Metabolism and biologica.

24R,24,25-Dihydroxyvitamin D3 is capable of inducing a minimal intestinal calcium transport response in chicks when compared to an equal amount of 25-hydroxyvitamin D3. 1,24,25-Trihydroxyvitamin D3 is also less active than 1,25-dihydroxyvitamin D3, and its activity is much shorter lived than that of 1,25-dihydroxyvitamin D3. A comparison of the metabolism of 25-hydroxy[26,27-3H]vitamin D3 and 24,25-dihydroxy[26,27-3H]vitamin D3 in the rat and chick shows that 24,25-dihydroxyvitamin D3 and 1,24,25-trihydroxyvitamin D3 disappear at least 10 times more rapidly from the blood and intestine of chicks. Furthermore, examination of the excretory products from both of these species demonstrates that chicks receiving a single dose of 24,25-dihydroxy[26,27-3H]vitamin D3 excrete 66% of the total radioactivity by 48 hours, whereas rats receiving the same dose excrete less than one-half that amount. These results demonstrate that 24,25-dihydroxyvitamin D3 is considerably less biologically active in the chick than in the rat, probably due to more rapid metabolism and excretion.     

Metabolism of pyrimidine L-nucleosides.

The intraperitoneal application of L-nucleosides (L-Cyd, L-Urd, L-dThd) to mice results in distribution of these compounds into tissues of the organism and their gradual excretion in the unchanged form. The residual level has been observed with L-ribonucleosides only and contains in addition to the L-nucleoside its 5'-phosphate. The phosphorylation in vivo is catalyzed by nucleoside-kinase and utilizes ATP as the phosphate donor while glycerol 1-phosphate and creatine phosphate are inactive. The L-cytidine derivatives are in vivo deaminated to the derivatives of L-uridine. On the other hand, when L-uridine is applied in vivo, derivatives of L-cytidine are obtained on the level of both the nucleoside and 5'-ribonucleotide.     

Metabolism of verruculogen in rats.

Radiolabeled verruculogen was detected in a wide range of body tissues 6 min after intravenous administration, but after a further 20 min it was mainly being excreted via the biliary route. In isolated liver perfusion, [14C]verruculogen was rapidly taken up by the liver and metabolized completely, principally to the related tremorgen TR-2 but also to a desoxy derivative of verruculogen. In addition, a smaller amount of an isomer of TR-2 was detected. These metabolic products were excreted in the bile.     

Metabolism of prostacyclin in rat.

Following a single intravenous administration of [11-3H]prostacyclin in rat, 77% of the administered dose was excreted within 3 days with 33% in urine and 44% in feces. Urinary metabolites were accumulated by chronic intravenous infusions of [11-3H]prostacyclin for 14 days. The drug was extensively metabolized and the structures of seven metabolites were elucidated by combined gas chromatography and mass spectrometry. The urinary products include the dinor and 19-hydroxy dinor derivatives of 6-keto-PGF1alpha and 13,14-dihydro-6,15-diketo-PGF1alpha, omega-hydroxy and omega-carboxyl dinor derivates of dihydro-6,15-diketo-PGF1alpha, and a dihydrodiketotetranordicarboxylic acid. The metabolic pathways of PGI2 in rat are similar to that of PGF2alpha.     

Metabolism of brassinosteroids in plants.

Brassinosteroids represent a class of plant hormones. More than 70 compounds have been isolated from plants. Currently 42 brassinosteroid metabolites and their conjugates are known. This review describes the miscellaneous metabolic pathways of brassinosteroids in plants. There are some types of metabolic processes involving brassinosteroids in plants: dehydrogenation, demethylation, epimerization, esterification, glycosylation, hydroxylation, side-chain cleavage and sulfonation. Metabolism of brassinosteroids can be divided into two categories: i) structural changes to the steroidal skeleton; and ii) structural changes to the side-chain.