We conducted a medical survey on subjects living in the mountain districts, located at about 400 to 500 m above sea level, near Malang City in the eastern part of Java, the Republic of Indonesia. Serum levels of thyrotropin (TSH) and thyroid hormones were measured in 163 subjects from 9 to 70 years of age, of which 45 were male and 118 were female. A synthesized thyrotropin releasing hormone (TRH) 500pg infusion test was performed on 41 of the subjects from 14 to 70 years of age (7 males, 34 females) and on 15 normal Japanese subjects from 19 to 35 years of age (7 males, 8 females) as controls.
Serum TSH and triiodothyronine (T₃) were measured by means of radioimmunoassay, serum thyroxine (T₄) by competitive protein binding analysis, and serum PBI by the auto-analyser method. The incidence of antithyroglobulin antibody (thyroid test) and antimicrosomal antibody (microsome test) was also studied to assess the role of auto-immunity in goitrogenesis. Goiter size was classified into five grades : from Grade 0 (without goiter) to Grade IV (with huge goiter) by our criteria.
Mean serum PBI values were low in all groups with goiters, especially in subjects with huge goiters, but there was no significant difference between non-goitrous and goitrous groups. In one of the 28 non-goitrous subjects, the serum T₄ level was low while that of the remaining 27 was within the normal range. Serum T₄ values of subjects with big and huge goiters were significantly lower than those of the non-goitrous group. There was no significant difference between the control and non-goitrous groups.
On the other hand, serum T₃ levels were normal in only two of the 28 non-goitrous subjects and were low in the remaining 26. In the group with huge goiters, serum T₃ levels were low in 9, normal in 20, and elevated in only one. T₃ values in the groups with big and huge goiters were significantly higher than those of the non-goitrous group. As mentioned above, there was a negative correlation between serum T₄ and T₃ in subjects with goiters, and relative hypersecretion of T₃ occurred in the goitrous groups in contrast to the non-goitrous group. The result of our study confirms that preferential secretion of T₃ by the thyroid occurs in goitrous subjects and may represent an important homeostatic mechanism to combat against iodine deficiency.
Serum TSH levels in 28 non-goitrous subjects were all within the normal range, and there were elevated serum TSH levels in only 19 out of the 135 goitrous subjects. Although serum log TSH levels do not significantly correlate with the degree of goiter, the mean serum log TSH of the goitrous groups was higher than that of the non-goitrous group, the mean of which was higher than that of the control subjects.
Following TRH infusion, 7 non-goitrous subjects showed normal serum TSH response to TRH. In 34 goitrous subjects, there were various serum TSH responses, which included a normal response in 17, delayed in 6, hypo in 4, non in 5 and hyper in 2. According to our results of the TRH test, the secretion of TSH by the pituitary in goitrous subjects following TRH infusion may be different from that in a normal control. There were two inverse relations between basal TSH and T₄ (r=-0.43, P<0.01) and peak TSH and T₄ (r=-0.44, P<0.01) following TRH infusion. There was, however, no significant relation between serum TSH and T₃. Since serum TSH correlated with serum T₄ in the TRH test, the TSH secretion of the pituitary may be partially controlled by the serum T₄ level. There was no positive case in the thyroid test and only one positive case in the microsome test.
Many of the subjects with goiter have hypothyroidism, if judged by serum T₄, T₃ and PBI.