The biological activity of cyclopropyl analogs of all-trans- and 13-cis-retinoic acid in the rat vaginal smear assay

The biological activity of a series of cyclopropyl analogs of all-trans- and 13-cis-retinoic acid has been evaluated in the vaginal smear assay carried out in vitamin A-deficient rats. These analogs were designed to probe the role of the 13-cis isomer in the actions of the parent all-trans-retinoic acid by blocking the interconversion of these two compounds. Although relatively less active, the potency of some of the cyclopropyl analogs suggests that 13-cis-retinoic acid is a fully active metabolite of all-trans-retinoic acid. Since 13-cis-retinoic acid represents a small percentage of the retinoic acid metabolites, the physiological significance of this activity is still unclear. Possible reasons for the reduced activity of the cyclopropyl analogs, as well as an aromatic analog of retinoic acid, are discussed.     

1H nuclear magnetic resonance studies of the conformations of vitamin D compounds in various solvents

Using proton NMR, the solution conformation of the A ring of vitamin D3 and its analogs has been studied by application of the Karplus relation to the observed coupling constants. The A-ring conformations of vitamins D3, D2, and 25-hydroxyvitamin D3 were found to be solvent dependent, with a clear preference for an equatorial hydroxyl group in polar solvents such as methanol and dimethyl sulfoxide. Conversion of the hydroxyl group to an acetate did not affect solution conformation appreciably, but the corresponding t-butyl-dimethylsilyl ether derivative of vitamin D3 showed a strong preference for the 3 beta-equatorial conformer. The A-ring conformation of the active hormone, 1,25-dihydroxyvitamin D3, which has two hydroxyl groups competing for the equatorial position, was found not to be solvent-dependent.     

A glia-derived neurite-promoting factor with protease inhibitory activity.

Brain cells and glioma cells in culture release a protein which induces neurite outgrowth in neuroblastoma cells. This neurite-promoting factor (NPF), which has been purified from serum-free glioma conditioned medium, has an apparent mol. wt. of 43 000. NPF inhibits urokinase as well as plasminogen activator-dependent caseinolysis or fibrinolysis. NPF and urokinase form an SDS-resistant complex. The fact that this glia-derived NPF is a potent protease inhibitor indicates that glial cells modulate the proteolytic activity associated with neuronal cells and suggests that this phenomenon is one of the biochemical events involved in the regulation of neurite growth.     

Support of embryonic chick survival by vitamin D metabolites

The provision of 1,25-dihydroxyvitamin D3 as the only source of dietary vitamin D3 to laying hens failed to support normal embryonic development in their fertile eggs. Significant (P less than .001) improvement in embryonic survival to hatching in these eggs resulted from injections of 1,25-dihydroxyvitamin D3, 24,25-dihydroxyvitamin D3, 25-hydroxyvitamin D3, or 24,24-difluoro-25-hydroxyvitamin D3 prior to incubation. Maximum embryonic survival with lowest embryonic mortality was observed when 0.20 micrograms/egg of 1,25-dihydroxyvitamin D3 or 0.60 micrograms/egg 25-hydroxyvitamin D3 was injected. These results indicate that several forms of vitamin D, two of which cannot be converted to 24,25-dihydroxyvitamin D3, can provide this activity; and of the vitamin D compounds tested, 1,25-dihydroxyvitamin D3 may be the most active in supporting embryonic survival in the chick when delivered directly by injection.     

Studies on the site of 1,25-dihydroxyvitamin D3 synthesis in vivo

Anephric, vitamin D-deficient male rats were injected with a physiologic dose of 25-hydroxy[26,27-3H]vitamin D3 (specific activity of 160 Ci/mmol), and 18-20 h later, intestine, bone, and serum were analyzed by high performance liquid chromatography for 1,25-dihydroxy-[26,27-3H]vitamin D3. Identical studies were carried out using sham-operated rats and rats with ligated ureters. No 1,25-dihydroxy[26,27-3H]vitamin D3 was detected in the tissues from anephric rats, while large amounts were detected in sham-operated and ureteric ligated controls. This result demonstrates that in the nonpregnant rat, 1,25-dihydroxyvitamin D3 is either not synthesized or is synthesized in vanishingly small amounts in bone and intestine in vivo, casting considerable doubt of the physiological importance of reports of in vitro synthesis of 1,25-dihydroxyvitamin D3 by cells in culture derived from bone and elsewhere.