VASOACTIVE INTESTINAL PEPTIDE (VIP): VARIATION OF THE JEJUNO-ILEAL CONTENT IN THE DEVELOPING RAT AS MEASURED BY RADIORECEPTORASSAY

Abstract

Variations in the vasoactive intestinal peptide (VIP) content of rat jejuno-ileum (JI) with age were investigated. VIP was measured by its ability to competitively inhibit the binding of [125I]pork VIP (pVIP) to rat liver plasma membranes. The radioreceptor assay was sensitive to 0.5 ng/ml. VIP fragments 1-6, 14-28 and 18-28 exhibited no cross reaction with [125I]pVIP. Glucagon had no effect, and secretin was about 100 times less effective than pVIP. Rat VIP was extracted from JI by 0.5 M acetic acid and partially purified by adsorption on silicate. The effect of JI extracts in inhibiting the binding of [125I]pVIP paralleled that of pVIP used as standard. The VIP content of JI showed a 340-fold increase between day 21 post coitum (p.c.): 41 .+-. 4 ng/JI and day 63 post partum (p.p.): 14,110 .+-. 954 ng/JI. On a gut weight basis, VIP increased slightly from day 21 p.c. (591 .+-. 51 ng/g of JI) to day 14 p.p. (906 .+-. 109 ng/g of JI) and then increased more sharply (day 21 p.p.: 1508 .+-. 222 ng/g of JI) until day 63 p.p. (2672 .+-. 207 ng/g of JI). The VIP content seemed to reach a plateau after 2 mo. A similar pattern was observed when the results were expressed per milligram of JI protein. The rise in VIP content is probably related to the role of this peptide in the regulation of the gastro-intestinal function and/or the distribution of fuels in the organism.