The kinin system and ovulation: changes in plasma kininogens, and in kinin-forming enzymes in the ovaries and blood of rats with 4-day estrous cycles

Abstract

Rats with 4-day estrous cycles showed a 51% fall in plasma kininogen in early proestrus (1200–1500). Levels remained depressed throughout ovulation, and then recovered steadily. The initial fall corresponded well with the LH surge. Initial attempts were made to detect enzymes which might be responsible for the change. Kinin-forming enzymes, in either precursor or active forms, were absent from the ovaries in diestrus, but appeared at the onset of the fall in kininogen (kinin-forming activity, 2.87 ± 0.83 ng bradykinin (BK) equiv.∙g wet tissue−1∙min−1). They rose 10-fold just before ovulation, and then declined rapidly. This major peak, and a corresponding one in plasma, may have reflected the presence of follicular proteases. Plasma kinin-forming enzymes showed no apparent change when the kininogen first declined. They then disappeared, suggesting a more delayed activation and destruction. It seems possible that LH induces kinin-forming enzymes in the ovaries, and induces a later activation of plasma enzymes, to produce kinins which may be involved in vascular and permeability changes important in ovulation, and perhaps concerned in the mechanisms of positive feed-back with the pituitary.