Abstract
Abstract
Groups of rats were studied between the ages of 36 and 43 days. Phenobarbital was injected at noon in order to remove the source of endogenous LH-RH. Beginning at 1400 hr, blood samples were obtained at 1/2-hr intervals during the 3-hr period when LH-RH was infused at 50 ng/hr through a double-lumen jugular cannula implanted 1-4 days earlier. Vaginal opening occurred at proestrus or estrus on Days 41-43. The peak level of circulating LH following LH-RH was significantly greater at age 42 than at 36, 38, 40, or 43, Responses at other ages were not statistically different from one another. However, five of the seven animals studied at 42 days were in proestrus, and the peak LH response was most significantly correlated with the stage of the estrous cycle: that observed at proestrus was significantly greater than those of diestrous, estrous, or anestrous (prepubertal) animals. These results fail to suggest an essential role of altered pituitary responsiveness in the onset of puberty. Rather, in agreement with the results of previous investigators, they reflect events at the initial proestrus, indicating that cyclic mechanisms have already been set in motion.
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