Effects of luteolytic doses of prostaglandin F2 alpha and cloprostenol on concentrations of progesterone, luteinizing hormone, follicle-stimulating hormone, glucose, insulin, growth hormone, thyroxine, prolactin and cortisol in jugular plasma of lactating dairy cows.

Three groups of five lactating dairy cows in the mid-luteal phases of oestrous cycles were given an injection (at time 0 h) of the naturally-occurring prostaglandin F2 alpha (PGF2 alpha) or cloprostenol (a synthetic analogue of PGE2 alpha) at doses recommended for inducing luteolysis, or injection vehicle. Concentrations of glucose and hormones in jugular plasma were measured from 26 h before to 12 h after the injections and the significance (P < 0.05) of the effects of the prostaglandins on these concentrations was determined. Both prostaglandins induced falls in progesterone concentration and rises in luteinizing hormone concentration; neither influenced follicle-stimulating hormone. PGF2 alpha increased glucose concentration; neither prostaglandin influenced insulin concentration. Both prostaglandins increased growth hormone concentration and resulted in declining thyroxine concentration. PGF2 alpha increased prolactin and cortisol concentration. There were, however, no significant differences between the effects of the two prostaglandins on any hormone (or glucose) concentration.