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1. A single dose of pentazocine induces cross-tolerance the analgesic effects of the kappa agonist U 50488H. Tolerance is observed by means of the hot plate test or by the i.p. administration of acetic acid 6 or 24 hr after the priming dose, respectively. 2. The administration of the calcium channel antagonists, diltiazem, nifedipine or verapamil, reduces the degree of tolerance as assessed by the hot plate test or acetic acid administration. 3. The adenosine agonist N6-cyclopentyl adenosine significantly reduced the intensity of the process; in contrast, N6-cyclohexyladenosine antagonized the analgesic response to the opiate obscuring its influence on the process. 4. The results are discussed in relation to the interaction of calcium channel function in the analgesic response to the kappa opiates.

1. The chronic toxicity of pentachlorophenol (PCP) was studied in rats after 90-120 days of oral administration ad libitum of 0.3-3 mM PCP aqueous solutions. 2. Morphological studies of their sciatic nerves were performed by optical and electron microscopy. 3. They showed degenerative changes in about 10% of the A and B type of nerve fibers. 4. The myelin sheath was discontinued by complete separation in several concentric rings while some other parts of the nerve exhibited a variable loss of neurotubules, neurofilaments and other axoplasmic components. 5. However, the C type of nerve fibers, the blood vessels and the perineurium did not show any morphologic alteration. 6. It was also found that in the liver PCP caused hemodynamic vein changes and injury in the hepatocytes such as cellular swelling and vacuolar degeneration. 7. The damage in the kidney occurred primarily in the glomeruli and secondarily in the proximal tubules causing turbid tumefaction and the formation of casts in the tubular lumen.