The Role of The Thyroid Gland in Regulating Synthesis and Release of Luteinizing Hormone in The Rat

The effects of thyroidectomy and thyroxine (T(,4)) therapy on the synthesis and release of luteinizing hormone (LH) by the anterior pituitary gland (AP) of ovariectomized (Ovx) rats were investigated. Immediately after ovariectomy, rats were thyroidectomized (Tx) or sham-Tx. Starting thirty days later they were injected with saline or T(,4) for 9 days. On the thirty-ninth day, the APs were incubated in vitro with 3.6 x l0('-8)M gonadotropin-releasing hormone (GnRH) and radioactive precursors, (('14)C) alanine and (('3)H) glucosamine, for 4 h at 37 C. Labeled LH was isolated by immunoprecipitation with specific anti-LH-(beta) serum. The levels of T(,4) and triiodothyronine (T(,3)) in the serum as well as the immunoreactive LH (IR-LH) in the serum, medium, and APs were measured by radioimmunoassay. Thyroidectomy resulted in an undetectable T(,4), and decreased but detectable T(,3) in the serum of Ovx rats. T(,4) replacement in Ovx-Tx rats restored the serum T(,4) to normal levels. Serum LH concentrations were higher in Ovx-Tx rats than in Ovx rats. T(,4) therapy depressed the elevated serum LH in Ovx-Tx rats to the level found in Ovx rats. The total IR-LH content in the pituitary and the release of IR-LH by APs in response to GnRH were increased in Ovx rats following thyroidectomy. Also, thyroidectomy stimulated the incorporation of both (('14)C) alanine and (('3)H) glucosamine into LH in APs from Ovx rats. The interaction of T(,4) and estradiol benzoate (EB) on the synthesis and release of LH in Ovx-Tx rats were examined. Both EB and T(,4) reduced serum LH in Ovx-Tx rats. EB decreased pituitary IR-LH and stimulated the release of stored IR-LH by APs of Ovx-Tx rats. EB also accelerated the release of de novo synthesized (('3)H) glucosamine-LH, whereas it decreased the incorporation of (('14)C) alanine and (('3)H) glucosamine into LH. The in vitro release of de novo synthesized LH was not affected by T(,4), whereas T(,4) reduced the incorporation of (('14)C) alanine into LH in APs of Ovx-Tx rats. These results suggest that thyroid hormones and estrogen modulate the synthesis and release of LH in Ovx rats by acting at both hypothalamic and AP levels. Both T(,4) and estrogen may inhibit GnRH output. At the AP level, both T(,4) and estrogen inhibited synthesis of the polypeptide chains and glycosylation of LH. However, T(,4) inhibited, whereas estrogen stimulated, the release of LH in the presence of GnRH.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Veterinary Medical Science

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Wang, Paulus Shyi-Gang

• Biology, Animal Physiology

Language dc:language

eng

Identifier

(UMI)AAI8026614

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/68233