Ultrastructural changes in the rat thyroid gland during iodine deficiency

Thyroid ultrastructure changes were studied during the course of a low iodine diet in rats. At day 20, follicles were normal, but a number of them contained cells of higher density and with greatly elongated microvilli. Endoplasmic reticulum cisternae were frequently dilated. From day 20 until day 80, the most characteristic changes in the thyroid cells were the progressive accumulation of subapical peroxidase-positive exocytotic vesicles. After 80 days of the low iodine treatment, Golgi apparatuses were very active. Cell division could be observed. At this stage, exocytotic vesicles were generally very abundant. These data suggest that the remarkable accumulation of subapical exocytotic vesicles between day 20 and day 120 might represent an adaptation to the moderate and gradual increase in TSH stimulation that occurs in the conditions of low iodine diet.     

A chronomorphological structural model of rat thyroid gland

Circadian rhythmicity of the structural morphometric model of thyroid has been studied in 36 Wistar rats kept in LD 12:12. The parameters evaluated are: a. the volume fraction occupied by: 1. follicle epithelium, 2. colloid, 3. interstitium at 6 time points in 24h; b. the follicle size distribution; c. the number of follicles per unit tissue volume. The circadian rhythms of mean follicular diameter and of follicular cavity mean diameter have been demonstrated (p less than 0.03 and p less than 0.01 respectively) and show overlapping acrophases of -120 degrees (-64 degrees/-176 degrees) and -108 degrees (-99 degrees/-116 degrees). The synchronization between rhythms, shown for mean follicular diameter and for follicular cavity mean diameter, suggests a rhythmical pulsation of the whole follicle, while the thickness of the follicular epithelium does not undergo a statistically significant periodic variation.     

Effect of vitamin A deficiency on cardiovascular function in the rat

Selected parameters of cardiovascular function were evaluated in vitamin A-deficient rats at 70 days of age. Resting heart rate was increased by an average of 100 bpm (21.4+/-2.7%), whereas resting systolic blood pressure was normal in vitamin A-deficient animals. The maximal contractile force developed per milligram weight of tissue by aortic rings excised from vitamin A-deficient animals was reduced in response to high potassium (-25.0+/-8.7%) and phorbol 12,13-dibutyrate (-36.8+/-8.4%) but was only slightly reduced in response to norepinephrine (-17.8+/-11.1%). Intimal rubbing to remove the endothelium had no effect on the loss in contractile responsiveness, and the relaxant response to acetylcholine was similar between control and vitamin A-deficient tissue groups. This suggests that the decrease in contractility of vascular smooth muscle from the vitamin A-deficient rats did not involve altered release of endothelium-derived vasoactive factors. Western blot analysis suggested a reduction in the protein levels of several differentiation markers including alpha-actin (-22%), calponin (-37%), desmin (-37%), and vinculin (-40%), whereas the level of PKCalpha was unchanged from control values. Our findings indicate a significant decrease in contractile responsiveness of aortic smooth muscle of the vitamin A-deficient rat that may be associated with a down regulation in the expression of contractile-related proteins.     

Alterations in estrogen receptor isoforms in the mammary gland and uterus of the rat during differentiation

1. Estrogen receptors in lactating mammary glands and uteri of rats which were 10 and 19 days postpartum exhibited molecular heterogeneity based on their surface charge properties. 2. The polymorphism of estrogen receptors detected by high-performance ion exchange chromatography may be monitored in-line with a radioisotope detector. 3. Estrogen receptors from the mammary gland and uterus of rats at 10 days of lactation exhibited primarily two receptor isoforms eluting at 200-250 mM and 250-300 mM phosphate, whereas three ionic isoforms (eluting at 50-150, 200-250 and 325-375 mM phosphate) were found in the mammary glands of rats at 19 days of lactation. Similar changes in the profiles of estrogen receptor isoforms were observed in uterine cytosol preparations at each stage of postpartum differentiation. 4. The elution pattern of receptor-associated radioactivity was not altered by the addition of diisopropylphosphate, a potent inhibitor of trypsin-like proteases, either before, during or immediately after homogenization. This indicates that the differences observed in the receptor elution profile of 10 and 19 day postpartum lactating mammary glands were not due to artifactual proteolysis. 5. In summary, our data indicate that the differentiation stage of lactating mammary glands may dictate the final profile of receptor isoforms detected.     

Structure of the thyroid gland in the rat during hypokinesia and after its elimination

The aim of the investigation is to objectively ascertain and study stages of the processes taking into account the zonal structure of the thyroid gland, that is along the whole distance from the center up to the surface of the lobe. Hypokinesia lasts from 1 to 56 days; rehabilitation begins after 28 days of hypokinesia and lasts 28 days. Morphometric analysis of 8 parameters demonstrating the state of the gland are used. In control animals the structural changes from the center towards the surface of the gland lobe occur gradually, the degree of the changes is different and diversily directed [increasing volumetric part (Vv) of the follicular epithelium, decreasing Vv of the colloid, stable Vv of the vascular component]. When both hypokinesia and rehabilitation develop, all signs change wavily. Natural borders of the waves are defined--5, 16, 28 and 51 days for hypokinesia and 13 and 23 days for readaptation. Different structural components of the gland respond variously to the factors mentioned. Changes of every sign in different zones are also not equal and they can be diversily directed. In the course of rehabilitation for 1 month, there is no return to the normal state.     

Measurement of thyroid hormone in the rat thyroid gland by radioimmunoassay

The present paper describes (i) a hydrolysis technique with Pronase and leucine aminopeptidase using one rat thyroid gland, resulting in maximum release of thyroid hormones and minimum deiodination, and (ii) a simple and rapid procedure for thyroid hormone radioimmunoassays in thyroid hydrolysates using commercial kits intended for serum thyroid hormone determinations. The procedure is used to determine T4, T3, and rT3 concentrations and hormonal molar ratios in a thyroid gland from a male Wistar rat. The reliability of the method is also studied.     

Changes in rat liver mitochondrial lipids in vitamin A deficiency

The alterations in the lipid profiles of rat liver mitochondria due to vitamin A deficiency were studied. The amount of total lipids and phospholipids were decreased with a concomitant increase in triglycerides and cholesterol levels in mitochondria, isolated from vitamin A-deficient animals. Of particular significance was the observation that the content of lysolecithin, a potent cytolytic agent, was increased. An analysis of individual fatty acids showed that the percentage of polyunsaturated fatty acids was decreased significantly in vitamin A deficiency. Further, mitochondria from vitamin A-deficient animals, when incubated in 0.1 M Tris-HCl buffer (pH 7.4)in vitro, produced increased amounts of malondialdehyde and lipofuchsin pigments indicating increased susceptibility of the mitochondrial membrane to peroxidative damage. These results suggest a possible role of vitamin A in the prevention of the decomposition of structural lipids.     

Effect of vitamin D deficiency on skeletal development during early growth in the rat

To define the role of vitamin D in early development, female weanling rats were grown to maturity on a vitamin D-deficient diet and mated with normal males. At Day 20 of pregnancy the weight and total body calcium of fetuses were determined. At various times after parturition, pups were sacrificed. Plasma samples were analyzed for calcium and phorphorus, and femurs were characterized as to volume, dry weight, ash weight, and total calcium. The results indicate that vitamin D deficiency with its accompanying hypocalcemia does not impair placental transfer of calcium nor weight gain of the fetus. Vitamin D deficiency does appear to increase calcium accumulation in the fetus. After parturition vitamin D is functional in maintaining a normocalcemia as early as 3 days postpartum and its importance increases with age of the neonate. Bone mineralization is clearly disrupted by Day 14 as judged by calcium content per unit bone volume and the severity of the defect increases with age. Both vitamin D and normal concentrations of calcium and phosphorus appear to be essential for proper skeletal development during early growth postpartum.