Fasting-Induced Changes in Pulsatile Luteinizing Hormone (LH) Secretion in Male Rats. The Role of Testosterone and the Hypothalamic Paraventricular Nucleus

We have previously shown that 48-h fasting profoundly suppresses pulsatile LH secretion in female rats in the presence of estrogen, and that the paraventricular nucleus (PVN) is an estrogen action site mediating this inhibition. The present study determined whether fasting suppresses pulsatile LH secretion in male rats in a testosterone-dependent manner, and whether the PVN is involved in the fasting-induced changes in pulsatile LH release. Mean LH concentrations and baseline levels of LH pulses were significantly reduced by 48-h fasting in castrated males implanted with various length (6, 12, and 24 mm) of subcutaneous testosterone implants. LH pulse frequency was significantly lower in fasted rats with a 24-mm testosterone implant compared with unfasted controls. On the contrary, mean LH levels and the amplitude and baseline of LH pulses were significantly increased by fasting in castrated rats without testosterone treatment. PVN lesions partially blocked the inhibitory effect of fasting on LH release in the testosterone-implanted rat model. In addition, local implantation of testosterone or estradiol into the PVN reversed fasting-induced increase in both mean LH levels and the pulse amplitude in castrated males, but did not cause a further suppression of these pulse parameters. These results suggest that testosterone is required to suppress LH pulses during fasting in the male rat. The PVN may mediate, at least partly, the fasting-induced inhibition of LH secretion, and is not the single steroid feedback site mediating the fasting-induced suppression of LH secretion in the male.