ELEVATED GROWTH-HORMONE SECRETORY RATE IN PREMATURE-INFANTS - DECONVOLUTION ANALYSIS OF PULSATILE GROWTH-HORMONE SECRETION IN THE NEONATE

Premature infants have higher circulating concentrations of growth hormone (GH) than term infants. Previous investigations of these differences have used sampling frequencies of every 30 min with subsequent application of pulse detection algorithms, such as the CLUSTER program, to assess serum GH pulse parameters. To determine differences in GH secretory rates or GH t1/2 values between premature and term infants, we have sampled 11 neonates at 15-min intervals. We performed deconvolution analysis of the resultant plasma GH values to estimate GH secretory and clearance parameters. Five premature infants (gestational age range 24-34 wk) and six term infants (gestational age range 38-42 wk) were sampled every 15 min for 6 h. All subjects had indwelling arterial catheters. GH was measured (in duplicate) by RIA using 10-mu-L of plasma. Premature infants had higher secretory burst amplitudes (2.2 +/- 0.13-mu-g/L/min versus 1.4 +/- 0.27-mu-g/L/min, p = 0.02), higher production rates (product of the total number of bursts and the mean mass of GH secreted per burst, 811 +/- 173-mu-g/L/6 h versus 283 +/- 77-mu-g/L/6 h, p = 0.03), and a higher mass of GH per secretory burst (106 +/- 25-mu-g/L versus 38 +/- 11-mu-g/L, p = 0.049) than term infants. The integrated plasma GH concentration exhibited a strong trend toward a higher value in the premature infants (18 100 +/- 800-mu-g/L versus 10 200 +/- 2 700-mu-g/L, p = 0.067). There were no differences between GH secretory burst frequency (7.8 +/- 0.2 pulses/6 h versus 7.7 +/- 0.6 pulses/6 h), GH t1/2 (20 +/- 4 min versus 24 +/- 6 min), half-duration of burst (the time elapsed at half-maximal amplitude, 45 +/- 11 min versus 25 +/- 4 min), or mean interval between peaks (48 +/- 2 min versus 48 +/- 3 min) comparing the premature and term groups, respectively. In summary, we have demonstrated an elevation in GH secretory burst amplitude, GH production rate, and the mass of GH secreted per burst in premature compared with term infants. Because the estimated GH t1/2 is similar between these two groups, amplified secretion rather than decreased clearance accounts for the differences in circulating GH concentrations. We suggest that the augmented GH secretory activity in premature infants reflects an increase in hypothalamic GH-releasing hormone activity and/or reduced somatostatin tone.