Metabolic changes associated with sustained 48-hr shivering thermogenesis in the newborn pig.

Metabolic changes associated with sustained 48-hr shivering thermogenesis were studied in piglets maintained at 34 (thermoneutrality) or 25 degrees C (cold) between 6 and 54 hr of life. Despite their high shivering activity and elevated heat production, cold-exposed piglets exhibited a slightly lower rectal temperature than thermoneutral animals (-1.1 degrees C; P < 0.01) at the end of the treatment. The enhancement of heat production and shivering activity were associated with a decrease in muscle glycogen (-47%; P < 0.05) and total lipid content (-23%; P < 0.05), a reduction of blood lactate levels (P < 0.05) and an enhancement of muscle cytochrome oxidase activity (+20%; P < 0.05) which suggests that muscle oxidative potential was increased by cold exposure. Potential for capturing lipids (lipoprotein lipase activity) was also higher in the red rhomboideus muscle (+71%; P < 0.01) and lower in adipose tissue (-58%; P < 0.01) of the cold-exposed piglets. Measurements performed at the mitochondrial level show no changes in rhomboideus muscle, but respiratory capacities (state IV and FCCP-stimulated respiration) and intermyofibrillar mitochondria oxidative and phosphorylative (creatine kinase activity) capacities were enhanced in longissimus dorsi muscle (P < 0.05). These changes may contribute to provide muscles with nonlimiting amount of readily oxidable substrates and ATP necessary for shivering thermogenesis. A rise in plasma norepinephrine levels was also observed during the second day of cold exposure (P < 0.05).

Interactive effects of thermal environment and energy intake on thyroid hormone metabolism in newborn pigs.

The aim of the study was to determine the effects of 48-hour cold exposure (25 vs. 34 degrees C), starting at 6 h of age, and energy intake on thyroid hormone plasma levels, hepatic 5'-deiodinase activity and nuclear 3,3',5-triiodothyronine (T3) receptors in newborn pigs. In the cold, piglets were fed either a similar milk intake (C piglets) to the piglets at thermal neutrality (TN piglets) or were given an extra amount of milk to compensate for the increased heat production (C+ piglets). Concentrations of plasma thyroxine (T4) decreased steadily over the 48-hour investigation and were affected neither by ambient temperature nor by energy intake. At the end of 48 h, plasma levels of T3 and liver 5'-deiodinase activity were similar in TN and C+ piglets and higher than in C piglets. The numbers of T3 receptors were greater in the liver from C and C+, as well as in skeletal muscle from C, than from TN piglets. Results of the study suggest that plasma T3, liver 5'-deiodinase and liver nuclear T3 receptors of the newborn pig can be regulated by energy intake and ambient temperature.

Effect of thyroid status in the perinatal period on oxidative capacities and mitochondrial respiration in porcine liver and skeletal muscle.

Regulatory thermogenesis is reduced in newborn piglets which have been made hypothyroid during late gestation by giving the sow a high glucosinolate rapeseed diet (test animals). Thereafter, the progressive increase in thermogenic capacity parallels the development of a marked postnatal hyperthyroid state. To explain these effects of thyroid hormones at the tissue and mitochondrial levels, we have examined both liver and skeletal muscle to determine possible underlying changes in (i) tissue oxidative capacities (cytochrome oxidase (CO) activity), between 80 d of gestation and 48 h after birth, and (ii) mitochondrial content and respiratory capacities at 24 h of life. In control piglets, CO activity increased sharply during late gestation and the first 2 d of life in liver and rhomboideus (RH) muscle (P < 0.01), whereas only a prenatal increase was observed in longissimus dorsi (LD) muscle. Test fetuses were hypothyroid and had lower CO activities than controls during late gestation in RH muscle (P < 0.06, at 110 d of gestation; P < 0.08, at birth) and in liver (P < 0.001, at birth). The postnatal increase in CO activity in RH muscle and liver was higher (P < 0.05) in test than in control piglets, and as a result the difference between the 2 groups was not significant by 24-48 h of life. There was no effect of treatment on LD muscle. At 24 h, hyperthyroid test piglets had lower amounts of mitochondrial proteins than controls (P < 0.05) in all three tissues, possibly reflecting reduced mitochondrial protein synthesis during fetal life and suggesting that high postnatal T3 levels did not bring about major increases in protein synthesis within 24 h. However, test piglets exhibited higher rates of mitochondrial respiration than controls in liver and RH muscle, as shown by increases in State III and FCCP-stimulated respirations (P < 0.05), and mitochondrial CO and creatine kinase activities (P < 0.05). In RH muscle, both subsarcolemmal and intermyofibrillar mitochondria showed the same trends. No changes were observed in LD muscle. Our results describe for the first time the effect of thyroid hormones on perinatal oxidative capacities and neonatal mitochondrial respiration in liver and skeletal muscle of the pig, through both the short-term regulation of mitochondrial respiration and the long-term control of mitochondrial biogenesis. The differential sensitivity of LD and RH muscles to thyroid hormones is discussed.

Cold-induced changes in circulating levels of catecholamines and thyroid hormones are modulated by energy intake in newborn pigs.

Newborn pigs were kept at a low ambient temperature from 6 until 54 h of age and supplied with a limited (LI, 415 g (kg body weight)-1) or a high (HI, 655 g (kg body weight)-1) intake of milk. At the end of the treatment, both groups had similar deep body temperatures and metabolic rates. However, plasma adrenaline and noradrenaline levels were, respectively, 5.8- and 3.0-fold lower (P < 0.01) in HI than LI piglets, whereas plasma 3,5,3'-triiodothyronine (T3) was 1.5-fold higher (P < 0.01) in HI piglets. It is concluded that the hormonal control of cold-induced thermogenesis is modulated by energy intake, with catecholamines and thyroid hormones acting in a closely related and complementary manner.

Assessment of thermoregulatory and postprandial thermogenesis over the first 24 hours after birth in pigs.

Heat production was continuously measured from birth to 24 h after birth in pigs tube-fed 14 g kg-1 of colostrum or water (sham-fed animals) at hourly intervals, and maintained at thermoneutrality (34 degrees C) or in moderate cold (24 degrees C). Results indicate that colostrum was necessary to initiate and sustain the postnatal rise in metabolic rate observed at 34 degrees C. It provided about 75% of the energy required for heat production at 24 degrees C. Heat production was increased by 74% in the cold and decreased by 30% during starvation. In both cases, maintenance of the energy balance was achieved with a compensatory drop in body temperature. At 34 degrees C, variations in postmeal heat production represented 12% of the total 24 h energy expenditure and were almost equally due to the thermogenic effect of colostrum and to confounding factors, including physical activity. In the cold, calculated postmeal thermogenesis accounted only for 3% of 24 h energy expenditure and for 9% of the extra heat produced in the cold. Our results highlight the main role of colostral energy in the energy metabolism of the newborn pig in a typical birth environment (24 degrees C) and in thermoneutral conditions (34 degrees C). Thermoneutral postmeal thermogenesis is low and its contribution to the extra heat produced in the cold very limited.

Modification of thermogenic capacity in neonatal pigs by changes in thyroid status during late gestation.

This study was designed to determine the effects of hypothyroidism during late fetal life in pigs on (1) the perinatal pattern of plasma levels of thyroxine (TT4), total 3,5,3'-triiodothyronine (TT3) and free T3 (FT3), and liver 5'-deiodinase activity, and (2) the early postnatal development of thermoregulation. Fetal hypothyroidism (test animals) was induced by feeding the sow a high glucosinolate rapeseed diet. Plasma levels of thyroid hormones, thyroid gland weights and liver 5'-deiodinase activity of control animals increased during late gestation (P < 0.01). The early postnatal period was characterized by a surge in thyroid hormone levels during the first 6 h (P < 0.05), followed by a transient decrease at 12 h and a second rise by 24 h after birth. This surge was much higher (P < 0.01) for TT3 than for TT4, but liver 5'-deiodinase activity did not change during the first 24 h of life. Fetal hypothyroidism was characterized by lower plasma levels of thyroid hormones (P < 0.05), and lower hepatic 5'-deiodinase activities (P < 0.01) than in control fetuses at 110 d of gestation. During the first 6 h of life, test pigs had lower levels of TT4 (P < 0.05) but exhibited a greater postnatal surge in TT3 and FT3 (P < 0.05) than did the controls. The minimal and summit metabolism of the control pigs increased markedly (P < 0.01) during the first 2 d of life, without any significant change in thermal body conductance, suggesting that this age-related improvement in thermoregulation was due to the development of the ability to produce heat.(ABSTRACT TRUNCATED AT 250 WORDS)

[Blood pressure variation]. / Etude de la variabilité tensionnelle.

A blood pressure profile at rest was recorded in 2,000 patients (1,069 females, 931 males) by DINAMAP 845 (from 8 AM to 8 PM. a record every fifteen minute). The limit between normotensive and hypertensive patients in this settled by WHO (BP = 160/95 mmHg). The analysis of percentage of pathological values (BP greater than 160/95 mmHg) allowed us to identify eight type of recordings. Normal (295), Border line hypertension less than or equal 20 p. 100 of pathological values (573), Paroxysmal hypertension (58), hypertension with predominance (963) of whom 484 with systolic predominance and 479 with diastolic predominance, Isolated systolic hypertension (15), Isolated diastolic hypertension (47), hypertension without predominance (15) and Permanent hypertension (82). The variability of blood pressure was studied by using the coefficient of variation = p. 100 of standard deviation/mean.(ABSTRACT TRUNCATED AT 250 WORDS)