THE EFFECT OF ESTRADIOL AND OVARIECTOMY ON TYROSINE-HYDROXYLASE, TYROSINE AMINOTRANSFERASE AND PHENYLALANINE-HYDROXYLASE

Although the regulatory activity of steroid hormones on amino acid met abolism 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 liv er, kidney and urine. 32 animals were used in the study, 12 animals we re sham operated, 9 animals were ovariectomized and 11 rats were ovari ectomized and supplemented with estradiol. No quantitative changes wer e detected comparing liver and kidney phenylalanine and tyrosine betwe en the groups. The phenylalanine/tyrosine ratio in liver and urine of ovariectomized rats showed a significant decrease of the quotient, whi ch was restored by estradiol replacement, whereas the ratio was unaffe cted 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 ovarie ctomized with estradiol replacement. Tyrosine aminotransferase was in liver (0.004 +/- 0.002 U/h), kidney (0.01 +/- 0.002 U/h) in the sham o perated 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 (0.0 12 +/- 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 rat s with estradiol replacement. No significant difference in the enzyme activities between the groups was found. The impairment of the phenyla lanine/tyrosine ratio in liver could be assigned to an endocrine contr ol of amino acid uptake and/or transport, in the urine by different po ols, proteolytic and synthetic enzyme activities, filtration/reabsorpt ion effects.