Preovulatory spike bursts in hen uterus.

The changes in uterine contraction (UC) in relation to ovulation were studied by recording electrical activity of the uterus in conscious laying hens. The frequency of electrical activity remained low for several hours after oviposition of the terminal egg (Ct) of a clutch, but was elevated for about 5 h and showed a transient peak about 1 h before ovulation of the first egg (C1) of the succeeding clutch. The phase of this frequency pattern was advanced when premature ovulation was induced by progesterone injection. The time of the phase shift was about 6 h, which was coincident with the interval between spontaneous and premature ovulations. In contrast, such a frequency pattern was not observed when the C1 ovulation was interrupted by ligation of the stalk of the largest preovulatory (F1) follicle. Neither ligation of the stalk of the second largest preovulatory (F2) follicle nor section of the oviduct affected the C1 ovulation or occurrence of the preovulatory frequency pattern of UC. These results suggest a specific relationship between the preovulatory changes in UC and ovulation.