In-vivo myometrial electrical activity in the cyclic mare.

The research paper discusses how uterine electromyography in mares varies throughout their oestrous cycles and after injection with fluprostenol, a hormone-regulating drug. They observed three different patterns of myometrial electrical activity each corresponding with a different stage of the cycle, oestrus, dioestrus, and luteolysis. Plasma progesterone levels were found to be associated with these changes in electrical activity. Furthermore, they observed that any non-specific environmental stimulus, like insemination during oestrus or injection of fluprostenol during dioestrus led to a notable increase in myometrial electrical activity, although typically short-lived.

Research Methodology

In this study:

• The researchers performed uterine electromyography, a technique for recording the electrical activity of the myometrium or the uterine muscle, on three Pony mares using chronically implanted surface electrodes.
• This was done during their natural oestrous cycles and after their luteolysis was induced by a prostaglandin analogue, fluprostenol.
• The mares’ progesterone and inconjugated oestrogen levels were also monitored.

Observations and Findings

The researchers identified three distinct patterns of myometrial electrical activity:

• During oestrus, they observed phases of well-defined and intense activity separated by periods (10-45 min) of total inactivity.
• During dioestrus, they saw more diffuse and less intense phases of activity, separated by variable periods of relative inactivity.
• In the luteolysis phase and 1-3 hours post-fluprostenol injection, they noticed short, frequent phases of activity between the electrodes on one uterine horn.

They also found a close correlation between levels of progesterone in the plasma and the characteristics of myographic activity during the cycle. However, this was not the case with total inconjugated estrogen levels.

Effects of External Stimuli

The researchers discovered that non-specific environmental stimuli, such as insemination during oestrus or fluprostenol injection during dioestrus, led to a significant and prolonged increase in myometrial electrical activity. Other types of stimuli, including per-rectal palpation of the genital tract and vaginoscopic examination, also caused an increase, albeit brief, in myometrial electrical activity. Typically, the normal pattern of activity was quickly reestablished after these manipulations.