Circulating Thyrotropin in the Ovine Fetus: Evidence for Pulsatile Release and the Effect of Hypothermia in Utero
| Autor: | Peter D. Gluckman, John H. Butler, Tania R. Gunn, Mhoyra Fraser, B M Johnston |
|---|---|
| Rok vydání: | 1985 |
| Předmět: |
medicine.medical_specialty
Ovine fetus Pulsatile flow Thyrotropin Hypothermia Fetus Pregnancy Internal medicine Animals Medicine Sheep business.industry Obstetrics Stomach Radioimmunoassay Fetal Blood medicine.anatomical_structure Endocrinology Animals Newborn In utero Pediatrics Perinatology and Child Health Gestation Female medicine.symptom business |
| Zdroj: | Pediatric Research. 19:208-212 |
| ISSN: | 1530-0447 0031-3998 |
| DOI: | 10.1203/00006450-198502000-00013 |
| Popis: | The secretion of thyrotropin (TSH) has been investigated in the chronically catheterized ovine fetus (term 145–150 days). Forty-two random plasma samples from 25 fetuses (86–149 days of gestation) were measured for TSH concentrations by radioimmunoassay. Plasma TSH concentrations were highest in the youngest fetuses [86–110 days, 3.9 ± (SD) 5.5 μU/ml, n = 13]. Thereafter TSH concentrations declined to 0.4 ± 0.6 μU/ml (n = 13, p < 0.05) at 130–150 days of gestation. However, serial sampling at 15–20 min intervals for 180 min from 14 individual fetuses (91–139 days) showed that TSH was secreted in a markedly exaggerated pulsatile manner compared to that observed after birth. The mean amplitude of TSH pulses fell (p < 0.005) from 5.9 ± 8.1 μU/ml in the fetuses to 2.1 ± 1.1 μU/ml in five neonatal lambs (6–22 days) and to 1.5 ± 0.4 μU/ml in three adult nonpregnant ewes. The mean pulse frequency for the 14 fetuses was 0.7 ± 0.3 pulses/h and was reduced (p < 0.001) to 0.3 ± 0.1 pulses/h in lambs and to 0.3 ± 0.1 pulses/h in the ewes. In the neonate, hypothermia is a potent stimulus to TSH release. To examine the ontogeny of this response, the temperature of the fetus in utero (106–127 days of gestation) was lowered by circulating water (14–18°C) at either a fast or slow rate through a coil placed either externally around the fetus or internally in the fetal esophagus and stomach. The fetuses were cooled for a period of 1 h during which fetal samples were obtained. In eight fetuses (106–127 days), the mean plasma TSH concentration rose (p < 0.001) from 1.5 ± 1.6 μU/ml to 6.7 ± 2.1 μU/ml during 1 h of fast external cooling (maximum fetal temperature fall 3.5°C). Plasma TSH values also rose (p < 0.02) during fast internal cooling (maximum temperature fall 1.9°C) from 1.4 ± 1.9 to 5.9 ± 8.2 μU/ml (n = 5, 116–132 days). A slower rate of cooling either externally (temperature fall 1.1°C) or internally (temperature fall 0.9°C) induced a variable response. The marked pulsatility of fetal TSH secretion which decreases after birth is postulated to be a consequence of immature negative feedback by thyroid hormones on fetal TSH release. The presence of a TSH response to hypothermia from 0.7 gestation is evidence that neuroendocrine mechanisms mediating TSH release and hypothalamic thermoregulatory responses have differentiated by this age. |
| Databáze: | OpenAIRE |
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