PMID: 2504867Jul 1, 1989Paper

Gonadotrophin-releasing hormone regulation of gonadotrophin subunit gene expression: studies in tri-iodothyronine-suppressed rats

The Journal of Endocrinology
D J HaisenlederJ C Marshall

Abstract

We have previously shown that a pulsatile gonadotrophin-releasing hormone (GnRH) stimulus can increase steady-state levels of alpha and LH-beta subunit mRNAs in the male rat pituitary. Since alpha subunit is produced in both thyrotroph and gonadotroph cells, the effect of GnRH specifically on gonadotroph alpha gene expression is uncertain. To address this tissue, adult male rats were given injections of tri-iodothyronine (T3; 20 micrograms/100 g body wt, i.p.) daily for 8 days (day 8 = day of death) in order to decrease thyrotroph alpha mRNA levels (+T3 group). Saline injections (i.p.) were given to control animals (-T3group). Three days before GnRH administration, the animals were castrated and testosterone implants inserted s.c., to inhibit endogenous GnRH secretion. GnRH pulses (25 ng/pulse; 30-min interval) were given to freely moving animals (saline pulses to controls) via an atrial cannula for 12,24 or 48 h. Serum LH and FSH were measured before and 20 min after the last GnRH pulse. Pituitary RNA was extracted and alpha, LH-beta, FSH-beta and prolactin mRNA levels were determined by dotblot hybridization using 32P-labelled cDNA probes. Castration and testosterone replacement reduced alpha and LH-beta mRNA levels by 30 and...Continue Reading

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