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Modulation of the secretion of luteinizing hormone by testosterone
Abstract
Effects of episodic gonadal steroids on endogenous LH release in rams were investigated with LHRH antagonists NPTAA and SB-75 (Horvath et al., 1982 and Bajusz et al., 1988) in single and multiple doses in three experiments. During windows of LH suppression, endogenous episodic responses of testicular androgens were induced with exogenous ovine LH (NIADDK-oLH-26, iv; 5 $\mu$g/100 kg BW) at various times post-antagonist. LH release was examined as the rams recovered from LH inhibition to test the hypothesis that normal LH secretion by the pituitary requires periodic exposure to testosterone. Serial plasma samples were collected via jugular catheters at 15 min intervals for 72 h in Exp. 1 (n = 5 rams) and 2 (n = 6 rams) and 96 h in Exp. 3 (n = 6 rams). Testosterone and LH secretion during inhibition of LH secretion when rams were or were not given exogenous oLH (24 to 48 h, Exp. 1 and 2; 24 to 60 h, Exp. 3) and during recovery from inhibition of LH secretion (48 to 72 h, Exp. 1 and 2; 66 to 96 h, Exp. 3) were compared to that prior to antagonist administration (0 to 24 h). Steady decrease in mean LH was induced by the LHRH antagonist and followed closely by reduction in mean testosterone. Both hormones were reduced to below detectable limits of the assay. Even though exogenous oLH produced a pulse of testosterone similar in amplitude to pulses of testosterone encountered prior to antagonist, treatment did not affect LH or testosterone secretion during the recovery period. All pulses of testosterone in the preantagonist period were elicited by pulses of LH. Few pulses of testosterone were detected during LH inhibition when rams received no exogenous oLH. During recovery from inhibition, pulses of LH were of low frequency and low amplitude and were absent in some rams. In contrast, testosterone pulses and mean plasma testosterone were similar to those prior to antagonist and were not altered by exogenous oLH treatment. Based on our results, we reject our hypothesis. However, testosterone pulses that were not in response to detectable LH pulses may indicate that testosterone secretion can be disconnected from LH stimulation and be elicited by a stimulus other than LH during the recovery period.
Subject Area
Veterinary services|Obstetrics|Gynecology|Anatomy & physiology|Animals
Recommended Citation
Dayalu, Elizabeth, "Modulation of the secretion of luteinizing hormone by testosterone" (1993). ETD collection for University of Nebraska-Lincoln. AAI9415957.
https://digitalcommons.unl.edu/dissertations/AAI9415957