Effects of polyamines on tyrosine hydroxylase activity in adrenals

The ability of polyamines (putrescine, spermidine, and spermine) to modify tyrosine hydroxylase (TH) activity was examined in crude or purified enzyme preparation and in adrenal tissue slices. Polyamines showed biphasic effects on TH activity in vitro at physiological pH 7.0, with an inhibitory effect at low concentrations (<1 mM) and a stimulatory effect at high concentrations. The degree of both inhibition and stimulation produced by polyamines at low and high concentrations, respectively, were proportional to the number of the amino group in the polyamines (putrescine < spermidine < spermine). The degree of inhibition by polyamines was much greater with purified enzyme than with crude enzyme preparations. Tyrosine hydroxylation in situ in adrenal tissue slices was stimulated by polyamines without inhibition at any concentrations tested. This evidence suggests that TH molecules in vivo could interact with polyamines or polyamine-like substances which inhibit the TH activity at physiological concentrations less than 1 mM.