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Biomedical subjects

R C Smallridge

Publications and source records attributed to R C Smallridge.

At least 109 records · Page 6Linked to original sources
PubMed1983

Hyperthyroidism due to thyrotropin-secreting pituitary tumors. Diagnostic and therapeutic considerations.

Hyperthyroidism may be caused by the inappropriate secretion of thyroid-stimulating hormone (TSH) from a pituitary tumor. Of 33 reported cases, 17 have occurred in women and 16 have occurred in men. All patients had large tumors, and secretion of a second hormone (growth hormone or prolactin) has been common. Diagnosis requires the detection of TSH in the serum when patients are clinically and biochemically hyperthyroid. Ancillary tests supporting the diagnosis include an alpha-subunit to TSH molar ratio greater than 1.0, an absent TSH response to protirelin, suppression of serum TSH (but not alpha-subunit) by glucocorticoids, and a lack of suppression of serum TSH by dopaminergic agonists. Successful treatment of this disorder requires pituitary surgery and/or pituitary irradiation.

Adolescent↗
PubMed1982

Investigations into the etiology of elevated serum T3 levels in protein-malnourished rats.

Thyroid function studies and the peripheral metabolism of thyroid hormone were examined in rats fed a low protein diet (9% casein) for 4-8 wk. Compared to animals fed a normal protein diet ad libitum, both the low protein rats and a pair-fed control group weighed less at the end of the study. However, serum total T3 levels were significantly higher only in the protein deficient rats. The elevated serum T3 was not explainable by enhanced peripheral T4 to T3 conversion, as there was no evidence of any change in hepatic or renal 5'-deiodinase activity when homogenates were examined for conversion of T4 to T3, reverse T3 to 3,3'-diiodothyronine, or 3',5'-diiodothyronine to 3'-monoiodothyronine. Neither was there an effect on hepatic T3 receptor maximal binding capacity (204 +/- 24 versus 168 +/- 15 fmol/mg DNA control) or binding affinity (2.07 +/- 0.38 versus 2.49 +/- 0.24 x 10(-10) M control). In two separate experiments the dialyzable fraction of T3 was significantly lower in the low protein group while free T3 concentrations were unchanged or reduced. In contrast, serum total and free T4 were either normal or reduced and dialyzable T4 was unaffected by protein deficiency. We conclude that while serum total T3 is elevated in rats chronically fed a low protein diet, this elevation is not due to enhanced T4 to T3 conversion. Rather, the increased T3 levels can be accounted for by a striking alteration in protein binding to T3. Moreover, the failure to demonstrate similar changes in serum total and dialyzable T4 suggests that in the rat, protein deficiency has different effects on binding to the two major thyroid hormones. Dietary induced changes in serum thyroid hormone binding must be kept in mind in nutrition studies in the rat.

Animals↗
PubMed1982

Transsphenoidal surgery for prolactin-secreting pituitary tumors: a study of 28 cases and review of the literature.

Twenty-eight patients (22 women, six men) underwent transsphenoidal microsurgery for suspected prolactin-secreting pituitary tumors. Amenorrhea was present in 19 of the 22 women, and galactorrhea, in 21 of the 22 women and two of the six men. Prolactin values preoperatively ranged from 62 to 38,130 ng/ml, and the mean percentage decrease in serum prolactin (PRL) after surgery was 80% (range: 38% to 99%). Twenty patients had microadenomas (tumors less than 10 mm), and seven had macroadenomas (greater than 10 mm). Although no tumor was found in one patient, her serum PRL fell from 65 to 24 ng/ml postoperatively. Surgical results depended upon both the initial PRL level and the tumor size. All eight patients with tumors of less than 10 mm and PRL levels of less than 200 ng/ml had normal postoperative prolactin values, whereas serum PRL returned to normal in only four of eleven patients with microadenomas but with preoperative PRL of greater than 200 ng/ml. None of the five patients with macroadenomas in who serum PRL had been measured preoperatively had normalization of serum PRL postoperatively, including one patient with a preoperative level of less than 200 ng/ml. Menses resumed in 11 of 18 women; galactorrhea improved in six of 11 subjects, and nine pregnancies have occurred. Analysis of these data, as well as those of 12 published series, suggests that both tumor size and the preoperative serum prolactin level are important factors in predicting the success of surgical therapy. Longitudinal follow-up is imperative to determine which patients are truly cured.

Adenoma↗
PubMed1982

The effect of experimental hyperthyroidism and hypothyroidism on 5'-monodeiodination of 3,3',5'-triiodothyronine and 3',5'-diiodothyronine by rat liver and kidney.

To study the effect of alterations in thyroid status on 5'-monodeiodinase activity, conversions of rT3 to 3,3'-diiodothyronine and 3',5'-diiodothyronine (3',5'-T2) to 3'-monoiodothyronine were examined in vitro. Rats were injected either with T4 (10 micrograms/100 g BW, ip, daily for 12 days) to make them thyrotoxic or thyroidectomized to render them hypothyroid, and liver and kidney homogenates were prepared. Liver homogenates from hyperthyroid animals demonstrated a 2-fold increase in 5'-monodeiodination of both rT3 and 3',5'-T2; both reactions were also significantly increased in the kidneys of hyperthyroid rats. Hypothyroidism produced a significant decrease in 5'-deiodination of both rT3 and 3',5'-T2 in liver and kidney homogenates. These data indicate that the in vitro 5'-deiodination of both rT3 and 3',5'-T2 is increased in hyperthyroidism and decreased in hypothyroidism and suggest that these two iodothyronines are metabolized in a similar fashion in rat liver and kidney homogenates in states of altered thyroid function.

Animals↗
PubMed1982

Hyperthyroidism due to a thyrotropin-secreting pituitary adenoma. Studies of thyrotropin and subunit secretion.

A 58-year-old man had symptoms of hyperthyroidism and congestive heart failure. While hyperthyroid, his serum thyrotropin (TSH) level was inappropriately elevated at 6.1 microunits/mL. The molar ratio of alpha subunit to TSH was 2.5, suggesting the presence of a TSH-secreting pituitary tumor. Further evaluation disclosed an enlarged sella turcica with posterior erosion, and an intrasellar mass was visualized on computed tomographic scan. Neither serum TSH nor alpha subunit levels became elevated after administration of thyrotropin-releasing hormone, nor were they suppressed by a dopamine infusion. Serum TSH but not alpha subunit levels rose during antithyroid drug therapy. Estrogens produced a partial reduction in serum alpha subunit concentration (presumably reflecting the nontumorous gonadotroph contribution to circulating alpha subunit). Dexamethasone completely suppressed serum TSH level but had no effect on the alpha subunit level, suggesting a differential feedback of glucocorticoids on TSH and alpha secretion. The patient was treated with pituitary irradiation rather than surgery because of his underlying heart disease.

Adenoma↗
PubMed1981

Hypocalcemia with osteoblastic metastases in patient with prostate carcinoma. A cause of secondary hyperparathyroidism.

A 68 year old man with prostatic carcinoma and extensive painful osteoblastic metastases was discovered to have hypocalcemia (serum calcium 7.1 mg/dl) without evidence of hypoalbuminemia, renal failure or malabsorption. Baseline studies revealed hypocalciuria (24 hour urine calcium less than 5 mg/day), normal serum phosphate (3.4 mg/dl), low tubular reabsorption of phosphate (68 percent), undetectable serum calcitonin, normal serum 25-hydroxyvitamin D, slightly elevated serum parathyroid hormone level and increased urinary cyclic AMP (8.87 mumol/g creatinine). These studies were compatible with secondary hyperparathyroidism. The intravenous administration of parathyroid extract produced no further change in urinary phosphate but a 25-fold increase in nephrogenous cyclic AMP. Three days administration of intramuscular parathyroid extract slowly and temporarily restored serum calcium to normal levels while increasing urinary cyclic AMP and phosphate. Chemotherapy with cyclophosphamide and 5-fluorouracil rendered the patient free of pain while reducing serum acid and alkaline phosphatase levels and restoring serum total and ionized calcium and urinary cyclic AMP excretion to normal.

Adenocarcinoma↗
PubMed1981

Pituitary and thyroid function in male cynomolgus monkeys.

In four male cynomolgus monkeys, serum thyroxine was 6.2 +/- 0.9 micrograms/dl, and triiodothyronine was 207 +/- 12 ng/dl (mean +/- SE). Kinetic studies using 131I-thyroxine and 125I-triiodothyronine showed that the disappearance of both hormones was non-linear and best fit a biexponential equation. The metabolic clearance rates and production rates for thyroxine were 21.5 +/- 0.6 ml/kg/day and 1.34 +/- 0.23 micrograms/kg/day, respectively, and T1/2(beta) = 29.6 +/- 2.0 hours. For triiodothyronine, the metabolic clearance rate was 156.6 +/- 12.0 ml/kg/day, the production rate was 0.33 +/- 0.04 micrograms/kg/day, and T1/2 (beta) was 13.3 +/- 1.3 hours. Basel serum thyrotropin levels in five euthyroid animals were 1.4 +/- 0.6 microU/ml and increased after thyrotropin-releasing hormone to 6.7 +/- 2.2 microU/ml. Serum prolactin was 5.8 +/- 0.7 ng/ml, and it increased to 26.6 +/- 4.5 ng/ml after thyrotropin-releasing hormone. Four animals received chronic dexamethasone therapy (1 mg twice daily for 5.5 months). While baseline and thyrotropin-releasing hormone stimulated thyrotropin values were lower (0.8 +/- 0.2 microU/ml and 3.2 +/- 0.5 microU/ml, respectively), these reductions were not significant.

Animals↗
PubMed1980

Hypoglycemia in pregnancy. Occurrence due to adrenocorticotropic hormone and growth hormone deficiency.

Severe symptomatic hypoglycemia (serum glucose level, 24 mg/dL) developed in a 23-year-old, 147.3-cm-tall woman during her late second and third trimesters of pregnancy. Endocrine studies disclosed insulin levels less than 2 microU/mL; growth hormone level less than 3 ng/mL; and cortisol level less than 1 microgram/dL. Hydrocortisone therapy corrected her hypoglycemia, and she was delivered of a healthy female infant. Postpartum, her evaluation included normal thyroid function studies, a normal thyroid-stimulating hormone response to protirelin (thyrotropin-releasing hormone), normal serum and urine gonadotropin levels, normal serum prolactin, normal sella turcica tomograms, and a normal EMI brain scan. Urine 17-hydroxycorticosteroids increased during a four-day cosyntropin infusion, but failed to rise after metyrapone administration. The growth hormone level failed to rise after stimulation with levodopa and propranolol administration. The patient was believed to have idiopathic partial hypopituitarism, with hypoglycemia being due to adrenocorticotropic hormone (ACTH) and growth hormone deficiency and the drain of maternal glucose by the fetus. It is suggested that pregnant women with symptomatic hypoglycemia be treated with glucocorticoids while awaiting the results of their endocrine evaluation.

Adrenocorticotropic Hormone↗
PubMed1980

Nature of suppressed TSH secretion during undernutrition: effect of fasting and refeeding on TSH responses to prolonged TRH infusions.

TSH responses to 4-hr continuous TRH infusions of approximately 0.8 microgram/min were assessed during feeding (1500 Kcal), fasting, and refeeding (1500 Kcal) intervals in 9 euthyroid obese subjects. The total area under the TSH response curve was 1854 +/- 322 muU/ml . 4-hr during feeding, decreased to 1359 +/- 199 muU/ml . 4-hr (p less than 0.01) on the 10th day of fasting, and remained low, being 1405 +/- 185 muU/ml . 4-hr, despite refeeding a 1500 Kcal diet (40% carbohydrate, 40% fat, 20% protein) for 5 days. Baseline serum T3 concentrations were 167 +/- 11 ng/dl during feeding, 86 +/- 8 ng/dl during fasting, and 119 +/- 12 ng/dl during refeeding. The observed decreases in TSH release appeared to correlate with decreased biologic action on the thyroid gland since the net rise in T3 during the infusion was less in fasting and refeeding than in the control (fed) period. Basal serum rT3 levels were 42 +/- 5 ng/dl during feeding, rose as expected to 56 +/- 5 ng/dl during fasting (p less than 0.005), and were completely restored to normal during refeeding (36 +/- 5 ng/dl). These data suggest that: (1) TSH responsiveness to prolonged TRH infusion is diminished during fasting and does not return to control (fed) values despite 5 days of refeeding a 1500 Kcal diet; (2) net T3 increases observed during the TRH infusion are greater in the fed period than in the fasting or refeeding periods; and (3) 5 days of refeeding a 1500 Kcal diet (40% carbohydrate, 40% fat, 20% protein) did not return the T3 to its original fed value whereas rT3 was completely restored to control values. Lastly, since the TSH response was lower both during the early and late phases of the infusion, the decrease in delta TSH to a bolus of TRH during fasting appears to represent one manifestation of a more general suppression of TSH neogenesis associated with caloric deprivation.

Adult↗