Acute stress attenuates but does not abolish circadian rhythmicity of serum thyrotrophin and growth hormone in the rat.

The effects of acute immobilization (IMO) on daily rhythms of corticosterone, thyroid-stimulating hormone (TSH) and growth hormone (GH) were studied in adult male rats. Two hours of IMO increased serum corticosterone, this increase still being observed 3 h after finishing stress exposure. In the dark period corticosterone levels did not differ in control and IMO rats, but higher levels were observed again in the morning of the day after.

Effect of perinatal hypothyroidism on the developmental regulation of rat pituitary growth hormone and thyrotropin genes.

We studied the effects of thyroid hormone (T3) on GH, TSH, and T3 receptor (TR) gene expression as well as deiodinase activities during rat pituitary development. By reverse transcriptase-polymerase chain reaction, GH and TSH beta transcripts were detectable on fetal day 15. Although with certain differences, the expression of both GH and TSH beta genes was under T3 control during fetal and neonatal life.

Comparative effects of food restriction, fasting, diabetes and thyroidectomy on growth hormone and thyrotropin gene expression in the rat pituitary.

To examine the molecular basis for the decreased pituitary growth hormone (GH) and thyrotropin (TSH) content during restricted feeding, fasting and diabetes, we measured steady-state levels of mRNA for TSH-alpha, TSH-beta and GH in the pituitary from normal rats either fed ad libitum (C), limited to 75%, 50% and 25% (FR75, FR50, FR25, respectively) of ad libitum intake, or deprived of food for 2 and 4 days (F2 and F4, respectively), and also in streptozotocin-diabetic (D) and D insulin-treated animals. The results from these experimental groups were compared with those in thyroidectomized (Tx) rats. Pituitary mRNA was quantified by Northern blot hybridization with cDNA probes specific for rat TSH-alpha, TSH-beta and GH.

Insulin regulation of malic enzyme gene expression in rat liver: evidence for nuclear proteins that bind to two putative insulin response elements.

Diabetes in rats is characterized by insulin deficiency accompanied by a decrease in lipogenic enzymes. The malic enzyme (ME) gene, which encodes an important lipogenic enzyme, was used to investigate insulin regulation of gene expression. ME mRNA levels were reduced by more than 90% in the liver of diabetic rats.

Triiodothyronine receptor complex in developing rat brain and pituitary.

In vitro saturation analysis combined with nuclear 3,5,3'-triiodothyronine (T3) quantification was used to examine the changes in T3 binding parameters in rat pituitary and cerebrocortical nuclei from fetal day 14 to postnatal day 20. T3 receptors were first detectable in neuronal, glial, and pituitary nuclei on fetal days 14, 17, and 18, respectively. Thereafter T3 receptor concentrations in neuronal, glial, and pituitary nuclei increased throughout the developmental period studied, reaching maximal levels during neonatal life (1,129, 1,025, and 635 fmol/mg DNA, respectively).

Effect of regularity of exposure to chronic immobilization stress on the circadian pattern of pituitary adrenal hormones, growth hormone, and thyroid stimulating hormone in the adult male rat.

Circadian variation of serum levels of adrenocorticotropin hormone (ACTH), corticosterone, growth hormone (GH), and thyroid-stimulating hormone (TSH) were studied in three groups of adult male rats exposed to chronic intermittent immobilization stress (IMO) for 2 hr daily under different schedules. IMO resulted in reduced food intake, body weight loss, and increased adrenal weight. ACTH levels were not affected but corticosterone levels were increased in all IMO rats as compared to control ones during the diurnal phase of the circadian cycle.

Effects of chronic immobilization stress on GH and TSH secretion in the rat: response to hypothalamic regulatory factors.

The effect of chronic immobilization (2 h/day) for 13 days on basal and stress levels of GH and TSH, and their response to various hypothalamic regulatory factors was studied in male Sprague-Dawley rats. Chronic immobilization (IMO) resulted in reduced serum TSH levels in stress situations but not in resting conditions. GH secretion was inhibited both in resting and stress situations.

Effect of restricted feeding, fasting, and diabetes on the relationship between thyroid hormone receptor occupancy, growth hormone induction, and inhibition of thyrotropin release in thyroidectomized rats.

The present study was undertaken to test the effect of food restriction, fasting, and diabetes on the relationship between thyroid hormone receptor occupancy and two biological end points, GH production and the inhibition of TSH secretion, in thyroidectomized rats. The estimated maximal binding capacity (MBC) in diabetic (D) and fasting (F) rats and in animals limited to 25% (FR25) of the food consumption of normal (C) rats was decreased to 57%, 73%, and 76%, respectively, of C values (P < 0.01-0.

Expression of thyroglobulin gene in maternal and fetal thyroid in rats.

The relationship between the changes in thyroglobulin (Tg) mRNA and Tg proteins during thyroid development in the fetus and in maternal thyroid glands during gestation and lactation is studied. While the appearance of Tg mRNA (fetal day 15) showed good temporal correlation with that of 12S Tg, no 19S Tg could be detected until 3 days later. The 12S Tg was the predominant protein on days 18 and 19 of gestation in the fetus, while 19S Tg was the predominant protein on fetal days 21-22 and during the postnatal period in the offspring; by the 20th postnatal day, the 19S Tg content per gland was 4 times the amount of 12S (155 vs.

Expression of the growth hormone gene and the pituitary-specific transcription factor GHF-1 in diabetic rats.

Diabetes in the rat is associated with poor growth and decreased GH in the pituitary. In this study we have examined whether this reduction reflects an impairment of GH gene expression. Diabetes was induced by the administration of streptozotocin (7 mg/100 g BW), and 18 days later, GH content, GH mRNA, and GH transcription rate were determined.

The role of somatostatin and/or dopamine in basal and TRH-stimulated TSH release in food-restricted rats.

The present study was carried out to examine the role of endogenous dopamine and somatostatin in the mechanisms involved in the restricted feeding-induced inhibition of TSH secretion in rats. GH secretion was examined in parallel. Restricted feeding by 50% or 75% was associated with a decrease in the pituitary and circulating levels of TSH and GH in both untreated and TRH-treated groups (p less than 0.

Triiodothyronine-receptor complex in rat brain: effects of thyroidectomy, fasting, food restriction, and diabetes.

In vitro saturation analysis combined with quantification of T3, by an isotopic equilibrium technique or RIA, were used to examine the effects of thyroidectomy, fasting, diabetes, and food restriction on T3 concentration and specific binding in cerebral cortex and cerebellum. Fasting and food restriction did not affect the T3 binding parameters in the brain areas studied. Both thyroidectomy and diabetes were accompanied by a reduction in T3 content in nuclei from both cerebral cortex and cerebellum, but a decrease in T3 binding sites was only observed in both brain areas of diabetic animals.

Triiodothyronine and insulin effects on malic enzyme in hypothyroid and diabetic rats.

We examined the effects of T3 and insulin on the activity of hepatic mitochondrial alpha-glycerophosphate dehydrogenase and cytosolic malic enzyme in control, thyroidectomized, thyroidectomized food-restricted, and thyroidectomized diabetic rats. In the three untreated thyroidectomized groups, the decrease in hepatic nuclear T3 content was accompanied by a marked reduction in the levels of alpha-glycerophosphate dehydrogenase and malic enzyme activity. Although the levels of both enzymes were increased by a receptor-saturating dose of T3, the alpha-glycerophosphate dehydrogenase response in the thyroidectomized groups was almost identical to that in controls, whereas that of malic enzyme was reduced to 45-62% of control values.

Sensitivity of thyrotropin secretion to TSH-releasing hormone in food-restricted rats.

The aim of the present study was to identify the mechanisms involved in the reduction of TSH secretion during prolonged food restriction. The basal TSH secretion rate, the TSH secreted in response to TRH, both in vivo and in vitro, and the TSH, nuclear T3, and plasma membrane TRH binding sites in the pituitary were determined in rats receiving 75% (FR75), 50% (FR50) and 25% (FR25) of the food consumed by the ad libitum fed rats (controls). The basal TSH secretion rate (microgram.

Blockade of opioid receptors with naltrexone inhibits thyrotropin increase after noise stress but does not prevent the decrease caused by immobilization.

The influence of naltrexone-induced opioid receptor blockade on the response of thyrotropin to two different acute stressors was studied in adult male rats. Naltrexone slightly but significantly reduced basal thyrotropin levels and abolished the increase in serum thyrotropin caused by acute noise stress. In contrast, the opioid antagonist did not prevent the decrease in serum thyrotropin caused by another much more severe stressor such as immobilization.

Plasma clearance of heterogeneous growth hormone components in the rat: effects of diabetes and starvation.

Two forms of immunoreactive rat GH (rGH), bit rGH (b.rGH) and little rGH (l.rGH) are predominant in both pituitary and plasma from control (C), fasted (F), food-restricted (FR), diabetic (D) and insulin-treated D (D +l) rats.

Influence of intensity and duration of exposure to various stressors on serum TSH and GH levels in adult male rats.

The effect of stressor intensity and duration of exposure to the stimuli on adrenocorticotropin (ACTH), somatotropin (GH) and thyrotropin (TSH) concentration in serum was studied in adult male Sprague-Dawley rats. The stressors used were noise, restraint in plastic tubes and immobilization on wood boards. The greatest ACTH release was found in immobilized rats and the smallest in noise-exposed animals.

Response of hepatic mitochondrial alpha-glycerophosphate dehydrogenase and malic enzyme to 3,5,3'-triiodothyronine in streptozotocin-diabetic rats.

Hepatic mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and cytosolic malic enzyme (ME) response to a single injection of a receptor-saturating dose of T3 were measured 10, 20, and 30 days after diabetes induction, and compared with values in controls either fed ad libitum (C) or under a restricted diet (FR). An insulin-treated diabetic (D + I) group was also included. Basal enzyme levels as well as enzyme response to T3 injection were correlated with nuclear T3 content, maximal nuclear T3-binding capacity (MBC) and equilibrium association constant (Ka).

Crowding-induced changes in basal and stress levels of thyrotropin and somatotropin in male rats.

The effects of crowding on thyrotropin (TSH) and somatotropin (GH) secretion were studied in two-month-old male rats. Crowded rats (9-10 per cage) showed lower serum GH levels than controls (3 per cage). Likewise, serum GH was lower in crowded rats after acute exposure to stress.

Diabetes decreases liver and kidney nuclear 3,5,3'-triiodothyronine receptors in rats.

The liver and kidney nuclear T3 content and the maximal nuclear T3-binding capacity (MBC) were measured 1 month after streptozotocin administration and compared with values in controls either fed ad libitum (C) or offered a restricted diet (FR). A group of insulin-treated diabetic (D+I) rats was also included. Plasma T4 and T3 concentrations decreased to low levels in diabetic (D) rats.

The effects of chronic stress on corticosterone, GH and TSH response to morphine administration.

The effects of a chronic stress model in which several acute stressors were applied on a random basis on corticosterone, growth hormone (GH) and thyroid stimulating hormone (TSH) responses to morphine administration were studied in adult male rats. Chronic stress resulted in lower corticosterone response to the drug. In contrast, GH response to morphine was enhanced in the former animals and TSH response remained unchanged.

Chronic food restriction and the circadian rhythms of pituitary-adrenal hormones, growth hormone and thyroid-stimulating hormone.

Adult male Sprague-Dawley rats were subjected to food restriction so that they ate 65% of food ingested by control rats. While control rats had free access to food over the 24-hour period, food-restricted rats were provided with food daily at 10 a.m.

The effects of chronic intermittent stress on basal and acute stress levels of TSH and GH, and their response to hypothalamic regulatory factors in the rat.

The effect of chronic stress on basal and stress-induced alterations of TSH and GH was studied in adult male rats. Chronically stressed rats were subjected 6 days per week for 4 weeks to several acute stressors including saline injections, noise, ether and forced swimming. Each day, one stressor was chosen randomly.

Sensitivity of anterior pituitary hormones to graded levels of psychological stress.

The effect of graded levels of stressor intensity on anterior pituitary hormones was studied in adult male rats. Corticosterone, considered as a reflection of ACTH release, and prolactin responses showed a good correlation with the intensity of the stressors. On the contrary, neither LH, GH nor TSH release showed a parallelism with the intensity of the stressors in spite of the fact that they clearly responded to all the stimuli.

Intrathyroidal thyroglobulin in streptozotocin-diabetic rats.

In order to elucidate whether or not the 'coupling defect' observed in thyroids from diabetic rats is due to a structural defect of intrathyroidal thyroglobulin (Tg), the sedimentation pattern and the stability of the thyroidal soluble iodoproteins were studied in control (C), food restricted (FR), diabetic (D) and insulin-treated diabetic (D+I) rats fed a low iodine diet either with (NID) or without (LID) iodide supplementation and labelled with 125I: acutely, 24 h prior to sacrifice and chronically, by feeding the corresponding diet labelled for 60 days. Diabetes resulted in a decrease of thyroidal weight, an increase of both thyroidal 127I content and concentration and decreased plasma TSH, irrespective of the diet. Insulin treatment reversed these alterations.