The effect of estradiol and ovariectomy on tyrosine hydroxylase, tyrosine aminotransferase and phenylalanine hydroxylase.

Although the regulatory activity of steroid hormones on amino acid metabolism has been described, no information is published on the effect of ovariectomy. We studied the influence of ovariectomy in Wistar rats determining the amino acids such as phenylalanine and tyrosine in liver, kidney and urine. 32 animals were used in the study, 12 animals were sham operated, 9 animals were ovariectomized and 11 rats were ovariectomized and supplemented with estradiol. No quantitative changes were detected comparing liver and kidney phenylalanine and tyrosine between the groups. The phenylalanine/tyrosine ratio in liver and urine of ovariectomized rats showed a significant decrease of the quotient, which was restored by estradiol replacement, whereas the ratio was unaffected in the kidney. Tyrosine hydroxylase was in liver (0.04 +/- 0.04 U/min), kidney (0.4 +/- 0.04 U/min) in the sham operated rats; liver (0.06 +/- 0.02 U/min), kidney (0.3 +/- 0.2 U/min) in ovariectomized and liver (0.07 +/- 0.055 U/min), kidney (0.4 +/- 0.1 U/min) in the ovariectomized with estradiol replacement. Tyrosine aminotransferase was in liver (0.004 +/- 0.002 U/h), kidney (0.01 +/- 0.002 U/h) in the sham operated panel; liver (0.005 +/- 0.001 U/h), kidney (0.01 +/- 0.004 U/h) in the ovariectomized and liver (0.005 +/- 0.002 U/h) and kidney (0.012 +/- 0.007 U/h) in the ovariectomized with estradiol supplementation. Phenylalanine hydroxylase was in liver (0.12 +/- 0.07 U/min), kidney (0.5 +/- 0.3 U/min) in the sham operated group; liver (0.19 + 0.16 U/min), kidney (0.5 +/- 0.2 U/min) in the ovariectomized and liver (0.15 +/- 0.09 U/min), kidney (0.4 +/- 0.2 U/min) in the ovariectomized rats with estradiol replacement. No significant difference in the enzyme activities between the groups was found. The impairment of the phenylalanine/tyrosine ratio in liver could be assigned to an endocrine control of amino acid uptake and/or transport, in the urine by different pools, proteolytic and synthetic enzyme activites, filtration/reabsorptioneffects.