Synthesis of cytochrome P-450 heme in ascorbic acid-deficient guinea pigs

Ascorbic acid deficiency in guinea pigs: contrasting effects of tissue ascorbic acid depletion and of associated inanition on status indices related to collagen and vitamin D

To investigate the sensitivity of guinea pig tissues to ascorbic acid depletion, as distinct from inanition, young male guinea pigs were maintained with either ascorbic acid restriction or total diet restriction for 8 weeks. One group (A) received no ascorbic acid for 3 weeks, then 0.5 mg/d for 5 weeks; one group (B) was weight-matched by restricted food intake to the first group; a third (marginally deficient) group (C) received 1 mg ascorbic acid/d throughout; a fourth was weight-matched to this group (D); and a fifth group received the control diet ad lib. (E). Both of the groups with restricted ascorbic acid intakes (A and C) developed very low tissue ascorbic acid contents, but only the first group (severely deficient group A) also exhibited a severely reduced growth rate. This group also exhibited reduced femur calcium and hydroxyproline contents and reduced skin hydroxyproline content. These changes were not seen in the corresponding weight-matched group (B). Neither plasma alkaline phosphatase (EC 3.1.3.1) activity, nor a variety of indices of vitamin D status exhibited changes which could be attributed specifically to reduced ascorbic acid intake and hence to lowered tissue ascorbic acid content. It is concluded that low tissue ascorbic acid levels in guinea pigs clearly alter the connective tissue composition of growing femur and skin, but do not necessarily produce a major, specific effect on vitamin D status. Moreover, the control of inanition is crucial to permit interpretation of the changes in metabolism that are caused by ascorbic acid deficiency.

Dietary ascorbic acid and hepatic mixed function oxidase activity in the guinea pig

Studies were carried out to characterize the response of hepatic mixed function oxidase (MFO) activity to chronic ascorbic acid deficiency and excessive ascorbic acid intake in the guinea pig. When guinea pigs were fed excessive ascorbic acid, there was a small increase in hepatic cytochrome P-450 which was unaccompanied by any alteration in drug-metabolizing enzyme activity. Similarly, induction of MFO activity by phenobarbital was not modified by excessive ascorbic acid administration. Chronic ascorbic acid deficiency resulted in depressed metabolism of aniline, aminopyrine, ethoxycoumarin and benzphetamine, but not of ethylmorphine, in comparison with animals fed diets containing control and/or excessive amounts of ascorbic acid. In contrast to the metabolism of all drugs studied, the 7 alpha-hydroxylation of cholesterol was depressed by both inadequate and excessive vitamin C intake, demonstrating the unique sensitivity of cholesterol 7 alpha-hydroxylase to dietary ascorbate.