The identification of false positive responses to the pentagastrin stimulation test in RET mutation negative members of MEN 2A families.

OBJECTIVE: The pentagastrin stimulation test is the traditional test used for the identification of asymptomatic individuals in multiple endocrine neoplasia type 2A (MEN 2A) and familial medullary thyroid carcinoma (FMTC). The identification of mutations in the RET proto-oncogene segregating with the disease phenotype in MEN 2A and FMTC families has made it possible to re-examine the validity of using this test for the identification of affected family members. DESIGN: Sequential and single pentagastrin stimulation test data were collected following the identification of RET mutation positive and RET mutation negative members of families with MEN 2A or FMTC. PATIENTS: RET mutations were identified in 16 Australian and New Zealand MEN 2A or FMTC families. An analysis of 39 individuals from these families was included in this study. Thirty-two individuals (14 males, 18 females) had previously been determined as RET mutation negative. Seven individuals (6 males, 1 female) had previously been determined as RET mutation positive. Two RET mutation negative males had thyroidectomy based on prior pentagastrin test results. MEASUREMENTS: Serum calcitonin levels in response to stimulation with pentagastrin were measured at 0, 1, 2, 5 and 10 minutes post injection. Mutation analysis of the RET proto-oncogene was performed in all individuals. In two RET mutation negative individuals from two MEN 2A families, thyroidectomy was performed and C-cells were quantitated in order to determine the diagnosis of C-cell hyperplasia. RESULTS: There was a statistically significant difference (P < 0.013) between RET mutation negative male and female mean peak calcitonin responses of 282 +/- 236 and 96 +/- 62 (mean +/- SD) ng/l respectively. False positive responses to pentagastrin stimulation were identified in seven individuals who were RET mutation negative in two of the 16 families. Histologic examination of the thyroid glands in the two RET mutation negative individuals who had thyroidectomy demonstrated C-cell hyperplasia in one but not in the other. CONCLUSIONS: There is considerable overlap between pentagastrin test results in individuals who are RET mutation positive and those who are RET mutation negative. These results indicate a need for routine performance of RET proto-oncogene analysis on all individuals at risk of developing MEN 2A or FMTC and a coupling of pentagastrin test results and RET proto-oncogene analysis in the decision to proceed with thyroidectomy.

Quantitation of APC mRNA in human tissues.

The aim of this study was to develop a method for quantitation of APC mRNA and to measure APC mRNA levels in human tissues. This was done using a competitive reverse transcription PCR with a synthetic RNA control. APC mRNA (pg/microgram total RNA) was quantitated in the following tissues: normal colon 133.6 +/- 69.0; normal duodenum 16.6 +/- 15.7; normal thyroid 30.4 +/- 20.3; normal esophagus 65.2 +/- 58.8; colonic carcinoma 66.5 +/- 30.3; esophageal carcinoma 54.7 +/- 26.5; papillary thyroid carcinoma 55.8 +/- 32.9 and colonic adenomas from patients with familial adenomatous polyposis 46 +/- 15. APC mRNA levels were significantly lower in the duodenum and thyroid than in the colon and esophagus. The quantity of APC mRNA was lower in colonic adenomas from FAP patients than in normal colonic mucosa (p < 0.05).

Impaired regulation of hepatic fructose-1,6-bisphosphatase in the New Zealand obese mouse model of NIDDM.

The New Zealand obese mouse, a model of NIDDM, is characterized by hyperglycemia, hyperinsulinemia, and hepatic and peripheral insulin resistance. The aim of this study was to investigate the biochemical basis of hepatic insulin resistance in NZO mice. Glycolytic and gluconeogenic enzyme activities were measured in fed and overnight fasted 19- to 20-wk-old NZO and control New Zealand chocolate mice. The NZO mice were twice as heavy as the NZC mice. The activity of the glycolytic enzymes glucokinase and pyruvate kinase was higher, whereas that of the gluconeogenic enzymes PEPCK and glucose-6-phosphatase was lower in fed and fasted NZO mice. These enzyme changes are consistent with a normal response to the hyperinsulinemia in NZO mice. In contrast, the activity of the third regulated gluconeogenic enzyme, fructose-1,6-bisphosphatase, was similar in fed and fasted NZO and NZC mice despite the higher insulin and glucose levels in the NZO mouse. This enzyme is primarily regulated by the powerful inhibitor fructose-2,6-bisphosphate. The levels of this metabolite were measured and found to be increased in both the fed and fasted states in the NZO mouse, suggesting that the activity of the bifunctional enzyme that regulates the level of inhibitor (6-phosphofructo-2-kinase/fructose-2,6- bisphosphatase) is normally regulated in the NZO mouse. We conclude that most insulin-responsive gluconeogenic and glycolytic enzymes are normally regulated in the NZO mouse, but an abnormality in the regulation of fructose-1,6-bisphosphatase may contribute to the increase hepatic glucose production in these mice.