Growth promotion by silk sutures in the urinary bladder of rat

A silk suture in the urinary bladder of rats induces tumorous growths of urothelia. Whether these tumorous growths are due to initiation or due to promotion by the suture remains unknown. A 3-O silk suture was therefore placed in the bladders of rats for 4 or 8 weeks. After removal of the suture and a period of recovery, the bladders of these and sham-operated control rats were exposed to N-methyl-N-nitrosourea (MNU) in order to examine whether the effects of the suture were reversible following its removal from the bladder. In addition, the bladder mucosa was exposed to either MNU or Ringer's solution followed by placement of the silk suture in the bladder wall in order to examine promotor activity of the suture. The tumor incidence induced by MNU was little influenced by the prior temporary placement of the suture in the bladder wall, thus indicating a reversibility of the effects of the suture. The placement of the silk suture in the bladder wall that had a prior exposure to MNU resulted in a significant incidence of invasive tumors. All these results are consistent with the fact that a silk suture in the bladder acts as a promoter but not as an initiator.