Edward T. Knych

Effect of Amphetamine on Plasma Corticosterone in the Conscious Rat

The effect of amphetamine (AMPH) on plasma corticosterone was studied in the conscious, unstressed rat. AMPH (0.5-5.0 mg/kg) produced a dose-dependent increase in plasma corticosterone. This rise in plasma corticosterone was not altered by the adrenergic blocking agents phenoxybenzamine or propranolol. In contrast, the serotonergic depleting agent p-chloroamphetamine significantly inhibited the AMPH-induced rise in corticosterone. In addition, the serotonergic blocking agent methysergide, but not cyproheptadine, inhibited the corticosterone increase induced by AMPH.

Effect of chronic intoxication and naloxone on the ethanol-induced increase in plasma corticosterone

Abstract Ethanol (0.5–4.0 g/kg) induced an immediate, dose-dependent rise in plasma corticosterone in the conscious, undisturbed male rat. Chronic intoxication for at least two days resulted in tolerance to this effect. Chronic intoxication also significantly elevated the morning trough levels of this steroid. Co-administration of naloxone (1 mg/kg) prevented the development of tolerance to the immediate stimulatory effect of ethanol but did not alter the elevated trough levels of corticosterone. Naloxene (1 mg/kg) did not alter the stimulatory effect of ethanol on corticosterone in ethanol-naive animals. These data suggest that the process of tolerance development to the ethanol-induced rise in corticosterone is mediated by an opiate receptor. Alterations in the ability of ethanol to stimulate corticosterone secretion may be a useful endpoint for future studies of tolerance development to ethanol.

Tolerance to ethanol-induced contractions of vascular smooth muscle: Role of endothelium

Ethanol, at high concentrations, produced a dose-dependent contraction of male rat aortic rings, in vitro. Mechanical removal of endothelial cells from aortic rings of control rats resulted in a small, but significant, shift of the ethanol dose-response curve to the right without a change in the maximal contraction. Removing the endothelial cells of aortic rings obtained from rats intoxicated with ethanol for two days significantly shifted the ethanol dose-response curve to the left and significantly increased the maximal contraction induced by ethanol. A comparison of the ethanol dose-response curves in aortic rings with endothelium obtained from control rats with those obtained from intoxicated rats indicated a significant shift to the right with no change in maximal response. No significant changes were observed when the responses of aortic rings without endothelium obtained from control and intoxicated rats were compared. These observations confirm that tolerance to ethanol can be demonstrated in vascular smooth muscle. In addition, they demonstrate that the endothelium is required for the development of tolerance to ethanol in the aorta.

Endothelium-dependent transfer of ethanol tolerance in the aorta.

Recent studies have suggested that the endothelium-dependent tolerance to the direct vasoconstrictor effect of ethanol in the rat aorta is mediated by endothelium-derived relaxing factor (EDRF). This hypothesis was tested directly by employing a sandwich technique which has been used to demonstrate the release and action of EDRF. These experiments measured the ethanol-induced contraction of a spirally-cut aortic strip without endothelium obtained from an ethanol naive control rat. The response of the spiral strip was measured before and after it was sandwiched with a longitudinally-cut aortic strip with or without endothelium obtained from either control or ethanol tolerant rats. There was no significant difference in the ethanol-induced contraction of the spiral strip after beginning sandwiched with a longitudinal strip with or without endothelium obtained from a control rat or with a longitudinal strip without endothelium from a tolerant rat. In contrast, when a longitudinal strip with endothelium from a tolerant rat was sandwiched with the spiral strip the ethanol-induced contraction was significantly reduced. This effect was inhibited by methylene blue but not by indomethacin. Further, the magnitude of the carbachol-induced relaxation of the sandwiched preparation was significantly greater when the longitudinal strip with endothelium was obtained from a tolerant rat than from control rat. These data demonstrate the involvement of EDRF in the endothelium-dependent tolerance to ethanol in the rat aorta.

Effect of fluoxetine and metergoline on amphetamine-induced rise in plasma corticosterone.

Abstract The effect of the serotonin reuptake inhibitor, fluoxetine, and the serotonin antagonist, metergoline, on the rise in plasma corticosterone induced by amphetamine was studied in the conscious, unrestrained rat. Fluoxetine (2.5 mg/kg) did not affect plasma corticosterone. However, this dose of fluoxetine when administered two hours prior to amphetamine (0.1 or 0.5 mg/kg) significantly potentiated the amphetamine-induced rise in plasma corticosterone. Fluoxetine had no effect on the response induced by the highest dose of amphetamine (1.0 mg/kg) utilized in the study. In contrast, metergoline produced a dose-dependent increase in plasma corticosterone over the range 0.1 – 5.0 mg/kg. This response reached maximum 30 minutes after drug administration and had a duration of approximately 120 minutes. Pretreatment of animals with metergoline (5.0 mg/kg) three hours before the administration of amphetamine (1.0 mg/kg) resulted in a significant decrease in the corticosterone rise induced by amphetamine. Lower doses of metergoline were ineffective in reducing the amphetamine-induced response. These observations support the hypothesis that the amphetamine-induced rise in plasma corticosterone is due, in part, to stimulation of serotonergic neurons.

Cross-tolerance between ethanol and levorphanol with respect to stimulation of plasma corticosterone

Male rats chronically intoxicated with ethanol for at least two days were tolerant to the ethanol-induced stimulation of hypothalamic-pituitary-adrenal axis. Chronically intoxicated rats also were tolerant to stimulation of this axis by levorphanol but not by amphetamine or ether. In a similar manner, animals treated with levorphanol for two days were tolerant to stimulation of the hypothalamic-pituitary-adrenal axis by either levorphanol or ethanol. These observations provide further support for the hypothesis that endogenous opioids may be involved in the development of tolerance to ethanol.

Anti-inflammatory Agents

Descriptions of inflammation are found in the earliest medical records of civilization. The Greeks referred to it as phlogsis and the Romans as inflammatio. Cornelius Celsus (c. 30 b.c.e. to 38 c.e.) is generally given credit for describing the four cardinal signs of inflammation as rubor et tumor cum calore et dolore: redness and swelling with heat and pain. This nonspecific response of tissues is induced by diverse insults or stimuli. Most observations suggest that the inflammatory response is a beneficial reaction of tissues to injury, leading to removal of the inducing agent and repair of the injured tissue. However, if the stimulus persists, the process may become chronic and produce permanent tissue damage or inappropriate healing.

Effect of Acute and Chronic Ethanol on Nonadrenergic, Noncholinergic Neurotransmissiona

The anococcygeus muscle (ANO) is innervated by inhibitory nonadreneqc, noncholinergic neurons (NANC). Recent studies suggest that the neurotransmitter which mediates relaxation induced in the A N 0 by NANC stimulation is nitric oxide (NO) or by a substance which releases NO.l.2 Ethanol inhibits the action of endotheliumdependent vasodilators whose action is mediated by the release of NO.3 This study was therebre designed to investigate the effect of acute and chronic ethanol administration on NANC-induced relaxation of the rat ANO. Male Sprague-Dawley rats weighing 350-400 g were used in this study. All protocols were approved by the University Animal Care and Use Committee. Chronic ethanol administration consisted ofthe oral administration ofethanol twice daily for 2 days according to Majchrowicz.4 This treatment protocol produces tolerance to ethanolinduced changes in plasma corticosterone, body temperature, and ethanol-induced contraction of the rat a o ~ t a . ~ . ~ The A N 0 was removed from either ethanol-naive control or chronic ethanol-treated tolerant rats after sacrifice with ether. The muscle was mounted between platinum electrodes in a 10 ml muscle bath containing Krebs Ringer bicarbonate buffer, p H 7.4, at 37OC and aerated with 95% 02:5% COz. It was equilibrated at an initial tension of 1 g fbr 45 min. Guanethidine (20 pM) was added to contract the muscle and to block any further release of norepinephrine. When the contraction stabilized a frequency-response curve was generated by transmurally stimulating the NANC nerves at varying frequencies (0.5-16 Hz) for 20 seconds every 2 min. The frequencies were randomly varied in each experiment. In those experiments designed to study the effect of ethanol on NANGinduced relaxation of the ANO, the NANC nerves were stimulated at 2 Hz b r 20 seconds every 2 min until a stable response was obtained. At this time ethanol was added in cumulatively increasing concentrations. The response to nerve stimulation was allowed to equilibrate bebre each addition of ethanol. The concentration of ethanol which produced a 50% decrcase (ECw) in the relaxation induced by nerve stimulation in the absence of ethanol was determined using linear r e p i o n analysis. Mean responses of control and ethanol-tolerant A N 0 were compared using repeated measure ANOVA or unpaired student t-test, as appropriate. A p 4 0.05 was considered significant. Initial experiments confirmed previous observations1.2 that the relaxation induced