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Two analogues of PGI2, FCE 21258 (5E-13,14-didehydro-carboprostacyclin) and FCE 21292 (5E-13,14-didehydro-20-methyl-carboprostacyclin) have been evaluated in comparison with PGI2 in different in vitro and in vivo screening tests. The rank order of potency was PGI2 greater than FCE 21292 greater than FCE 21258 in the following tests: potentiation of bradykinin-induced increased plasma protein extravasation in the guinea pig skin, inhibition of guinea pig platelet aggregation in vivo where the duration of action of FCE 21292 was longer than that of PGI2, lowering of mean systemic arterial pressure in conscious normotensive and spontaneously hypertensive rats and inhibition of rabbit platelet aggregation in vitro. In the relaxation of bovine coronary artery in vitro the rank order of potency was FCE 21292 greater than PGI2 greater than FCE 21258.

The preparation of 125I-labelled tracer for digoxin radioimmunoassay (125I monoiodinated 3-succinyl digoxigenin-1-tyrosine) is described, and its performance in radioimmunoassay of plasma samples is compared with that obtained with tritiated digoxin. The accuracy levels were assessed through the evaluation of different potential sources of systematic errors, such as interference from digoxin-related molecules and plasma proteins and methodological artefacts possibly associated with the immunocomplex instability, and through a series of checks including the recovery and parallelism tests and the correspondence of results obtained with the two tracers. The slope and the repeatability with time of the calibration curves and the spread of replicate estimates were taken into consideration to assess the assay precision. An essential equivalence in terms of reliability of measurement was proved for the two methodological variants, so that practical aspects and economic factors, remain the main criteria to evaluate the relative merits: from this point of view, the advantages of using 125I-labelled tracer, as an alternative to tritiated digoxin, are discussed.

The effects of methodological variables on the quality of insulin radioimmunoassay were studied, including: (a) the individual characteristics of antiserum and tracer preparations; (b) the incubation modality (non-equilibrium, delayed addition of tracer); (c) the procedure of separation of free from bound antigen (adsorbents and immunoprecipitation); (d) the non-identity of sample and standard solutions as for the protein content. A number of experimental factors were expectedly found to influence the sensitivity of response. Conversely, important effects on assay accuracy were found to be associated only with the double-antibody method used and with non-identity of samples and standards. The results of investigations on the possible sources of the systematic errors involved and on their relevance in routine measurements are reported and discussed.

Summary The biological activity of four unnatural prostaglandins: ent-11, 15-epi PGE 2 , ent-11-epi PGE 2 . ent-11,15-epi PGF 2α and ent-11,15-epi PGF 2β has been evaluated. These compounds are definitely less active than the natural ones, with the exception of enantio-11,15 epi PGE 2 which, in the rat, in comparison to prostaglandin E 2 (PGE 2 ) is nearly half as potent in inhibiting stress — induced gastric ulcers, almost as potent in decreasing arterial blood pressure and 10 times more potent in contracting isolated uterus “in vitro”, while having very little activity on gastro-intestinal smooth muscle.

Two microanalytical methods for the determination of iodine in material of biological interest were studied: neutron-activation analysis and automated colorimetry (iodide catalysis of the As(III)-Ce(IV) system). The methods were applied to the analysis of samples of water, biological fluids, common salt and solid substances such as tissues, stools and foods. The particular procedures set up and optimized for the different substances with both methods are described and discussed, and the respective advantages in terms of sensitivity, accuracy, precision and speed are compared. The sensitivity and accuracy of both techniques were found to be quite adequate. Automated colorimetry is to be preferred for its precision and operative simplicity, while activation analysis retains full validity as a reference check method.

A series of synthetic analogues of prostacyclin (PGI2) have been compared for their ability to increase the formation of cyclic AMP and to inhibit the aggregation of human platelets, and for relaxation of isolated bovine coronary arteries and lowering of the blood pressure of concious rats. The most active inhibitors of aggregation were derivatives of PGI2 with a triple bond at C14:15. There was good aggreement between the inhibition of platelet aggregation and elevation of cyclic AMP in platelets, and both effects were enhanced by phosphodiesterase inhibitors. The most active compounds of the series were K13415 (14,15-didehydro 20-methyl PGI2), and a carbocyclic analog, FCE21258 (5e-14,15-didehydro carbo PGI2) which were both more active than PGI2 itself. In addition, the carbocyclic compounds were stable at neutral pH. Compounds K13817 (14,15-didehydro 16-methyl PGI2) and FCE21292 (5e-14,15 didehydro 20-methyl carbo PGI2) were similar in activity to PGI2 as platelet inhibitors, but had less vasodilator and depressor activity. The results show considerable differences in the structural specificities of the platelet and vascular activities of PGI2.

Summary A novel chemical synthesis of nat- and rac-Prostacyclin (PGI 2 ) and 5,6-dihydro-PGI 2 is described. Like PGI 2 , both stable analogs inhibit human platelet aggregation induced by ADP, Arachidonic Acid (AA), Collagen and Adrenaline. In all forms of aggregation, 5,6 α -dihydro-PGI 2 resulted 10 times more potent than 5,6 β -dihydro-PGI 2 . The potency ratio of 5,6 α -dihydro-PGI 2 to PGI 2 was variably estimated between 1:100, in the case of ADP-induced aggregation, and 1:10 in the case of AA-induced aggregation. The availability of stable mimics of PGI 2 should be of considerable value in future studies of this substance and may have therapeutic implications.

Esterification with inversion is a highly stereospecific reaction by which one-step conversion of PGF2alpha to PGF2beta is obtained with very satisfactory yield.

Monoiodinated angiotensin II at a specific activity in the order of 1 C/mg can be prepared with high yields by controlling the pH of iodination and can be purified on G-25 Sephadex. The fractions from the head to the centre of the single peak of radioactivity obtained by gel filtration of the iodination mixture contain pure monoiodinated angiotensin. The monoiodinated derivative shows an immunoreactivity very close to that of the native hormone; in contrast, the diiodinated derivative has a low immunoreactivity and its use as a tracer results in a loss of sensitivity in the radioimmunoassay of angiotensin II. It is suggested that the use of the monoiodinated derivative in pure form should be recommended whenever a small hormonal polypeptide labelled at high specific activity is to be prepared for radioimmunoassay purposes.

A compound representative of a new series of oestradiol ether derivatives (dioxanylethers and oxathianylethers) corresponding to 17β-(1′,4′-dioxan-2′-yloxy)-oestra-1,3,5(10)-trien-3-ol (DE) was studied in various biological tests for the evaluation of its oestrogenic and antifertility activities. Ethinyloestradiol (EE) was used as reference standard. The potency ratio between DE and EE in the uterotrophic response was 0.170 in the rat and 0.0195 in the mouse showing a clearcut decrease in oestrogenic activity which was also confirmed by the findings of vaginal cornification (ED50 for EE 0.32 and for DE 9.4) and dehydrogenase activity of the vaginal epithelium in the mouse (DE/EE 0.014). A complete antifertility effect was obtained in the rats with DE in a dose of 10 μg daily though this was still not definite with EE in a dose of 30 μg. In tests on the gonadotrophin inhibiting activity the DE/EE ratio was 0.500 in parabiotic couples, 0.695 in the test on the inhibition of the weight increase of the testes in immature rats and 2.1007 in the test on the prevention of compensatory ovarian hypertrophy. While the significant dissociation between the oestrogenic and antifertility action of DE appears of particular interest, its marked antifertility effect seems to be due to mechanism(s) other than gonadotrophin blockade.