JOURNAL OF SURGICAL RESEARCH 63, 364–368 (1996) ARTICLE NO. 0277 Roles of Gastrin and Somatostatin in the Regulation of Gastric Acid Secretion in the Fetal Rabbit LAURENCE F. YEE, M.D., HELEN C. WONG,EDNA Q. CALAUSTRO, AND SEAN J. MULVIHILL, M.D. Gastrointestinal Research Laboratory, Department of Surgery, University of California, San Francisco, California 94143 Presented at the Annual Meeting of the Association for Academic Surgery, Dearborn, Michigan, November 8 – 11, 1995 peptides have been detected in the fetal stomach [14, In adult gastric epithelium, gastrin and somato- 26]; however, their developmental expression and func- statin regulate parietal cell acid secretion; however, tion during gestation are largely unknown [19]. Since their expression and function in the fetus are largely gastrin is a potent acid secretagogue in adult animals unknown. We defined the developmental expression of [29], it is possible that the onset of fetal gastric acid gastrin and somatostatin in the fetal rabbit stomach secretion is regulated, to some degree, by gastrin. An- and determined their effects on fetal acid secretion. To other possible mechanism governing the onset of fetal define peptide expression, fetuses from 12 time-mated gastric acid secretion may involve overcoming the tonic New Zealand white rabbit does were analyzed at suc- inhibition of somatostatin on parietal cell secretion cessive ages during the third trimester (term is 31 [23]. We have recently demonstrated that the onset of days). Peptides were extracted from fetal gastric tissue gastric acid secretion in the fetal rabbit occurs between by boiling in water and then in acetic acid. Amidated days 24 and 26 of gestation (term is 31 days) [33]. The gastrin and somatostatin levels were measured by ra- two aims of this study were: 1) to define the develop- dioimmunoassay using antisera 1296 for gastrin and mental expression of gastrin and somatostatin in the 8402 for somatostatin. To determine the effects of gas- fetal rabbit stomach in relative to the onset of gastric trin and somatostatin, pentagastrin (64 mg/kg/hr) or acid secretion, and 2) to determine the effects of exoge- octreotide (35 mg/kg/hr) were infused intravenously in nous gastrin and somatostatin on fetal gastric acid se- conscious pregnant rabbits at 28 days of gestation for cretion. 3 hr. Fetuses (n Å 45) were harvested and gastric acid was titrated with 0.02 N NaOH. Gastrin and somato- statin tissue content were 12 { 3 and 51 { 6 pmol/g at MATERIALS AND METHODS gestational day 20, respectively, and increased to 146 To define the developmental expression of fetal gastrin and so- { 10 and 162 { 5 pmole/g by day 30 (P õ 0.05). Between matostatin, a total of 24 fetuses from 12 pregnant, time-mated New days 24 and 26, when gastric acid was first detectable, Zealand white rabbit does (Grimaud Farms, Stockton, CA) were stud- the molar ratio of somatostatin to gastrin decreased ied at successive gestational ages during the third trimester (term from 5.0 { 1.0 to 1.1 { 0.1 (P õ 0.05). Fetal gastric acid is 31 days). Pregnant does were anesthetized with intravenous pento- content (mmole) was 28.5 { 1.7 in controls, 27.5 { 1.9 barbital (20 mg/kg) (Abbott Laboratories, Chicago IL) through an with pentagastrin treatment, and 15.8 { 1.4 mmole with ear vein. After sterile preparation, the bicornate gravid uterus was delivered through a midline laparotomy. Fetal rabbits were har- octreotide (P õ 0.05). In summary, 1) In fetal gastric vested by Caesarean section. Does were sacrificed by pentobarbital tissue, gastrin increased 12-fold and somatostatin in- overdose and bilateral thoracotomy. After fetal sacrifice by decapita- creased 3-fold between days 20 and 30 of gestation. 2) tion, stomachs were removed by transection at the esophageal and The decreased ratio of somatostatin to gastrin be- pyloric junctions. The fetal stomachs were opened along the greater tween days 24 and 26 of gestation coincides with the curvature, gently rinsed, blotted dry, and weighed. For each gesta- onset of fetal gastric acid secretion in the fetal rabbit. tional day, four fetuses were analyzed. Peptides were extracted from the fetal gastric tissue by a standard 3) Maternal administration of octreotide inhibited fe- method [20]. Briefly, one part of minced gastric tissue was boiled in tal gastric acid content; however, pentagastrin had no five parts of deionized water for 10 min. The tissue was then centri- effect. We conclude that, in the fetal rabbit stomach, fuged for 15 min at 3000 rpm. The supernatant (water extract) was the relative expression of gastrin and somatostatin recovered and assayed for gastrin. To the pellet, 0.5 M acetic acid may regulate the onset of parietal cell acid secretion. was added (5 ml/gm tissue) and homogenized for 1 min. The mixture  1996 Academic Press, Inc. was heated for 10 min in a boiling water bath, and centrifuged for 15 min at 3000 rpm. The supernatant (acid extract) was removed for assay for somatostatin. Amidated gastrin levels were measured in these gastric peptide extracts by radioimmunoassay using antisera 1296, which recognizes INTRODUCTION all amidated C-terminal gastrins larger than the pentapeptide, as previously described [21]. Somatostatin levels were determined by In the adult gastric epithelium, gastrin and somato- a modification of a radioimmunoassay described previously using antisera 8402 [1]. Briefly, fetal gastric peptide extracts were allowed statin regulate parietal cell acid secretion. These two 364 0022-4804/96 $18.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved. AID JSR 4845 / 6n0e$$1101 05-22-96 03:37:29 srga AP: Surg Res