To Thyrotropin-releasing Hormone Administration Research Articles

Comparison of Cortisol andACTHResponses after Administration of Thyrotropin Releasing Hormone in Normal Horses and Those with Pituitary Pars Intermedia Dysfunction

Changes in both adrenocorticotropin (ACTH) and cortisol concentration in response to thyrotropin releasing hormone (TRH) administration have been used to diagnose equine pituitary pars intermedia dysfunction (PPID), but the use of the 2 hormones has not been compared. Measuring ACTH concentration is superior to measuring cortisol concentration after TRH administration in differentiating between normal horses and those with PPID, and the 2 hormone concentrations are disassociated in PPID horses. Eleven horses and 2 ponies with PPID and 19 normal horses. A study evaluating cortisol and ACTH concentrations before and at 14, 30, and 60 minutes after TRH administration. At 14 and 30 minutes after TRH administration, cortisol concentration increased in PPID horses, and ACTH increased in all groups; ACTH, but not cortisol concentration, was significantly higher in PPID horses compared with normal horses. A relationship between cortisol concentration and ACTH concentration was seen in normal horses, but not in horses with PPID. Compared with normal castrated males, normal female horses had a greater change in cortisol concentration per unit change of ACTH concentration. ACTH and cortisol concentrations are disassociated in horses with PPID. Measuring ACTH concentration after TRH administration appears superior to measuring cortisol concentration as a diagnostic test for PPID.

Thyrotropin stimulating hormone response to thyrotropin releasing hormone in patients with panic disorder.

The aim of this study is to assess thyrotropin stimulating hormone (TSH) response to thyrotropin releasing hormone (TRH) in patients with panic disorder (PD). The effects of TRH administration on the release of TSH were examined in 15 patients who met DSM-III-R criteria for PD and compared their test results with those of 15 normal control subjects. Blood samples were taken before TRH administration (baseline values) and at 15, 30 and 60 min. delta max TSH values were lower in the panic disorder patients than in the control subjects. Using the criterion of delta max TSH < or = 7 mlU/l, nine of the 15 panic disorder patients and four of the 15 control subjects had a blunted TSH response to TRH. These results confirm the findings from earlier reports that patients with PD show blunted TSH response to TRH which is similar to that seen in depressed patients.

The hypothalamic-pituitary response in SLE. Regulation of prolactin, growth hormone and cortisol release.

It has been suggested that neuroendocrine regulation plays an important role in the pathogenesis and activation of autoimmune diseases. The aim of this investigation was to clarify the hypothalamic-pituitary response to a well-defined stimulus under standardised conditions in patients with SLE. Plasma concentrations of prolactin (PRL), growth hormone (GH) and cortisol were determined in venous blood drawn through an indwelling cannula during insulin-induced hypoglycaemia (0.1 U/kg b.w., i.v.) in ten patients and in 12 age-, gender- and weight-matched healthy subjects. Basal PRL concentrations were higher in patients vs healthy controls (12 vs 6 ng/ml, P < 0.01), though still within the physiological range. Insulin-induced plasma PRL and GH were significantly increased both in patients and healthy subjects; however, the increments or areas under the curves were not different in the two groups. Plasma cortisol response showed moderate attenuation in patients. Sensitivity of pituitary lactotrothrops to thyrotropin-releasing hormone (TRH) administration (200 microg, i.v.) was the same in patients and control subjects. In SLE patients with low activity of the disease the sensitivity of pituitary PRL release to TRH administration remained unchanged. The hypothalamic response to stress stimulus (hypoglycaemia) was comparable in patients and healthy subjects.

Thyrotropin-releasing hormone in critical illness

The aim of this study was to examine the effect of dopamine infusion on the thyrotropin (TSH), thyroid hormone, prolactin, and growth hormone responses to thyrotropin-releasing hormone (TRH) in critically ill patients. Prospective, randomized, controlled, open-labeled clinical study. The intensive care unit, University Hospital Gasthuisberg, Leuven, over a 1-month period. In 15 critically ill patients receiving dopamine treatment (5 micrograms/kg/min) for a mean of 43.3 +/- 1.2 (SEM) hrs after trauma or cardiac surgery, we studied the TSH, thyroid hormone, prolactin, and growth hormone responses to the administration of two consecutive intravenous TRH boluses of 200 micrograms, with a 6-hr interval. The dopamine infusion was continued in the control group and discontinued in the study group. Serum concentrations of TSH, prolactin, and growth hormone were measured before and 20, 40, 60, and 120 mins after TRH administration. Serum concentrations of thyroxine (T4), triiodothyronine (T3), reverse T3, and thyroid hormone binding globulin were determined before and 120 mins after each TRH injection. There was a > 100-fold interindividual variation in the baseline TSH concentration and in the TSH peak value after TRH administration. Two consecutive doses of TRH evoked a mean 16% increase in serum T4 concentration (p = .003) and a mean 47% increase in T3 (p = .001), whereas serum reverse T3 and thyroid hormone binding globulin values remain unaltered. Each of the TRH boluses increased serum growth hormone concentrations in the continued dopamine and discontinued dopamine groups, by a median of 60% (p = .001) and 68% (p = .001), respectively. Three hours after dopamine withdrawal, there was a three-fold increase of the peak TSH response (p = .001), a higher T3 response (p = .01), and a ten-fold increase of the peak prolactin value (p = .001) in response to TRH administration. The TSH response to TRH administration in critical illness presents a striking interindividual variation and dopamine dependent. Repeated TRH administration results in a repetitive increase of TSH, prolactin, growth hormone, T4, and T3, without increasing reverse T3. These observations point toward a potential for TRH as a strategy for reversing the euthyroid sick syndrome, growth hormone deficiency, and immune dysfunction associated with critical illness.

Antisense to Thyrotropin Releasing Hormone Receptor Reduces Arterial Blood Pressure in Spontaneously Hypertensive Rats

We report in the present study the effect of intrathecal treatment with antisense oligonucleotides complementary to thyrotropin releasing hormone (TRH) receptor mRNA on the pressor response to intrathecal administration of TRH and on resting arterial blood pressure in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). In 16-week-old male WKY rats, 18-base phosphodiester antisense or mismatch oligonucleotides to TRH receptor mRNA (100 micrograms per day) were injected intrathecally for 3 days. Twenty-four hours after the last injection, the magnitude of the pressor response to intrathecal TRH (10 micrograms) was significantly smaller in the antisense-treated group (n = 7) compared with mismatch-treated controls (n = 7) (change in mean arterial pressure, +20.3 +/- 3.0 versus +32.6 +/- 2.5 mm Hg, P < .01). No differences were observed in the pressor responses to injection of N-methyl-D-aspartic acid. Resting arterial blood pressure was unaffected by antisense treatment in WKY rats. In separate experiments, 16-week-old male SHR were treated with antisense (n = 7) or mismatch (n = 6) oligonucleotides for 3 days. Mean resting arterial blood pressure was significantly reduced by treatment with antisense oligonucleotides (from 157 +/- 4.8 to 119 +/- 8.8 mm Hg, P < .01), but no significant changes were observed in mismatch-treated animals. Our results suggest that the expression of TRH receptors in spinal sympathetic preganglionic neurons can be selectively reduced by intrathecal treatment with antisense oligonucleotides and that TRH projections to sympathetic preganglionic neurons play an important role in the elevation of arterial blood pressure in SHR.

Effect of glucocorticoids on the paradoxical growth hormone response to thyrotropin-releasing hormone in patients with acromegaly

It has been hypothesized that in acromegalic patients, as well as in normal subjects, acute increases in serum cortisol levels may cause an enhancement of hypothalamic somatostatin secretion, which in turn may be responsible for the glucocorticoid-mediated growth hormone (GH) inhibition. The aim of this study was to investigate short-term effects of an intravenous (IV) infusion of hydrocortisone on the GH response to thyrotropin-releasing hormone (TRH) in acromegaly. We studied six adult patients with active acromegaly. The group was composed of four women and two men with a mean age of 55.8 ± 6.4 years (range, 27 to 68) and a mean body mass index of 26.7 ± 1 kg/m 2 (range, 23.3 to 30). All patients underwent the following treatments: (1) hydrocortisone alone: a bolus IV injection of hydrocortisone succinate 100 mg in 2 mL saline at time −60 minutes, followed by a 120-minute IV infusion of hydrocortisone succinate 250 mg in 250 mL saline from −60 to 60 minutes; (2) TRH + hydrocortisone: a bolus IV injection of TRH 200 μg 60 minutes after initiation of a 2-hour hydrocortisone infusion; (3) TRH alone: a bolus IV injection of TRH at time 0, 60 minutes after initiation of a 2-hour saline infusion. In all six patients, TRH induced large GH increases (absolute peak GH level, 58.1 ± 23.2 μg/L; maximum % GH change with respect to baseline, 1,397.8% ± 807.8%; range, 205% to 5,219%). In the whole group of acromegalic patients, hydrocortisone infusion did not significantly affect the mean GH response to TRH (absolute peak GH level, 45.4 ± 19.5 μg/L; maximum % GH change with respect to 0-minute level, 894.8% ± 320%; range, 106% to 1,988%). After hydrocortisone + TRH administration, all six patients showed significantly higher absolute GH values as compared with values obtained with hydrocortisone alone from time 15 to 45 minutes. Our data show that the paradoxical GH response to TRH in acromegaly is resistant to the inhibitory action of an acute and sustained elevation of serum cortisol level.

Influence of erythropoietin on paradoxical responses of growth hormone to thyrotropin-releasing hormone in uremic patients

Several alterations in growth hormone (GH) secretion have been reported in patients with chronic renal failure. The aim of the present report has been to assess the effect of acutely administered recombinant human erythropoietin (rHuEPO) infusion on GH responses to thyrotropin-releasing hormone (TRH) in uremic patients. Twelve male patients (mean age 46.2 years, range 24 to 69) were studied. Seven of them were on continuous ambulatory peritoneal dialysis (CAPD), two on chronic hemodialysis (HD) and two in pre-dialysis (PreD). None had been treated before with rHuEPO. Each patient was tested with TRH (400 micrograms i.v. in bolus), and with TRH plus rHuEPO (40 U/kg in constant infusion for 30 min) on different days. TRH administration provoked a paradoxical response of GH (peak > 5 micrograms/liter) in nine (5 CAPD, 2 HD, 2 PreD) out of 12 patients. In this group of patients with anomalous GH responses, rHuEPO infusion produced an abolishment of the paradoxical responses (GH peak < 5 micrograms/liter) in eight patients and a marked decrease in a further one. On the contrary, in patients with no paradoxical GH response, stimulation with TRH plus rHuEPO did not induce any change in GH release compared with that observed after TRH alone. rHuEPO had no effect on TRH-induced thyrotropin release. These results suggest that the paradoxical GH response to TRH in patients with chronic renal failure is blocked by rHuEPO administration. This rHuEPO action might be mediated by an increased release of somatostatin or an inhibited GH-releasing hormone secretion.

Blunted TSH and unaltered PRL responses to TRH following repeated administration of TRH in neurologic patients: A replication of neuroendocrine features of major depression

A blunted thyrotropin (TSH) and an unaltered prolactin (PRL) responses to thyrotropin-releasing hormone (TRH) are widely recognized in neuroendocrinology of depression. We studied effects of repeated TRH administration of 1 mg/day for 10 days on the pituitary-thyroid axis function and PRL secretion in 16 euthyroid patients with neurological disorders. Although levels of serum thyroid hormones and of nonstimulated PRL were not affected by the treatment, baseline TSH levels were markedly inhibited. A blunted response of TSH to TRH was found without a significant effect on a PRL response to TRH after long-term treatment with TRH in four patients in whom a TRH test was performed. These changes are similar to those in depressed patients. TRH administration in this manner replicates a lowered sensitivity of thyrotrophs of the pituitary with a normal responsibility of lactotrophs in depression.

Corticotropin-releasing hormone inhibition of paradoxical growth hormone response to thyrotropin-releasing hormone in insulin-dependent diabetics

A paradoxical growth hormone (GH) response to thyrotropin-releasing hormone (TRH) has been observed in type 1 diabetic patients and was hypothetically attributed to a reduced hypothalamic somatostatin tone. We have previously reported that corticotropin-releasing hormone (CRH) inhibits GH response to growth hormone-releasing hormone (GHRH) in normal subjects, possibly by an increased release of somatostatin. To study the effect of CRH on anomalous GH response to TRH, we tested with TRH (200 μg intravenously [IV]) and CRH (100 μg IV) + TRH (200 μg IV) 13 patients (six males and seven women) affected by insulin-dependent diabetes mellitus. A paradoxical GH response to TRH was observed in seven of 13 patients, one man and six women. In these subjects, the simultaneous administration of CRH and TRH significantly reduced the GH response to TRH, as assessed by both the maximal GH mean peak ± SE (2.18 ± 0.67 v 9.2 ± 1.26μg/L, P < 0.005) and the area under the curve (AUC) ± SE (187 ± 32 v 567 ± 35μg · min/L, P < .001). CRH had no effect on TRH-induced thyroid-stimulating hormone (TSH) release. Our data demonstrate that the paradoxical GH response to TRH in patients with type 1 diabetes mellitus is blocked by CRH administration. This CRH action may be due to an enhanced somatostatin release. Our data also show that exogenous CRH has no effect on TSH response to TRH, thus suggesting the existence of separate pathways in the neuroregulation of GH and TSH secretion.

Growth hormone response to thyrotropin-releasing hormone in acromegalic patients: reproducibility and dose-response study.

The aim of the study was to analyze 14 consecutive patients with active acromegaly who had not undergone any therapy, the dose response of growth hormone (GH) to thyrotropin-releasing hormone (TRH), the existence of reproducibility of such response as well as to rule out the possibility of spontaneous fluctuations of GH which would mimic this response. On several nonconsecutive days, we investigated the GH response to saline serum, 100, 200 (twice) and 400 micrograms of TRH administration. We also studied both basal serum prolactin, serum prolactin after TRH administration and thyrotropin values. Our results show an absence of GH response after saline serum infusion, whereas after TRH doses, 36.3 42.8 and 45.4% positive responses were obtained, respectively. All GH responders were concordant to the different doses administered. The mean of GH concentrations of the different doses at different times did not reach significant differences. The response to the administration of the same dose brought about a significative increase, although it was not identical. It demonstrated a progressive increase of the area under the response curve, as did the means of increments after each TRH administration, albeit without reaching statistical significance. Between the GH-responding and GH-nonresponding groups there were no differences in either basal serum prolactin or serum prolactin and thyroid-stimulating hormone levels after TRH stimulation. The present study clearly shows that TRH elicits serum GH release from GH-secreting pituitary tumors. The response was reproducible in qualitative terms rather than quantitative, and no dose-response relationship was found between the TRH concentrations and the amounts of GH secreted.

Inappropriate growth-hormone (GH) response to thyrotropin-releasing hormone (TRH) occurs infrequently in well-regulated diabetes mellitus

We randomly administered thyrotropin-releasing hormone (200 micrograms, as an i.v. bolus) or control saline (in isovolumic amount) to 30 male diabetic subjects (23 IDDM, 7 NIDDM) in fair metabolic control (HbA1 9.7 +/- 0.3%, means +/- SEM) and to 12 healthy male controls on two different mornings. While GH in the basal state was similar in IDDM, NIDDM and normal subjects, TRH administration evoked a significant GH release only in a single IDDM individual. The only GH-responder to TRH was a newly-diagnosed (two weeks) IDDM patient, still with a high glycated hemoglobin level (HbA1 11.1%), despite normal plasma glucose levels. Saline infusion did not affect GH concentrations either in normals or in diabetics. Exaggerated GH responses to TRH are uncommon in diabetic patients in good metabolic conditions.

Thyrotropin and Growth Hormone Responses to TRH Stimulation Are Normal in 6–12 Year-Old Children with Major Depression

ABSTRACT Thyrotropin-stimulating hormone (TSH) and growth hormone (GH) responses to thyrotropin-releasing hormone (TRH) stimulation were examined as potential biological markers of childhood depression in 20 drug-free children on a children's psychiatric unit. Six children fulfilled DSM-III-R criteria based on KIDDIE–SADS–E interviews for major depression (MD). The control group consisted of 14 children with other psychiatric disorders. TSH and GH were measured before and over the course of 90 minutes after administration of TRH (400 μg i.v.). There were no significant differences between children with major depression and children with other psychiatric disorders in TSH or GH response to TRH stimulation, as measured by mean baseline levels, mean peak levels, mean change in levels (peak minus baseline), and mean time of peak levels. These results suggest that, unlike adolescents and adults with major depression, children with major depression do not demonstrate a blunted TSH response. Similarly, unlike ad...

The paradoxical response of growth hormone (GH) to thyrotropin-releasing hormone (TRH) in constitutionally tall children involves a cholinergic pathway

To investigate whether or not a cholinergic pathway is involved in the paradoxical response of GH to TRH in constitutionally tall children, we studied 8 healthy prepubertal children aged 4 2/12-7 10/12 yr, whose heights were over the 95th percentile of the NCHS tables. We defined as "paradoxical" a GH increment greater than 5 ng/ml in response to TRH. Five out of 8 children showed a paradoxical response of GH to TRH (mean GH peak after TRH of 10.7 +/- 1.1 ng/ml). Pretreatment with atropine (0.01 mg/kg IM 30 min prior to the TRH administration) abolished the TRH induced GH rise (peak GH after TRH of 1.5 +/- 1.0 ng/ml, p less than 0.01) but did not modify the TSH response (peak TSH after TRH: basal conditions 8.7 +/- 0.8 microU/ml, post atropine: 9.5 +/- 1.4 microU/ml, p greater than 0.05). Our results demonstrate that a cholinergic pathway is involved in the paradoxical response of GH to TRH in constitutionally tall children.

Prolactin and thyroid status in prepubertal children with mild to moderate obesity.

Prolactin (PRL) response to thyrotropin releasing hormone (TRH) in 21 prepubertal children with mild to moderate obesity was compared with that in 21 normal prepubertal children (controls). Basal PRL levels were normal but the mean peak PRL response and mean increment in PRL levels following TRH administration were significantly lower in prepubertal obese children (p less than 0.001). The mean PRL responses to TRH were significantly impaired at all time intervals in prepubertal obese boys and girls compared to the control subjects. Linear regression and correlation coefficient analysis did not reveal any significant relation between the percent overweight and PRL response. Basal T4, T3 levels and T3 and TSH response to TRH were similar in both groups. The findings suggest that neuroendocrine regulation of prolactin is impaired in prepubertal children even with mild to moderate obesity. This could be secondary to altered neurotransmitter status at the hypothalamic level. Further studies are needed to determine whether the defect is innate or acquired, primary or secondary.

Serum thyrotropin (TSH) responses to thyrotropin-releasing hormone (TRH) in patients with anorexia nervosa and bulimia: Influence of changes in body weight and eating disorders

Serum thyrotropin (TSH) responses to thyrotropin-releasing hormone (TRH) were studied in 47 women with anorexia nervosa (AN) (group I) and in 11 bulimic patients of normal weight (group II). In group I, TSH responses were low in nine patients, delayed in 32 and normal in six. Patients with a normal TSH response had a lesser degree of anorexia than those with a delayed TSH response. Bulimia and vomiting were more frequently observed in the low response group. The maximum increase in TSH concentrations following TRH administration in the group I patients with vomiting (4.0 ± 0.90 μU/ml, mean ± S.E.) was significantly lower than that in the group I patients without vomiting or in normal controls (11.2 ± 0.82 μU/ml and 11.1 ± 2.34 μU/ml, respectively). Twenty-five patients with abnormal TSH responses in group I were retested after weight gain. Initially, TSH responses were low in six and delayed in 19. Following weight recovery, responses continued to be abnormal in five of the six and in eight of the 19, respectively. The symptoms of eating disorders continued in all patients with abnormal TSH responses even after weight recovery, whereas patients with normal responses after weight gain recovered from all symptoms. Of 11 patients in group II, six had abnormal TSH responses to TRH; the responses were delayed in four and low in two. Patients with normal responses had a lesser degree of eating disorder, compared with abnormal responders. These observations suggest that abnormal TSH responses in patients with AN were not necessarily due to weight loss alone; rather, they may be related to the eating disorder itself.

Prolactin response to thyrotropin-releasing hormone in early and advanced human breast cancer.

While prolactin (PRL) has been shown to stimulate the development of mammary carcinoma in several animal species, its role in human breast cancer remains to be established. To further investigate PRL secretion in human breast cancer, its basal levels and response to thyrotropin-releasing hormone (TRH) were evaluated in 16 patients (6 with no metastases and 10 with metastatic locations). The control group consisted of 19 healthy women. High PRL basal concentrations were seen in 2 patients only; no significant differences were found between the other patients and the normal subjects. The PRL increase induced by TRH administration was significantly higher in patients than in controls. Finally a change in the hormonal secretion was found after chemotherapy in 3 of the 5 patients in whom PRL response to TRH was evaluated either before or 10-12 days after a cycle of intravenous CMF adjuvant chemotherapy. These results demonstrate the existence of an exaggerated response of PRL to TRH in patients with breast cancer, even in the presence of normal basal levels. Moreover, they would seem to suggest a possible influence of CMF on PRL response to TRH stimulation.

Use of TSH response to TRH as an independent variable.

The thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) was assessed in 35 consecutive male admissions. Patients with TSH blunting were identified; they were compared with patients without blunting and with normal subjects. Patients without TSH blunting were normal as regards all endocrine variables. Patients with TSH blunting showed reduced TSH (but normal prolactin) levels before and after TRH administration, although their thyroid hormone levels and cortisol levels were normal. Height, weight, and body surface were unrelated to TSH blunting. The test-retest reliability of a blunted TSH response was acceptable.

STUDIES ON SERUM PROLACTIN (PRL) AND TSH IN PATIENTS WITH BREAST CANCER

Serum prolactin (PRL) and TSH basal levels and the responses of serum PRL and TSH to thyrotropin releasing hormone (TRH) were investigated by radioimmunoassay in patients with breast cancer, who were classified in the following four groups : New T13, M0 breast cancer patients (N = 70), M1 or recurrent breast cancer patients (N = 50), locally advanced breast cancer patients (N = 8) and post-biopsied breast caner patients (N =28).Serum samples were taken 7 times before and for 3 hours after administration of TRH (0.5mg, i.v.). These were examined for basal and peak values, and reaction patterns.PRL levels : Patients with locally advanced and post-biopsied breast cancer indicated high PRL levels in the basal and peak values (P < 0.01), and showed an excessive-prolonged pattern to TRH.TSH levels : Patients with locally advanced and M1 or recurrent breast cancer indicated high TSH levels in the basal and peak values and showed an excessive-prolonged pattern to TRH.To examine the detailed variations within the group of the patients with recurrent breast cancer, they were classified in the following 3 subgroups : locoregional recurrent breast cancer (N =10), skeletal metastatic breast cancer (N = 22), and visceral metastatic breast cancer (N =6).The locoregional recurrent patients showed high PRL levels in the basal and peak values. The skeletal metastasized patients with breast cancer tended to show high TSH levels in the basal and peak values.To comfirm whether local (intercostal nerve) stimulation gives any effect on high serum PRL levels in the patients with locally advanced breast cancer, epidural anesthesia was performed 24 hours in accordance with Keegan's dermatome.As a result, basal PRL values tended to decrease in the cases blocked satisfactorily, but peak PRL values indicated no change even though blocked satisfactorily. It might be caused by short anesthetic duration.Post-biopsied breast cancer patients indicated also high PRL levels in the basal and peak values, but compared post-biopsied breast cancer to post-biopsied benign mammary tumor, both indicated increment of serum PRL peak values. High serum PRL levels of post-biopsied breast cancer patients might be caused by manipulation of biopsy itself.

Prolactin hyperstimulation in response to thyrotropin-releasing hormone in patients with endometriosis

In order to clarify the role of hyperprolactinemia as a possible cause of infertility in patients with endometriosis, baseline serum prolactin (PRL) concentrations and the PRL response to thyrotropin-releasing hormone (TRH) stimulation were measured in 14 infertile women with endometriosis and in 13 normal, fertile women. Baseline PRL concentrations were 2-fold greater in the endometriosis group than in normal subjects, but the mean values did not differ significantly. Following TRH administration, a significant increase in peak PRL concentrations was observed in patients with endometriosis (211.5 +/- 34.9 ng/ml) when compared with corresponding values in control subjects (117.1 +/- 14.9 ng/ml, P less than 0.05). This hypersecretory state was selective for PRL because no significant differences between the baseline and TRH-stimulated thyroid-stimulating hormone (TSH) concentrations or total serum thyroxine concentrations were observed. In summary, some infertile women with endometriosis exhibit a greater capacity for PRL secretion than normal women. These results suggest that relative hyperprolactinemia may be responsible for the infertility associated with endometriosis, and that PRL suppression may be indicated in these patients.

Significance of Transient Postnatal Hypothyroxinemia in Premature Infants With and Without Respiratory Distress Syndrome

The significance of relatively low thyroxine (T4) levels in preterm infants with and without respiratory distress syndrome (RDS) was assessed by evaluating the free T4 level, the thyrotropin (TSH) response to thyrotropin releasing hormone (TRH), and intellectual development in infants less than or equal to 35 weeks with cord blood T4 concentrations less than 6.5 microgram/100 ml. Fifty-four (19 well, 28 with RDS, and seven without RDS and sick) of 215 premature infants (25%) and 27 of 8,831 term infants (0.3%) had cord T4 levels less than 6.5 microgram/100 ml. Serum T4 levels were measured in 39 surviving preterm infants (20 RDS and 19 well) during the first 5 days of life and at 2, 4, 24, and 52 weeks postnatally. Serum total T4 level during the first week was 4.5 +/- 0.3 microgram/100 ml (mean +/- SEM). Free T4 levels ranged from 1.1 to 2.2 ng/100 ml (normal adult range 0.8 to 2.3 ng/100 ml). Administration of TRH resulted in a clear increase in both TSH and T4 levels in all infants. T4 levels increased significantly (r = .70, P less than .01) with increasing postnatal age, reaching stable levels by 6 to 7 weeks. Developmental quotients obtained in the infants with low T4 levels were no different from those found in a matched control population at 12 months of age. The low T4, free T4, and TSH concentrations and normal TSH responses to TRH found in these infants are characteristic of hypothalamic (tertiary) hypothyroidism, but differ from classic tertiary hypothyroidism in that the disorder was transient. The normal intellectual development at 12 months of age and the spontaneous increase in T4 levels that occurs over the first six weeks of life suggest that the low T4 levels in these infants reflect a benign relative delay in maturation of hypothalamic-pituitary-thyroid control.