Naomi Hizuka

A simple diagnostic test using GH-releasing peptide-2 in adult GH deficiency

OBJECTIVE The international, first-line diagnostic test for adult GH deficiency is the insulin tolerance test (ITT), which is contraindicated in some patients due to severe adverse events. Alternatives such as GH-releasing hormone combined with arginine or GH-releasing peptides (GHRP) have been proposed. We validated the use of GHRP-2 for diagnosing adult GH deficiency (GHD). METHODS Seventy-seven healthy subjects and 58 patients with peak GH<3 microg/l by ITT were enrolled. After overnight fasting, a 100 microg dose of GHRP-2 was administered intravenously; blood samples were taken during the subsequent 2 h and GH measured by immunoradiometric assay. RESULTS Serum GH peak occurred within 60 min after GHRP-2 administration in all subjects. GH responses to GHRP-2 were not affected by gender, but were slightly lower in elderly subjects and those with adiposity, although these did not influence diagnosis of GHD. Repeated tests showed favourable reproducibility. Peak GH concentrations after GHRP-2 were significantly (P<0.001) lower in patients (1.36+/-2.60 microg/l) than the healthy group (84.6+/-60.9 microg/l) with no difference between hypothalamic and pituitary diseases. Serum GH concentration at the point where sensitivity of response crossed with specificity ranged from 15 to 20 microg/l. A cut-off value of 15 microg/l for diagnosing GHD with GHRP-2 corresponded to the diagnostic value of 3 microg/l in the ITT. CONCLUSIONS The GHRP-2 provocative test showed favourable reproducibility and was mildly influenced by age and adiposity. Severe GH deficiency could be diagnosed with high reliability using a 15 microg/l (9 microg/l when GH calibrated with recombinant World Health Organization 98/574 standard) cut-off for peak GH concentration.

A nationwide attempt to standardize growth hormone assays.

The Growth Hormone (GH) and Its Related Factors Study Committee of the Foundation for Growth Science, Japan, has been conducting a quality control study for 15 years to improve the equality of diagnosis of GH deficiency. It found that the greatest differences in measured GH values were due to the different potencies of the kit standards, which were primarily adjusted to WHO standards for human GH of pituitary origin. With the collaboration of kit makers and the Study Group of Hypothalamo-Pituitary Disorders of the Ministry of Health, Labor and Welfare, all GH kits in Japan have begun using the same recombinant human GH standard since April 2005. As a result the diagnostic cut-off peak GH has changed from 10 to 6 ng/ml.

Hyponatremia after Transsphenoidal Surgery for Hypothalamo-Pituitary Tumors

Transient diabetes insipidus is a well-known complication after transsphenoidal surgery (TSS). On the other hand, transient hyponatremia has been reported as being a delayed complication of TSS. Transient hyponatremia has been attributed to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), but the details of hyponatremia have not been clarified. In the present study, we retrospectively reviewed 110 consecutive patients (39 males and 71 females, age 9–80 years) operated on transsphenoidally for pituitary and hypothalamic tumors. We investigated the frequency, time of onset, duration of hyponatremia after TSS, and analyzed possible factors associated with it. A postoperative sodium concentration <135 mEq/l was observed in 29 (26%) patients. Five patients were excluded from this study because their hyponatremia could be due to either overdose of desmopressin or SIADH for meningitis. Therefore, we investigated 24 (22%) patients with hyponatremia in this study. The sodium levels in the patients with hyponatremia ranged from 110 to 134, with a mean of 126.2 ± 5.3 mEq/l. Hyponatremia was observed on average on postoperative day 9.5 ± 2.4, the serum sodium levels normalized within 3.8 ± 1.7 days. Hyponatremia occurred in patients with non-functioning pituitary adenoma (26%, 11/42), Rathke’s cleft cyst (29%, 5/17), prolactinoma (31%, 4/13) and acromegaly (15%, 4/27). 18 patients (75%, 6/24) who developed hyponatremia had macrotumor (>10 mm), and 6 patients (25%, 6/24) had microtumor. The plasma arginine vasopressin (AVP) levels in the patients with hyponatremia ranged from 0.21 to 2.1, with a mean of 0.79 ± 0.46 pg/ml, and the levels were inversely correlated with plasma osmolality (r = –0.80, p = 0.002). The urine to plasma osmolality ratios were >1. All the patients received appropriate hormonal replacement, including hydrocortisone. These data showed that postoperative hyponatremia after TSS was not rare, and the hyponatremia was mainly associated with SIADH. As the hyponatremia could be a life-threatening complication, all patients should be screened for serum electrolytes after TSS.

Pediatric nonalcoholic steatohepatitis associated with hypopituitarism.

We experienced two cases of pediatric nonalcoholic steatohepatitis (NASH) associated with hypopituitarism. The first patient was diagnosed with a craniopharyngioma at 5 years of age. After an operation to treat the condition, the patient gradually became obese, and an elevation of transaminases was observed. At 16 years of age, the patient was diagnosed as having NASH with liver cirrhosis. He was started on hormone replacement therapy; however, his insulin resistance and liver fibrosis, as evaluated by hyaluronic acid and platelet count, progressed. In addition, his hyperleptinemia continued. The second patient was diagnosed, at 10 years of age, as having pituitary dysfunction due to fetal asphyxia, and he was started on hormone replacement therapy. This patient was noted to have been obese throughout his life. He was diagnosed as having NASH with advanced fibrosis at 18 years of age. It is important for both hepatologists and endocrinologists to be aware of the association between pituitary dysfunction and NASH.

An insulin-like growth factor II-producing histiocytoma associated with hypoglycemia: Analysis of the peptide, its gene expression, and glucose transporter isoforms☆

An insulin-like growth factor II (IGF-II)-producing histiocytoma was detected in a patient presenting with the classical findings of tumor-related hypoglycemia (low serum insulin and IGF-I concentrations, glucose intolerance, and only modestly increased serum IGF-II levels). Acid-gel filtration of serum extracts showed a single peak of IGF-II immunoreactivity that emerged at the same site as the 125I-labeled human IGF-II standard. High-performance liquid chromatography (HPLC) analysis of the tumor IGF-II demonstrated that it had an identical retention time to that of recombinant human IGF-II. The tumor IGF-II content was extremely high, messenger RNA (mRNA) for IGF-II showed a 100-fold increase in expression compared with normal human liver tissue. Of special interest, a newly identified exon (hE1) was shown to be predominantly expressed in the tumor by Northern blot analysis using leader exon-specific rat IGF-II complementary DNA (cDNA) probes. Although the significance of this finding remains uncertain, this is the first evidence of a new transcription unit in the human IGF-II gene. In addition, immunoblotting showed that the levels of the glucose transporters, GLUT1 and GLUT4, in the tumor were low and undetectable, respectively. This finding makes it unlikely that increased glucose consumption by the tumor accounted for the hypoglycemia in this patient. This case report provides an interesting insight into the pathophysiology of tumor-induced hypoglycemia and new evidence of the abnormal regulation of IGF-II gene expression in human tumors.