THE EFFECTS OF ANTERIOR HYPOTHALAMIC DEAFFERENTATION ON THYROTROPIN (TSH) BIOSYNTHESIS AND RESPONSE TO TSH-RELEASING HORMONE

The effects of hypothalamic deafferentation on TSH synthesis was studied by making cuts of 180.degree. arc in the anterior hypothalamus (n = 18) or sham cuts (n = 12) in rats. After 21 days, pituitaries were incubated with [35S]methionine (MET), [3H]glucosamine (GLCN), with or without 10-8 m TRH for 24 h. TSH and free .alpha.-subunits were immunoprecipitated and analyzed by gel electrophoresis. In the deafferented group as compared to sham, MET incorporation into both subunits of secreted TSH was decreased [.alpha., 96 .+-. (SE) 9 .times. 103 vs. 180 .+-. 20 .times. 103 dpm/mg protein; .beta., 35 .+-. 9 .times. 103 vs. 84 .+-. 15 .times. 103 dpm/mg protein; P < 0.05). Basal GLCN incorporation into both subunits of secreted TSH was also decreased in the deafferented group (.alpha., 6.5 .+-. 11 .times. 103 vs. 132 .+-. 17 .times. 103 dpm/mg protein; .beta., 36 .+-. 8 .times. 103 vs. 101 .+-. 29 .times. 103; P < 0.05). In vitro TRH did not stimulate MET incorporation into secreted TSH in the sham controls but did in the deafferented group (.alpha., 270% of basal; .beta., 374% of basal; P < 0.01). In vitro TRH increased GLCN incorporation in secreted TSH in both the sham (.alpha., 253% of basal; .beta., 245% of basal; P < 0.02) and the deafferented group(.alpha., 692% of basal; .beta., 630% of basal; P < 0.01). GLCN/MET ratio, reflecting relative glycosylation, did not differ for sham or deafferented groups but increased 2-fold with in vitro TRH in each group for both secreted subunits (P < 0.01). Free .alpha.-synthesis and intrapituitary TSH were not altered by deafferentation or TRH. In summary, 1) anterior hypothalamic deafferentation decreases basal TSH protein and carbohydrate synthesis; 2) such deafferentation increases sensitivity to TRH stimulation of TSH synthesis, most notably apoprotein synthesis; 3) TRH increases relative glycosylation of secreted TSH in both deafferented and sham groups. These data suggest that TRH plays a significant role in regulating basal TSH protein and carbohydrate synthesis, glycosylation of TSH subunits, and subsequent bioactivity.