Cerebrospinal fluid activity of dynorphin-converting enzyme at term pregnancy.

Cerebrospinal fluid activity of a dynorphin-converting enzyme transforming prodynorphin-derived peptides to [Leu]enkephalin-Arg6 was measured in 12 women at term pregnancy before cesarean section and in eight nonpregnant, nonpuerperal controls. In pregnant women, the dynorphin-converting enzyme activity was significantly lower (mean +/- SD 6.8 +/- 3.8 U/L) than in nonpregnant controls (11.7 +/- 2.6 U/L; P less than .01). Furthermore, prodynorphin-derived [Leu]enkephalin-Arg6-containing polypeptides were significantly increased in samples from pregnant women (P less than .05). This indicates that a reduced activity of opioid peptide-degrading enzymes might contribute to an increased resistance to pain at term pregnancy.