Hormonal regulation of adult sympathetic neurons: the effects of castration on tyrosine hydroxylase activity.

The effects of the hormone testosterone on neurotransmitter synthesis in peripheral sympathetic ganglia were examined in adult male Sprague-Dawley rats. Tyrosine hydroxylase (T-OH), the rate limiting enzyme in catecholamine biosynthesis was examined in the hypogastric (HG), coeliac (CG), and superior cervical ganglion (SCG) subsequent to castration. Initial studies indicated that 2 weeks after surgery, HG T-OH activity fell to approximately 30% of control. In order to more clearly define the pattern of testosterone effects, HG was examined 1, 2 and 4 weeks after surgery. T-OH activity was 67%, 50% and 11% of control at these 3 respective time points, and the observed alteration in T-OH activity appeared to parallel changes in the size of pelvic target organs. Similar hormonal effects did not occur in other peripheral sympathetic ganglia; T-OH activity was unchanged in SCG and CG when examined 1 month after castration. Enzyme activity was restored following replacement therapy with testosterone, whereas the neural metabolite 17-beta estradiol was without effect. The recovery in T-OH activity was associated with partial recovery of target organ size. These studies suggest that hormonal factors regulate neurotransmitter synthesizing enzymes in adult sympathetic neurons and may do so via consequences of alterations in target organs. These observations parallel similar events in the developing nervous system.