Effects of Intracerebral Implantation, Microinjection, and Peripheral Application of Sexual Steroids on Plasma Luteinizing Hormone Levels in the Male Miniature Pig1

This study demonstrates that in castrated male miniature pigs either im injection of 5α-dihydrotestosterone (5α-DHT, 6 mg/kg BW), the implantation of crystalline 5α-DHT into the mediobasal hypothalamus (MBH) or amygdala (AMY), or microinjection of 5α-DHT (60 ng) into the AMY, elevated plasma LH in the majority of cases. On the other hand much larger amounts of im 5α-DHT (15 mg/kg BW) lowered plasma LH levels, as did testosterone (T) when injected im at 6 mg or 15 mg/kg BW or implanted as crystals into the AMY. Implantation of testosterone into the MBH, however, elevated plasma LH levels while microinjections of testosterone into the AMY (60 ng) failed to alter plasma LH levels. 17β-Estradiol (E2) (0.6 and 1.5 mg/kg BW im) inhibited plasma LH-levels, but had no effect when given by microinjection (60 ng) into the amygdala. An unexplained observation is, that 24 h after im DHT treatment, plasma DHT levels are lower with 15 mg/kg BW than with 6 mg/kg BW. The data assign a new and possibly important role to 5α-DHT in the regulation of plasma LH levels. Along with T or its metabolites, 5α-DHT participates in both the stimulatory and inhibitory mechanisms of LH secretion in the male. The sites of action of androgens are not only located within the mediobasal hypothalamus but also in the amygdala.