An electromyographic study of uterotubal activity in the ewe.

The electrical activity of the oviduct and uterus was automatically registered on a potentiometric pen recorder in ewes fitted with an extracellular multielectrode assembly. The duration and amplitude of local non-propagating activity of the uterus increased and became progressively grouped into phases as natural oestrus progressed. Phases of contractions lasting 5-6 min were initially propagated at a rate of 2/hr. Their frequency increased within 24 hr of the decline in plasma progesterone levels. Grouped activity was then resumed for the next 24 hr. Similar changes were seen in the activity of the oviduct although this region was active earlier in oestrus. The uterotubal activity developed in the same way 24 hr after withdrawal of a progestagen-impregnated sponge but lasted for 3 days. When another oestrus was induced by injection of a prostaglandin analogue, the activity patterns were qualitatively similar although they did not start until 36 hr after injection and lasted for only 2 days.