INHIBITION BY SOMATOSTATIN OF MOUSE THYROID ACTIVITY FOLLOWING STIMULATION BY THYROTROPHIN, ISOPRENALINE AND DIBUTYRYL CYCLIC-AMP

1977 ◽  
Vol 86 (2) ◽  
pp. 323-329 ◽  
Author(s):  
B. Ahrén ◽  
P. Hedner ◽  
A. Melander ◽  
U. Westgren
Keyword(s):  
Thyroid Hormone ◽  
Thyroid Gland ◽  
Cyclic Amp ◽  
Hormone Secretion ◽  
Inhibitory Effect ◽  
Dibutyryl Cyclic Amp ◽  
Thyroid Activity ◽  
Iodine Release ◽  
Mouse Thyroid

ABSTRACT The recent discovery of somatostatin-containing cells within the thyroid gland infers that somatostatin may influence thyroid activity. This possibility was investigated by measurements of radio-iodine release in mice pre-treated with 125I and T4. The animals were treated with TSH, isoprenaline or dibutyryl-cyclic AMP with and without concomitant injection of somatostatin. It was found that somatostatin reduced the blood 125I increase in response to each of the three thyroid-stimulating agents. The elimination rates of 125I-labelled T4 and T3 were unaffected by somatostatin. The observations suggests that somatostatin may participate in the regulation of thyroid hormone secretion, by an inhibitory effect exerted within the thyroid gland.

Thyrotrophin-releasing hormone (TRH) and hormone secretion from the follicular and C-cells of perfused dog thyroid lobes

1985 ◽  
Vol 109 (4) ◽  
pp. 499-504 ◽  
Author(s):  
E. Iversen ◽  
P. Laurberg
Keyword(s):  
Thyroid Hormone ◽  
Thyroid Gland ◽  
Hormone Secretion ◽  
Inhibitory Effect ◽  
C Cells ◽  
Follicular Cells ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Direct Inhibitory Effect ◽  
Thyroid Secretion

Abstract. Recently we found small amounts of TRH immunoreactivity in the thyroid gland of dogs and pigs. In the present study we investigated if exogenous TRH influences the release of T4, T3 and cAMP from the follicular cells, and calcitonin and somatostatin from the C-cells of perfused dog thyroid lobes. 10−5 mol/l TRH inhibited the TSH induced iodothyronine and cAMP release from the thyroid while 10−8 mol/l TRH had no effect. The relative proportions of T4 and T3 in thyroid secretion were not altered by TRH infusion. TRH did not influence the basal or the Ca++ induced release of somatostatin and calcitonin. Hence TRH has a direct inhibitory effect on the hormone secretion from thyroidal follicular cells. This opens the possibility that TRH in the thyroid participate in the regulation of thyroid hormone secretion. Even though the concentration of TRH found to be effective is high our results may indicate that TRH in the thyroid participates in the regulation of thyroid hormone secretion as an antagonist to TSH.

Thyroid function as measured by 131iodine release rate, weight and RNA/DNA in growing lambs, and its relation to growth rate

1969 ◽  
Vol 11 (3) ◽  
pp. 399-407 ◽  
Author(s):  
S. A. Draper ◽  
N. B. Haynes ◽  
I. R. Falconer ◽  
G. E. Lamming
Keyword(s):  
Growth Rate ◽  
Thyroid Hormone ◽  
Thyroid Gland ◽  
Thyroid Function ◽  
Rate Constant ◽  
Release Rate ◽  
Hormone Secretion ◽  
Thyroid Status ◽  
Thyroid Activity ◽  
Ad Libitum

SUMMARYThyroid activity was assessed in two groups of crossbred lambs and in Dorset Horn lambs fed ad libitum, by measuring the rate constant (K4) for the release of 131iodine from the gland. The results demonstrated a highly significant curvilinear correlation (P<0·001) between growth rate and the rate constant (K4) in experiments based on individual measurements in animals from three populations.Separate work carried out on the measurements of both thyroid size and RNA/DNA ratio suggests a need for caution when these are interpreted as parameters of thyroid activity. In the growing animal these may be more reflective of the growth of the thyroid gland itself, differences which may be governed by factors not directly related to variations in hormone secretion rate.The findings are discussed in terms of an explanation of the contradictory results obtained where attempts have been made to alter the thyroid status of growing animals by the use of thyroid hormone analogues and thyroid depressant drugs.

scholarly journals Secretion and degradation of parathormone as a function of intracellular maturation of hormone pools

1979 ◽  
Vol 83 (3) ◽  
pp. 521-528 ◽  
Author(s):  
JJ Morrissey ◽  
DV Cohn
Keyword(s):  
Cyclic Amp ◽  
Half Life ◽  
Calcium Concentration ◽  
Hormone Secretion ◽  
Ionized Calcium ◽  
Dibutyryl Cyclic Amp ◽  
Low Calcium ◽  
High Calcium ◽  
Parathormone Secretion

The biosynthesis, processing, and secretion of parthormone and the effect of calcium on these processes were measured in dispersed porcine parthyroid cells incubated with [(35)S]methionine. Proparathormone was detected at 10 min, the earliest time measured, and was rapidly and apparently quantitatively converted to parathormone. The half-life of the prohomormone pool was 15 min. Secretion of parathormone was detected by 20 min. In pulse-chase experiments there was a period between 20 and 40 min during which the wave of newly-synthesized parathormone was secreted. After 40 min during little additional radioactive hormone was secreted, but dibutyryl cyclic AMP, an agent that can mobilize stored parathormone, when added to the incubation mixtures enhanced radioactive parathormone secretion but only after 60 min, although it increased net hormone secretion as determined by radioimmunoassay to the same extent at all times studied. When the ionized calcium concentration of the medium was lowered, more radioactive hormone was secreted at all times but the effect was greatest on that hormone that was synthesized less than 60 min previously ; however, net hormone secretion in contrast to radioactive hormone was enhanced equally at all intervals. These data could mean that the refractoriness to secretion of parathormone 40-60 min of age was related to maturation of secretory container preparatory to storage. Low calcium (0.5 mM) stimulated hormone secretion up to fivefold compared to high calcium (3.0 mM) but did not affect synthesis of parathormone or proparathormne or conversion of the latter to hormone. During processing at least 70 percent of the intracellular parathormone was lost, presumably through proteolysis and this degradation was greater at high calcium. These data have been interpreted in light of the concept that two secretable pools of parathormone exist within the parathyroid.

Effects of intrathyroidal metabolism of thyroxine on thyroid hormone secretion: increased degradation of thyroxine in mouse thyroids stimulated chronically with thyrotrophin

1984 ◽  
Vol 105 (1) ◽  
pp. 57-65 ◽  
Author(s):  
Ken Kubota ◽  
Hidemasa Uchimura ◽  
Tomoaki Mitsuhashi ◽  
Shoo Cheng Chiu ◽  
Nobuaki Kuzuya ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Experimental Period ◽  
Physiological Significance ◽  
The Media ◽  
Bovine Tsh ◽  
Tsh Levels ◽  
Mouse Thyroid

Abstract. Mice were infused continuously with graded doses of bovine TSH (bTSH) and changes in plasma concentrations of bTSH and T4 were measured. Then mice infused with 100 mU TSH per day were sacrificed on days 0, 1, 3 and 5 and their thyroids were excised to determine in vitro secretion of T4, T3 and rT3 during 3 h of incubation. At the end of the incubation, thyroidal contents of T4, T3 and rT3 were also determined after pronase digestion. Plasma bTSH levels were increased on day 1 to a level of 110 μU/ml and remained unchanged thereafter. Plasma T4 concentrations increased approximately 2-fold on day 1, but decreased to initial levels on days 3 and 5. Changes in T4 secretion in vitro paralleled those in plasma T4 concentrations; T4 secretion increased 2-fold on day 1, and decreased to the pre-TSH levels on days 3 and 5. In contrast, T3 secretion increased throughout the experimental period. The T3/T4 ratio in thyroidal secretion in vitro was the same as that in thyroidal contents on days 0 and 1 of TSH infusion, but the former was significantly greater than the latter on days 3 and 5. PTU (5.9 × 10−5 m), a known inhibitor of T4 deiodination, added to the incubation media did not affect T4 secretion on days 0 and 1, but increased T4 secretion on days 3 and 5 to the level of day 1, but did not affect T3 secretion. In the presence of PTU, the T3/T4 ratio in thyroidal secretion did not differ from that in thyroidal contents throughout the experimental period. Secretion of rT3 was increased on days 3 and 5 and PTU augmented this increase. Thyroidal content of rT3 was much increased on days 3 and 5. In contrast, methimazole (10−3 m), which does not inhibit in vitro T4 deiodination, added to the incubation media did not affect T4, T3 and rT3 secretion in vitro. When [125I]T4 was added to the media and incubated with mouse thyroid, no labelled products of T4-deiodination were observed to appear in the media even in mice infused with TSH for 5 days. These results suggest that intrathyroidal metabolism of T4 has physiological significance in controlling thyroid hormone secretion at least in TSH-stimulated thyroids.

scholarly journals The regulation of growth hormone secretion from the isolated rat anterior pituitary in vitro. The role of adenosine 3′:5′-cyclic monophosphate

1971 ◽  
Vol 124 (4) ◽  
pp. 815-826 ◽  
Author(s):  
R. B. Lockhart Ewart ◽  
K. W. Taylor
Keyword(s):  
Growth Hormone ◽  
Cyclic Amp ◽  
Early Phase ◽  
Late Phase ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Hormone Release ◽  
Dibutyryl Cyclic Amp ◽  
Cyclic Monophosphate

1. The release of growth hormone from isolated fragments of rat anterior pituitary tissue incubated in vitro was studied by employing a double-antibody radioimmunoassay. 2. In the absence of added stimuli, two phases of hormone release could be distinguished, an early phase of 2h duration and a subsequent late phase. In the early phase, hormone release was rapid but could be significantly decreased by calcium depletion and by 2,4-dinitrophenol whereas the rate of release in the late phase was uninfluenced by these incubation conditions. These results have been interpreted as indicating the existence of a secretory component in the early phase of release. 3. In subsequent experiments, the effects of various agents on the rate of hormone output during the late phase of incubation were investigated. Hormone release was increased by theophylline and by dibutyryl cyclic AMP (N6-2′-O-dibutyryl-adenosine 3′:5′-cyclic monophosphate), the response to both of these agents being related to the concentration of the stimulant employed. 4. The stimulation of growth hormone output by theophylline was significantly decreased by calcium deprivation and by 2,4-dinitrophenol. The response to dibutyryl cyclic AMP was diminished by 2,4-dinitrophenol, iodoacetate and 2-deoxyglucose but not by malonate or colchicine. 5. Arginine, β-hydroxybutyrate, albumin-bound palmitate and variation in the glucose concentration of the incubation medium over a wide range were without any statistically significant effect on the rate of hormone release from either control pituitary fragments or those subject to secretory stimulation by dibutyryl cyclic AMP. 6. It is suggested that the regulation of growth hormone secretion is mediated by cyclic AMP (adenosine 3′:5′-cyclic monophosphate). The secretion observed in response to cyclic AMP requires the presence of ionized calcium and a source of metabolic energy but is independent of pituitary protein synthesis de novo. The integrity of the glycolytic pathway of glucose metabolism appears to be essential for cyclic AMP-stimulated growth hormone secretion to occur.

scholarly journals Effect of phenylpyruvate on enzymes involved in fatty acid synthesis in rat brain

1973 ◽  
Vol 134 (2) ◽  
pp. 557-563 ◽  
Author(s):  
D. J. Deery ◽  
K. W. Taylor
Keyword(s):  
Cyclic Amp ◽  
Insulin Release ◽  
Acid Synthesis ◽  
Inhibitory Effect ◽  
Dibutyryl Cyclic Amp ◽  
Cell Content ◽  
Nad Synthesis ◽  
Arginine Hydrochloride ◽  
Rat Islets Of Langerhans

1. The effects of azaserine and nicotinamide, agents which inhibit and stimulate hepatic NAD synthesis respectively, on the content of NAD+ and NADH in isolated rat islets of Langerhans incubated in vitro were studied. The effects of these compounds on the rates of insulin release, from isolated islets incubated in vitro, in response to various secretagogues were also measured. 2. Preincubation of islets in the presence of azaserine (0.3mm) caused a marked depletion of the normal islet-cell content of both NAD+ and NADH and prevented the secretion of insulin in response to stimulatory concentrations of d-glucose, xylitol, d-xylulose, l-arginine hydrochloride and l-leucine. 3. Preincubation of islets in the presence of nicotinamide (2mm) increased the islet content of NAD+ and enhanced the rate of release of insulin in response to d-glucose. Also when nicotinamide was present the inhibitory effect of azaserine on insulin release and the azaserine-induced depletion of the islet content of NAD+ and NADH was prevented. 4. Preincubation with azaserine was without effect on the stimulation of insulin release caused by theophylline or dibutyryl cyclic AMP. 5. It is suggested that insulin release caused by sugars and amino acids is dependent on the maintenance of NAD concentrations, though this may not be the case for release due to theophylline and dibutyryl cyclic AMP.

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