Mary J. Ruwart

Protective effects of 16,16-dimethyl PGE2 on the liver and kidney

The ability of subcutaneous 16,16-dimethyl PGE2 to protect the liver and the kidney against damage induced by carbon tetrachloride and ANIT (alpha-napthylisothiocyanate) was examined. Rats were given 5-75 micrograms/kg of 16,16-dimethyl PGE2 24 and 0.5 hrs before challenge with 1 ml of oral carbon tetrachloride with an additional prostaglandin dose 6 hrs later. Twenty-four hrs after carbon tetrachloride animals was sacrificed by decapitation. 16,16-Dimethyl PGE2 partially prevented fat accumulation and necrosis in the liver with complete or partial reduction in the SGPT caused by the hepatotoxin. Higher doses of carbon tetrachloride (1.5 ml) caused elevation in BUN and uric acid also; these changes were prevented by 16,16-dimethyl PGE2 even when doses of the prostaglandin were too low to protect against liver necrosis. Elevated serum bilirubin observed 48 hrs after oral ANIT (30 mg/kg) was prevented by 100 micrograms/kg of 16,16-dimethyl PGE2 given 24 and 0.5 hrs prior to the challenge with additional doses 6 and 24 hrs after ANIT. Higher doses of oral ANIT (200 mg/kg) when combined with small doses of carbon tetrachloride (0.25 ml per rat) resulted in elevated BUN and uric acid levels in the serum although neither compound produced these changes when given alone. 16,16-Dimethyl PGE2 (75 micrograms/kg) administered by the same schedule as used for protection against ANIT resulted in normalization of these parameters in the absence of significant liver protection. Thus, it appears that 16,16-dimethyl PGE2 can protect the liver against necrosis induced by moderate amounts of carbon tetrachloride and ANIT. At higher doses of these hepatotoxins, the liver is not protected by prostaglandins. Elevation of BUN and uric acid is observed under these conditions, however, and can be prevented by 16,16-dimethyl PGE2.

Carbachol stimulation of gastrointestinal transit in the postoperative lleus rat

Abstract Postoperative ileus was studied in a rat model which allowed simultaneous and quantitative measurement of gastric emptying (GE), small intestinal transit (SIT), and colonic transit (CT). Measurement of CT for the first time in an animal ileus model was made possible by the injection of solidified, ink-stained agar into the proximal colon. Methoxyflurane and Cyclopal anesthesia were found to delay GE. Abdominal skin incision, but not dorsal skin incision, decreased SIT. Laparotomy caused maximal decrease in GE, SIT, and CT, but laparotomy coupled with intestinal manipulations slowed the spontaneous recovery of the small intestine. The colon regained normal propulsion 9 hr after surgery, followed by the small intestine (12 hr), and then the stomach (18 hr). Carbachol given before or after surgery increased propulsive ability of all three organs, normalizing GE and CT, but not SIT. The rat appears to be an appropriate model for studying postoperative ileus if care is taken to measure transit in each part of the gastrointestinal tract with separate transit markers. The stomach, small intestine, and colon respond differently to various conditions and possibly have dissimilar neuronal inputs controlling propulsion.

NALOXONE INHIBITS THE ANTI‐DIARRHOEAL ACTIVITY OF LOPERAMIDE

1 Subcutaneous prostaglandin E2 (2.5 mg/kg) produces profuse diarrhoea in fed rats. 2 Pretreatment of rats with subcutaneous loperamide (1.0 mg/kg) completely prevents prostaglandin‐induced diarrhoea. If naloxone is administered prior to loperamide injections the activity. of the antidiarrhoeal compound is completely destroyed. 3 These data provide strong evidence that the antidiarrhoeal activity of loperamide is mediated via the opiate receptor.

Hepatic protection by 16,16-dimethyl prostaglandin E2 (DMPG) against acute aflatoxin B1-induced injury in the rat

Studies were conducted to assess the possible protective action of 16,16-dimethyl prostaglandin E2 (DMPG) against acute aflatoxin B1 (AFB1) induced hepatic injury in the rat. Evaluation of liver damage by histopathologic techniques and clinical chemistry indicated that hepatic necrosis was ameliorated by treatment with DMPG even though binding of radiolabeled (3H)-AFB1 to hepatic DNA was unaffected by this prostaglandin. However, DMPG did not protect rats against AFB1-induced mortality. These data suggest that hepatic protection by DMPG was due to mechanisms other than an interference with the activation or hepatic binding of AFB1.

Partial characterization of the gastrointestinal weight changes produced in the female rat by 16,16-dimethylprostaglandin E2

Oral and subcutaneous administration of 16,16-dimethylprostaglandin E2 (16,16-dimethyl PGE2) resulted in an increase in the dry weight of the stomach and small intestine of the female rat. This weight response was rapid, controlled rather than continuously progressing, dose dependent and reversible. The dry weight of the colon also increased but this was not studied in detail. Two-day treatment with 16,16-dimethyl PGE2 caused an increase in the incorporation of 3H-thymidine into the duodenum, jejunum and colon suggesting an increase in cell number. Incorporation into the stomach and ileum was not changed. The number of goblet cells per crypt was increased by prostaglandin treatment in all parts of the small intestine. Since these are mucus producing cells, the small intestine may have increased in cell number and mucus production. Both anti-secretory and cytoprotective doses of 16,16-dimethyl PGE2 caused weight increases in the stomach and small intestine. However, the weight gain by itself was not sufficient to protect the stomach or small intestine from necrotic agents after the prostaglandin was discontinued.

The role of accelerated colonic transit in prostaglandin‐induced diarrhoea and its inhibition by prostacyclin

1 Rats treated with subcutaneous 16,16‐dimethyl prostaglandin E2 (16,16‐dimethyl PGE2, 100 μg kg−1) exhibited diarrhoea even when their ileo‐caecal junctions were tied, thereby eliminating contributions from small intestinal transit or fluid accumulation (enteropooling). 2 The origin of the watery stool appeared to be the caecum, since tying the caecal‐colonic junction eliminated it. 3 The acceleration of colonic transit is likely to be a primary mechanism of PGE2‐induced diarrhoea in the rat, since both normal animals and those with tied ileo‐caecal junctions exhibited almost the same incidence of diarrhoea. 4 Subcutaneous prostacyclin (PGI2) (2 mg kg−1 every 60 min) suppressed 16, 16‐dimethyl PGE2‐induced diarrhoea in normal rats and in those with tied ileo‐caecal junctions. 5 Colonic transit measured in rats with cannula preimplanted in their proximal colon indicated that 16, 16‐dimethyl PGE2 enhanced colonic transit and PGI2 suppressed this increase. Thus, PGI2 can inhibit diarrhoea in the rat caused by 16, 16‐dimethyl PGE2 by suppressing colonic transit exclusive of its effects on small intestinal transit and enteropooling.

Adrenergic and cholinergic contributions to decreased gastric emptying, small intestinal transit, and colonic transit in the postoperative ileus rat

Abstract The depression of gastric emptying (GE), small intestinal transit (SIT), and colonic transit (CT) was studied in laparotomized rats 45 min after surgery to systematically determine neuronal contributions to postoperative ileus in this species. Chemical sympathectomy by intravenous 6-hydroxydopamine (100 mg/kg) 48 hr prior to surgery normalized CT and increased GE and SIT. If GE was measured 5 hr instead of 45 min after laparotomy, sympathectomized values were normal, but those of vehicle-treated controls were still depressed. Subcutaneous atropine (6 mg/ kg) administered 20 min prior to laparotomy prevented the augmentation of GE and CT by prior sympathectomy. Intraperitoneal phentolamine (0.25 mg/kg) but not propranolol (0.25 mg/kg) 20 min prior to surgery mimicked the effects of 6-hydroxydopamine pretreatment. Subcutaneous bethanechol (0.05, 0.1, or 1.0 mg/kg), neostigmine (0.01, 0.05, or 0.1 mg/kg), or guanethidine (1.0, 5.0, or 10.0 mg/kg) 20 min prior to laparotomy normalized CT and increased GE as compared to vehicle-treated controls. SIT was slightly augmented by neostigmine or bethanechol treatment. Combining chemical sympathectomy with carbachol (0.03 mg/kg) or neostigmine (0.03 mg/kg) normalized GE and increased CT and SIT more than with either compound alone. Subcutaneous methysergide (20 mg/kg) or naloxone (0.5 mg/kg) 20 min prior to surgery had no effect on transit. Subcutaneous indomethacin (10 mg/kg) 3 hr prior to laparotomy was likewise ineffective in increasing propulsion. These results suggest that postoperative ileus is caused both by increased α, but not β sympathetic activity in the stomach, small intestine, and possibly the colon, as well as depression of propulsive stimuli in stomach, small intestine, and the colon. Recovery of propulsive stimuli occurred prior to diminution of sympathetic activity in the stomach. Combination therapy with compounds to reverse both these phenomena appear to normalize propulsion most effectively. Some discrepancies in past reports on this subject were resolved.

Prevention of cecitis in hamsters by certain prostaglandins

Acute inflammation of the colon (cecitis) was produced in hamsters by daily subcutaneous administration of an antibiotic for 3 days. The following prostaglandins completely prevented the cecitis: 16,16-dimethyl-PGE2, 15(R)-15-methyl-PGE2, and 2-acetyl-2-decarboxy-15(S)-15-methyl-PGF2 alpha. PGF2 beta was less active. The synthesis of 2-acetyl-2-decarboxy-15(S)-methyl-PGF2 alpha is described. Castor oil also prevented the cecitis and peanut oil exerted partial protection. Since these oils contain linoleic acid, a precursor of PGE1, protection may have been due to endogenous formation of that prostaglandin. A partial block of the protective effect of castor oil by treatment with indomethacin supports such mechanism. The tissue level of endogenous prostaglandins seems to exert protection since administration of cyclooxygenase inhibitors, indomethacin and aspirin, markedly increased the incidence of cecitis. Magnesium sulfate given orally and sodium salicylate given subcutaneously reduced the incidence of cecitis only partially. The following agents were inactive: loperamide, an antidiarrheic agent; carbachol, a cholinergic and diarrheogenic agent, atropine, an anticholinergic agent; and acetazolamide, a carbonic anhydrase inhibitor. These results, show that certain prostaglandins, which have been shown earlier to be cytoprotective for the stomach and the small intestine, are cytoprotective for the large intestine as well.

Prostaglandin stimulation of gastrointestinal transit in post-operative ileus rats

The prostaglandins PGF2 alpha, PGE2 and 16,16-dimethyl PGE2, when administered intravenously, orally, subcutaneously or intraduodenally to laparotomized rats, decreased gastric emptying, small intestinal transit and colonic transit as compared to unoperated controls. All three prostaglandins increased colonic transit above that found with unoperated controls. This activity was independent of small intestinal fluid accumulation (i.e., enteropooling) since ligating the ileal-cecal junction had no effect on colonic transit. Small intestinal transit was increased, but not normalized, by PGE2 and 16,16-dimethyl PGE2. 16,16-Dimethyl PGE2 completely restored gastric emptying when given intravenously to laparotomized rats of doses greater than 5.0 microgram/kg. This effect on gastric emptying lasted approximately 4 hrs. Thus, 16,16-dimethyl PGE2, when given intravenously, normalized gastric emptying, significantly increased small intestinal transit, and made the colon hypermotile. Prostaglandins may be beneficial in the treatment of postoperative ileus and other conditions of sluggish gastrointestinal propulsion.

16,16 Dimethyl prostaglandin E2 decreases the formation of collagen in fibrotic rat liver slices.

The effect of 16,16 dimethyl prostaglandin E2 (DMPG) on fibrogenesis was studied in slices from normal and fibrotic rat liver. Rats received a cirrhogenic diet for seven months; supplemented controls received a diet with the deficient nutrients restored. Slices from fibrotic livers incorporated more 14C-proline and produced more 14C-hydroxyproline in TCA precipitable proteins than slices from control livers. DMPG (10(-10) M) decreased the incorporation of labeled proline and the synthesis of labeled hydroxyproline in slices from fibrotic livers to the same extent, suggesting that DMPG did not affect the hydroxylation of proline per se. The magnitude of the DMPG induced decrease in labeled proline incorporation correlated with the hydroxyproline content in the liver (i.e. with increasing fibrosis there was a greater effect of DMPG: while in control rat liver slices, DMPG had no effect). DMPG did not change the size of the proline pool, its specific activity, or the activity of proline oxidase. We conclude that under these conditions of enhanced fibrogenesis, DMPG decreases the formation of collagen in vitro, possibly by lowering the incorporation of proline into collagen precursors. This may explain, at least in part, the inhibition of fibrogenesis by DMPG in vivo.