The influence of anesthetics on the estrogen-induced afternoon prolactin surge. Althesin does not block the surge

The effect of continuous anesthesia produced by ether, ketamine, urethane and althesin on the afternoon prolactin (PRL) surge was examined using aortic catheters in ovariectomized, estrogentreated rats. Ether and ketamine (ip or ia) completely abolished the diurnal PRL surge. Urethane (ip) from two sources and administered at two doses, which produced surgical anesthesia, initially suppressed the PRL surge, however, PRL levels rose slightly in the early evening. The effect of althesin (ip) on the afternoon PRL surge was variable; in some animals the surge was similar to that seen in unanesthetized controls, while in others the surge was reduced or absent. The variable effect of althesin (ip) seemed to be a result of fluctuations in the depth of anesthesia since ia infusion of althesin at a constant rate did not suppress the afternoon PRL surge.