AJP - Endocrinology and Metabolism, Vol 260, Issue 1 E53-E58, Copyright © 1991 by American Physiological Society
Thyrotropin-releasing hormone in ovine fetus: ontogeny and effect of thyroid hormone
D. H. Polk, A. Reviczky, R. W. Lam and D. A. Fisher
Department of Pediatrics, King-Drew Medical Center, Los Angeles 90059.
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)
