1. An in vitro technique for measuring secretory rate in rat isolated seminiferous tubules is described. 2. The basal rate of fluid secretion was 0-44+/-0-06 nl. cm-1 min-1 (S.E.) (n=21). The rate was found to be inhibited by cooling, addition of metabolic inhibitor 2,4-dinitrophenol (2-5 x 10(-4) M) and removal of glucose from the incubating solution. This indicates that fluid secretion in isolated rat seminiferous tubules is an energy dependent process. 3. Removal of K+ from the incubating medium inhibited the secretory rate in the isolated seminiferous tubules, whereas a fivefold increase in [K+]0 to 23-5 mM had no effect. The secretory rate was also unaffected by the absence of Cl- in the peritubular fluid. 4. Removal of Ca2+ from the peritubular medium caused a rise in the secretory rate. 5. Ouabain (10(-3) M) and acetazolamide (4 x 10(-5) M) caused a fall in the rate of fluid secretion in isolated seminiferous tubules. 6. These results are discussed in relation to the nature of the ionic secretion produced in the tubules.

The level and release pattern of plasma melatonin in the confluens sinuum of 28 sighted and 18 blinded (i.e. acute bilateral orbital enucleation) rabbits anesthetized with pentobarbital were studied. The animals had been adapted to a 12:12 h light-dark regime. Blood samples were collected from the cannulated confluens sinuum and/or the femoral artery at either 2- or 4-min intervals in both the light and dark phases. Plasma melatonin was determined by radioimmunoassay. In all rabbits studied, plasma melatonin in the confluens sinuum exhibited an episodic release pattern, with pulses superimposed on a basal level. At 4-min sampling intervals, the pulsatile release of melatonin in sighted rabbits were 3.8 peaks/h in the light phase; shorter sampling interval (2-min) revealed more frequent pulsatile release of melatonin (5.1 peaks/h). In sighted animals in the light phase, the level of melatonin in the plasma of confluens sinuum was 7–15 times higher than that obtained from the plasma collected at the same time from the peripheral artery where the level of melatonin also exhibited pulsatile pattern. In blinded animals, melatonin levels in terms of mean concentration, mean maximum level and mean minimum (or baseline) level obtained in the dark phase were 12–14 times higher than those obtained in the light phase. These results suggest that the level of melatonin exhibits a diurnal rhythm in the confluens sinuum of rabbits.

The plasma melatonin in the confluens sinuum of anesthetized rabbits and rats exhibited an episodic release pattern, with pulses superimposed on a basal level. The rhythmicity of pineal melatonin release revealed by our experimental paradigm was dependent on the blood sampling interval. In rabbits, it was found that the plasma melatonin level in the confluens sinuum was 7–15 times higher than that obtained from the plasma collected at the same time from the peripheral artery where the melatonin level also showed a pulsatile pattern. Diurnal variation in pineal melatonin level in the confluens sinuum was observed only in acutely blinded rabbits and rats. Electrical stimulation of the unilateral cervical sympathetic trunk of rabbits resulted in elevation of the level of plasma melatonin in the confluens sinuum, while the frequency of pulse peaks of plasma melatonin revealed at 4-min intervals was not affected. Similar results were obtained in rabbits with systemic administration of beta-adrenergic agents. These findings suggest that the release of pineal melatonin into the confluens sinuum is under the regulation of the cervical sympathetic system. The sympathetic influence on pineal melatonin secretion seems to vary with age. Furthermore, age-related fluctuation of systemic blood melatonin appeared to be the results of changes in the rate of pineal melatonin secretion, body growth and ageing.

No abstract

Microcystin (MC), a hepatotoxin that is associated with cyanobacterial blooms in freshwater lakes, threatens the quality of drinking water resources. Biodegradation of MC using biofiltration is emerging as a cost-effective solution for drinking water treatment. This study reports isolation of five MC-degrading microbial consortia and investigation of their community structure and kinetics in the presence or absence of a readily-bioavailable organic carbon source. The results indicated that the presence of a bioavailable organic carbon source caused: (1) the proliferation of community members previously unobserved in each consortium cultured without ethanol; (2) a shift in abundance of representative taxa; (3) a fluctuation in genera affiliated with MC-biodegradation; and, (4) a unique response in simulated diversity among consortia. These changes to each microbial consortium were paralleled by a significant decline in MC degradation kinetics. Overall, this study highlights the importance of integrating environmental conditions into the design and operation of biofiltration systems for MC biodegradation.Previous studies have demonstrated the complete biodegradation of MC-LR within laboratory scale biofiltration systems following a preliminary lag phase of removal [14][15][16][17]. However, the toxin removal efficiency and extent of this lag phase can vary significantly with bacterial composition, nutrient concentration, and other environmental parameters that are associated with the source water. Efforts to evolve biofiltration from a passive process into a more standardized, controlled, and perhaps "engineered", biological treatment process for targeted removal of pollutants will require a better understanding of the physiology and genetics of MC-degrading bacteria [12][13][14][18][19][20].Significant efforts have been made to isolate and characterize the specific MC-degrading bacterial populations during algal bloom events in the source water and sediments, and from full scale biological treatment units in drinking water treatment facilities [7][8][9]17,[21][22][23][24]. However, these studies have not fully explored how these isolates function in mixed bacterial communities, nor the influences of mutualistic or antagonistic interactions on biodegradation kinetics. Several previous studies, however, have considered the effects of environmental stimuli (i.e., varying organic carbon concentrations) on MC-degrading bacterial consortia under aerobic conditions [7,8,23,[25][26][27][28][29]. Research showed that addition of organic carbon sources (i.e., glucose, acetate, or uncharacterized dissolved organic carbon (DOC)) significantly inhibits MC degradation kinetics of bacterial consortia [7,23,25,29]. Catabolite repression is postulated as a mechanism underlying this inhibition, where MC-degrading populations may prefer more energetically-favorable (easily metabolized) over more energetically-intensive substrates, such as MC [30]. Other (fewer) studies have demonstrated that the addition of an alternative organic ca...