Prolactin response to metoclopramide in hyperthyroidism

Clinical features of primary hyperthyroidism caused by Graves' disease admixed with resistance to thyroid hormone (P453T)

A 34-year-old Japanese woman was referred to the hospital because of general fatigue and palpitations. She was diagnosed as having resistance to thyroid hormone (RTH) and Hashimoto's thyroiditis at the age of 28. She felt general fatigue, palpitations, heat intolerance, and sweating for 6 months. Thyroid function tests demonstrated elevated levels of free triidothyronine (T3) and free thyroxine (T4) that were above detectable ranges and a completely suppressed level of TSH that was below the detectable range. Titers of anti-TSH receptor antibody (TRAb) and thyroid-stimulating antibody (TSAb) were positive. A 20-minute Technetium-m99 pertechnetate thyroid uptake imaging study showed an elevated value of 39.53% and a normal-shaped thyroid gland. These results indicated that Graves' disease (GD) caused primary hyperthyroidism. Pituitary and peripheral tissues responded to the presence of excess thyroid hormone in the patient. Oral administration of methimazole was started and continued for 1 year 10 months, after which it was ceased. Two years after the cessation of methimazole treatment, level of free T4 was elevated compared to reference range, but levels of TSH and free T3 were within normal reference ranges. Titers of TRAb and TSAb remained negative for 2 years. These findings indicated that the patient's GD was in remission. In conclusion, it is difficult to make a differential diagnosis between GD with RTH and GD alone if RTH is not diagnosed before the onset of GD. An antithyroid drug is able to cause the remission of GD with RTH.

Evaluation of thyroid hormone action in a case of generalized resistance to thyroid hormone with chronic thyroiditis: discovery of a novel heterozygous missense mutation (G347A)

Resistance to thyroid hormone (RTH) is a dominantly inherited syndrome of variable tissue hyporesponsiveness to thyroid hormone (TH). Its characteristics are a high level of TH and inappropriate lack of TSH suppression. RTH is mainly categorized as generalized RTH (GRTH), pituitary RTH (PRTH), and peripheral tissue RTH (PTRTH). Untreated subjects with GRTH usually achieve a normal metabolic state. We describe a 21-year-old Japanese woman with GRTH and coincidental chronic thyroiditis. Physical examination revealed palpable goiter, congenital alopecia on top of the head, and short stature. She showed elevated levels of free triiodothyronine (FT3) and free thyroxine (FT4), and an inappropriately normal level of TSH. Anti-thyroglobulin and anti-thyroid peroxidase antibodies were positive. A TRH stimulation test showed a normal TSH response. The patient received the standardized diagnostic protocol, administration of incremental doses of liothyronine (L-T3). The peak TSH level after the TRH stimulation test gradually decreased. The patient showed low sensitivity to TH in terms of bone metabolism, protein catabolism, lipid metabolism, and urine magnesium metabolism. Sequence analysis of the TR beta gene was performed with informed consent, and this revealed a novel heterozygous mutation at codon 347 resulting in a GGG (glycine) to GCG (alanine) substitution (G347A). The patient was diagnosed as having GRTH with chronic thyroiditis, and carrying a novel mutation, G347A, of the TR beta gene.

Hypothalamic-pituitary-testicular axis and seminal parameters in hyperthyroid males

Information on the effect of abnormal thyroid function on male reproduction is less available than that for the female. To assess the effects of hyperthyroidism on hypothalamic-pituitary-testicular axis and on spermogram parameters, 25 male patients (19-47 years old) suffering from active Graves' disease were studied. Serum luteinizing hormone (LH), follicle stimulating hormone (FSH), and prolactin (PRL) were measured before and after administration of 100 microg GnRH plus 200 microg thyrotropin-releasing hormone (TRH). Testosterone (T), estradiol (E2), and 17-hydroxyprogesterone (17-OHP) were determined before and after 5000 IU human chorionic gonadotropin (HCG) administration. Serum sex hormone-binding globulin (SHBG), cortisol-binding globulin (CBG), androstenedione and bioavailable testosterone (bioT), and bioavailable estradiol (bioE2) were also measured. Spermograms according to World Health Organization (WHO) criteria were determined in 21 patients. Hormonal and seminal studies were repeated in six patients after 7 to 19 months of euthyroidism achieved after treatment for hyperthyroidism. As a control group, 10 normal men were evaluated. Impaired sexual function, gynecomastia, and low testicular volume were found in 12, 6, and 3 hyperthyroid patients. Mean basal LH was significantly higher than the control group (7.8 +/- 4.7 vs. 5.0 +/- 1.9 mIU/mL, respectively, p < 0.02), with hyperresponse to GnRH. The response of PRL to TRH was lower in patients versus control group (30 minutes: 3.9 +/- 3.4 and 12.0 +/- 2.8 ng/mL, p < 0.01). Basal levels of steroids and SHBG were significantly higher in patients than in normal men (T: 9.3 +/- 3.3 vs. 5.4 +/- 1.6 ng/mL, p < 0.005; E2: 62.2 +/- 25.2 vs. 32.1 +/- 11.0 pg/mL, p < 0.005; 17-OHP: 2.4 +/- 0.9 vs. 1.1 +/- 0.5 ng/mL, p < 0.001; SHBG: 102.3 +/- 37.3 vs. 19.0 +/- 5.0 nmol/L, p < 0.01). The maximal increment of T and 17-OHP after HCG was lower in hyperthyroid patients than in normal men (p < 0.019 and p < 0.001, respectively). Basal bioT was lower in patients than controls (1.7 +/- 0.8 and 3.1 +/- 1.9 ng/mL, p < 0.02). The following incidence of abnormal semen parameters was found: asthenospermia 85.7%, hypospermia 61.9%, oligospermia 42.9%, necrospermia 42.9% and teratospermia 19.0%. In euthyroidism, a normalization of 85% of seminal alterations was observed in the limited number of patients evaluated. Our results confirm that hyperthyroidism causes marked alterations of the gonadotropic and PRL axis and dramatically affects spermatic function. BioT measurement was useful to identify hypoandrogenism in these patients in spite of the high concentration of total testosterone. The restoration of most semen parameters when euthyroidism was achieved suggests that the alterations were induced by the Graves' disease.

Impaired prolactin response to arginine in patients with hyperthyroidism

OBJECTIVE

Reduced PRL responses to TRH or dopamine antagonists have been described in hyperthyroid patients. Arginine stimulates PRL secretion through pathways other than the activation of TRH receptors or dopamine-dependent mechanisms. We therefore investigated PRL responses to arginine in patients with hyperthyroidism.

DESIGN

L-Arginine (30 g infused over 30 minutes) was administered at time zero.

SUBJECTS

Sixteen patients with untreated hyperthyroidism due to Graves' disease (8 female and 8 male), with a mean age (+/- SE) of 31.3 +/- 1.4 years (range 23-42), and 12 normal subjects (6 female and 6 male, ages 30.1 +/- 2.1 years, range 22-47) were studied.

MEASUREMENTS

Prolactin was measured by RIA between -30 and 120 minutes, at 15-minute intervals.

RESULTS

Basal PRL levels were similar in the hyperthyroid patients and normal control subjects. The hyperthyroid women showed blunted PRL responses compared to normal women (peak PRL levels, 364 +/- 44 mU/l, vs 760 +/- 156, P < 0.02). PRL responses to arginine, small but clearly detectable in normal men, were completely abolished in hyperthyroid men (peak PRL levels, 248 +/- 48 mU/l, vs 112 +/- 14, P < 0.01).

CONCLUSIONS

PRL responses to arginine are impaired in hyperthyroid patients. Therefore, arginine should be added to the list of PRL stimuli whose responses are blunted in hyperthyroidism. Inhibition of PRL gene expression, and thus reduced pituitary PRL synthesis and storage, may explain why PRL responses to all secretagogues are reduced in these patients.

The influence of thyroid disorders on the dopaminergic regulation of prolactin, thyrotropin and growth hormone

In order to clarify if hyper- and hypothyroidism change by feed-back mechanisms the dopaminergic controlled release of PRL, TSH and GH, the serum values of these hormones were measured before and following iv administration of 5 mg metoclopramide in 10 hyperthyroid, 11 euthyroid and 10 primary hypothyroid age-matched females, all consecutively investigated. The secretion pattern, as well as the quantitated response (area under the curve - AUC) of PRL were identical for the three groups, and uninfluenced by thyroid status. By contrast the TSH responses (AUC) were significantly and positively correlated to the basal TSH, suggesting that the effect of metoclopramide was dependent on the secretory capacity of the thyrotropic cells. The serum GH level was found to decrease in all three groups following metoclopramide, probably due to the inhibition of release. Stimulation of the same subjects with 200 micrograms TRH iv resulted in response curves of serum PRL and TSH, which were significantly and positively correlated to the basal serum TSH. The serum values of GH increased following TRH in the hypothyroid group, while the values of the hyperthyroid were depressed and unchanged. The present results suggest that the dopaminergic tonus on PRL, TSH and GH secretion is unaffected by thyroid feed-back mechanisms. The TRH-induced release of each of the three hormones is, however, dependent on thyroid status.