Vas deferens, a site of male contraception: an overview

The vas deferens is a site which can be exploited for male contraception without undue side effects. The only ef-fective technique available for male contraception is vasectomy, being practiced world wide, despite that it is a perma-nent surgical procedure and its successful reversal is not assured. Although no-scalpel vasectomy minimizes surgicalprocedures, the fate of its reversal is akin to that of vasectomy. Several occlusive and non-occlusive vasal procedureswhich claim to be reversible without surgical intervention, possess more disadvantages than advantages. Vas occlusionwith plug, ' Shug' or medical grade silicone rubber, although claimed to produce reversible azoospermia without affect-ing spermatogenesis, requires skilled microsurgery for their implantation and later removal. RISUG^R, a non-scleroticpolymer styrene maleic anhydride (SMA), could be more advantageous than vasectomy and other vas occlusive proce-dures in that it could be a totally non-invasive procedure by 'no-scalpel injection' and 'non-invasive reversal'. It isclaimed to offer long-term contraception without adverse side effects and also to be possible as a male spacing methodby repeated vas occlusion and non-invasive reversal. The drug is currently under multicentre Phase Ⅲ clinical trial.

Histological study of vas deferens following intravasallaser irradiation

<abstract>Aim: To study the histologic changes of the vas deferens following Nd: YAG laser irradiation. Methods: Intravasal laser irradiation was given to (i) 52 segments of rabbit (laser dosage: 2 seconds at 40 W-50 W) and 16 segments of human (3 seconds at 45 W-55 W) vas deferens in vitro, (ii) 25 rabbit vasa (2 seconds-2.5 seconds at 40 W-45 W) in vivo and (iii) 2 human vasa (3 seconds at 55W) in vivo. Segments of vasa were removed from the in vivo irradiated vasa deferentia 15 days-180 days (rabbit) or 15 days (man) after the exposure. All vas segments were embedded in methacrylate resin. Serial sections (thickness 25μm-30μm) were obtained and observed under a light microscope. Results: (i) Laser-induced damage reached the muscularis layer in 27 % and 94 % of the rabbit and human vas segments in vitro, respectively, (ii) Fourteen of the 25 in vivo rabbit vasa were completely occluded by fibrous tissue and the longer the time interval after treatment, the more likely was the vas occluded. Those unoccluded vasa had either a normal histology or a mucosal damage, (iii) One in vivo human vas was almost completely occluded by the fibrous tissue but the other had a relatively large lumen packed with sperm granulomatous tissue and partial destruction of the smooth muscle layer. Conclusion: Laser irradiation can induce long-term vas occlusion; for rapid occlusion, laser doses just completely destroying the mucosal layer will be advisable.

Prospective Comparative Study of Human Vas Occlusion with Chinese and Netherlandish Medical Materials

To find a new uas occlusive material and verily the efficacy of Zhao's traditional uas occlusion with medical polyurethane(MP),we used the aPProved medical silicone rubber (MSR) made in the Netherlands,for a prospective study in comparison with the contraceptive effect of these two materials.We adopted the standardized MPU uas occlusion method to 13subjects and the unified MSR uas occlusion method to 11 subjects. All subjects received semen analysis and related physical examination before the operation,and semen analysis and complication examination in the 3th, 6th and 12th months alter operation. Neither of groups had complication and notable uncomfortable symptoms following operation. The sperm disaPPearance rate in MPU group was 92.31%(12/13) while in MSR group, only one patient's sperm disaPPeared 3 moths after operation.During the other postoperative follow up periods all operated patients had spermatozoa allhough the sperm density decreased obviously and indicated partial vas occlusion.These results indicate that the MPU vas occlusion has a good sterilization elject,but the MSR has not.

Occlusion of Rabbit Vas Deferens with Nd^（2＋）： YAG Laser Irradiation： A Preliminary Experiment Report

Occlusion of vas deferens in uitro and in vivo with Nd2+ YAG laser of 100mW-1000mW was investigated. An optical fiber core in diameter of 200pm was inserted into the lumen of the uas uia a canula in & rabbits and 16 uasa deferens were irradiated in uiuo.The threshold lesion(denned as a half thickness of the uas wall being penetrated)at dijferent power and exposure duration was investigated in uitro. Temperature on the aduentitia was also determined.The uasa delerens were totally occluded in those irradiated with power of 800mW for 24 sec or with power of 1000mW for 16 sec 3 and 4 weeks after irradiation.The authors considered that it would be possible to insert percutaneously a fiber and coagulate vas deferens with laser for sterilization in the near future. However,more investigations are needed before it could be employed in the clinic.

Constraints in the development of contraceptives for men

Considerable efforts have been made to develop a male contraceptive and the studies have provided very useful infor-mation in this field. At least five different strategies to develop a male contraceptive have been pursued, namely: inhi-bition of sperm production, interference with sperm function, interruption of sperm transport, prevention of sperm de-position, and prevention of sperm-egg interaction. Of all these approaches, inhibition of sperm production by using an-drogens either alone or in combination with progestins have given the most encouraging results. A nmnber of clinicaltrials substantiate that it is indeed possible to have a reversible, effective and safe hormonal method of contraception. Apostmeiotic and epididymal approach to interfere with sperm function or the secretory and metabolic processes of theepididymis is another attractive option of male contraceptive development. A number of chemical compounds have beenidentified which interfere with sperm function in the epididymis without affecting sperm production, however, the com-pounds evaluated so far were found to be toxic. Interruption of sperm transport through the vas either by vasectomy orpercutaneous intmvasal injection of liquids which form cure-in-place plugs is also an attractive option. However, re-versibility of the methods is of concern in their wide scale use. The major constraint in developing a long-acting male contraceptive seems to be the need for greater investment forproduct development. The clinical trials for evaluating the efficacy and safety of the new products and formulationsstretch over several years and require enormous financial commitment. Nevertheless, the long-term gain of having along-acting reversible contraceptive for men is far greater than the financial commitments over few years. Male attitudetowards using methods of family planning is much more favourable than originally believed. The pharmaceutical indus-try as well as the health care providers therefore have a greater responsibility. For early development of a contraceptivefor men, it is essential to increase investment and simplify the drug regulatory procedures. The advent of newer tech-nologies coupled with the convergent efforts of scientists will certainly make it possible to have an effective, safe andreversible male contraceptive in the near future.

The contribution of Asian scientists to global research in andrology

Aim: To present a personal account of the involvement of the World Health Organization (WHO) in the collaborativedevelopment in Asia of those areas of andrology concerned with male contraception and reproductive health.Methods: The andrology training through workshops and institution support undertaken by the WHO HumanReproduction Programme (HRP) and how they contributed to the strengthening of andrology research in Asia aresummarised. Results: The author's experience and the Asian scientific contributions to the global research in thefollowing areas are reviewed: the safety of vasectomy and the development of new methods of vas occlusion; gossypoland its failure to become a safe, reversible male antifertility drag; Tripterygium and whether its pure extracts will passthrough the appropriate toxicology and phased clinical studies to become acceptable contraceptive drugs; hormonalmethods of contraception for men. Conclusion: The WHO policy of research capacity building through training andinstitution strengthening, together with the collaboration of Asian andrologists, has created strong National institutionsnow able to direct their own programmes of research in clinical and scientific andrology.