Anaesthesia with alphaxalone plus alphadolone acetate blocks the oestrogen-stimulated LH surge and impairs pulsatile LH secretion in ovariectomized female rats

Two experiments were undertaken to assess further the action of the steroid anaesthetic alphaxalone upon LH secretion in chronically ovariectomized female rats. For the first experiment, 31 rats were given two injections of oestradiol benzoate (20 micrograms/100 g body weight), each 72 h apart, to stimulate an LH surge 6 h after the second injection. However, one group of seven rats was anaesthetized with alphaxalone throughout the 6-h period and a second group of eight was similarly anaesthetized only for the last 2 h of the 6-h period. The steroid-stimulated LH surge was blocked in both groups of rats anaesthetized with alphaxalone. The second experiment involved a comparison of pulsatile LH secretion in Animals which were either unanaesthetized (n = 8) or anaesthetized with alpha xalone (n = 9). In six out of nine rats the anaesthetic did not affect the maximum or minimum plasma LH concentrations but significantly slowed the frequency at which LH pulses were measured. In the remaining three anaesthetized rats the drug blocked pulsatile LH secretion. The experiments confirm that some secretion of LH continues during alphaxalone anaesthesia but indicate also that the drug has a more deleterious action upon the oestrogen-stimulated LH surge than believed hitherto.