Effect of prostaglandin F2alpha on the luteal phase of the cycle in nonpregnant women.
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Monthly injectable contraceptives, containing a combination of a long-acting progestogen and an estrogen, have been used in Latin America and China for many years. While knowledge about the effects of other hormonal contraceptives on cancer risk is relevant, close analogies with monthly injectables cannot be made. The relation between use of these preparations and cancers of the breast and cervix has been examined in case-control studies, but no firm conclusions can be drawn because of limitations in sample size. Adequate studies of the influence of monthly injectable contraceptives on risk of neoplasia need to be carried out.
Long-acting contraception by monthly intramuscular injection is an attractive method for family planning which fills a gap in birth control technology. The main advantage of this approach over long-acting (2-6 months) progestin injectables is much better cycle control. To achieve this goal, an estrogen had to be included in the formulation with significant reduction in the progestin dose. Until 1976, there were only three monthly injectables available (Injectable No. 1, Cycloprovera and Deladroxate), but they were faced with logistic, toxicological or clinical problems. It took over 15 years to resolve many of these problems and add a new product (Mesigyna = 50 mg norethisterone enantate plus 5 mg estradiol valerate in an oily solution). Cycloprovera, at a lower dose, received the new name of Cyclofem and Deladroxate was manufactured under the trade names of Perlutal or Topasel. The latter requires in-depth re-evaluation of its toxicological hazards. There are many other formulations currently being developed with incomplete data so far on safety and efficacy.
The pharmacology and clinical assessment of existing first generation once-a-month combined injectable contraceptives, mainly Deladroxate and Chinese Injectable No. 1, are reviewed. Although these two types of monthly injectables have been used in some million women in China and Latin America, Deladroxate needs indepth re-evaluation of its long-term toxicity and possible accumulation. For injectable No. 1, its disadvantage of being administered on an erratic schedule will cause significant confusion in family planning practice. When used in a strict once-a-month schedule, it is not sufficiently effective for contraception. In order to attain predictable menstrual cycle control as well as high efficacy with a 30-day injection schedule, two improved once-a-month injectable formulations, Cyclofem and Mesigyna, were developed. Pharmacokinetic/pharmacodynamic study on estrogenic components suggested that estradiol valerate and cypionate were suitable estrogen esters to give elevated plasma estrogen levels for 7 to 11 days. After a single injection of Cyclofem and Mesigyna, both formulations showed equal contraceptive effect with inhibition of follicle maturation for some 30 days and ovulation, corpus luteum formation for some 60 days. Multicentre studies on the optimization of dosages of progestogens and estrogens in once-a-month injectables confirmed that the full doses of Cyclofem (DMPA 25 mg/estradiol cypionate 5 mg) and Mesigyna (NET-EN 50 mg/estradiol valerate 5 mg) are suitable for large scale clinical trials. Pharmacodynamics and progestogen/estrogen ratio study indicated the importance of not only the absolute amounts of the progestogen and estrogen but also of their ratio. Reduction of estrogen dose resulted in breakthrough ovulation with both Cyclofem and Mesigyna. Also, it is important to note that the second part of the injection cycle is dominated by the progestogen component of both monthly formulations. A longitudinal study indicated that there is no accumulation of norethisterone after 12 months of treatment with NET-EN 50 mg and estradiol valerate 5 mg.
Reports of the phase III clinical trials on four combined progestogen-estrogen once-a-month injectable contraceptives, Deladroxate, Cyclofem, Mesigyna and Chinese Injectable No. 1, are reviewed focussing on efficacy and reasons for discontinuation. Deladroxate, currently used in many Latin American countries has proved to be highly effective and well accepted. However, this combination was withdrawn by the original manufacturer because the progestogen component of this drug induced a high number of breast cancers in dogs and very curious pituitary hyperplasia in rats. Cyclofem and Mesigyna were found to be highly effective and highly acceptable drugs. Side-effects were minimal and were of minor importance. The Chinese Injectable No. 1 had unacceptably high failure rates with a monthly injection schedule. After doubling the dose in the first month of use, the efficacy was satisfactory. It was found that all monthly injectable contraceptives provided better cycle control than the every 3 months depot-medroxyprogesterone acetate, although abnormal bleeding was still the main drug-related complaint and reason for discontinuation. Missed appointment is another reason for discontinuation which might reflect the problem of frequent injection schedule, thus indicating the need for proper selection of the users and good counselling.
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A technique of incubation of testicular tissue in vitro with radiolabeled precursors was applied in the investigation of the steroid biosynthesis by testes of four young men after long-term, high-dose estrogen treatment. A positive correlation between plasma and testicular steroid levels, and in vitro capacity of the testes to metabolize progesterone was demonstrated. Estrogen administration produced a very significant inhibition of plasma and testicular levels of testosterone. The in vitro synthesis of testosterone from progesterone was very severely impaired; especially 17alpha-hydroxylation of progesterone. 20alpha-hydroxysteroid-dehydrogenase activity was found to be increased after estrogen treatment, both in vivo and in vitro. These findings suggest that testicular 17alpha-hydroxylase activity (and possibly also 17-20 lyase activity) is either under gonadotropin regulation, or is directly suppressed by estrogen. This could result by decreased enzyme synthesis, direct enzyme inhibition or affectation of the cofactors or cytochromes necessary for the enzymatic activity. 20alpha-reduction of C21-steroids would represent an alternative pathway for their catabolism, not regulated by gonadotropin or not affected by estrogen, that would be significant in situations with reduced 17alpha-hydroxylase activity.
The serum levels of progesterone (delta4P), 20alpha-dihydroxyprogesterone (20alpha-DHP), pregnenolone (delta5P) and estrogens at different time intervals during Silastic-PVP-PGF2alpha tube induced midterm abortion were measured by radioimmunoassay in the rat and rabbit. The concentrations of delta4P and delta5P were significantly reduced but that of 20alpha-DHP was increased significantly as early as 20 hours after PGF2alpha treatment. Estrogen levels showed slight reduction in the rat but remained unchanged in the rabbit. The ratio of delta4P/20alpha-DHP recorded were 2.15 and 16.86 (pretreatment) and dropped to 0.08 and 0.37 (60 hours after insertion of Silastic-PVP-PGF2alpha tube) in the rat and rabbit, respectively. These findings suggest that the suppression of circulating delta4P by PGF2alpha might be the result of a reduced precursor (delta5P) pool size as well as changes in the enzymic systems responsible for the formation and conversion of delta4P. It is still to be determined if changes in estrogen levels in the rat have any bearing on abortion induced by PGF2alpha.
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