Abstract
Summary
S-Adenosylmethionine: guanidinoacetate N-methyltransferase activities were determined in livers from rats after removal of either adrenals, pituitaries, gonads, or thyroids and parathyroids and in livers from intact rats given large doses of either insulin, estradiol, testosterone, cortisol, thyroxine, or growth hormone. The only differences that were statistically significant (p < 0.01) were between the activities of livers from intact rats and the slightly lower (~20%) activities of livers from rats with their thyroid and parathyroid glands removed or from intact rats given large doses of either testosterone, thyroxine, or growth hormone. Further, liver GA-methyltransferase activities were virtually unaffected by replacement of either thyroxine to thyroidectomized rats, growth hormone to hypophysectomized rats, or testosterone or estradiol to castrated rats. Therefore, direct hormonal regulation of rat liver GA-methyltransferase is contraindicated. Thus, the second enzyme involved in creatine synthesis (GA-methyltransferase) differs greatly from the first enzyme (arginine: glycine transamidinase) in that transamidinase activities have previously been reported to be altered markedly by removal of certain endocrine glands or by injections of large doses of certain hormones into intact rats.
The authors thank Neil Derechin for technical assistance.
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