In-vivo activity of the LH-releasing hormone pulse generator in castrated and intact male rats.

Abstract

The in-vivo LH-releasing hormone (LHRH) output from the mediobasal hypothalamus of conscious freely moving sham-castrated, acutely castrated (immediately after castration) and long-term castrated (greater than 20 days after castration) adult male rats has been studied. Five rats in each of the three conditions were perfused for an 8-h period (11.00-19.00 h). One animal in each condition was perfused for a 24-h period. In the sham-castrated and acutely castrated, but not in the long-term castrated rats, apparently random surges of LHRH output (greater than 5.6 pmol/l), separated by periods of non-detectable activity, were observed throughout the perfusion period. The LHRH output of the long-term castrated rats was characterized by an extremely low overall mean release and markedly attenuated pulse amplitudes, with both parameters significantly lower than those of the sham-and acutely castrated rats. These results indicate that the raised blood levels of LH in long-term castrated rats do not appear to be the consequence of high amplitude and high overall release of LHRH.