Direct Effects of Estradiol Benzoate and Testosterone on the Response of the Male Rat Pituitary to Luteinizing Hormone Releasing Hormone (LHRH)

Abstract

Castrated male rats with pituitary stalk sections (CSS rats) were used to examine the direct actions of estradiol benzoate (EB) or testosterone (T) upon LHRH induced gonadotrophin release. Using a ventral approach, the pituitary stalk was severed and a barrier placed between the divided ends to prevent vascular regeneration. Data indicative of a separation of the pituitary from direct hypothalamic control were the significant diminitions of LH and FSH in sera of castrated rats. In both unprimed and LHRH-primed CSS rats, gonadotrophmn secreting cells remain responsive to exogenous LHRH. After a 14-day recovery period, CSS rats were pretreated with LFIRH only or LI-IRH plus EB or T for 6 days. Sixteen to 18 h after their last pretreatment injections, CSS rats were challenged with 5 or 20 ng LHRH. The resting levels of LH and FSH values in the sera of CSS rats treated with LHRH only or with LHRU plus EB or T were similar to those of untreated CSS rats. The sera LH responses to the 5 ng dose of LHRH in the EB-treated CSS rats (1 Mg/kgBW 18 h before, or 800 ,ig/kgBW 3 h before LHRH challenge) were similar to those of CSS rats pretreated with LHRH only. In contrast, ER-priming (1 or 10 12g/kgBW) significantly enhanced (P<0.05) the sera LH response to 20 ng LHRH. Pretreatment with T (250 �g or 2.5 mg/kgBW) led to a decrease of the sera LH response to 5ng LHRH. Using 20 ng LHRH, both T (2.5 mg/kgBW) and EB (1 or 10 Mg/kgBW) augmented the magnitudes of the sera LU responses. Compared to the 1 Mg/kgBW EB-treated group, the LU releasing action of LHRH is prolonged in the 10 Mg/kgBW EB-pretreated group. No consistent effect of LHRH upon FSH release alone or in combination with EB or T priming was observed. While intraarterial administration of LHRH did not show any change in FSH release, i.v. administration appeared to stimulate it. Our results indicated that the modifying action of EB or T at the pituitary seemed to be related to the quantity of both the steroid used for priming and the challenging dose of LHRH, since both affected LU release.