Abstract
Concentration-response curves for the blocking action of norepinephrine were determined in the isolated stellate ganglion of the hamster. The blocking effect of norepinephrine on the postganglionic compound action potential from preganglionic nerve stimulation at 0.2 Hz was reduced by phentolamine (10(-5) M), but was not altered by propranolol (10(-6) M). Cocaine (10(-6) and 10(-5) M) increased the sensitivity of the ganglion to norepinephrine. These concentrations of cocaine produced less than 25% blockade when applied alone. The local anesthetic, procaine, did not change the sensitivity of the ganglion to norepinephrine. The blockade by norepinephrine in the presence of cocaine was antagonized by phentolamine and unaffected by propranolol. The time course of the blockade by norepinephrine was more rapid in onset and slower in recovery in the presence of cocaine. If it is assumed that cocaine is blocking norepinephrine uptake into cells within the ganglion, these results indicate that the catecholamine uptake mechanism is involved in terminating the blocking action of exogenously applied norepinephrine.
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|