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

Abstract

In castrated male miniature pigs either i.m. injection of 5.alpha.-dihydrotestosterone (5.alpha.-DHT, 6 mg/kg BW [body weight]), the implantation of crystalline 5.alpha.-DHT into the mediobasal hypothalamus (MBH) or amygdala (AMY), or microinjection of 5.alpha.-DHT (60 ng) into the AMY, elevated plasma LH [luteinizing hormone] in the majority of cases. On the other hand much larger amounts of i.m. 5.alpha.-DHT (15 mg/kg BW) lowered plasma LH [luteinizing hormone] levels, as did testosterone (T) when injected i.m. at 6 mg or 15 mg/kg BW or implanted as crystals into the AMY. Implantation of testosterone into the MBH elevated plasma LH levels while microinjections of testosterone into the AMY (60 ng) failed to alter plasma LH levels. 17.beta.-Estradiol (E2) (0.6 and 1.5 mg/kg BW i.m.) inhibited plasma LH-levels, but had no effect when given by microinjection (60 ng) into the amygdala. An unexplained observation if, that 24 h after i.m. 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 5.alpha.-DHT in the regulation of plasma LH levels. Along with T or its metabolites, 5.alpha.-DHT participiates 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.