Sequential Observation of Changes in Thyroxine, Triiodothyronine and Reverse Triiodothyronine during the Postnatal Adaptation of the Pig

Abstract

Principal serum iodothyronines, T₄, T₃ and rT₃, have been simultaneously measured by a specific radioimmunoassay in piglets kept for sequential observation with the mother from 1 to 21 days of age. During several hours postnatally, a high concentration of the hormone was noted as a result of an enhanced secretory activity of the thyroid gland. Later, a progressive decrease with a nadir at about day 3 was observed, followed by a second rise in the hormone level. Changes in T₃ and rT₃ levels from birth to the end of the 1st week, paralleled those for T₄. The T₃:rT₃ ratio of about 2 during the 1st week fell to about 1.5 during the 3rd week as a result of the progressive increase in rT₃ and decrease in T₃ concentrations. The T₄:rT₃ ratio fell with the progressing age to the level observed in post-weaned pigs. At birth, the newborn pig seems to possess a low capability of 5-deiodinase enzyme system thus the converting enzymes first work towards T₄–T₃ conversion while T₄–rT₃-converting ability progressively increases with age. The role of this variability for the neonatal thermogenic stability is discussed.

Influence of genotype on the differential ontogeny of uncoupling protein 2 and 3 in subcutaneous adipose tissue and muscle in neonatal pigs

“…T 3 was particularly sensitive to genotype on day 0, with Meishan piglets possessing 30% less circulating T 3 than commercial piglets, despite similar T 4 concentrations. As demonstrated previously in Polish Landrace piglets (Slebodzinski et al 1981), T 4 concentrations were highest during the first 24 h of life in both commercial and Meishan piglets. The commercial piglets followed the pattern of T 4 previously demonstrated (Slebodzinski et al 1981); however, Meishan piglets did not increase plasma T 4 between days 7 and 14.…”

“…As demonstrated previously in Polish Landrace piglets (Slebodzinski et al 1981), T 4 concentrations were highest during the first 24 h of life in both commercial and Meishan piglets. The commercial piglets followed the pattern of T 4 previously demonstrated (Slebodzinski et al 1981); however, Meishan piglets did not increase plasma T 4 between days 7 and 14. It is possible that the lower plasma concentrations of adrenaline previously described in Meishan piglets (Le Dividich et al 1991) may be partly responsible for the lower T 3 , as catecholamines have a stimulatory effect on 5 deiodinase, which catalyses the conversion of T 4 to T 3 .…”

Growth and development of adipose tissue and gut and related endocrine status during early growth in the pig: impact of low birth weight

“…Receptors are detected at 80 days of gestation in skeletal muscle, but not in liver, suggesting that porcine muscle can potentially respond to TH much earlier than liver (Duchamp et al, 1994). During the first 6 h after birth, there is a surge in T 3, free T 3 and T 4 plasma concentrations and apart from a transient decline at 12 h, TH concentrations remain high during the first 2 days and then decline slightly over the next 2 weeks (Slebodzinski, 1981;Berthon et al, 1993 and1996). The influence of birth weight on TH is controversial in the pig.…”

Differential effects of lipid and carbohydrate on enterocyte lactase activity in newborn piglets

“…Insulin and 3,5,3'-triiodothyronine (T3) both cause an elevation in LPH activity (Shulman, Tivey, Sunitha, Dudley & Henning, 1991;Tivey, Morovat & Dauncey, 1993). However, the surge in circulating T3 shortly after birth (Slebodzinski, Nowak & Zamyslowska, 1981) was unlikely to have induced the rise in LPH activity in the present study, since the increase in LPH would then have been similar in all treatment groups. Similarly, no correlation between plasma insulin levels and LPH activity was observed in the current investigation.…”