The Journal of pharmacology and experimental therapeutics
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The effects of opioids on testicular function were assessed in the rat through measurements of serum testosterone levels, testicular interstitial fluid (TIF) formation and TIF testosterone levels after morphine and opioid antagonist (naloxone, naltrexone) treatment. Serum and TIF levels of testosterone were significantly decreased 1 to 6 h after morphine (10 mg/kg) injection, and TIF volumes were decreased 2-3 h after injection morphine. Each of these decreases was dose-related. ⋯ Our results, therefore, indicate that morphine exerts effects on testicular function that are independent of its effects on LH. They furthermore support the hypothesis that both endogenous and exogenous opioids disrupt two major aspects of testicular function: Testosterone secretion and TIF formation. Because of the role of TIF in maintaining testicular function, our results suggest that opioid-induced changes in testosterone secretion into TIF and TIF formation may, at least in part, explain the well-established effects of opioids on reproductive endocrinology and function in the male.
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J. Pharmacol. Exp. Ther. · Jul 1993
Characterization of the antinociception produced by intrathecally administered muscarinic agonists in rats.
The present study was designed to characterize the antinociception produced by the administration of a potent muscarinic agonist into the intrathecal space of the lumbar spinal cord of male Sprague-Dawley rats. Seven days after surgical implantation of intrathecal catheters, animals were injected with graded doses of (+)-cis-methyldioxolane. (+)-cis-Methyldioxolane produced hot-plate and tail-flick antinociception for up to 90 min, peaking 5 to 30 min after injection. The dose of (+)-cis-methyldioxolane that inhibited nociception by 50% was 12 nmol in both the hot-plate and tail-flick tests. ⋯ Intrathecal pretreatment with graded doses of prazosin or naloxone enhanced the antinociception produced by (+)-cis-methyldioxolane in the tail-flick but not the hot-plate tests. Intrathecal vehicle, S(-)-propranolol or mecamylamine did not alter (+)-cis-methyldioxolane-induced antinociception. The data suggest that the antinociceptive responses produced by intrathecally administered (+)-cis-methyldioxolane involve the stimulation of muscarinic M1 and/or M2 cholinergic receptors, and may also involve activation of alpha-2 adrenergic, 5-hydroxytryptamine1c/2 and 5-hydroxytryptamine3 serotonergic receptor systems at the level of the lumbar cord.