tallwoodland) has been correlated with a soil fertility gradient. Based on thishypothesis, we investigated soil-vegetation relationships in thePé-de-Gigante Reserve (São Paulo State,SoutheasternBrazil). We randomly distributed 10 quadrats (10 × 10 m) oneach ofthe following physiognomies: campo cerrado, cerradosensu stricto, cerradão, andseasonal semideciduous forest, previously defined by the analysis of satelliteimages (LANDSAT-5). We sampled the woody individuals with stem diameter> 3 cm at soil level, identifying their species. In each quadrat, wecollectedsoil samples at the depths of 0–5, 5–25, 40–60, and80–100 cm, and determined pH, K, Ca, Mg, P, Al, H + Al, basesaturation, aluminium saturation, cation exchange capacity, and percentage ofsand, clay and loam. Obtained data were submitted to a canonical correspondenceanalysis (CCA) and to a detrended correspondence analysis (DCA). Our resultsshowed a clear distinction between semideciduous forest and the cerradophysiognomies, based in soil parameters. The former was related to higherconcentrations of cations and clay in the soil, while the latter was related tohigher concentrations of exchangeable aluminium in the soil surface. The threecerrado physiognomies – campo cerrado, cerradosensu stricto, and cerradão– could not be distinguished considering plant density and the analysedsoil features.