Correlation between cyclic AMP and LH release following prostaglandin E2 administration.

Five min following a single iv injection of PGE2 into ovariectomized mature rats pretreated with estrogen and progesterone, plasma LH and plasma and pituitary cyclic AMP levels were raised significantly. A close correlation was observed between increased pituitary cyclic AMP contents and release of plasma LH. The average level of cyclic AMP in the anterior pituitary and plasma cyclic AMP increased significantly, while the circulating plasma LH level was not changed at 1 min after PGE2 injection. Plasma LH le-el increased at 2 min after PGE2 and reached a maximum level at the above-mentioned time. This is consistent with hypothesis that increased release of hormone is a consequence of increased pituitary cyclic AMP content.     

Comparison between the effect of luteinizing hormone and prostaglandin E1 on ovarian cyclic AMP

Isolated whole ovaries from 23–24 day-old rats were studied in order to compare the effects of prostaglandin E₁ (PGE₁) and luteinizing hormone (LH) on ovarian cyclic adenosine 3′,5′-monophosphate (cAMP) production. Both substances produced a dose-dependent accumulation of cAMP in the ovarian tissue as well as in the incubation medium. The release of cAMP to the incubation medium was considerable after long periods of incubation (60–120 min). Time-relationships for LH- and PGE₁-effects were different. Maximal cAMP content in the tissue after addition of PGE₁ was seen already after 5–15 min of incubation whereas LH gave a maximal response after around 60 min. Accumulation of cAMP in the medium was approximately linear with time for both LH and PGE₁. Addition of theophylline potentiated the action of PGE₁ and LH but did not change the time-courses of the effects. It is concluded that the accumulation of cAMP in the medium should be considered in studies with various in vitro types of ovarian preparations. It is also pointed out that the different time-courses of the LH- and PGE₁-effects make the interpretation of additivity experiments difficult.     

Cyclic AMP formation and release by cultured bone cells stimulated with prostaglandin E2

PGE₂ produced a marked and dose-related increase in cAMP content of cultured bone cells and in the release of cAMP into the incubation medium. The amount of cAMP released from the cells by PGE₂ was proportional to the cellular concentration, and was dependent upon the time of incubation with PGE₂. The cAMP levels released into the media increased slowly at a linear rate during a 60 min treatment with PGE₂. This release was blocked by theophylline, probenecid, ouabain and dinitrophenol, suggesting that the release of cAMP was not a simple diffusive process and required energy. SC-19220 reduced the formation of cAMP more than the release, suggesting that the formation and the release may arise from separate events. Inability of D600 to inhibit PGE₂-induced release of cAMP indicates that the release does not require calcium.     

Comparative behavioral effects of dibutyryl cyclic AMP and prostaglandin E1 in mice

Three behavioral tests, spontaneous locomotor activity (SLMA), exploratory behavior (EB) and rotarod performance (RP), a measure of neuromuscular coordination, were used to study the interaction of PGE₁ (1 mg/kg i.p., 10 min. pretreatment) with DBcAMP (25 mg/kg i.p., 25 min. pretreatment) in mice. A dose-response relationship of PGE₁ (0.01–5.0 mg/kg) to SLMA was determined, with a significant decrease in SLMA produced by a dose of 0.1 mg/kg. Decreases in SLMA were produced by PGE₁ (79%), DBcAMP (41%) and DBcAMP-PGE₁ combination (71%). Similar decreases in EB were observed. Although no significant difference between controls and DBcAMP was observed in RP, 52% of mice tested were RP failures following PGE₁ and a 100% failure rate was induced by the combination. Mice were treated with a second injection of DBcAMP or PGE₁ or the combination 24 hr following the first injection. Behavioral activity of these mice was observed 25 min (DBcAMP) or 10 min (PGE₁) after the second dose was administered. A second injection of DBcAMP failed to decrease SLMA and EB from controls; moreover, SLMA began to return towards control levels as early as 2 hr between injections. The second injection of PGE₁ or DBcAMP+PGE₁ produced the same behavior as that produced by the first injection. On the basis of these results, the relationship of cyclic nucleotides and PGs to behavioral activity is discussed.     

Effect of prostaglandin E1 on hepatic cyclic AMP activity, carbohydrate and lipid metabolism

Prostaglandin E₁ (PGE₁) failed to stimulate rat liver cyclic AMP (cAMP), induce hyperglycemia, glycogenolysis or lipolysis or prevent epinephrine-induced hyperglycemia in isolated perfused rat liver, even though other known glycogenolytic agents (glucagon and epinephrine) activated cAMP in this same system. The data do not support a physiologic role for PGE₁ on hepatic glycogenolysis or lipolysis. Although the effects of PGE₁ on gluconeogenesis, lipogenesis, ureogenesis or amino acid transport in isolated perfused liver were not investigated, if PGE₁ is subsequently found to influence these metabolic parameters, such alterations would probably occur independent of a change in cAMP activity.     

Molecular conformation of prostaglandin E2

The crystal and molecular structure of prostaglandin E₂ (PGE₂) has been determined by X-ray diffraction. The compound crystallizes in the triclinic space group P1 with Z = 1 and , , , α = 87.347°, β = 94.042°, and γ = 91.010°. Gauche-gauche interactions appear in both side chains. The efficient molecular packing and hydrogen bonding network appears to stabilize the observed molecular conformation.     

Hyperventilation stimulates the release of prostaglandin I2 and E2 from lung in humans

It has been reported that hyperventilation (HV) increases the release of vasodilative prostaglandins (PGs) from animal lungs. However, it has not yet been clarified whether or not the results obtained from animal experiments are applicable to humans. To confirm this point, we performed this study. Healthy male volunteers, aged 22–28 years, were divided into two groups. Group I (n=11) breathed room air and showed respiratory alkalosis. Group II(n=11) breathed room air containing 5% CO2 and maintained normal arterial blood pH. Each subject hyperventilated voluntarily and vigorously for 10 min. The mean values of respiratory rates, tidal volumes and minute volumes during HV were 42.1±6.2 breaths/min, 1390±280 ml and 58.5±15.2 l/min, respectively. Arterial and venous blood samples were drawn simultaneously before and after HV from brachial artery and medial cubital vein, respectively. Plasma 6-keto PGF1 α, a metabolite of PGI2, and PGE2 were measured by radioimmunoassay (RIA). After HV, concentrations of 6-keto PG F1 α and PGE2 in both arterial and venous blood were increased significantly. There were no significant differences in the levels of 6-keto PGF1 α and PGE2 between two groups, nor between arterial and venous blood either before or after HV. We concluded that voluntary HV stimulates the release of PGI2 and PGE2 from lung in humans and respiratory alkalosis has no significant effect on the release of PGs.     

Effect of prostaglandin E2 upon release of pancreatic somatostatin-like immunoreactivity

Infusion of prostaglandin E₂ (1 ug/kg/min) in six normal dogs elicited a greater than two-fold rise in pancreaticoduodenal vein somatostatin-like immunoreactivity. Insulin and glucagon also rose. The results raise the possibility that the function of the canine pancreatic D-cell is under prostaglandinergic influence.     

Effects of prostaglandin E1, I2 and isoproterenol on the tissue cyclic AMP content in longitudinal muscle of rabbit intestine

Effects of prostaglandin E₁(PGE₁) and prostaglandin I₂(PGI₂) on the mechanical activity and tissue cyclic AMP content of the longitudinal muscle of rabbit intestine were examined, comparing that of isoproterenol. PGE₁ or PGI₂ caused a contraction and did not affect the tissue cyclic AMP content. Isoproterenol caused a relaxation and increasedtissue cyclic AMP content.     

Selective induction of labour following administration of an oral prostaglandin E2 0.5 mg tablet hourly

Induction of labour was performed on 20 patients with favourable induction features by amniotomy and administration of a fixed dose of 0.5 mg of prostaglandin E₂ (PGE₂) hourly. Effective uterine action resulted in a mean time to delivery of 6 hrs 57 mins in primagravid patients and 4 hrs 40 mins in multigravid subjects. In two patients an intravenous oxytocin infusion was used to assist labour. There were no significant maternal or fetal side effects.     

Labour induction using buccal prostaglandin E2

Prostaglandins may remain in the circulation for some two hours after oral therapy and any resultant hypertonus may be difficult to treat in these circumstances. Buccal administration based on the concept that tablets could be discarded should this occur, has been evaluated in 30 patients. Effective uterine stimulation occured in 90% of subjects receiving a dose of 1mg hourly. No hypertonus occured but two patients had a prolonged contraction on a single occasion during labour. The fact that the tablets dissolve rapidly and in addition produce an unpleasant taste with a high incidence of nausea and vomiting, indicates buccal prostaglandins do not have advantages over alternative methods of oxytocic administration.     

Ovulation rate and serum LH levels in rats treated with indomethacin or prostaglandin E2

Serum LH levels were determined by radioimmunoassay at the normal time of the proestrous LH peak (17.30 – 18.00) and ovulatory performance was examined on the morning of estrus in rats treated with indomethacin, an inhibitor of prostaglandin synthesis. When the drug was administered at 14.30 on the day of proestrus, only 21% of the rats ovulated and the total number of ova shed was reduced to 4% of that found in the untreated control group, but there was no significant change in peak serum LH level (1122 ± 184 vs. 975 ± 240 ng/ml ± S.E., treated vs. control). Prostaglandin E₂ (PGE₂) given late on the day of proestrus (25 to 750 μ g/rat at 24.00) was effective in overcoming this antiovulatory action of indomethacin: 71–90% of the rats ovulated, though the number of eggs shed was low (24–55% of control value). Indomethacin was still effective in blocking ovulation when given at 20.00, that is after completion of the proestrous LH surge, but not at 24.00. Administration of PGE₂ (2 × 750 μ g/rat) in the early afternoon of proestrus elicited a rise in serum LH levels in rats in which the cyclic LH surge had been blocked with Nembutal (470 ± 87 vs. 106 ± 17 ng/ml ± S.E.) and induced ovulation in two-thirds of these animals.The results confirm, by direct measurement, that indomethacin does not block LH release but interferes with a late phase of the ovulatory process. PGE₂ reverses this action of indomethacin on the ovary. In addition, PGE₂ has a central effect causing LH release.     

Prostaglandins E1 and E2 stimulate release of intestinal brush border enzymes

Rat small bowel was perfused and in the absence of biliary and pancreatic secretion. Intraluminal release of sucrase, alkaline phosphatase, aminopeptidase and enterokinase was significantly increased after administration of PG E₁ and E₂ 1 and 5 μg/kg. This suggests a direct stimulation of the intestinal mucosa, which might be mediated through cyclic AMP ; dibutyryl cAMP significantly stimulates intraluminal release of proteins, sucrase and enterokinase.     

Stimulatory effects of prostaglandin E1 on rat anterior pituitary cyclic amp and luteinizing hormone release

The effect of prostaglandin E₁ (PGE₁) on rat anterior pituitary cyclic AMP accumulation and luteinizing hormone (LH) release was studied both in vivo and in vitro. Addition of PGE₁ to incubation medium over a concentration range of 10^-6 to 10^-4 M produced a graded increase in pituitary cyclic AMP. At the lowest concentration (10^-6 M) there was no significant increase in LH release, but proportional increments in LH release were seen with increasing concentrations of PGE₁.Ten minutes after intravenous administration of 5 μg of PGE₁ to adult male rats, pituitary cyclic AMP was substantially increased while serum LH levels were not changed. Administration of a higher dose of PGE₁ (20 μg) produced a greater increase in pituitary cyclic AMP; and, at this dose serum LH was significantly increased. These results suggest that the PGE₁ effect on LH release is mediated by the adenyl cyclase — cyclic AMP system.     

Evidence of reduced uptake of convulsant in brain following prostaglandin E2

The toxic and convulsant effects of the acetylcholinesterase (AChE) inhibitor Soman, were examined in mice pretreated with various doses of prostglandin E₂ (PGE₂), administered by either intraperitoneal injection (i.p.) or by intracerebroventricular (i.c.v.) infusion. PGE₂ (i.p.) reduced the lethal effects of Soman slightly. PGE₂ (i.p. and i.c.v.) delayed the onset and reduced the severity of cholinergically-induced convulsions, resulting from Soman. Whole brain AChE was measured at various times after Soman or Soman preceded by PGE₂. PGE₂ (i.p. or i.c.v.) reduced the rate at which Soman inhibited brain AChE, which appeared to be related to the increased time to onset of convulsive activity. Repeated injections of PGE₂ did not delay convulsions indefinitely nor were convulsions terminated once they had started. The results suggest that the anticonvulsant properties of PGE₂ may have been due, in part, to decreased cerebral circulation with subsequent reduction in the access of the convulsant to the brain and in part to direct neuronal effects.     

Radioimmunoassay of 15-keto-prostaglandin E2 in peripheral plasma after oral administration of prostaglandin E2 tablets used for induction of labour

A radioimmunoassay of the 15-keto-metabolite of prostaglandin E₂ has been developed. The details of the assay are described. Using unextracted plama, serial measurements of 15-keto-PGE₂ have been carried out every 15 minutes for 3 hours in 9 women ingesting 0.5 mg PGE₂ oral tablets used for the induction of labour.     

Stimulation of bone formation by prostaglandin E2

We examined the effect of prostaglandin E₂ (PGE₂), in the presence or absence of cortisol, on bone formation in 21-day fetal rat calvaria maintained in organ culture for 24 to 96 h. [³H]Thymidine and [³H] proline incorporation were used to assess DNA and collagen synthesis, respectively. Changes in dry weight and DNA content were assessed after 96 h.PGE₂ (10⁻⁷ M) stimulated both DNA and collagen synthesis in calvaria. The effect on DNA synthesis was early (24 h), transient and limited to the periosteum. Collagen synthesis was stimulated at a later time (96 h), predominantly in the central bone. Cortisol (10⁻⁷ M) inhibited DNA and collagen synthesis. The addition of PGE₂ reversed the inhibitory effects of cortisol on DNA synthesis and content and increased collage synthesis in central bone to levels above control untreated cultures.We conclude that PGE₂ has stimulatory effects on bone formation and can reverse the inhibitory effects of cortisol. Hence the effects of cortisol may be mediated in part by their ability to reduce the endogenous production of prostaglandins.     

Stimulation by prostaglandin E2 of glucagon and insulin release from isolated rat pancreas

To ascertain whether prostaglandins (PG) may play a role in the secretion of glucagon and in an attempt to elucidate the conflicting observations on the effects of PG on insulin release, the isolated intact rat pancreas was perfused with solutions containing 1.1 × 10⁻⁹ to 1.8 × 10⁻⁵M PGE₂. In the presence of 5.6 mM glucose significant increments in portal venous effluent levels of glucagon and insulin were observed in response to minimal concentrations of 2.8 × 10⁻⁸ and 1.4 × 10⁻⁷M PGE₂, respectively; a dose-response relationship was evident for both hormones at higher concentrations of PGE₂. When administered over 60 seconds, 1.4^−10−6M PGE₂ resulted in a significant increase in glucagon levels within 24 seconds and in insulin within 48 seconds. Ten-minute perfusions of 1.4 × 10⁻⁶M PGE₂ elicited biphasic release of both islet hormones; Phase I glucagon release preceded that of insulin. Both phases of the biphasic glucagon and insulin release which occurred in response to 15-minute perfusions of 10 mM arginine were augmented by PGE₂. These observations indicate that PGE₂ can evoke glucagon and insulin release at concentrations close to those observed by others in the extracts of rat pancreas. We conclude that PG may be involved in the regulation of secretion of glucagon and insulin and may mediate and/or modify the pancreatic islet hormone response to other secretagogues.     

Failure of prostaglandins E1 and E2 to alter canine gastric mucosal cyclic nucleotides

The action of prostaglandins and indomethacin on gastric mucosal cyclic nucleotide concentrations was evaluated in 18 anesthetized mongrel dogs. Prostaglandins E₁ (PGE₁) and E₂ (PGE₂) (25 μg/kg bolus, then 2 μg/kg/min) were administered both intravenously (4 experiments; femoral vein) and directly into the gastric mucosal circulation (10 experiments; superior mesenteric artery). The possible synergistic effect of pre-treatment and continuous arterial infusion of indomethacin (5 mg/kg bolus for 5 min, then 5 mg/min), a prostaglandin synthetase inhibitor, with PGE₂ was studied in 4 experiments. Antral and fundic mucosa were biopsied and measured by radioimmunoassay for cyclic nucleotides. Doses of PGE₁ and PGE₂ which inhibited histamine-stimulated canine gastric acid secretion did not significantly alter antral or fundic mucosal cyclic nucleotide concentrations. Concomitant infusion of PGE₂ with indomethacin did not potentiate the mucosal nucleotide response compared to PGE₂ alone. These studies fail to implicate cyclic nucleotides as mediators of the inhibitory acid response induced by PGE₁ or PGE₂ in intact dog stomach.