Correlation of prostaglandin E1 receptor binding with evoked uterine contraction: modification by disulfide reduction

Down-regulation in vivo of PGE receptors and adenylate cyclase stimulation

Down-regulation in vivo of liver plasma membrane receptors for prostaglandin E (PGE) was investigated in Sprague-Dawley rats using the 16,16-dimethyl analogue of PGE2, This analogue was used for subcutaneous injections because it escapes the rapid pulmonic degradation characteristic of PGE and was recognized well by liver plasma membrane receptors. Following treatment with the analogue, the concentration of PGE receptors was significantly decreased (-37%, P less than 0.001), but the binding affinity was not altered. There was no evidence for carry-through of the analogue into the isolated plasma membrane preparation. It was also demonstrated that GTP decreased the binding affinity between PGE and its receptor. Down-regulation of receptor concentration was associated with a significant decrease (P less than 0.001) in PGE1-stimulated plasma membrane adenylate cyclase activity. These data provide the novel demonstration that rat liver plasma membrane receptor for PGE can be down-regulated in vivo and that this causes a corresponding decrease in PGE-induced plasma membrane adenylate cyclase activity.

Specific binding of prostaglandin E2 to membrane preparations from human skin: receptor modulation by UVB-irradiation and chemical agents

Human skin membranes bind prostaglandin E2 (PGE2) with high affinity (with an apparent dissociation constant, Kd, of 3.14 X 10(-9) M) and specificity. This binding is inhibited by trypsin or heat treatment suggesting that PGE2 receptors have protein components. Exposure of the membranes to ultraviolet irradiation (UVB) resulted in the loss of the membrane binding capacity for PGE2. This UVB-ihibitory effect could be prevented by 5,5'-dithiobis-(2-nitrobenzoic acid), a known protein sulfhydryl-oxidizing agent and alpha-tocopherol, a known lipid anti-oxidant. These results suggest that UVB-irradiation possibly initiate the reduction of critical protein disulfide groups and the peroxication of lipids in the membranes, which are essential for the receptor-PGE2 interaction.

Alteration of specific binding of prostaglandin F2 alpha by hyperproliferative skin membrane fractions from essential fatty acid-deficient rats

Specific binding of [3H] PGE2 and [3H] PGF2 alpha to smooth endoplasmic reticulum (SER) membranes prepared from rat skin at various stages of the development of essential fatty acid (EFA)-deficiency syndrome was demonstrated in these studies. The normal SER-binding capacity for [3H] PGE2 per mg of membrane protein was approximately two-fold that for [3H] PGF2 alpha in control rats fed a diet rich in essential fatty acids (EFA). Two weeks following the feeding of the animals with the EFA-deficient diet: histological evaluation revealed hyperplasia and acanthosis of the epidermal layer; a two-fold increase in labeling index (a marker for DNA synthesis) and no alteration in the SER-binding capacity for [3H] PGE2 or [3H] PGF2 alpha. By the 12th week however, labeling index had increased six-fold, accompanied by a five-fold increase in SER-binding capacity for [3H] PGF2 alpha. SER-binding for [3H] PGE2 was relatively unaltered. These results have demonstrated a relationship between marked alteration of skin SER-binding capacity for PGF2 alpha and the increase in epidermal hyperplasia and proliferation characteristic of the skin of the EFA-deficient rat. Refeeding of the animals with EFA-rich diet restored the epidermal proliferation and the SER-binding capacity to PGF2 alpha to normal conditions.

Studies on the nature of a prostaglandin receptor in canine and rabbit vascular smooth muscle

The contractile response of rabbit renal arteries and canine tibial arteries to prostaglandins A2, B2, F2alpha, E1, E2, D2, and B1 was associated with a reduction in total sulfhydryl group content of smooth muscle. The total sulfhydryl content of rabbit renal and canine tibial arteries and was not affected by norepinephrine or potassium chloride. Reduction of disulfide groups with dithiothreitol (DTT) selectively inhibited contractile responses to angiotensin and prostaglandins; 5,5'-Dithiobisnitrobenzoic acid (DTNB), a sulfhydryl group-oxidizing agent, reversed the inhibitory effect of DTT on the contractile responses to prostaglandins. Alkylation of free sulfhydryl groups with ethacrynic acid did not affect the contractile response of isolated canine tibial or rabbit renal arteries to any agonist studied. Ethacrynic acid added to muscle strips exposed to DTT resulted in alkylation of sulfhydryl groups produced by reduction of disulfide bonds and irreversibly prevented DTNB-induced reversal of DTT inhibition of contractile responses to prostaglandins. However, addition of ethacrynic acid to muscle strips contracted by prostaglandins did not inhibit subsequent responses to these acidic lipids. These findings support the hypothesis that contractile responses of rabbit renal and canine tibial arteries to prostaglandins are dependent on interactions between prostaglandins and disulfide groups located in or on the vascular smooth muscle cell, and the concept that membrane disulfide groups may be integral components of vascular smooth muscle receptors for prostaglandins.

Prostaglandin E1 high affinity binding sites of rat thymocytes. Specificity and blockade by non-steroidal antiinflammatory drugs and localization in a plasma membrane-enriched fraction

Great specificity is demonstrated for the prostaglandin E1 high affinity binding sites of rat thymocytes. Whereas prostaglandin E2 has the same affinity as prostaglandin E1, 13 other prostaglandin derivatives and antagonists are bound with 2-1000 times smaller affinities. 50% inhibition of the high affinity binding of prostaglandin E1 to rat thymocytes is demonstrated for three non-steroidal antiinflammatory drugs, indomethacin (3.6. 10(-5) M), salicylic acid (2.9. 10(-3) M) and acetylsalicylic acid (2.10(-2) M). The low affinity binding of prostaglandin E1 is enhanced by the same concentration of indomethacin, however, to a lesser degree and more variable than the inhibition of the high affinity binding of prostaglandin E1. Like intact cells a 50-fold purified plasma membrane fraction, isolated from a homogenate of rat thymocytes, shows reversible high affinity binding of prostaglandin E1 as well as irreversible binding of unidentified tritiated compounds. The binding data are compatible with a localization in the plasma membrane of high affinity sites for reversible binding with a considerably higher dissociation constant than that found for whole cells. Their identity remains to be demonstrated.

Prostaglandin E1 specific binding in rhesus myometrium

Myometrial low speed supernatant prepared from non-pregnant rhesus uteri was incubated with 3H-Prostaglandin (PG)E1 with or without addition of unlabelled prostaglandins. The uptake of 3H-PGE1 was inhibited in a dose dependent fashion by PGE2greater thanPGE1greater thanPGA1greater thanpgf2alpha=PGA1greater thanPGB1=PGB2greater than or equal toPGD2. PGE1 metabolites inhibited 3H-PGE1 binding in the following order: 13, 14-dihydro-PGE1greater than13,14-dihydro-15-keto-PGE1=15-keto-PGE1. The specific binding of 3H-PGE1 and 3H-PGF2alpha was similarly affected by the temperature and time of incubation. Equilibrium binding constants determined using rhesus uteri obtained during the luteal phase of the menstrual cycle indicate the presence of high affinity PGE1 binding sites with an average (n=3) apparent dissociation constant of 2.2 X 10(-9)M and a lower affinity PGE1 binding site with a Kd approximately equal to 1 X 10(-8)M. No high affinity - low capacity 3H-PGF2alpha sites could be demonstrated. Relative uterine stimulating potencies of some natural prostaglandins and prostaglandin analogs tested after acute intravenous administration in mid-pregnant rhesus monkeys corresponded with the PGE1 binding inhibition of the respective compound. The uterine stimulating potencies of the prostaglandin analogs tested were: (15S)-15-methyl-PGE2=16,16-dimethyl-PGE2greater than17-phenyl-18,19,20-trinor-PGE2greater than16 phenoxy-17,18,19,20-tetranor-PGF2alpha=PGE2=PGE1=(15S)-15-methyl-PGF2alpha greater than PGF2alpha.

Prostaglandin specific binding in hamster myometrial low speed supernatant

A charcoal adsorption method was developed to measure specific prostaglandin binding in low speed supernates of hamster myometrial homogenates. This method was used to characterize and quantitate PGE-1-specific binding. The equilibrium binding constants and the concentration of specific PGE-1 binding sites were determined during the hamster estrous cycle. The apparent association constant for 12 different preparations was 1.16 plus or minus 0.08 times 10-9M-1. The concentration of PGE-1 specific binding sites was significantly higher on days 2 and 3 of the estrous cycle that it was on days 1 or 4. The competition for PGE-1 binding sites by PGE-2, PGF-2alpha, tpga-1 and various PGE-1 metabolites and derivatives was measured in hamster myometrial homogenates. Relative affinities of the natural prostaglandins for the PGE-1 binding sites, calculated by parallel line assay, were: PGE-2 greater than PGE-1 greater than PGA-1 greater than PGF-2alpha. For PGE-1 metabolites the relative affinities were: PGE-1 greater than 13,14-dihydro-PGE-1 greater than 13,14-dihydro-15-keto-PGE-1 greater than 15-keto-PGE-1. For the analogs and derivatives the compounds tested ranked as: 16,16-dimethyl-PGE-1 greater than PGE-1 methyl ester greater than 17-phenyl-18,19,20-trinor-PGE-1 greater than 15(S) 15-methyl-PGE-1 methyl ester. Arachidonic acid, bis-homo-gamma-linolenic acid and 7-oxa-13 prostynoic acid had relative affinities greater than 0.1 compared to PGE-1 equal 100. Indomethacin had a relative affinity of 0.4 compared to PGE-1.