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

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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 [luteinizing hormone releasing hormone] induced gonadotropin 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 [luteinizing hormone] and FSH [follicle stimulating hormone] in sera of castrated rats. In both unprimed and LHRH-primed CSS rats, gonadotropin secreting cells remain responsive to exogenous LHRH. After a 14-day recovery period, CSS rats were pretreated with LHRH only or LHRH plus EB or T for 6 days. Sixteen-18 hours 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 LHRH 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 .mu.g/kgBW [body weight] 18 h before, or 800 .mu.g/kgBW 3 h before LHRH challenge) were similar to those of CSS rats pretreated with LHRH only. In contrast, EB-priming (1 or 10 .mu.g/kgBW) significantly enhanced (P < 0.05) the sera LH response to 20 ng LHRH. Pretreatment with T (250 .mu.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 .mu.g/kgBW) augmented the magnitudes of the sera LH responses. Compared to the 1 .mu.g/kgBW EB-treated group, the LH releasing action of LHRH is prolonged in the 10 .mu.g/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. 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 LH release.