Kenneth R. Larsen

The cytoprotective effects of (±)-15-deoxy-16-α,β-hydroxy-16-methyl PGE1 methyl ester (SC-29333) versus aspirin-shock gastric ulcerogenesis in the dog

Abstract SC-29333 (SC) has been reported to protect the gastric mucosa from the effects of topical aspirin. We compared SC and 16,16-dimethyl PGE2 (16-dm) in 20 chambered canine stomachs (6 controls and 7 of each PG). Prostaglandin was added to an acid solution (100 mM HCl; 54 mM NaCl) at 0, .001, .01, 0.1, and 1.0 ug/ml (two periods each). Then aspirin (20 mM) and PG (1.0 ug/ml) (two periods) were followed by hemorrhagic shock (near 60 mm Hg mean arterial pressure). 16-dm caused a significant efflux of fluid (−6.5 ± 5.3 to 17.3 ± 6.7 ul/min), Na+ (2.1 ± 0.5 to 6.8 ± 1.6 uEq/min), and Cl− (−0.9 ± 2.4 to 5.3 ± 1.3 uEq/min), but did not affect K+ or H+. 16-dm also caused a slight drop in potential difference (PD) (67.6 ± 1.7 to 60.3 ± 2.0 mV). 16-dm did not significantly affect total blood flow. Percent lesion formation was more severe than controls (20.2 ± 3.5 vs 11.6 ± 1.7 percent) but not statistically significant. SC had no significant effect on fluid, H+, Na+, K+, or Cl−. It caused an increase in blood flow (6.85 ± 1.46 to 26.20 ± 2.74 ml/min, p

Circadian rhythms of gastric mucus efflux and residual mucus gel in the fasting rat stomach

We hypothesized that two putative gastric protective factors, mucus efflux and residual mucus gel content, would manifest circadian rhythms, as reported in several other gastric functions. Rats were adapted for three weeks on a 12-hr light schedule, fasted 18-hr and studied at 3-hr intervals. Under anesthesia, the stomachs were cannulated and filled with test solution. Thirty minutes later, they were drained and the luminal fluid was analyzed for mucus content by Alcian blue binding. Residual mucus gel was determined by direct injection of dye into the lumen. Alcian blue binding of rat mucus was expressed as equivalent milligrams of porcine mucin. Both parameters showed a significant (P<0.001) circadian rhythm. Mucus efflux peaked at 5:03±0:52 HALO (hours after lights on), and residual mucus at 6:00±0.46 HALO. Thus, the interplay of circadian rhythms in aggressive and defensive gastric mucosal functions is supported.

Circadian rhythm in gastric mucosal blood flow in fasting rat stomach

Circadian rhythms are present in several gastric functions including acid secretion and emptying rates. We hypothesize that aggressive and defensive factors in the gastric mucosa follow similar circadian rhythms. The purpose of this study was to determine if gastric mucosal blood flow, a known defensive factor, manifests a circadian rhythm in fasting rats. Ninety-six male Sprague-Dawley rats were light-adapted in isolation chambers for 3 weeks prior to the study. Half the rats experienced light from 6:00 AM to 6:00 PM, the other half from 6:00 PM to 6:00 AM. After an 18-hr fast, 12 rats were studied at each of eight sampling times: 0100, 0400, 0700, 1000, 1300, 1600, 1900, and 2200 hr after lights on (HALO). After anesthesia and laparotomy, the stomachs were opened along the anterior surface, gently stretched with mucosal surface upmost, and trapped between two lucite rings, with blood supply intact. Mucosal blood flow (ml/min/100 g) was measured in the forestomach, corpus, and antrum with a laser Doppler flowmeter (TSI Laserflo BPM 403). Cosinor analysis showed a significant (P less than 0.01) circadian rhythm in gastric mucosal blood flow within the corpus and antrum, but not in the forestomach. Peak time for corpus blood flow was 21:45 +/- 0:56 HALO (3:45 AM). In the antrum it was 0:51 +/- 1:08 HALO (6:51 AM). These results support the hypothesis that circadian rhythms in mucosal defensive functions are an integral part of normal gastric physiology.

Circadian rhythm in prostacyclin activity in gastric tissue of the fasting rat.

Gastroduodenal ulcer disease may result from the desynchronization of the circadian rhythms of gastric protective and destructive factors. The purpose of this study was to evaluate whether gastric tissue 6-keto prostaglandin F1 alpha (PGF1 alpha), a catabolic derivative of the putative protective factor prostacyclin, is produced in a circadian fashion in the rat model. Forty-eight male Sprague-Dawley rats were acclimatized in sound-attenuated, lightproof chambers for 3 weeks on a 12:12 hour light/dark entrainment schedule. After an 18-hour fast, six rats were killed at each of eight sampling times. The stomachs were exposed, removed, and assayed for total 6-keto PGF1 alpha content by radioimmunoassay. Cosinor analysis of the data showed significant (p = 0.0262) circadian rhythmicity in 6-keto PGF1 alpha content with an acrophase (peak time) value of 0503 HALO (hours after lights on) or in the middle of the lights-on inactive period for the rats. Hypothetically, the circadian rhythm in some gastric protective factors may render the gastric mucosa vulnerable to injury in a circadian fashion.

Effects of Tolcapone, a Catechol-O-Methyltransferase Inhibitor, and Sinemet on Intestinal Electrolyte and Fluid Transport in Conscious Dogs

Tolcapone (T) is a novelcatechol-O-methyltransferase (COMT) inhibitor recentlyintroduced for the treatment of Parkinsons disease. Inclinical efficacy studies, T has been associated with alow incidence of diarrhea. The objectives of the study wereto examine whether T and its adjunctive drug Sinemet (S)could influence intestinal fluid and electrolytetransport as a possible cause for the diarrhea. The studies were conducted in conscious dogssurgically prepared with Thiry-Vella loops constructedfrom a 40-cm jejunal segment. A physiologically bufferedtest solution was perfused into the orad stoma and collected from the caudad stoma. Secretionswere collected at 15-min intervals and analyzed forvolume, electrolytes, lipid phosphorus, and protein. Theacute oral administration of T (10 and 30 mg/kg doses) was well tolerated. Concurrent acuteadministration of S (25 mg/kg) with T (30 mg/kg) wasalso well tolerated. The acute oral administration of Tinduced a dose-dependent efflux of intestinal fluid and electrolytes (sodium, potassium, chloride, andbicarbonate) secretion (P < 0.05). The oralcoadministration of S (25 mg/kg) with T (30 mg/kg)accelerated the onset of the stimulation of intestinalsecretion. Despite the significant stimulation ofintestinal secretion, none of the dogs developeddiarrhea, indicating the importance of intestinalcompensatory mechanisms. Neither T nor T&S affectedcalcium, lipid, or protein efflux rates, suggesting thatthe stimulated secretion was not a consequence ofintestinal mucosal injury. The chronic (seven-day)administration of T and T&S was associated withreduced intestinal secretory responses when comparedwith the acute administration of the same drugs; Senhanced the T-induced tolerance development. The basisfor such tolerance is unknown. In conclusion, the stimulatory systemic actions of tolcapone onintestinal secretion may, under certain conditions,contribute to the induction of diarrhea in susceptiblepatients.

Effect of constant light on rhythmic gastric functions in fasting rats.

The effects of four weeks of continuous illumination (LL), a subacute stress, on gastric mucosal endogenous aggressive and defensive factors were studied. Young male Sprague-Dawley rats were used with two different illumination regimens: LL and 12 hr light/12 hr dark (LD). At the end of three to four weeks of either regimen of illumination, gastric acid secretion, pepsin secretion, mucus secretion, and potential difference (PD) were studied. All gastric parameters, except mucus secretion, were significantly reduced by LL. The reduction in acid secretion (13.3%) was not significant after Bonferroni correction for the fourt tests Pepsin secretion and PD were 27.9% and 24.6% less, respectively. These differences were significant after Bonferroni correction. The LD rats showed significant circadian rhythms for acid, mucus, and pepsin secretion. The LL rats showed significant rhythmicity for these same parameters with period lengths different from 24 hr. Gross inspection of the gastric mucosa indicated that 69.8% of the LL rats had lesion scores of 1.0 or higher, while none of the LD rats had scores above 0.5.

Antiulcer drugs and gastric mucosal integrity. Effects of misoprostol, 16,16-dimethyl PGE2, and cimetidine on hemodynamics and metabolic rate in canine gastric mucosa.

Although prostaglandins (PGs) of the E series have gastric antisecretory and cytoprotective properties, many have different effects on the barrier integrity of the gastric mucosa. The direct effect of antiulcer drugs on gastric mucosal blood flow, mucosal barrier permeability, and metabolic rate have not been adequately studied. These factors are important in the defense of the gastric mucosa. Part of the difficulty relates to the possible influence of gastric mucosal blood flow on gastric acid secretion. To rule out this confounding factor, omeprazole can be used to reveal the true pharmacologic effects of these antiulcer drugs independent of the effect of gastric secretionper se. The study examined the effects of 16,16-dimethyl PGE2 (dmPGE2) misoprostol, and cimetidine on gastric mucosal blood flow, oxygen consumption, potential difference (PD), electrolytes, and fluid flux using theex vivo gastric chamber dog model. The PGs were administered intraluminally with an isotonic acid solution; cimetidine was administered by arterial infusion. None of the drug treatments had any significant effect on mean systemic arterial pressure, arterial blood gases, body temperature, or oxygen consumption. dmPGE2 significantly (P<0.001) decreased PD and enhanced the electrolytes (Na+, K+) and fluid flux across the mucosa (P<0.05). Misoprostol significantly increased gastric mucosal blood flow (P<0.02) and fluid efflux but decreased PD values. Cimetidine did not have any significant effects on barrier or metabolic functions of the stomach. These results suggest that a considerable difference exists in the pharmacology of gastric antisecretory drugs in relation to their effect on several factors affecting gastric mucosal integrity.

Asynchrony in circadian rhythms of gastric function in the rat : a model for gastric mucosal injury

A model for gastric mucosal injury is proposed in which a key pathogenetic event is the disruption in the normal relationships among several circadian rhythms of gastric function. In the rat a circadian rhythm in acid secretion was found to be out of phase with a circadian rhythm in gastric pepsin secretion, another aggressive factor, and several mucosal defensive factors (mucus and bicarbonate efflux and tissue prostacyclin content). Gastric corpus mucosal blood flow circadian patterns paralleled the rhythmicity in acid secretion and, therefore, was out of phase with the other measured mucosal defensive factors. Thus, gastric mucosal defense was maintained by different mechanisms over the 24-hr cycle. During the dark phase, when this species was active and when acid secretion was highest, enhanced damage by topical acidified aspirin was documented, despite increased mucosal blood flow. Natural asynchrony in circadian rhythms of gastric function can be protective of gastric mucosal integrity but disruption of this circadian interplay of gastric aggressive and defensive factors could theoretically lead to greater vulnerability to damage. In the human, a circadian rhythm in basal gastric acidity has been described but no information exists as to the possibility of similar rhythmic variation in other gastric factors (aggressive and defensive) and possible disruption of these rhythms in disease.

Circadian rhythm of pepsin efflux in the fasting rat stomach.

Gastric pepsin efflux, a putative aggressive factor because of its proteolytic activity, was examined to determine if it displays circadian rhythmicity as has been shown for other factors such as acid, bicarbonate, mucus, blood flow, potential difference, and tissue prostacyclin activity. Ninety-six fasted Sprague-Dawley male rats, 6-7 weeks of age were acclimated in sound-attenuating, light-proof chambers on a 12/12 light/dark schedule. They were studied in groups of 12 at 3-h intervals. After anesthesia and minor surgery, the stomach was cannulated and filled with 2 ml of saline for two sequential periods of 30 min. The samples were tested for pepsin according to the modified hemoglobin substrate colorimetric method. The data were analyzed with cosinor rhythmometric techniques. Pepsin efflux displayed significant (p < 0.05) circadian rhythmicity with an acrophase value or peak time at 06:49 h after lights on, during the lights-on resting phase. In contrast, the acrophase for acid secretion in the same model occurs during the dark period, when the rats are normally active. We postulate that differences in the circadian patterns of acid and pepsin may be protective.

Circadian Rhythm in Aspirin (ASA)-Induced Injury to the Stomach of the Fasted Rat

Circadian rhythms exist in several gastric parameters affecting ulcerogenesis. This study investigated possible circadian rhythmicity in observed aspirin (ASA)-induced gastric lesions in the rat. In five experiments 183 rats were studied at 14 time points over a 24-hr period. Rats were adapted for three weeks on a 12-hr light schedule, fasted 18 hr, then given oral acidified ASA. One hour later, the rats were sacrificed, the stomachs were removed, stretched flat, photographed, scanned, and measured for percent area of gross lesions in the gastric corpus by computer planimetry. Cosinor rhythmometric analysis showed a significant (P<0.001) rhythm. Mean of rhythm (MESOR) was 5.60±0.25% of total corpus. Amplitude was 25.80±6.07% of MESOR. Peak time (acrophase) was 1909±0101 hr after lights on. Thus, gastric vulnerability to ASA injury exhibited circadian rhythmicity with peak injury during the dark period in this species.