Rat liver DNA was treated in vitro with benzo[a]pyrene-diolepoxide (BPDE), the ultimate carcinogenic metabolite derived from the polycyclic hydrocarbon benzo[a]pyrene. On incubation of the reacted DNA, apurinic sites developed which gave rise to strand breakage in alkaline solution. The reduction in molecular weight produced by these breaks was measured by analytical ultracentrifugation. In the case of anti-BPDE this depurination was shown to occur in two stages. The first was mainly due to attack at the 7-position of guanine, to yield an adduct which was lost from the DNA within a few hours. The second stage was due to much slower loss of the major N2-guanine adduct. The separated enantiomers, (+)- and (-)-anti-BPDE, and syn-BPDE all caused depurination to various extents. It is argued that although these processes are important in a study of the action of BPDE on DNA in vitro, their contribution to the biological activity of BPDE is probably negligible.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMedDate not supplied

The bright pituitary gland--a normal MR appearance in infancy.

Signal intensities of the pituitary gland were measured on T1-weighted sagittal MR images of 25 patients younger than 20 years old. We found that the signal intensities in the eight patients who were 8 weeks old or younger were higher (shorter T1) than those in the 17 older patients. We also noted a difference in the signal intensities across the pituitary gland, the signal being higher in the posterior part of the gland than in the anterior part. We attribute the high signal intensities to the rapid intrauterine pituitary growth, so that at term pituitary protein synthetic activity is at a maximum. Possibly, an increase in the bound fraction of the water molecules of the gland may also be present in the neonatal pituitary as compared with the older gland, but this remains to be proved. The higher signal in the posterior pituitary gland may be due to lipid in the pituicyte cells of the posterior pituitary gland.

Adolescent↗