Comparison of the Effects of Prostaglandins E1, E2, and A2, and of Hypovolumic Hypotension on the Lower Esophageal Sphincter

GASTROENTEROLOGY 65: 608- 612, 1973 Copyright© 1973 by The Williams & Wilkins Co.

Vol. 65, No. 4

Printed in U.S.A.

COMPARISON OF THE EFFECTS OF PROSTAGLANDINS Eu E2, AND A 2 , AND OF HYPOVOLUMIC HYPOTENSION ON THE.. LOWER ESOPHAGEAL SPHINCTER RAJ K. GoYAL, M .D., SATISH RATIAN, B.V.Sc., AND THEODORE HERSH, M.D.

Gastroenterology Section, Department of Internal Medicine, Baylor College of M edicine, Houston , Texas

Studies were performed in a lightly anesthetized opossum to investigate the effect of prostaglandin E 2 and A 2 on the lower esophageal sphincter pressure. Intravenous injection of these agents as a single bolus caused a dose-dependent fall in the lower esophageal sphincter pressure. Prostaglandin (PG) E 2 was as potent as PGE, whereas PGA 2 was much less potent than the E compounds. The threshold dose of PGE 2 was 0.15 f.Lg per kg and maximal effect was found with a dose of 1 f.Lg per kg. Threshold dose of PGA 2 was 1 f.Lg per kg. All these prostaglandins caused a drop in the blood pressure, but this drop was transient. On the other hand, the effect on lower esophageal sphincter was much prolonged. The duration of the effect was related to dose; higher doses generally caused longer reductions in lower esophageal sphincter pressure. Hypotension produced by hemorrhaging and by intravenous injection of sodium pentobarbital produced no change in the lower esophageal sphincter pressure, suggesting that fall in blood pressure is not related to fall in the lower esophageal sphincter pressure. Goldblatt' and von Euler 2 independently observed the ability of human seminal plasma to stimulate smooth muscle and to lower blood pressure. von Euler 3 also found that a similar substance occurred abundantly in the extracts of prostate gland and named it prostaglandin. Subsequently it was shown that these effects were due to a mixture of prostaglandins. 4 These prostaReceived March 15, 1973. Accepted May 29, 1973. Part of this work was presented at the meeting of the Midwestern Section of the American Federation for Clinical Research, November 4, 1971, Chicago, Illinois . Address requests for reprints to: Dr. Raj K. Goyal, Department of Internal Medicine, University of Texas Southwestern Medical School, ·5323 Harry Hines Boulevard, Dallas, Texas 75235. This study was supported in part by a grant from the Kelsey and Leary Foundation, Houston, Texas . The authors thank Mrs . Gay Grubb and Judy Chmiel for their help, and Dr. John Pike of the Upjohn Company for the gift of prostaglandins.

glandins (PG) 5 • 6 have been found to be widely distributed in the body and many naturally occurring prostaglandins have been identified. These belong to four series of compounds, arbitrarily named E, F, A, and B. Different prostaglandins show qualitative and quantitative differences in their actions on different tissues of the body. Moreover, the relative activity of these agents may vary with the species of the animal and the mode of administration. 5 • 6 Actions of different prostaglandins on the gastrointestinal tract have been reviewed. 7 • 8 We have found that PGF2a causes an increase in the lower esophageal sphincter pressure (LES) in the opossum in vivo. 9 On the other hand, PGE, causes inhibition of the LES pressure. 10 The studies presented here compare the inhibitory effect of PGE, with that of PGE 2 and PGA2 on the LES in the intact opossum. All these agents caused a fall in arterial blood pressure. We also present evidence to show that

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PROSTAGLANDINS ON LOWER ESOPHAGEAL SPHINCTER

the fall in LES pressure is not related to the fall in the blood pressure.

Methods Studies were performed in 21 opossums (Didelphis virginiana) of either sex and weighing between 3 and 5 kg. In the opossum the lower part of the esophagus including the lower esophageal sphincter, as in man , is composed of smooth muscle fibers. 11 The animals were anesthetized with intraperitoneal pentobarbital (50 mg per kg) and they were secured supine to the animal board. Lower esophageal sphincter pressures were measured with an assembly of continuously perfused catheter systems as described elsewhere. 10 The direct blood pressure measurements were performed by a MikroTip'm pressure transducer (Model PC350; Millar Instruments , Houston, Texas) inserted into the carotid artery of the animal. Drugs were injected through an intravenous cannula as a single bolus. At least 10 min of normal base line pressure were recorded between injections. The LES pressures were measured at end inspiration. The maximum change that was seen on administration of drug was considered in the results . To make the data uniform, change in the sphincter pressure was expressed as a percentage of the resting LES pressure. Prostaglandins were dissolved in ethanol to make a stock solution. Prostaglandin (1 mg) was dissolved in a solution of 0.1 ml of 95% ethanol and 0.9 ml of 0.15 N saline. Further dilutions were made in 0.15 N saline so that final concentration of prostaglandin varied from 5 f.lg per ml to 20 f.lg per mi. To study the effect of pentobarbital sodium, the animals were allowed to become very lightly anesthetized. Sodium pentobarbital in the dose of 3 f.Lg per kg was then injected intravenously as a single bolus. To study the effect of acute hypotension on the LES pressure, the animals were bled by withdrawing 15 to 20 ml of blood from a brachial artery in 20 to 30 sec in a heparinized syringe. T'he blood pressure fell rapidly . After 1 to 2 min , the blood was injected back into the animal. The changes in blood pressure were expressed separately for both systolic and diastolic pressures.

Results Figure 1 depicts a typical response of LES and blood pressure to a single intravenous injection of PGE 2 • Injection of normal

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saline or the vehicle for PGE 2 (0.19% ethanol up to 2 ml) caused no significant change in the sphincter or blood pressure. The fall in the LES pressure caused by PGE 2 administration was dose-dependent. PGEz in the dose of 0.15 /J.g per kg caused about 9% fall in LES pressure. Maximum effect of 90% reduction in LES pressure was found with a dose of 1 /J.g per kg. The duration of action also varied with the dose, larger doses (up to 1 /J.g per kg) causing a fall in LES pressures of longer duration (table 1). PGA 2 injection also caused a fall in LES pressure. A dose of 0.5 /J.g per kg caused no change in LES pressures, whereas a dose of 1 /J.g per kg caused about 10% fall in LES pressure. With PGA 2 in the dose of 8 /J.g per kg, blood pressure fell from 140/100 mm Hg to 72/48 mm Hg. This dose caused a 41% fall in LES pressure. Higher doses were not tolerated by the animals. Dose-response curves of PGE 2 and PGA 2 for their effect on LES inhibition are compared with that of PGE 1 in figure 2. The curve of PGE 2 was very similar to that of PGE 1 and the two drugs were equipotent. On the other hand, PGA 2 was less active. PGA 2 in doses higher than 8 /J.g per kg could not be tested, and the effect of higher doses on the LES pressure is hard to predict. Therefore, precise ED 50 of this agent could not be calculated. We could say, however, from the study of the doseresponse curves, that for a 10 to 40% fall in LES pressure PGE 1 as well as PGE 2 were about 4 to 20 times as potent as PGAz, the

..... ESOPHAGUS

2.: r_ _ _ _ _ _ _ _ _ _ _ _ __

"'::[""\ ~ BLOODP~ESSURE::r~

,t ..

FIG. 1. A representative response of the lower esophageal sphincter (LES) pressure and blood pressure to prostaglandin E 2 administration. PGE 2 was given in the dose of 1 f.l.g per kg intravenously as a single bolus (arrow) . Note a prompt fall in LES pressure which lasted about 10 min. The fall in blood pressure was only transient. PGE, showed similar response.

TABLE

1. Effect of prostaglandins (PC) E , and A, on the lo wer esophageal sphincter pressures No. of observations

Dose Ji{!,/k{!,

PGE , 0.15 0.25 0.35 0. 5 1 2 4 8 PGA , 0.5 1 2 4 8 •Mean ±

100

80

..;

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GOYAL ETAL.

610

60

Resting

Fallin

press urea

press urea

mmHt;

mmHt;

Percentage of fa ll in pressure•

Duration of action• min

7 7 6 9 8 9 6 6

41.0 54.3 44.8 42.2 49 .6 50.6 47. 1 37.1

± ± ± ± ± ± ± ±

3. 1 8.3 4.6 4.7 3.4 2.8 3.2 4.4

4.1 ± 5.7 ± 16.0 ± 35.0 ± 45.3 ± 46.3 ± 43.0 ± 32.7 ±

3.0 3.9 8.0 5.9 3.8 3.2 4.0 4.2

9.0 8.5 32.5 72.5 90.1 89 .9 89.1 88.3

± ± ± ± ± ± ± ±

6 .6 4.7 14.2 10.1 3.7 2.6 3.4 6.1

1.5 ± 3. 1 ± 3.5 ± 6.2 ± 10.2 ± 7.3 ± 8.5 ± 10.5 ±

6 7 7 10 9

39.0 43.9 48.6 39 .4 43.9

± ± ± ± ±

2.3 5.6 2.9 1.9 4.4

4.3 8.1 12.8 14.7

0 ± ± ± ±

3.0 2.6 5.1 7.0

0 9.8 ± 16.7 ± 34 .6 ± 41.5 ±

7 .2 7.8 12.2 11 .8

0.5 1.1 5.7 4.0

0.3 1.7 1.3 1.6 2.6 1.8 1.3 5.5

±0 ± 0.9 ± 1.4 ± 1.1

SE.

been summarized in figure 3. Intravenous injection of sodium pentobarbital also caused a significant drop in blood pressure but no change in LES pressure.

Comments There are many studies of the effect of ::. 20 different prostaglandins on the gut muscle z u in vitro . 12 - 15 Strips of longitudinal muscle "' :;' of small and large intestine from several 0.!5 0.25 0.35 0.5 species of animals usually contract in reDOSE I N ug / Kg ILOG SCA LE I sponse to prostaglandin E. 1 2 • 13 In some FIG. 2. Dose-res ponse cu rves of prostagland in tissues contraction may be preceded by (PG) E ., PGE,, an d P GA, on the lower esophageal relaxation or there may be only relaxation sphincter (L .E.S.) pressure. The curves of PGE, and as in rat duodenum . 14 On the other hand, PGE, were similar. The dose-response curve of PGA, was shifted to the right. PGA, in the dose higher than strips of circular muscle are usually 8 !J.g per kg could not be used because the animals did inhibited 15 ; rat stomach is an exception, not tolerate higher doses. Each point represents a however, as its circular muscle strips conmean of six to 11 studies and the vertical lines inditract to PGE. 7 Prostaglandin A has very cate SEM. little effect on the gut muscle strips. 7 • 16 Injection of prostaglandins into the potency of PGE being higher with greater blood stream also influences gastrointestiresponses of LES inhibition. nal motility but the effect varies in differProstaglandins E 1, E 2 , and A 2 caused a ent species of animals. PGE causes an drop in both systolic and diastolic blood increase in the intraluminal pressure of the pressure. To evaluate the effect of hypoten - ileum in anesthetized rat. 17 The effect on sion on the LES, we performed studies in 5 guinea pig small bowel is variable 17 and the animals. Hypotension was produced by intestinal motility of dog is inhibited. 18 hemorrhaging the animals. The LES and · PGE 1 infused at the rate of 1 J.Lg per kg per blood pressure responses to prostaglandin min reduces gastric antral activity. 19 Some A 2, E 1 , and E 2 and acute bleeding have of these differences between the in vivo and ::: ~

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PROSTAGLANDINS ON LOWER ESOPHAGEAL SPHINCTER

in vitro studies may be due to metabolic alterations in the prostaglandin in the body as well as due to secondary effects of these agents such as on gastrointestinal secretions and systemic blood pressure. 7 Our studies show that PGE 1 and PGE 2 in vivo cause a dose-related fall in LES pressure. This is consistent with the inhibitory action of E compounds on the circular muscle of gut. PGE 1 and E 2 were equiactive . The dose of prostaglandin causing a 50% fall in LES pressure was 0.35 to 0.4 llg per kg for both E 1 and E 2 • Antilipolytic activity of E 2 has been reported to be greater than that of E 1 • 16 On the other hand, E 2 was found to be equiactive to E 1 as regards their actions on isolated smooth muscle strips and circulatory system. 20 In contrast PGE 3 possesses much less activity. Prostaglandin A 2 also caused a fall in LES pressure. The PGA 2 was much less active as compared with PGE 2 ; a 40% drop in LES pressure was caused by a PGA 2 dose of 8 /lg per kg. Higher doses could not be used because of the profound cardiovascular effects on the animals with higher doses of PGA 2 • PGA compounds are known to have very mild effect on the isolated gut muscle as compared with PGE. It appears that the PGA 2 caused a more significant fall in the LES pressure in vivo as com160

B.P

fYSTOLIC OIASTOLIC

l. E.S. PRESSURE

~~~~~ 1-----i PGE1 C

r--i !---i

PGA1 C

HGE C

140 110 100

~

80~ E

60

40 10 0

PENTO

FIG. 3. Responses of lower esophageal sphincter (L.E.S.) pressure and blood pressure (B.P.) to prostaglandins (PG) E 1 , E,, and A, and hemorrhaging and intravenous sodium pentobarbital (PENTO) . PGE 1 and PGE, were injected in the dose of l)lg per kg and PGA, in the dose of 2!'g per kg. Sodium pentobarbita l was injected intravenously in the dose of 3 mg per kg. Each point represents mean ± SE of five to seven observations. Note a drop in systolic and diastolic blood pressure with all these treatments. Significant (asterisk) drop in LES occurred only with PGE 1 and E,. In other cases LES pressure remained unchanged. C, control; HGE, hemorrhage.

611

pared with its known in vitro effectiveness as compared with PGE 2 • This difference may be due to the fact that PGE 2 is very rapidly inactivated in the lungs, up to 90% in one circulation, whereas PGA is very resistant to such an inactivation. 5 • 20 The prostaglandins E 11 E 2 , and A 2 all caused a fall in blood pressure, and an increase in the heart rate as well as the respiratory rate. The hypotensive effect of the single intravenous injection of these agents was only transient, but the effect on the lower esophageal sphincter was more prolonged. Moreover, for a comparable hypotensive effect PGE 2 was a more potent inhibitor of LES than PGA 2 • Several studies have shown that PGA 2 is a more specific hypotensive agent with mild effects on the other tissues. 2 ° Furthermore, acute arterial hypotension produced by hemorrhaging did not significantly alter the LES pressure. These studies indicate that inhibitory effect of these prostaglandins on the LES was not due to associated arterial hypotension. Studies on the mechanism of the action of PGE 1 on the LES have suggested that this action may be a direct action on the sphincter muscle. 10 The effect of PGE 1 on the LES was not antagonized by a or (3 adrenergic antagonism, muscarinic, or nicotinic cholinergic antagonism. Moreover, serotonin antagonism with methysergide, and finally neural blockade with local intraarterial tetrodotoxin, did not modify the action of PGE 1 on the LES (R. K. Goyal, S. Rattan, unpublished observations). Prostaglandins E 2 and A 2 also may have a similar direct action on the LES. There is evidence to suggest that this direct action may be mediated via the enhancement of cyclic adenosine monophosphate levels in the LES muscle. 10 Do these prostaglandins have any physiological role in the esophageal motor function? A role for prostaglandins in the regulation of lower esophageal sphincter is not established but several indications suggest that such a possibility exists. Prostaglandin E causes potent inhibition of LES. Rashid 2 1 has reported a small spontaneous release of prostaglandin from the frog esophagus . On electrical stimulation there

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is a 20-fold increase in the prostaglandin content from the esophagus as compared with only about a 5-fold increase in the prostaglandin content from the stomach. Furthermore, the prostaglandin release was predominantly of E type. Electrical stimulation of muscle strips from the LES in the oposssum causes sphincter relaxation. 22 The neurotransmitter of these inhibitory nerves is not known, although adenosine triphosphate-like compounds have been suggested as possible candidates. 23 The possibility that PGE compounds may be the neurotransmitter of these inhibitory nerves deserves consideration.

11.

12.

13.

14.

15.

16. REFERENCES 1. Goldblatt MW: A depressor substance in seminal fluid . J Soc Chern Ind (Lon d) 52 :1056- 1057, 1933 2. von Euler US: A depressor s ubstance in the vesicular gland. J Physiol (Lond) 84 :21 P, 1935 3. von Euler US: On the specific vasodilating and plain muscle stimulating substances from accessory genital glands in man and certain animals (prostaglandin and vasiglandin). J Physiol (Lond) 88:213-234, 1936 4. Bergstrom S, Carlson LA, Weeks JR: The prostaglandins: a family of biologically active lipids. Pharmacal Rev 20:1-48, 1968 5. Horton EW: Prostaglandins. Monographs on endocrinology, vol 7. New York, Springer-Verlag, 1972 6. Ramwell P , Shaw JE: Prostaglandins . Ann NY Acad Sci 180, 1971 7. Bennett A , Fleshier B: Prostaglandins and the gastrointestinal tract. Gastroenterology 59:790-900, 1970 8. Wilson DE: Prostaglandins and the gastrointestinal tract. Prostaglandins 1:281- 292, 1972 9. Rattan S, Hersh T , Goyal RK: Effect of prostaglandin F 2 a and gastrin pentapeptide on the lower esophageal sphincter. Proc Soc Exp Bioi Med 141 :573- 575 , 1972 10. Goyal RK , Rattan S: Mechanism of lower esophageal sphincter relaxation : action of prostaglandin

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E, and theophylline . J Clin Invest 52:337-341 , 1973 Christensen J , Lund GF: Esophageal response to distension and electrical stimulation. J Clin Invest 48:408- 419, 1969 Horton EW, Main IHM : A comparison of the biological activities of four prostaglandins . Br J Pharmacal 21:182-189, 1963 Bennett A, Eley KG , Scholes GB : Effects of prostaglandins E, and E 2 on human, guinea pig and rat isolated small intestine. Br J Pharmacal 34:630- 638, 1968 Khairallah PA, Page IH, Tucker RK: Some properties of prostaglandin E, action on muscle. Arch Int Pharmacodyn 169:328-341, 1967 Fleshier B , Bennett A: Responses of human , guinea pig and rat colonic circular muscle to prostaglandins . J Lab Clin Med 75 :872- 873, 1969 Weeks JR, Sekhar CN, Ducharme DW: Relative activities of prostaglandins E,, E 2 , A, and A 2 on Jypolysis, platelet aggregation, smooth muscle and cardiovascular systems. J Pharm Pharmacal 21:103- 108, 1969 Bennett A, Eley KG, Scholes GB: Effect of prostaglandins E, and E 2 on intestinal motility in the guinea pig and rat. Br J Pharmacal 34:639- 647, 1969 Shehadeh Z, Price WE, Jacobson ED: Effects of vasoactive agents on intestinal blood flow and motility in the dog. Am J Physiol 216:386- 392, 1969 Chawla RC, Eisenberg MM: Prostaglandin inhibition of innervated antral motility in dogs. Proc Soc Exp Bioi Med 132:1081-1086, 1969 Higgins CB, Braunwald E: The prostaglandins. Biochemical, physiological and clinical considerations . Am J Med 53:92- 107, 1972 Rashid S: The release of prostaglandin from the esophagus and the stomach of the frog (Rana temporaria). J Ph arm Pharmacal 23:456-457, 1971 Tuch A, Cohen S: Lower esophageal sphincter relaxation : studies on the neurogenic inhibitory mechanism. J Clin Invest 52:14-20, 1973 Burnstock G, Campbell G, Satchell D, et a!: Evidence t hat adenosine triphosphate or a related nucleotide is the transmitter substance released by non-adrenergic inhibitory nerves in the gut. Br J Pharmacal 40:668- 688, 1970