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Plasma substance P and neurokinin A in neonates - variation with gestation and postnatal age

Presented at the Neonatal Society 2003 Summer Meeting (programme).

Wong CM, Boyle EM, Laing IA, Stephen RI, Smith J, McIntosh N

Neonatal Unit, Simpson Centre for Reproductive Health, Royal Infirmary of Edinburgh, Edinburgh EH16 4SA, UK

Background: Substance P (SP) and neurokinin A (NKA) are neuropeptides involved in transmission and modulation of pain signals (1). They are measurable in plasma and have been associated with pain in adults (2,3). There is a potential role for them as neurochemical markers of pain in neonates, but this has never been previously investigated.

Aim: As a baseline to studying plasma SP and NKA as possible markers of pain in neonates, the effect of gestation and postnatal age was studied to establish 'normal' values.

Methods: From July 2000 to December 2001, longitudinal once-daily morning blood samples were collected on days 1, 2, 3, 7 and 14 from 142 neonates, gestation 23-40 weeks. Peptides were extracted, then quantified using an in-house radioimmunoassay. Infants with presumed painful conditions were excluded.

Results: Overall, SP levels ranged from 0.0-11.2 pmol/L (median 1.7 pmol/L) and NKA levels from 1.8-74.6 pmol/L (median 6.0 pmol/L). Gestation and birth weight had no significant correlation with peptide levels. Postnatally, there was a gradual rise in median SP during the first three days which decreased again by day 14. Median NKA showed a similar rise over the first three days but decreased by day 7. These patterns were more apparent in preterm infants <=32 weeks' gestation.

Conclusions: This is the first description of normative values of SP and NKA in neonates. SP and NKA show changes with postnatal age, more marked in preterm infants. In early postnatal days, multiple factors may influence SP and NKA levels, including antenatal circumstances, ventilation, parenteral nutrition, and drugs. Further elucidation of these factors is warranted.

1. Fleetwood-Walker S. Current Opinion in Anaesthesiology 2:645-648, 1989.
2. Marshall KW. Arthritis and Rheumatism 33(1):87-90, 1990.
3. Gallai V. Cephalalgia 15(5):384-390, 1995.

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