This study tested the effects of different iodine intakes on thyroid ultrastructure and function in thyroid remnants after subtotal thyroidectomy (sub-tx). Removal of most of the thyroid gland causes an elevation of endogenous TSH, which chronically stimulates the residual tissue. Male Sprague-Dawley rats were divided into three groups; Low Iodine Group (LIG), Moderate Iodine Group (MIG), and High Iodine Group (HIG). There was no significant difference among total thyroid weights removed by sub-tx, but thyroid remnant weights and TSH levels were higher at death (6 weeks after sub-tx) in LIG than in MIG and HIG. Total specific activities of cathepsin D and of arylsulfatase A in the sedimentable and nonsedimentable subcellular fractions were at least 38% lower in LIG than in MIG and HIG. The ratio between relative follicular volume and colloid volume determined by morphometry was higher in LIG than in MIG and lower in HIG than in MIG. Ultrastructurally, the relative volume occupied by secondary lysosomes was higher in HIG than in MIG, whereas the number of secondary lysosomes was not higher in LIG than in controls. Autoradiographic studies with 125I revealed that a large part of the radioactivity was in thyroid cell secondary lysosomes in MIG and HIG when radioiodine was injected 3 weeks before death. It is concluded that after sub-tx, iodine 1) regulates the weight of thyroid remnants, perhaps only indirectly through TSH, 2) modulates the number of secondary lysosomes in thyroid cells, and 3) slows down the turnover of secondary lysosomes. An iodine-deficient regimen impedes the secondary lysosomes to increase. Because of these findings, we postulate that chronic TSH stimulation along with a possible toxic role of iodine after sub-tx could induce an accumulation of lysosomal bodies.

This is a morphological study of changes in thyroid cells following iodine deficiency and iodine excess. Fifteen young male Sprague-Dawley rats were divided into three groups and fed one of the following diets for 6 weeks: low iodine (LID), normal iodine (NID) and high iodine (HID). Then the thyroid glands were removed and processed for light and electron microscopy. Thyroid tissue from the NID group was normal in appearance. The most outstanding feature of HID thyroids was the presence of numerous cells which contained irregularly shaped and stained lysosomes. These displaced other cell organelles and caused the apical cell surfaces to project into the follicle lumen. Thyroids from the LID group were three times heavier than the other two groups. Their follicles were very small, contained very little colloid. They were surrounded by dilated capillaries. Mitoses were frequent. Cells were columnar and contained abundant dilated endoplasmic reticulum, numerous apical vesicles, long microvilli and many mitochondria. Mitochondria were especially abundant in greatly infolded lateral and basal cell membranes. These findings show that there is a redistribution of organelles in thyroid cells in response to iodine deficiency and iodine excess which can be related to alterations in intracellular iodine metabolism.

A procedure was devised for fractionating crude thyroid lysosomal particles (P750-15,000) by self-forming density gradient centrifugation with colloidal silica. Two discrete particle-containing peaks were observed, based on 131I-labeling and acid phosphatase activity: a heavy peak (density, 1.11-1.12) and a light peak (density, 1.05). Ultrastructural analysis revealed that the heavy peak consisted almost entirely of lysosomes, whereas the light peak represented a heterogeneous mixture of small vesicles and fragments of other intracellular organelles. In thyroids removed from rats 30 min after 131I injection, almost all of the 131I was present in the low density peak. This 131I appeared on sucrose density gradient centrifugation as a 19S peak, and it was almost completely insoluble in trichloroacetic acid. This was interpreted as indicating that the low density peak contained pinocytotic vesicles. In thyroids removed 4 days after 131I injection, the radioactivity appeared largely in the high density peak. Both the trichloroacetic acid solubility and the pattern on sucrose density gradient centrifugation indicated that the [131I] thyroglobulin had undergone extensive proteolysis. Thyroglobulin proteolytic activity was found primarily in the high density particles and to only a small extent in the low density particles. Studies performed at intervals after 131I injection combined with double labeling (131I and 125I) experiments provided evidence that radioactivity was transferred from the low density to the high density particles. Heterogeneity existed within the dense peak, related to the degree of thyroglobulin degradation, as it was observed that thyroid lysosomes become denser with increasing proteolysis of thyroglobulin. The acid phosphatase in the low density particles could be distinguished from that in the high density (lysosomal) particles by its elution pattern on Sephadex G-200 column chromatography, its response to freezing and thawing, and its reactivity with p-nitrophenylphosphate. It was concluded, therefore, that the acid phosphatase in the low density fraction was derived from prolysosomal structures such as vesiculated Golgi-endoplasmic reticulum-lysosomes. The prolysosomal acid phosphatase associated with the low density fraction appeared to be a large membrane-bound molecule which could be transformed into lysosomal acid phosphatase by incubation at pH 5.0.

Subtotal thyroidectomies were performed in rats to increase the level of endogenous TSH, creating a condition of chronic TSH stimulation. The activities of various classes of lysosomal enzymes (cathepsin D, beta-glucuronidase, and aryl sulfatase A) were studied in thyroid tissue remaining in situ at various time intervals after subtotal thyroidectomy (sub-tx). These alterations were correlated with morphometric and ultrastructural changes in tissue lysosomes and with serum T4 and TSH. Specific activities of all three lysosomal enzymes were elevated in the residual tissue as compared with those in control tissue during 7 weeks after sub-tx in the first experiment. In the second experiment, the activities of all three enzymes were elevated both 3 and 6 weeks after sub-tx, and the activities of cathepsin D and aryl sulfatase A in the postnuclear homogenate (S2) were significantly elevated. Plasma TSH was elevated and T4 was decreased both 3 and 6 weeks after sub-tx. The results of the third experiment determined that there were significant alterations in nuclear cytoplasmic ratios as well as in the number, area, and volume density of lysosomes in both groups compared with respective control values. In addition, both lysosomal area and volume density in animals 6 weeks after sub-tx were significantly larger than those in animals 3 weeks after sub-tx. We conclude that chronic stimulation of residual thyroid tissue 6 weeks after sub-tx causes alterations in lysosomal ultrastructure as well as in lysosomal enzyme activity.

To determine the requirement of thyroid hormones for the expression of diet-induced thermogenesis (DIT) in the protein-malnourished rat, groups of male weanling Sprague-Dawley rats were thyroidectomized (Tx) or left surgically intact, and fed isoenergetic diets containing normal (22%, control) or decreased (8%, protein malnourished, PM) casein for 8 weeks postweaning. Half the Tx rats of either group received thyroxine (T4) replacement. Weight gains were least in PM-Tx rats, intermediate in control-Tx, PM and PM-Tx + T4, and greatest in control and control-Tx + T4 groups. Interscapular brown adipose tissue (IBAT) weight and brown adipocyte diameter were similar in control and PM rats and were greater in both Tx groups. Brown adipocyte diameter was normal but IBAT greater in both Tx + T4 groups. Both resting (ROC) and minimal (MOC) oxygen consumptions were increased in PM rats after 7 weeks, but the differences between ROC and MOC were similar in both dietary groups. MOC and ROC were decreased following Tx and became normalized in both Tx groups with T4. The effects of norepinephrine (100 µg/kg body weight, s.c.) on MOC were markedly reduced in both Tx groups and were normal after T4 replacement. These observations indicate that the increased thermogenesis observed in the protein-deficient rat is due to a thyroid-dependent increase in MOC, and that the thyroid hormones are required for the sympathetic-dependent component of DIT and total thermogenesis in the protein-malnourished rat model.

Throtrophs of the woodchuck anterior pituitary are described through the four seasons of the year. Evidence of an increase in number and activity in the spring is presented. Activity of the thyrotroph is seen to continue through the summer and decline in the autumn to quiescence during the hibernatory period of winter. The significance of these findings is discussed in relation to thyoid follicular cell morphology, serum T3 and T4 levels and the physiological activities of the animal. High levels of thyroid hormones in the serum may be consistent with the appearance of great activity seen in the thyrotroph and follicular cell when taken in context with breeding season, ambient temperature and lack of food.

Antihypertensive drugs were given to 25-week-old spontaneously hypertensive rats (SHR) and Wistar Kyoto rats, and the animals were sacrificed at 45–47 weeks of age. The effects of the decreased blood pressure on the adrenal zona glomerulosa and zona fasciculata were studied ultrastructurally and morphometrically. It was found that both groups of animals responded to the lower blood pressure in a similar manner, but the ability to respond is structurally compromised in the zona glomerulosa of SHR. This malfunction may be congenital in origin.

Two experiments were conducted to study the effects of protein malnutrition on thyroid function. Resting oxygen consumption and serum concentrations of triiodothyronine (T3), thyroxine (T4) and thyroid stimulating hormone (TSH) were measured and correlated with thyroid histology, gain in weight, feed efficiency and carcass energy content in male rats fed isoenergetic diets ad libitum containing 22% (control) or 8% (protein malnourished, PM) casein for 28 or 32 days postweaning. A third group was pair-fed to the PM rats with the control diet. In experiment 2 additional groups were pair-fed to the PM rats with 8% casein diets in which the casein was substituted with different mixtures of carbohydrate and fat. Resting oxygen consumption/body weight (0.75) decreased as body weights increased in all groups, but was consistently greatest in PM rats. In PM rats, plasma T3 was 130% of controls after 11 days of the dietary regimen and averaged 215% of controls from days 18 through 32. In experiment 2 both T3 and T4 concentrations were approximately twice controls in all PM groups. TSH concentrations were within the normal range in all groups throughout. Feed efficiency averaged 36 to 40% of controls and mean weight gain was 30 g after 28 days in the PM groups, compared to 114 and 91 g, respectively, in the pair-fed control rats. Carcass energy content of PM rats after 28 days was significantly lower than in control or pair-fed control rats. Thyroid morphology was compatible with increased secretory activity in all the protein-malnourished groups, compared with normal activity in the control and pair-fed control groups. Thermogenesis, as measured by oxygen consumption, was markedly increased in the PM rats compared to controls. These observations are consistent with a diet-induced thermogenesis in the protein-malnourished rats. In contrast to simple under-nutrition where energy expenditure may be conserved by decreases in thyroid function and thermogenesis, increases in thyroid function and thermogenesis in protein malnutrition could provide an energy balancing mechanism whereby unneeded non-protein energy in the diet could be dissipated as heat, and survival enhanced.

Woodchuck plasma was collected during four seasons of the year and assayed for total and dialyzable (free) T4 and T3 and for rT3. Plasma concentrations of total and free T4 and T3 were higher in the spring (T4, 5.4 +/- 0.6 microgram/dl; free T4, 3.0 +/- 0.4 ng/dl; T3, 202 +/- 22 ng/dl; free T3, 0.51 +/- 0.04 ng/dl) and lower in the prehibernatory fattening period in summer (T4, 2.3 +/- 1.0 microgram/dl; free T4, 1.2 +/- 0.5 ng/dl; T3, 45 +/- 27 ng/dl; free T3, 0.16 +/- 0.10 ng/dl) and fall (T4, 3.2 +/- 1.0 microgram/dl; free T4, 1.3 +/- 0.2 ng/dl; T3, 130 +/- 12 ng/dl; free T3, 0.25 +/- 0.02 ng/dl). In spite of the extremely high concentrations of T3 in the winter (437 +/- 32 ng/dl), free T3 concentrations (0.034 +/- 0.003 ng/dl), when measured at the appropriate temperature for hibernation, were significantly lower than those found at other seasons of the year. Plasma binding of T3 was lower during the summer and increased again to approximately double the spring value during the winter. rT3 was at or below the sensitivity of the method (6 ng/dl) at all seasons. It is suggested that the wide seasonal variations in thyroid hormone concentrations and altered plasma protein binding may represent important adaptations influencing the metabolic rate and the process of hibernation in the woodchuck.

1. Thyrotropin-releasing hormone (TRH), norepinephrine (NE), epinephrine (E), dopamine (DA), serotonin (5-HT), tyrosine hydrxylase (TH), and tryptophan hydrosylase (TpOH) were measured in several areas of the brains of woodchucks studied prior to, during, and immediately after hibernation.