Umbilical Cord Cutting Triggers Hypertriiodothyroninemia and Nonshivering Thermogenesis in the Newborn Lamb

Abstract

EXTRACTThe present studies in the newborn sheep were undertaken to further clarify the mechanism or mechanisms responsible for the early increases in serum thyroid hormone concentrations in the newborn as well as the significance of these changes to newborn nonshivering thermogenesis. Six groups of animals were studied to determine the influence of neonatal cooling, cord cutting, and the effects of thyrotropin-releasing hormone ( T R H ) and triiodothyronine iT3) iniections. ~ , . ,Group I newborns were delivered into room air with immediate cord cutting. Group I1 animals were delivered into room air and cord cutting was delayed 60 min. Group III animals were delivered into a 39' water bath and maintained for 60 min with the umbilical cord intact; the cord was cut at the time of removal from the water bath. Group I V animals were handled similarly to group 111 animals except that cord cutting was delayed 60 min after removal from the water bath. Group V and VI newborns were handled similarly to group I V animals except that T R H (group V) or T 3 (group IV) was injected at the time of removal from the water bath. Deep rectal temperature and serum free fatty acids (FFA), thyroxine (T4), and T 3 concentrations were measured in all newborns; FFA was measured as an index of catecholamine release. Serum thyroid-stimulating hormone ( T S H ) was measured in newborns from groups I and II.The results indicate that the newborn lamb responds to par turition similarly to the human newborn. There are marked increases in mean serum T 3 (50-242 ng/100 ml) and FFA levels (245-744 pEq/liter) during the first 60 min with only a transient fall in body temperature (39.1' to 37.4"), indicating effective nonshivering thermogenesis. Serum T 4 concentrations do not increase significantly during this time. Warming in the water bath (groups III and IV) prevented the FFA and T 3 responses, indicating that parturition per se is not the stimulus to these events. Delayed cord cutting (groups II and IV) produced marked hypothermia (to 35.6 and 34.4"), and the increases in serum FFA and T 3 concentrations were not observed until the cord was cut.Mean baseline serum T S H concentrations were 4.7 and 5.3 pU/ml, respectively, in groups I and II animals and increased modestly to peak values a t 30-60 min whether or not the umbilical cord was cut. T R H (group VI) did not increase serum T 3 levels during the first 60 min, but a significant 4-hr response (to 336 ng/100 ml) was observed. T 3 (group VI) did not stimulate the FFA or thermogenic responses directly, but significantly augmented both responses to cord cutting. In addition, there was a significant correlation between serum FFA or T 3 concentrations 60 min after cord cutting and minimal rectal temperature ( r = 0.53 and 0.71, respectively; P < 0.005).The present results indicate that in the newborn sheep: ( I ) umbilical cord cutting, rather than cooling, stimulates FFA release, T 3 production, and nonshivering thermogenesis; (2) that the early T 3 response is not mediated via T R H and TSH...

Fetal-to-Maternal Transfer of Thyroid Hormone Metabolites in Late Gestation in Sheep

“…The placental transfer of T 2 S and other T 3 metabolites to the maternal circulation appears to be an active process helping maintain serum T 3 in fetuses at very low levels. This is consistent with the previous findings of Sack and co-workers (20), who showed that umbilical cord cutting triggers hypertriiodothyroninemia in the newborn lamb, and that the postnatal T 3 surge can be delayed until well after the TSH peak by delaying umbilical cord cutting. Santini et al (21) also have shown that the placenta plays an important role in maintaining the low serum T 3 in fetuses late in gestation.…”

Neonatal Adaptation: Sympatho-Adrenal Response to Umbilical Cord Cutting

“…Similarly, a variety of metabolic events are stimulated including hepatic glucose output, free fatty acid mobilization, nonshivering (chemical) thermogenesis, and production of triiodothyronine by peripheral tissues. We and others have demonstrated the importance of umbilical cord cutting itself in the initiation of these metabolic events (28,17).…”

“…Similarly, a variety of metabolic events are stimulated including hepatic glucose output, free fatty acid mobilization, nonshivering (chemical) thermogenesis, and production of triiodothyronine by peripheral tissues. We and others have demonstrated the importance of umbilical cord cutting itself in the initiation of these metabolic events (28,17).The present studies were designed to assess the individual effects of delivery and umbilical cord cutting on the stimulation of the sympatho-adrenal system during parturition. The results indicate that umbilical cord cutting is an important stimulus for CAT release.…”

Reversible Umbilical Cord Occlusion: Effects on Thermogenesis In Utero

“…The neonatal surge in plasma Ti has been suggested as the signal for the initiation of nonshivering thermogenesis by Fisher and Klein (1980) (26), and circulating T3 levels rise rapidly after cord snare in the lamb (10,27). Thyroidectomy in midgestation resulted in the birth of profoundly hypothermic lambs that died (28).…”