GASTRIC SECRETION IN HYPERTHYROIDISM

The thyroid and the gut

Thyroid disease is common, and its effects on the gastrointestinal system are protean, affecting most hollow organs. Hashimoto disease, the most common cause of hypothyroidism, may be associated with an esophageal motility disorder presenting as dysphagia or heartburn. Dyspepsia, nausea, or vomiting may be due to delayed gastric emptying. Abdominal discomfort, flatulence, and bloating occur in those with bacterial overgrowth and improve with antibiotics. Reduced acid production may be due to autoimmune gastritis or low gastrin levels. Constipation may result from diminished motility, leading to an ileus, megacolon, or rarely pseudoobstruction. Ascites in myxedema is characterized by a high protein concentration. Graves' disease accounts for 60% to 80% of thyrotoxicosis. Hyperthyroidism is accompanied by normal gastric emptying with low acid production, partly due to an autoimmune gastritis with hypergastrinemia. Transit time from mouth to cecum is accelerated, resulting in diarrhea. Steatorrhea is due to hyperphagia and stimulation of the adrenergic system. Diarrhea in medullary carcinoma of the thyroid (MCT) may be due to elevated calcitonin, prostaglandins, or 5-hydroxyindoleacetic acid. Ileal or colonic function may be abnormal. The esophagus may be compressed by benign processes, but more often by malignancies. MRI and CT scans are the best diagnostic modalities. The gastrointestinal manifestations of thyroid disease are generally due to reduced motility in hypothyroidism, increased motility in hyperthyroidism, autoimmune gastritis, or esophageal compression by a thyroid process. Symptoms usually resolve with treatment of the thyroid disease.

Serum gastrin levels in patients with thyroid dysfunction

Fasting serum gastrin levels measured by radioimmunoassay were found to be elevated in patients with hyperthyroidism and low in patients with hypothyroidism. The oral administration of beef extracts resulted in more increase of serum gastrin in hyperthyroid patients than in normal subjects. After restoration of the euthyroid state by treatment, no more increase in serum gastrin levels was observed. Slight correlation between gastrin levels and serum T3 levels was observed in pretreated hyperthyroid patients (r = 0.40), but significant correlation between them was found after restoration of the euthyroid state by treatment (r = 0.50). However, it seemed to be able to divide into two groups in the pretreated patients. One was a patient group whose gastrin levels correlated closely to serum T3 levels (r = 0.83, p less than 0.01). The other was a group whose serum gastrin levels remained in low even in high T3 levels (r = 0.81, p less than 0.01). Different sensitivity to thyroid hormone in the G-cells of gastrointestinal tract may exist in these two groups, because patients age and duration of their illness were not different between them.

Gastric secretion in hyperthyroidism

The coexistence of hyperthyroidism and peptic ulcer is considered to be extremely rare. We have treated 24 patients with both hyperthyroidism and peptic ulcer during the years 1968-1978. With regard to the correlation between hyperthyroidism and peptic ulcer, we found that the mean value of gastric acid output was higher in the hyperthyroid patients than in the controls, and an extremely high gastric acid output was noted in 8 of the hyperthyroid patients. These results suggest that hyperthyroidism coexisting with peptic ulcer may not be so rare.

Gastric acid secretion, serum gastrin and parietal cell histology in rat hyperthyroidism

Experimental hyperthyroidism was produced in rats by thyroxin injection, and changes in gastric acid secretion and serum gastrin level were determined to analyze the relation between these changes and hyperthyroidism. Administration of thyroxin to two groups of rats-20 micrograms per 100 g of body weight for 20 days and 75 micrograms for 7 days-brought about significant increases in serum T3 level, gastric pH and serum gastrin level. An increase in gastric pH took place later than that in serum T3 level; this time lag implies that a decrease in acid secretion was not caused by an direct effect of thyroxin on the parietal cell but by its secondary effect. In the T4-injected rats with decreased gastric acid secretion, the parietal cell remained normal in form and succinic dehydrogenase activity was also normal. The electron microscopical observations showed nothing abnormal in the parietal cells. These findings suggest that a decrease in acid secretion was not due to any structural changes in the gastric mucosa but to functional suppression. The serum gastrin level rose in correlation with an increase in gastric pH and fell by HCl administration to the stomach. Feedback inhibition by pH remained in the G cell.

Gastric acid secretion, serum gastrin and parietal cell histology in hyperthyroidism

A decrease in MAO by gastrin stimulation was observed in 13 of 20 hyperthyroid patients. Five of these 13 cases had achlorhydria. The decrease in gastric acid secretion had no relation to the duration of symptoms, serum T3 and T4 levels, serum antithyroglobulin antibody levels and serum antithyroid microsomal antibody levels. Gastroscopy with biopsy was performed in 17 cases. In patients with achlorhydria, macroscopic and histological atrophy was not observed in the body, and parietal cells were present and their succinic dehydrogenase activity was normal. Electron microscopy of the parietal cells of patients with achlorhydria showed that their cells were similar to those in the resting state of healthy subjects with the ability to secrete normal amounts of gastric acid. These findings demonstrate that the decrease in gastric acid secretion in hyperthyroidism is not caused by any structural changes in the gastric mucosa but by functional suppression. In the present experiment, this suppression was found resistant to gastrin. A rise in serum gastrin level was observed in 8 cases. Either achlorhydria or marked hypoacidity was found in 6 cases with the level more than 400 pg/ml. The HCl administration temporarily lowered elevated gastrin levels, and feedback inhibition by HCl was found to be maintained. A rise in gastric pH was considered to be one of the prerequisites for an increase in serum gastrin level.

High serum gastrin levels in thyrotoxic patients

High gastrin levels were found in twenty-one out of fifty-six consecutive patients (38%) with thyrotoxicosis. Following return to euthyroidism gastrin levels generally fell, but twelve patients (21%) remained hypergastrinaemic. Six of these patients (11%) had achlorhydria indicating atrophic gastritis of the antrum sparing type. No correlation between gastrin and triiodothyronine values was found. It is suggested that gastrin levels should be measured in thyrotoxic patients after treatment, and further control instituted in patients with raised gastrin levels. The relationship between gastric function, gastrin release and thyroid function seems complex. The interactions may involve both a direct effect of thyroid hormone on gastric acid production, adrenergic influences on gastrin release and linked phenomena with development of thyroid and gastric auto-immune diseases.

Parietal cell antibodies. Part I. Clinical and pathological studies of parietal cell antibodies

The incidence of parietal cell antibodies (P.C.A.) in patients with various diseases was investigated by complement fixation test (C.F.T.). The relationship between the incidence of P.C.A. and clinical and pathological findings was also investigated. The incidence of P.C.A. with simple atrophic gastritis was 34.8% in total cases, 29.0% in male and 48.1% in female, respectively. The difference between the sexes was statistically significant (p less than 0.05). The incidence of P.C.A. in superficial gastritis was 37.5%, showing the same incidence as atrophic gastritis. The difference between the two groups was not statistically significant (p less than 0.05). The incidence in patients with hypo- and hyperactivity was 43.0% and 11.8%, respectively. The difference was statistically significant, but that between hypo- and normoacidity was not significant (p less than 0.05). The author postulated the conclusion that the superficial gastritis could be included in the category of atrophic gastritis. The dissociation of correlation of titer of C.F.T. with acidity and histological findings was found. The correlation was more significantly observed with acidity than with histological findings. The relatively high incidences of P.C.A. were noted in patients with peptic ulcer, gastric carcinoma and chronic thyroiditis. The incidence of P.C.A. in other diseases showed the nearly equal incidence to that of other investigators. Three cases of postgastrectomy patients were noted, in which the P.C.A. disappeared four to six months after total or subtotal gastrectomy.