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Response of Several Hepatic Adaptive Enzymes to a Shift from Low to High Protein Diet in Intact and Adrenalectomized Rats¹

McArdle Laboratory, University of Wisconsin Medical Center, Madison, Wisconsin 53706

Intact and adrenalectomized rats were shifted from a 12% to a 60% protein diet and the change in levels of tyrosine aminotransferase, serine dehydratase and glucose-6-phosphate dehydrogenase was followed for 9 days after the shift. Tyrosine aminotransferase activity increased greatly by 6 hours after the shift to the high protein diet, and oscillated daily thereafter. There was no difference in activity levels between intact and adrenalectomized rats until 6 days following the shift in diet when the peak level of tyrosine aminotransferase became slightly lower in the adrenalectomized rats. Serine dehydratase activity increased after the shift in diet but only following a 24- to 30-hour lag after which it increased daily during the fasting period, while TAT activity was declining. The differences in activity or rate of increase between the intact and adrenalectomized rats were of borderline significance. Glucose-6-phosphate dehydrogenase activity levels dropped at approximately the same rate in both intact and adrenalectomized rats following the shift in diet but the activity level in the adrenalectomized rats continued to drop to a lower final level than in the intact rats. The participation of the adrenal glands in the initial adaptation of these three enzymes to a 60% protein diet appears to be minimal or nonessential. However, the presence of the adrenals may be necessary in order to maintain the levels of some enzymes after the adaptation to the shift in diet is complete.

² Present address: Biochemisches Institut der Universität, Hermann-Herder Strasse 7, 78 Freiburg, Germany.

³ Person to whom reprint requests should be sent.

⁴ Career Development Awardee of the National Cancer Institute (CA-29,405).

Manuscript received 8 December 1970.