Showing papers by "Stephen Brimijoin published in 1971"

Effects of 6-hydroxydopamine on the activity of tyrosine hydroxylase and dopamine- -hydroxylase in sympathetic ganglia of the rat.

Abstract: Administration of 6-OH-dopamine daily for two days causes a nearly complete depletion of endogenous norepinephrine and a persistent, although not total, loss of activity of dopamine-β-hydroxylase from the heart. In adrenal glands, 6-OH-dopamine administration increases the activity both of tyrosine hydroxylase and dopainine-β-hydroxylase without affecting catecholamine levels. In both normally innervated and decentralized sympathetic ganglia, administration of 6-OH-dopamine causes no change in tyrosine hydroxylase activity and a long-lasting 50% decrease in dopamine-β-hydroxylase activity. Pretreatment with 6-OH-dopamine prevents reserpine-induced. increases in the activity of these enzymes in ganglia. A similar effect is also produced by surgical section of the postganglionic axons of the superior cervical ganglion.

Reserpine-induced release of norepinephrine from isolated spontaneously beating guinea-pig atria

Abstract: In a series of experiments on isolated spontaneously beating guinea-pig atria, acutely administered reserpine had dual chronotropic effects. A rate-lowering effect appeared to be exerted directly on the pacemaker, while a rate-increasing effect depended on the release of physiologically significant amounts of norepinephrine. Inhibition of monoamine oxidase simultaneously increased norepinephrine release 5-fold and antagonized norepinephnine depletion. It was calculated that no more than 7% of the depletion in atria from unpretreated animals could have represented escape of free norepinephrine, while 93% or more must have represented degradation by monoamine oxidase.