Possible role of plasma neurotensin on growth hormone regulation in neonates.

OBJECTIVE: To evaluate secretion of plasma neurotensin (NT) which could be involved as a peripheral signal in growth hormone (GH) regulation, NT release was measured during early postnatal life, a period of striking changes in GH secretion. METHODS: Blood samples were collected from 19 normal full-term neonates on day 5 and at 3 months of age to evaluate plasma NT concentrations by radioimmunoassay, serum growth hormone (GH) levels using an immunofluorometric assay, and serum insulin-like growth factor-I (IGF-I) values by radioimmunoassay. RESULTS: Five day-old neonates showed significantly higher (p < 0.001) mean (+/- SEM) plasma NT levels (83.55 +/- 12.07 fmol/ml) compared with those in 11 prepubertal children and those in 14 adults who were studied as control subjects (13.30 +/- 2.90 and 9.70 +/- 1.10 fmol/ml, respectively). In 5 day-old neonates we observed significantly higher (p < 0.001) serum GH levels (29.53 +/- 3.40 ng/ml) compared with those in the prepubertal children (1.26 +/- 0.28 ng/ml). Five day-old neonates showed significantly lower (p < 0.001) serum IGF-I concentrations (27.01 +/- 0.77 ng/ml) than those in the prepubertal children (210 +/- 25 ng/ml). At 3 months of age, plasma NT levels (59.37 +/- 7.47 fmol/ml) and serum GH values (4.40 +/- 0.60 ng/ml) were significantly decreased (p < 0.001). At the 3rd month of life, serum IGF-I levels (44.88 +/- 4.30 ng/ml) were increased significantly (p < 0.001). CONCLUSIONS: The human neonate showed very high concentrations of NT and GH in comparison with those observed in control subjects. The postnatal rise in IGF-I values is presumed to determine the fall in serum GH concentrations by stimulating somatostatin secretion. Neurotensin could be involved as a peripheral signal in the inhibitory mechanisms mediated by release of somatostatin.

Quantitative RT-PCR: limits and accuracy.

In this paper we determine the limits and accuracy of quantitative reverse transcription (RT)-PCR using a modification of the original protocol. The quantification of mRNA with this procedure requires a preliminary estimation of the target molecule (TM) concentration, established from experiments with an internal control molecule (ICM). A definitive quantification is then attained from serial dilutions of the reverse transcription reaction. The success of this latter step is dependent on maintaining an equivalent number of TM and ICM in the reaction. The purpose of our study was to evaluate the influence of the deviation between the TM and the ICM on the result. We show here that we can control the accuracy of the assay by fixing the limit of the TM/ICM ratio. Indeed, when the TM/ICM ratio is between 0.66 and 1.5 (i.e., the difference between TM and ICM is 1.5-fold), the final result has an error of approximately 10%. Exceeding this limit produces errors approaching 60%, as in the case of TM/ICM = 2. When the above conditions are respected, a difference as small as 20% between two samples can be determined with an accuracy of 95%.