Regulation of δ‐Aminolevulinic Acid Synthetase by Drugs and Steroids in vivo and in Isolated Perfused Rat Liver

Abstract

8-Aminolevulinic-acid-synthetase induction by drugs depends upon the nutritional state of the animal. I n allylisopropylacetamide-treated animals the enzyme induction is reduced in fed compared with starved rats whereas after phenobarbital treatment an induction of the enzyme seen in starved animals is not observed in fed rats. 8-Aminolevulinic-acid-synthetase induction is studied in relation to the synthesis of cytochrome P450.I n the isolated rat liver perfused with either rat blood or washed bovine erythrocytes and Eagle minimal essential medium, 8-aminolevulinic acid synthetase decreases sharply. This decrease can be prevented by the continuous addition of dexamethasone (9a-fluoro-l6a-methylpregna-1,4-diene-li,9,i7a,2l-triol-3,20-dione) or hydrocortisone (pregn-4-ene-l1,9,17a,21-triol-3,20-dione) but not by testosterone (androst-4-ene-178-01-3-one) or etiocholanolone (5P-androstan3a-ol-17-one). 8-Aminolevulinic acid synthetase cannot be significantly induced by allylisopropylacetamide unless corticoids are added to the perfusion medium. The results indicate that the synthesis of heme and, consequently, hemoproteins is controlled by corticoids or their metabolites in adult rat liver.Our interest in the mechanism(s) of cytochrome P450 induction by phenobarbital led us to the study of 8-aminolevulinic acid synthetase, because this rate limiting enzyme in heme biosynthesis is also induced rapidly and early after phenobarbital treatment [ I]. During hemoprotein formation heme and apoprotein synthesis have to be closely correlated if the intracellular heme pool is ony small. I n addition to phenobarbital, allylisopropylacetamide, the porphyria-producing moiety of the drug Sedormid, was studied as another compound affecting both enzymes-i. e. inducing d-aminolevulinic acid synthetase and, in contrast to phenobarbital, initially decreasing cytochrome P450 [2-41.I n the present study d-aminolevulinic-acid-synthetase regulation was investigated in livers in vivo and in the isolated perfused organ. The conditions for induction of the enzyme by allylisopropylacetamide and phenobarbital were first studied in intact rats.Since it was found that the induction of this enzyme by phenobarbital is a special event not seen in rats fed ad libitum, the studies in the isolated organ focusEnzyme. Tyrosine aminotransferase or L-tyrosine : 2-oxoglutarate aminotransferase (EC 2.6.1.5).Trivial Names. Etiocholanolone, 5B-androstan-3a-01-17-one; testosterone, androst-4-ene-17B-ol-3-one; hydrocortisone, pregn-4-ene-ll~,l7n,21-triol-3,20-dione; dexamethasone, 9a-fluoro-16a-methyl-pregna-1,4-diene-l1~,17a,21-triol-3,20-dione. sed on induction by allylisopropylacetamide. I n this system an induction comparable to that found in vivo could only be achieved after addition of corticoids to the perfusion medium. The dependence of8-aminolevulinic acid synthetase and consequently heme synthesis, upon corticoids will be discussed in relation to the induction of hemoproteins. I n addition, a model for 8-aminolevulinic-acid-synthetase induction by phe...

Tryptophan pyrrolase in haem regulation. The mechanism of the permissive effect of cortisol on the enhancement of 5-aminolaevulinate synthase activity by 2-allyl-2-isopropylacetamide in the adrenalectomized-rat liver

“…Administration of cortisol to starved shamoperated rats increased both holoenzyme and total pyrrolase activities by 50% (P=0.005-0.001) and did not therefore alter the haem-saturation ratio. Liver 5-aminolaevulinate synthase activity in fed rats is half of that in starved rats (Bock et al, 1971), and this is confirmed by our results with sham-operated animals ( Table 1). In agreement with the finding by Marver et al (1966), cortisol does not exert a significant effect on synthase activity in control (sham-operated) rats (Table 1), and this is consistent with the inability of the hormone to alter the haem-saturation ratio of tryptophan pyrrolase.…”

Regulation of σ-Aminolevulinic Acid Synthetase by Drugs and Steroids in Isolated Perfused Rat Liver

“…Enzymes were tested in liver homogenates. ALA synthetase was normally assayed with a radiochemical procedure according to Ebert et al [1970] and frequently checked by a colorimetric method as described in more detail in a previous publication [Bock et al, 1971]. Only the mi tochondrial form of the enzyme can be detected with our methods.…”

“…Unless otherwise indicat ed, food was withheld 24 h before hepatectomy. Livers were perfused with 70 ml Eagle minimal essential medium containing 25% bovine erythrocytes, 2% bovine serum albumin, and 0.1% heparin as previously described [Bock et al, 1971Matern et al, 1972]. Enzymes were tested in liver homogenates.…”

UDP‐glucuronyltransferase in Perfused Rat Liver and in Microsomes: Influence of Phenobarbital and 3‐Methylcholanthrene

“…In this report the perfused liver was chosen as a model for intact cells since in this (a) Absorption of a lipid-soluble substrate for UDPglucuronyltransferase (XOH); (b) enzyme reaction within the endoplasmic reticulum (UDP-GlcUA = UDP-glucuronic acid); (c) transport and secretion of glucuronides (X-GlcUA) into the bile and the blood or perfusate system an accurate time course and balance sheet of product formation can be established, while the cellular metabolism is close to that operating in vivo. The functional state of this model system has been previously characterized by its ability to synthesize albumin [l 11 and by the induction of enzymes [12]. 1-Naphthol was chosen as substrate since there are only two major pathways for its metabolism, leading to the glucuronide and sulfate conjugates 11 31.…”