Combined Effect of AMPK/PPAR Agonists and Exercise Training in mdx Mice Functional Performance

The present investigation was undertaken to test whether exercise training (ET) associated with AMPK/PPAR agonists (EM) would improve skeletal muscle function in mdx mice. These drugs have the potential to improve oxidative metabolism. This is of particular interest because oxidative muscle fibers are less affected in the course of the disease than glycolitic counterparts. Therefore, a cohort of 34 male congenic C57Bl/10J mdx mice included in this study was randomly assigned into four groups: vehicle solution (V), EM [AICAR (AMPK agonist, 50 mg/Kg-1.day-1, ip) and GW 1516 (PPARδ agonist, 2.5 mg/Kg-1.day-1, gavage)], ET (voluntary running on activity wheel) and EM+ET. Functional performance (grip meter and rotarod), aerobic capacity (running test), muscle histopathology, serum creatine kinase (CK), levels of ubiquitined proteins, oxidative metabolism protein expression (AMPK, PPAR, myoglobin and SCD) and intracellular calcium handling (DHPR, SERCA and NCX) protein expression were analyzed. Treatments started when the animals were two months old and were maintained for one month. A significant functional improvement (p<0.05) was observed in animals submitted to the combination of ET and EM. CK levels were decreased and the expression of proteins related to oxidative metabolism was increased in this group. There were no differences among the groups in the intracellular calcium handling protein expression. To our knowledge, this is the first study that tested the association of ET with EM in an experimental model of muscular dystrophy. Our results suggest that the association of ET and EM should be further tested as a potential therapeutic approach in muscular dystrophies.     

REGULATION OF GUANOSINE 3'',5'' CYCLIC MONOPHOSPHATE IN THE RAT PINEAL AND POSTERIOR PITUITARY GLANDS

Potassium and norepinephrine stimulate the accumulation of cyclic AMP and cyclic GMP in rat pineal glands and their efflux into the medium. The efflux of both cyclic nucleotides was blocked by probenecid. The accumulation and efflux of cyclic GMP, but not of cyclic AMP, depends upon the presence of intact nerve endings and extracellular calcium. The calcium-dependent release of norepinephrine caused by veratridine was accompanied by the efflux of both cyclic AMP and cyclic GMP. In contrast, the calcium-independent release of norepinephrine caused by tyramine was accompanied by the efflux of cyclic AMP but not cyclic GMP. Changes in cyclic GMP therefore, may be related to exocytosis from the sympathetic nerve endings in the gland. High concentrations of potassium also increased tissue levels of cyclic GMP in the posterior pituitary gland. Veratridine and potassium, but not norepinephrine, stimulated the efflux of cyclic GMP from this neurosecretory gland. Thus, the relationship between cyclic GMP and exocytosis may extend beyond sympathetic nerve endings. The enhanced accumulation of cyclic GMP in the pineal gland after potassium does not appear to be mediated by extracellular (released) norepinephrine. Desmethylimipramine blocked the norepinephrine-stimulated changes in cyclic GMP, but not those caused by potassium. Investigation of the possible relationship between cyclic GMP and release of neurotransmitters is complicated by the apparent seasonal variation in the response of pineal cyclic GMP to potassium or norepinephrine.     

Results of blind testing a method to detect carriers of the Duchenne muscular dystrophy gene.

We blind-tested a method that in earlier studies had shown increased leucine uptake in muscle fibers of biopsy specimens from three obligate carriers and seven of 11 putative carriers of the gene for Duchenne muscular dystrophy. Here, muscle samples obtained at biopsy in seven obligate carriers and nine control subjects from Brazil were examined in Canada without knowledge of the carrier status or serum enzyme concentrations. Leucine uptake was increased in four controls and within normal range in four carriers, a rate of false-positives and -negatives that underscores the need for blind-testing methods for detecting carriers of this disease.     

A new method for the analysis of age trends in CPK levels with application to Duchenne muscular dystrophy.

Measurement of serum creatine phosphokinase (CPK) is the most commonly applied test for carrier detection in Duchenne muscular dystrophy. About two thirds of all carriers have markedly elevated CPK levels. Age correction of CPK measurements would be straightforward if carriers of all ages could be unambiguously identified. Since such identification is impossible, we elaborate an indirect statistical method which is based on Haldane's theory of the balance between selection and mutation for X-linked lethals. We also apply this method to a large body of data gathered on female relatives of Duchenne muscular dystrophy patients and on controls. The results are compared with earlier partial findings.     

Melatonin rhythms: Trekking toward the heart of darkness in the chick pineal

Chick pineal cells make melatonin rhythmically, even in culture. Light pulses have two effects on these cells: acute suppression of melatonin synthesis and phase shifts (entrainment) of the underlying pacemaker. The two effects use different mechanistic pathways: the first goes through cAMP, and the second goes through the clock. Both converge on serotonin N-acetyltransferase, whose gene has recently been cloned, with cAMP acting on mRNA levels, but primarily on, enzyme activity, and the clock acting primarily on mRNA levels. Aspects of calcium regulation, not yet well-understood, may impinge on both pathways. These cells also have a novel calcium channel and a novel photopigment.