Paul E. Hyman

Gastric acid secretory function in preterm infants

To establish normal values for gastric secretory function in preterm infants, we studied 34 healthy preterm infants once a week during hospitalization. Basal acid output, pentagastrin-stimulated acid output, fasting serum gastrin, and fasting serum pancreatic polypeptide were measured during each study. Basal acid output at 1 week of age was 12 mumol/kg/hr, increasing over the first 4 weeks to 30 mumol/kg/hr. Administration of pentagastrin 6 micrograms/kg subcutaneously increased acid output in all age groups. Pentagastrin-stimulated acid output at 1 week was 21 mumol/kg/hr, increasing over the first 4 weeks to 44 mumol/kg/hr. Acid secretion did not change significantly over the next 4 to 6 weeks. Fasting serum gastrin concentration was stable over the first 6 weeks of life, but doubled during the end of the second month. Pancreatic polypeptide was found at low levels throughout the study. These studies confirm that the majority of healthy preterm infants secrete acid in quantity sufficient to maintain the gastric pH less than or equal to 4, providing a barrier to bacteria and protein antigens.

Antroduodenal motility in children with chronic intestinal pseudo-obstruction.

Chronic intestinal pseudo-obstruction describes a heterogeneous group of disorders characterized by signs and symptoms of intestinal obstruction in the absence of a mechanical lesion. We studied antroduodenal motility in 13 children with pseudo-obstruction. The diagnosis was based on radiographic evidence in all, surgery in 11, and specific pathologic features in four. Antroduodenal motility was abnormal in all 13. Qualitative abnormalities in the patterns of antroduodenal contractions permitted separation into groups: (1) postprandial hypomotility (n = 3), (2) absent migrating motor complexes, with phase 3-like activity at the start of meals (neuropathic variety) (n = 5) (3) very low amplitude or absent contractions (myopathic variety) (n = 2); the remaining patients (n = 3) had other distinctive abnormalities. Cisapride, a new gastrointestinal prokinetic drug, stimulated proximal duodenal contractions in the 30 minutes after a meal in nine of 10 patients tested. These studies indicate that antroduodenal manometry is useful for characterizing intestinal pseudo-obstruction, and cisapride stimulates postprandial duodenal contractions in patients with pseudo-obstruction.

Effect of Metoclopramide and Bethanechol on Gastric Emptying in Infants

ABSTRACT.: In a double-blind, placebo controlled study of 10 infants with upper gastrointestinal motor disorders, metoclopramide (1 mg/kg, intravenous) but not bethanechol (0.075 mg/kg, subcutaneous), signficantly increased the fractional rate of gastric emptying following a 5% glucose meal. Infants were tested on 3 consecutive days with a phenol red dye-dilution technique which, if combined with acid titration of gastric samples, permits simultaneous measurements of gastric volume, fractional emptying rate, fluid output, and acid output. Metoclopramide increased the fractional emptying rate in eight of 10 infants (mean ± SE increasing from 4.6 ± 0.6 to 7.3 ± 1.0%/min, p < 0.02). Neither drug altered gastric acid secretion, but metoclopramide significantly increased gastric fluid output (mean ± SE increased from 3.5 ± 0.6 to 6.5 ± 1.4 ml/min, p < 0.02). No undesirable side effects or complications occurred during testing. We conclude that trials are warranted to assess the clinical efficacy of metoclopramide in infants with nonobstructive causes of delayed gastric emptying.

Neonatal Necrotizing Enterocolitis Inflammatory Bowel Disease of the Newborn

Neonatal necrotizing enterocolitis is the most common serious gastrointestinal disorder encountered in neonatal intensive care units. It is a major cause of morbidity and mortality in the newborn, particularly in premature infants. Consistent risk factors are birth weight and prematurity. Polycythemia and hyperviscosity altering blood flow and infectious agents are also implicated. Clinical findings include abdominal distention and diarrhea, and systemic symptoms such as apnea, acidosis, and lethargy. Pneumatosis intestinalis can be demonstrated radiographically. Mucosal ulcerations, hemorrhage, and thrombosis occur early, followed by inflammatory changes. Later still necrosis develops. Ischemia, infection, and enteral feedings are suspected to be involved in the pathophysiology. Eicosanoids, especially thromboxane, platelet-activating factor, and leukotrienes are likely mediators.

Anatomic contribution to differences in rabbit colonic muscle contraction

The aim of this study was to determine if differences in the force of contraction in different regions of the rabbit colon are associated with variations in the histology of the corresponding muscle tissues. Circular and longitudinal muscles were isolated from strips of proximal and distal colonic muscle. Muscle strips stretched to L0 were either stimulated to contract or were processed for electron microscopy. Cross-sections of the smooth muscle cells of the taenia coli had a larger perimeter (P less than 0.001) and were surrounded by increased extracellular matrix (28% of the standardized box) compared with the muscle cells from the other sites in the colon (7%-13%) (P less than 0.001). Cross-sections of the proximal circular muscle cells had a smaller perimeter and were present in a greater number than the cells from other areas of the colon. The distal circular muscle generated a larger force than the other muscles after stimulation with bethanechol or K+ (P less than 0.05). The taenia developed less force than the other muscles (P less than 0.05). Bethanechol was a less potent stimulant for the longitudinal muscles than for the circular muscles (P less than 0.05). This study suggests that (1) the decreased efficacy of bethanechol and K+ stimulation of the taenia coli is caused in part by the smaller number of cells that are available to contract and (2) the increased efficacy for the stimulation of the distal circular muscle compared with the proximal circular muscle is unrelated to the mass of muscle and seems to be related to an inherent property of the muscle.

Response of Smooth Muscle from Proximal and Distal Human Colon

Regional differences in colonic motility may be responsible for the orderly transit of intraluminal contents through the colon. The aims of this study were to compare the effect of stretch on active and passive stress development in colonic muscle from the proximal and distal colon and to compare the responses of these tissues to KC1 or bethanechol stimulation. Strips of taenia or circular smooth muscle were obtained from the disease‐free segment of the colon removed for adenocarcinoma. Passive, active, and total isometric stress were measured on full‐thickness strips of circular or longitudinal taenial muscle stimulated with bethanechol (10−4 M) as the muscles were stretched to 120% of the length of optimum tension (Lo.) The tissues then were stimulated with increasing concentrations of KCI and bethanechol while being stretched at Lo. The active stress in the proximal circular muscle was greater at all levels of stretch than in distal circular or longitudinal muscle (p <.001). The resting and passive stress were greater in distal circular and longitudinal taenial muscle than in proximal circular muscle (p < .05). There was a dose‐dependent increase in stress development to bethanechol and KCl in each type of muscle. Proximal circular muscle had the greatest response. The EDSO was shifted to the right in distal circular muscle (2.6 ± 0.1 × 10−5 M) compared to proximal circular muscle (1.1 ± 0.1 × 10−5 M) (p < .001). These studies suggest that muscle stress differs in different locations of the colon and the role of active and passive stress development must be considered in models explaining in vivo colonic motility disturbances.

Effect of 5-hydroxytryptamine and its antagonists on colonic smooth muscle of the rabbit

The effect of 5-hydroxytryptamine (5HT) was studied in circular and longitudinal muscle from the proximal and distal colon of New Zealand white rabbits. 5HT stimulated a dose-dependent isometric contraction of distal and proximal circular muscle that was greater than in distal longitudinal muscle (P<0.01). 5HT did not stimulate taenia coli longitudinal muscle. The EC50 for 5HT stimulation of distal circular muscle (−7.0±0.1), distal longitudinal muscle, and proximal circular muscle was similar. Methysergide dose-dependently inhibited the 5HT stimulation of both proximal and distal circular muscle. The IC50 for methysergide inhibition of 5HT (5×10−7 M) stimulation was −5.5±0.2. Ketanserine and ICS 205-930 did not inhibit 5HT stimulation of colonic muscle. Tetrodotoxin (TTX) decreased the potency, but not the efficacy of 5HT stimulation of proximal and distal circular muscle. Atropine decreased the potency (EC50=−6.6±0.1) (P<0.05) and the efficacy by 40%. Electrical field stimulation (EFS) caused an on-contraction and off-contraction of distal circular muscle and an on-contraction of proximal circular muscle. 5HT decreased the off-contraction of the distal circular muscle but did not affect the on-contraction of the other muscle strips. 5HT receptor antagonists did not affect EFS of the tissue. The studies suggest: (1) 5HT stimulates circular colonic muscle with greater efficacy than longitudinal muscle, (2) 5HT stimulates circular muscle through a 5HT1 receptor, (3) there is atropine-sensitive and atropine-insensitive 5HT stimulation of circular colonic muscle, (4) 5HT inhibits neurons responsible for the off-contraction in distal circular muscle without affecting the on-contraction. Thus, 5HT affects colonic contraction by a direct effect on muscle and indirectly through the enteric nerves.

Development of Calcium Channels in Gastric Smooth Muscle

ABSTRACT: We used [3H]nitrendipine to characterize dihydropyridine sensitive calcium channels on cells isolated from neonatal (1 d) and weanling (11 wk) rabbit gastric fundic and antral smooth muscle. Incubating with and without nifedipine 20 µM, specific binding was 56 ± 4% of total binding at 0.1 nM [3H]nitrendipine. Specific binding was saturable, reversible, achieved equilibrium by 10 min at 4°C, and was linearly related to cell concentration. The affinity constant for (3H]nitrendipine was higher in weanling fundus (kd=243 ±121 pM) versus antrum (kd=771 ± 190 pM), p<0.05. There were no age-related changes in affinity. In the antrum, the number of binding sites (Bmax) increased from 6 000 ± 266/cell in neonates to 27 500 ± 8 440/cell in weanlings (p<0.05). In the fundus Bmax was 7 750 ± 2 100/ceIl in neonates, and there was no age-related change. To assess function, we compared isometric stress in full thickness muscle strips oriented to the circular layer. Bethanechol stimulated dose-dependent tonic contractions in the fundus and phasic contractions in the antrum. Maximal stress increased with age from 305 ± 54 mN/cm2 to 1140 ± 73 mN/cm2 (p<0.05) in the fundus and from 72 ± 20 mN/cm2 to 154 ± 30 mN/cm2 (p<0.05) in the antrum. Preincubation and incubation without calcium resulted in reversible inhibition of contraction at both ages. Nifedipine 10-µM inhibited 100% of bethanechol-stimulated contraction in the antrum, but only 25% in the fundus at both ages. In summary, in rabbit gastric smooth muscle: 1) [3H]nitrendipine identified functional calcium channels in neonates and weanlings, 2) there are age-related increases in calcium channels on antral, but not on fundic cells, 3) there are age-related increases in stress in strips from antrum and fundus, 4) the fundus utilizes intracellular calcium stores for bethanechol-stimulated contraction, whereas the antrum requires extracellular calcium. Age-related increases in dihydropyridine sensitive calcium channels are consistent with the requirement of the antrum for extracellular calcium to support contraction.

Postnatal changes in receptor-mediated rabbit gastric smooth muscle relaxation.

The aims of this study were to identify mediators of relaxation in rabbit proximal gastric circular smooth muscle and to assess age-dependent changes in tissue response. Vasoactive intestinal peptide (VIP), adenosine, and norepinephrine induced tetrodotoxin-insensitive, concentration-dependent relaxation in bethanechol-precontracted (3 microM) gastric muscle strips from newborns and weanlings. Maximally effective concentrations of 10 microM VIP induced complete relaxation in newborns, but only 30% relaxation in weanlings (p < 0.01). Maximally effective concentrations of adenosine induced complete relaxation at both ages. Adenosine (ED50 3 microM) was more potent than adenosine triphosphate, indicating the presence of P1 purinergic receptors. In newborns norepinephrine induced complete relaxation (ED50 0.5 microM). The response to norepinephrine changed in age-dependent increments from relaxation in newborns to strong contraction in weanlings. In weanlings phentolamine inhibited norepinephrine-stimulated contraction, revealing persistent propranolol-sensitive relaxation. Tetrodotoxin and atropine had no effect on norepinephrine-stimulated contraction. In summary, in rabbit gastric circular smooth muscle: (1) VIP, adenosine, and norepinephrine induce relaxation; (2) VIP loses efficacy with age; (3) there is a beta-adrenergic receptor mediating relaxation in the newborn which persists, and (4) an alpha-adrenergic receptor mediating contraction emerges early in postnatal life. Age-dependent changes in response to VIP and norepinephrine may contribute to the postnatal maturation of the gastric motility.

Effect of cell culture on rabbit colonic smooth muscle bradykinin receptors

The aim of this study was to assess the effect of cell culture on the bradykinin receptor of rabbit colon myocytes. In longitudinal muscle strips prepared from distal colon, bradykinin stimulated dose-dependent contraction that was 62% of the maximal response to bethanecol. At 4 degrees C, [3H]bradykinin binding to fresh muscle homogenates from the distal colon was time dependent, saturable, and linearly related to tissue concentration. Specific binding of 0.6 nmol/L [3H]bradykinin was 80% +/- 2% of total binding. In competitive binding studies, Hill coefficients approached unity, suggesting the presence of a single class of receptors. The order of potency was bradykinin greater than [D-Phe7]bradykinin much greater than des-Arg9, [Leu8]bradykinin, which is consistent with results of a B2 receptor subclass. Colon myocytes from the longitudinal muscle layer achieved confluence and were harvested for studies after 12-14 days in culture. Bradykinin receptors were of high affinity [disassociation constant (Kd) = 672 pmol/L] and numbered 10,217 +/- 2567/cell. To show that the receptors on cultured myocytes were functional, the effect of bradykinin was measured (a) on intracellular calcium concentration using Fura 2 and (b) on prostaglandin E2 concentration in the culture media using radioimmunoassay. In cells grown to confluence on cover slips and preloaded with Fura 2, bradykinin stimulated the threshold response at 1 nmol/L and maximal response (increased intracellular calcium concentration from 229 to 633 nmol/L) at 1 mumol/L. Bradykinin, 100 nmol/L, increased Prostaglandin E2 in the culture media threefold. In summary, colon myocytes express functioning bradykinin receptors, which, unlike muscarinic receptors, persist in culture. Bradykinin appears to be a suitable agonist for studies of receptor-mediated intracellular events in cultured colon myocytes.