Human liver morphine UDP-glucuronyl transferase enantioselectivity and inhibition by opioid congeners and oxazepam.

1. Morphine uridine diphosphate glucuronyl transferase (UDP-GT) was studied in human liver microsomes. The (-)- and (+)-morphine enantiomers were used as substrates and inhibitors, such as oxazepam and various opioid congeners were employed to characterize the different glucuronidation pathways. The kinetics of the oxazepam inhibition were studied in the rat liver. 2. The overall glucuronidation of (+)-morphine was higher than that of (-)-morphine. The morphine congeners tested, potently inhibited the formation of (-)-morphine-3-glucuronide ((-)-M3G), except for normorphine and codeine. The formation of (+)-morphine-6-glucuronide [+)-M6G) was potently inhibited by only dextromethorphan and (+)-naloxone. All drugs except normorphine inhibited the formation of (+)-M3G by 18-50%. 3. The metabolism of (-)-morphine to (-)-M3G was more sensitive to oxazepam inhibition than the formation of (+)-M3G from (+)-morphine in the rat liver. 4. The glucuronidation of natural morphine is subject to in vitro interaction with oxazepam and several opiate drugs. Our study supports the theory of more than one type of UDP-GT being involved in morphine glucuronidation.

Glucuronidation of morphine and six beta 2-sympathomimetics in isolated rat intestinal epithelial cells.

The metabolism of morphine and six beta 2-sympathomimetics (orciprenaline, terbutaline, fenoterol, salbutamol, ritodrine, and bamethan) in isolated rat intestinal epithelial cells was investigated. Only conjugates with glucuronic acid were detected. With regard to observed Vmax values the beta 2-sympathomimetics can be divided in two groups. The three resorcinols (orciprenaline, terbutaline, fenoterol) have a Vmax value comparable to that of morphine (70-230 pmol/min X mg cell protein). The phenolic beta 2-sympathomimetics (salbutamol, ritodrine, bamethan) exhibit a Vmax value comparable to the Vmax value of 1-naphthol (500-1100 pmol/min X mg cell protein). Calculation of intestinal intrinsic (metabolic) clearance and intestinal first pass extraction ratios from Vmax and Kappm values suggests that most of these drugs may undergo substantial intestinal first pass metabolism after oral administration. The glucuronidation of morphine in isolated mucosal cells could be completely inhibited by addition of 1-naphthol (50 microM), salicylamide (5 mM), or fenoterol (5 mM). Glucuronidation of fenoterol could be partially inhibited by 1-naphthol, salicylamide, and morphine. Preliminary data obtained with microsomes suggest that 1-naphthol and morphine are metabolized by different forms of the intestinal microsomal UDP-glucuronosyltransferase. Fenoterol and ritodrine are probably glucuronidated by the form, which also glucuronidates morphine. The results demonstrate that rat intestinal epithelial cells can be used to predict intestinal metabolism of morphine and other drugs at least qualitatively and that phenolic food constituents (e.g. 1-naphthol) and non-prescription drugs (e.g. salicylamide) may affect the intestinal first pass metabolism of morphine and fenoterol.

Biosynthesis of morphine alkaloids in Papaver bracteatum Lindl.

Administration of 1-3H-N-methyl-14C-(+/-)-reticuline to Papaver bracteatum gave good incorporation of carbon-14 into thebaine and a decrease in the tritium to carbon-14 ratio indicative of racemization. The incorporation of carbon-14 and the extent of tritium loss were the same whether reticuline was administered to the intact plant or to isolated leaves. Carrier dilution with cold codeine, codeinone, and morphine showed only insignificant incorporation of radioactivity into codeine and none at all into codeinone and morphine. When codeinone was administered to the living plant, it was converted to codeine rapidly and efficiently, but no O-demethylation to morphine could be detected. The experimental data indicate that the biosynthesis of thebaine in P. bracteatum proceeds by the same pathway as in the opium poppy. The limiting step in the sequence is the demethylation of the enol ether group of thebaine to neopinone.