Thyrotropin-releasing hormone in ovine fetus: ontogeny and effect of thyroid hormone.
The ontogenesis of hypothalamic and extrahypothalamic thyrotropin-releasing hormone (TRH) and the effect of altered thyroid status on tissue TRH levels were studied in fetal sheep. At 62 days gestation (term = 145 days) TRH was detectable in serum and in hypothalamic, placental, and pancreatic tissues; pancreatic, placental, and serum levels exceeded hypothalamic levels two- to fivefold. Analysis of tissues obtained from 88-day gestation fetuses were comparable: TRH levels in placenta (54 +/- 15 pg/mg tissue protein), pancreas (34 +/- 5 pg/mg protein), and serum (93 +/- 9 pg/ml) exceeded those in hypothalamic extracts (15 +/- 9 pg/mg protein). By 120 days gestation, TRH values in the hypothalamus (610 +/- 52 pg/mg protein) exceeded those in extrahypothalamic sites; values were comparable at 140 days gestation. Fetal thyroidectomy resulted in a 2-fold elevation of hypothalamic TRH concentrations (1,030 +/- 139 vs. 522 +/- 29 pg/mg protein) and 2 to 20-fold elevations of TRH in the placenta (147 +/- 23 vs. 42 +/- 8 pg/mg protein), pancreas (195 +/- 11 vs. 29 +/- 7 pg/mg protein), duodenum (363 +/- 97 vs. 29 +/- 7 pg/mg protein), and serum (2,563 +/- 212 vs. 131 +/- 16 pg/ml). 3, 5, 3'-Triiodothyronine (T3) infusion in thyroidectomized fetuses resulted in elevated serum T3 values (480 +/- 80 ng/dl) and suppressed hypothalamic TRH (249 +/- 68 vs. 522 +/- 29 pg/mg protein) and serum TRH concentrations (30 +/- 4 vs. 131 +/- 156 pg/ml). Placental, pancreatic, and duodenal TRH concentrations in thyroidectomized T3-infused animals were below the level of detection of the assay (5 pg/mg tissue protein).(ABSTRACT TRUNCATED AT 250 WORDS)
Polk
D H
DH
Department of Pediatrics, King-Drew Medical Center, Los Angeles 90059.
Reviczky
A
A
Lam
R W
RW
Fisher
D A
DA
D000818:Animals; D005260:Female; D005333:Fetus / Q000187:drug effects / Q000502:physiology*; D005865:Gestational Age; D007031:Hypothalamus / Q000737:chemistry / Q000196:embryology*; D010179:Pancreas / Q000737:chemistry / Q000196:embryology*; D010920:Placenta / Q000737:chemistry; D011247:Pregnancy; D012016:Reference Values; D012756:Sheep; D013961:Thyroid Gland / Q000502:physiology*; D013965:Thyroidectomy; D013972:Thyrotropin / Q000097:blood; D013973:Thyrotropin-Releasing Hormone / Q000032:analysis* / Q000097:blood; D014284:Triiodothyronine / Q000097:blood / Q000494:pharmacology*
D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin