INFLUENCE OF NOREPINEPHRINE ON THE MOTILITY OF THE HUMAN VAS DEFERENS: A NEW HYPOTHESIS OF SPERM TRANSPORT BY THE VAS DEFERENS*t

Transcription

1 FERTILITY AND STERILITY 1973 by The Williams & Wilkins Co. Vol. 24, No. I, January 1973 Printed in U.S.A. INFLUENCE OF NOREPINEPHRINE ON THE MOTILITY OF THE HUMAN VAS DEFERENS: A NEW HYPOTHESIS OF SPERM TRANSPORT BY THE VAS DEFERENS*t W. P. VENTURA, PH.D., M. FREUND, PH.D.,t J. DAVIS, M.D., AND C. PANNUTI, M.S. Laboratory of Reproductive Pharmacology, Departments of Pharmacology and Obstetrics and Gynecology, New York Medical College, Flower and Fifth Avenue Hospitals, New York, New York The effects of vasectomy, that is the blockage of the output of the testes and epididymides, on the morphology and physiology of the male reproductive tract must be profound. However, the effects of vasectomy on the male reproductive tract of man are not known. There is a lack of published research on the clinical effects of the operation on the reproductive tract in man and very little on experimental results in animals. Fundamental information is required on what happens to the testis, epididymis, vas deferens, prostate, and seminal vesicles in man after vasectomy. The use of vasectomy as a contraceptive method has increased over the last few years. Concurrently, the need for the development of reversibility to induce younger men to adopt this form of contraception has also increased. The standard for efficient reversibility would be some type of simple vasectomy operation which causes little tissue reaction or loss of vas function and which would allow for the return to normal function of the vas and the ejaculation of functional sperm. Unfortunately, the success rate of vasovasostomy (the surgical restoration of the continuity of the vas), as measured by Received April 21, * Presented at the 28th Annual Meeting of The American Fertility Society, February 28-March 1, 1972, New York, N.Y. t Supported in part by the Pathfinder Fund through a subcontract under Contract AID/csd t Dr. Matthew Freund was a Career Scientist of the Health Research Council of the City of New York (1-218) during the course of this study. conception rate, is low. While there are numerous reports on the reappearance of sperm in the ejaculates of men after vasovasostomy,1-3 the resulting conception rate is too low to consider the operation a practical reversible procedure. The low functional success rate of vasovasostomy is not understood because it occurs despite the fact that the surgeon can routinely produce a successful anatomical vasovasostomy. The lack of data on the physiologic mechanisms regulating sperm transport in the male reproductive tract makes it difficult to construct working hypotheses to explain the failure of vasovasostomy. There is a lack of information on the interrelationships among the physiologic mechanisms involved in regulating motility in the human male reproductive tract. Studies on the physiology and pharmacology of the human vas and epididymis have been primarily limited to the period before Macht,4 Boeminghaus, 5 Iwaki,6 and Valle, and Porta 7 studied the pharmacology of the human vas and reported that only one-half of their preparations displayed spontaneous motility in vitro. Martins et al. 7 were the only investigators to study the pharmacology of the human epididymis. They reported that only 6 of 11 epididymides showed spontaneous motility. They reported that 29 of 42 human vasa given doses of epinephrine (1: 5,000,000-1 : 500, 000) showed tonic-rhythmic contraction and that 11 of 15 epididymides showed tonic contraction to epinephrine. Norepi- 68

2 January 1973 NOREPINEPHRINE ON MOTILITY OF VAS DEFERENS 69 nephrine was not tested because the existence and role of norepinephrine as a neurohumor was not known at that time. Acetylcholine (1: 280,000-1: 20,000) produced a less constant response with tonicrhythmic responses in the vasa and tonic responses in the epididymides. Pitocin (0.5-3 LU'/50 or 80 ml. bath) produced no definite response. Their results indicated that both epinephrine and acetylcholine produced excitatory responses in their in vitro system. Unfortunately, in all of the papers reviewed, there were no quantitative data to build on for this research program. While there have been few in vitro studies on the physiology and pharmacology of the human vas deferens there have been many on the guinea pig vas. Most investigators use the isolated hypogastric nerve-vas deferens preparation established by Hukovic. 8 This preparation is used because the isolated guinea pig vas is reported to be quiescent without nerve stimulation and insensitive to exogenously applied drugs even when stripped of its mesenteric coating. The investigator using the Hukovic method excises a segment of vas with hypogastric nerve and places it in a 5-ml. bath containing Krebs-Ringer solution. The solution is aerated with a 95% oxygen-5% carbon dioxide mixture, the temperature is maintained at 37 C., and the tissue is preloaded with 200 or 300 mg. tension. Electrical stimulation of the hypogastric nerve produces a contraction of the vas. Dose-response curves to various drugs are obtained by adding doses every 4 min. and washing repeatedly between each application. The modifications of this procedure consist of different size baths; C. temperature; 12 a kymograph-musde-lever recording system; 13 and different oxygen-carbon dioxide gas mixtures. 14 No investigator has reported on the p02 levels of the bath solution. Only the most recent papers on these preparations have been listed to emphasize that even today there is no uniform in vitro procedure or technic used by all investigators. When an in vitro study of the effect of an agent on the spontaneous motility of an excised segment of vas is initiated, the investigator must first decide which of the many modifications of the Hukovic technic is most accurate and reliable and indeed if the vas has spontaneous motility without hypogastric nerve stimulation. The decision is difficult to make because of the wide variations in bath volume, bath solution, temperature, ph, and sensitivity of the recording system, as well as the complex interactions among these factors. The rationale for this investigation was that basic studies on the mechanisms controlling vas motility will yield data and information that may lead to the construction of hypotheses on the mechanisms controlling sperm transport in the male reproductive tract. The knowledge derived from basic studies may provide the scientific basis for the development of a standard vasectomy operation and for an improvement in the vasovasostomy success rate. The objective of this investigation was to study the spontaneous motility of the human vas, in vitro, and to determine the effects of a constant infusion of norepinephrine. Norepinephrine was chosen because it is probably the neurohumor regulating vas motility, in vivo. 15 MATERIALS AND METHODS Vasa obtained from cadavers (27 segments), and from vasectomies under general (8 segments), spinal (6 segments), or local anesthesia (54 segments), were used in this investigation. Vasa obtained from vasectomies in the doctor's office were removed under local anesthesia, while vasa obtained from vasectomies and prostatectomies in the hospital operating room were removed under spinal or general anesthesia. The vasa fromca-

3 70 VENTURA ET AL. Vol. 24 davers were divided into three 3-cm. segments, the "proximal," the "central," and the "distal" segments. The proximal segment of the vas was taken as the first 3 cm., the central segment of the vas as the sequential 3 cm., and the distal segment of the vas as the next sequential 3 cm., starting from the straight vas which is approximately 2 cm. from the epididymis and proceeding distally towards the urethra. Vasa from vasectomies in the doctor's office and hospital operating room were called the central segment. The spontaneous motility and response to norepinephrine of the human vas was studied in the in vitro system described by Freund, Wiederman, and Saphier.16 The in vitro system is nearly isotonic and provides a consistent and accurate determination of the true "rest length" of the muscle (no preloading). It offers two distinct advantages over the conventional methods of recording smooth muscle motility in that the preparation is not preloaded and the muscle can do work by shortening against a weak calibrated spring. The important aspects of the system are, as follows: (1) the ph of the bath fluid is held constant at 7.4 ± 0.2; (2) the p02 is kept at mm. Hg; (3) the temperature is maintained at 37 C.; (4) the perfusion flow is set at 5 ml./min. and is used to wash out tissue metabolites, drugs, and their breakdown products from the 50-ml. organ bath at a constant and rapid rate; and (5) drugs are infused so that either a constant concentration is maintained or a known change in rate is produced with preceding control and succeeding recovery periods to determine the effects of the drugs on the force, duration, and frequency of contraction. A Locke's-glucose solution containing 63 gm. (150 mm) of NaCI, 1.40 gm. (2 mm) of MgCI2, 2.94 gm. (5 mm) of KCI, 3.50 gm. (4 mm) of glucose, 1.68 gm. (2 mm) of CaCI 2, and 3.50 gm. (6 mm) of NaHC0 3, dissolved in 7 L. of double distilled water, was used as the perfusion solution. The effects of a constant concentration of norepinephrine were determined on the proximal, central, and distal segments of cadaver vas. Each run was divided into nine 30-min. periods. The first four periods served as preaddition controls, the next four periods were used to test the effects of norepinephrine (Ys JIg./ml.), and the last period was the postaddition control period. A constant concentration of Ys JIg./ml. of norepinephrine was maintained in each bath by injecting Ys JIg./ml. during the 1st min. and then by injecting a dose of Yso JIg./ml. at I-min. intervals for 2 hr. to replace the norepinephrine lost by perfusion (perfusion flow = 5 ml./min.). RESULTS Results were obtained on the in vitro spontaneous motility of cadaver vas (nine proximal, nine central, and nine distal segments) of eight central vas segments from vasectomies under general anesthesia, and of six central vas segments from vasectomies under spinal anesthesia. Fifty-four central vas segments from vasectomies under local anesthesia (2% lidocaine injected subcutaneously into the scrotum) were also tried in this system. None of the 54 segments showed spontaneous motility but 26 segments responded to Ys or Ys JIg.I ml. of norepinephrine. The time interval from mounting the tissue in the bath to the start of regular spontaneous motility was 5-65 min. for cadaver vasa, 5-35 min. for vasa removed under general anesthesia, and min. for vasa removed under spinal anesthesia. The spontaneous motility of the cadaver vas segments was studied for 4 hr. while the vas segments obtained under general and spinal anesthesia were studied for only 11/2 hr. because of the schedule of hospital operations. The proximal, central, and distal ca-

4 January 1973 NOREPINEPHRINE ON MOTILITY OF VAS DEFERENS 71 daver vas segments showed a constant force and duration of contraction for 3 hr. with a slight decline during the last hour of the 4-hr. run and the frequency of contraction declined slightly during the course of the 4 hr. (Table 1). The relatively low mean frequency for period 1 (0-30 min.) of the distal vas segment occurred because three of nine tissues showed a slow start up of regular spontaneous motility. The results listed in Table 1 demonstrate the existence of a rhythmicity gradient with an increase in frequency of contraction progressing from proximal to distal vas segments. The results (Table 1) demonstrate that there was a marked difference in motility patterns between the central vas segments obtained from vasectomies under general anesthesia and from cadavers on the one hand and from vasectomies under spinal anesthesia on the other hand. The central vas segments from vasectomies under general anesthesia and from cadavers showed a high force-low frequency series of contractions while the central vas segments from vasectomies under spinal anesthesia showed a low force-high frequency series of contractions. The results from the norepinephrine infusion study indicate that norepinephrine, at a constant concentration of Y5 }Lg./ml., produced a marked increase in force and TABLE 1. Spontaneous Motility of the Human Vas Deferens, in Vitro Control period (0-30 (30-60 (60-90 ( ( ( ( ( n~ min.) min,) min.) min.) min.) min.) min.) min.) Force of contraction (gm.) Proximal segment Centml segment Distal segment Mean Geneml anesthesia Central segment Spinal anesthesia Centml segment Duration of contraction (min.) Proximal segment Central segment Distal segment Mean Geneml Anesthesia Central segment Spinal anesthesia Central segment Frequency of contraction (c/hr.) Proximal segment Centml segment Distal segment Mean Geneml anesthesia Centml segment Spinal anesthesia Centml segment

5 72 VENTURA ET AL. Vol. 24 frequency of contraction with no change in the duration of contraction. During the postaddition control period ( min.), force, duration, and frequency of contraction decreased markedly, in all tissues (6 of 13 stopped contracting completely) indicating that the motility of the vas segments was being controlled by norepinephrine during the infusion. Similar findings were noted with vas segments from vasectomies under local anesthesia. Fiftyfour central vas segments from vasectomies under local anesthesia were tried in our in vitro system but none showed spontaneous motility. Twenty-six of these 54 preparations did respond to a dose of norepinephrine (Ys or Ys ~g./ml.) and showed a low force (0.2 gm.)-high frequency (100/ hr.) series of contractions only when the norepinephrine was present in the bath. These results are not tabulated because of the lack of spontaneous motility in all of the preparations and the lack of response to norepinephrine of one-half of the preparations. DISCUSSION Our initial review of literature was a search of the nervous innervation of the human male reproductive tract. Our search extended back to the beginning of the 19th century and included the German and French literature. While we were able to find reference to the innervation of the testes, epididymides, and vasa, we were unable to find reference to the pathways that nerves follow to these tissues. For example, do the nerves spiral around the vas or do they course along its dorsal and ventral sides? We were also unable to locate any studies on the question of whether the severed nerves distal to the point of vasectomy (that is, nerves on the urethral side of the vas) regenerate after they are tied by the surgeon in the sheath surrounding the vas. One very important point that emerged from our literature search relates to the difference in innervation between man and other mammals. In mammals, the superior testicular nerves arise from the renal plexus and intermesenteric nerves and course along the testicular arteries to innervate the testes. 17 Also, in man and other mammals, the inferior testicular nerves arise from the inferior hypogastric plexus and form a plexus around the vas; then they course along its length and innervate the epididymides. 17 The main difference between man and other mammals occurs with the middle testicular nerves. In man, these nerves arise from the hypogastric plexus or hypogastric nerves and course along the testicular arteries to innervate the epididymides, while in other mammals the middle testicular nerves are usually absent; but, if they are present, they course along the surface of the vasa. 17 The physiologic dependence of the activity of the human vas deferens on an intact nerve innervation is not known. It has been shown in rats and guinea pigs, following vasectomy, that the adrenergic terminals on the proximal side of the operation (toward the testes) disappeared several days after the operation, while the adrenergic terminals on the distal side (toward the urethra) remained unchanged. 1s Vasectomy in man could lead to a partial or complete hypogastric denervation depending on whether the surgeon has blunt dissected the nerves from the surface of vas or tied and cut them when the segment of vas was removed. How partial or complete denervation ofthe proximal end of the vas would affect vas motility is not known. Our data show that there is a rhythmicity gradient along the human vas deferens (Table 1), that is, the frequency of contraction increased along each segment proceeding from the epididymis towards the urethra. These results are in agreement with data obtained by Melin 19 who recorded the contractile activity of the vas deferens in rabbits in vivo and found that the frequency of contraction

6 January 1973 NOREPINEPHRINE ON MOTIUTY OF VAS DEFERENS 73 of the rabbit vas increased along its length with the proximal segment having a lower frequency than the distal segment. These data on the existence of a rhythmicity gradient in the male reproductive tract suggest that sperm are continually transported along the length of the vas and that, during ejaculation, the synchronous firing of nerves innervating the vas propels sperm along the length of the vas and results in emptying of the vas deferens. Our data showed that the human vas deferens has spontaneous motility in vitro without nerve stimulation. It is not inferred that nerve stimulation plays no role in regulating the motility of the vas, but rather suggests that the results obtained by others on the isolated guinea pig vas deferens,9, 10 in which no spontaneous motility was observed unless there was nerve stimula tion, must be carefully re-examined. The easiest explanation for this apparent difference between the human and guinea pig vasa is "species difference." We do not accept this explanation because it cannot be proven or disproven scientifically, but rather suggest that the in vitro systems used by other investigators12, 13 were not sensitive enough to record the very small contractions that are characteristic of the spontaneous motility of the guinea pig vas deferens. We have shown repeatedly in studies on the guinea pig and rat female reproductive tracts20, 22 that our in vitro system provides a means of obtaining consistent and repeatable data during the estrous cycle or following ovariectomy. In preliminary studies on the guinea pig vas deferens and seminal vesicles, we have found, using our in vitro system without nerve stimulation, that 10 vasa and 10 seminal vesicles showed a regular pattern of motility and response to norepinephrine. The results (Table 1) demonstrate that the human vas deferens obtained from cadavers, and from vasectomies under general and spinal anesthesia exhibits a regular and quantitative pattern of spontaneous motility in vitro. There was a marked difference in motility patterns between central vas segments obtained from vasectomies under general anesthesia and from cadavers on the one hand and from vasectomies under spinal anesthesia on the other hand. Central vas segments from vasectomies under general anesthesia and from cadavers showed a high force-low frequency series of contractions while central vas segments from vasectomies under spinal anesthesia showed a low forcehigh frequency series of contractions (Table 1). Vasa obtained from vasectomies under local anesthesia showed no spontaneous motility, but one-half of these preparations contracted when norepinephrine was used. The lack of spontaneous motility of the vasa obtained under local anesthesia may be explained either by depression of nerve or of muscle function. De Jong 23 reported that local anesthetics depress both nerve and muscle activity when applied directly to tissues in vivo. The mechanism of local anesthetic depression of nerve function is dependent on many factors including drug concentration, diffusion, dispersion, and uptake into nerve as well as the complex interactions of these factors. The most important anatomical barrier to nerve penetration by local anesthetic molecules is the perilemma of the perineurium. 24 Developmentally, the perilemma is identical to and continuous with the pia-arachnoid membrane covering the brain and spinal cord. 24 The peril emma binds the local anesthetic and accounts for the relatively short period of time required for induction of block but the long period of time for recovery. 25 The fact that cadaver vasa displayed regular spontaneous motility and consistent response to norepinephrine while vasa obtained from vasectomies under local anesthesia did not, indicates that data obtained on these latter preparations

7 74 VENTURA ET AL. Vol. 24 are not representative of vas motility or response to norepinephrine because the investigator does not know if the local anesthetic depressed either nerve or muscle function or both. It is suggested that vasa obtained from vasectomies under local anesthesia should not be used in testing the effects of pharmacologic agents until the mechanism of the anesthetic depression of activity is clarified. Quite unexpectedly, vasa obtained from vasectomies under spinal anesthesia displayed spontaneous motility patterns which differed from those obtained with vasa from vasectomies under general anesthesia. It may be proposed that this difference in motility pattern might be due to a depression of a spinal center which controls vas function since it could not be due to a direct depression of muscle activity as would be the case with local anesthesia. It is known that the spinal roots lack a perineurium (the main diffusion barrier to nerve penetration) and are nearly devoid of fibrous support. Roots floating in the spinal fluid are blocked nearly as rapidly as a single axon or a desheathed nerve and at very low anesthetic concentrations. 23 It is suggested that spinal anesthetics may produce a depression of a spinal center which controls the tone of the sympathetic fibers innervating the vas and, therefore, reduce the amount of norepinephrine produced and released and the amount of motility induced. Two-hour norepinephrine infusion studies (at a constant concentration of \Is tlg./m1.) yielded a marked increase in force and frequency of contraction as compared to controls (Table 2). The finding that all tissues showed a marked reduction in force, duration, and frequency of contraction (6 of 13 actually stopped contracting) during the postaddition control period ( min.) indicates that the motility of the vas segments was being controlled by norepinephrine during the infusion. Proximal, central, and distal segments of vas showed similar changes in motility pattern during the infusion indicating that a release of norepinephrine from nerves innervating the vas during ejaculation would maintain the rhythmicity gradient and could propel sperm along the length of the vas. Differences in norepinephrine content of the human male reproductive tract could account for the rhythmicity gradient along the vas deferens. Baumgarten et a1. 26 have reported that the human vas deferens contains 1.43 tlg. of norepinephrine/gm. tissue while epididymis contains 1.04 tlg./gm. and testis contains 0.07 tlg./gm. Similar results have been reported in other mammalian species. IS. 27 We propose that the intrinsic rhythmicity of the human vas is dependent upon the local concentration or norepinephrine while the powerful and coordinated series of contractions that propel the sperm from the epididymis to the urethra during ejaculation are initiated and controlled by the release of substantial amounts of norepinephrine from the sympathetic nerve endings. The use of vasovasostomy-the surgical restoration of the continuity of the vas deferens-to restore the fertility of vasectomized men has not been successful as measured by postoperative conception rate. While numerous procedures for vasovasostomy have been reported 1-3, 28 the resulting conception rate has been very low despite the reappearance of sperm in the ejaculates of most of the patients. A typical recent report is that of Lee 28 who found sperm in the ejaculates of 62 of 71 men after vasova.sostomy, but only 10 of these patients were able to cause pregnancies (14% success rate). Recently, an improved microsurgical technic has been developed in dogs 29 and better and more consistent results have been reported than in earlier experimental work with dogs. 30, 31 However, an improvement in conception rate has yet to be demonstrated. Microsurgical technics, with and without the use

8 January 1973 NOREPINEPHRINE ON MOTILITY OF YAS DEFERENS 75 TABLE 2. Effect of Norepinephrine (II, p.g./ml./min.) on Spontaneously Active Vas, in Vitro Norepinephrine constant infusion (Ysl'g./ml.) Control period Period (0-30 (30-60 (60-90 ( ( ( ( ( ( n ~ min.) min.) min.) min.) min.) min.) min.) min.) min.) Force of contraction (gm.) Proximal segment Central segment Distal segment Mean* Duration of contraction (min.) Proximal segment Central segment Distal segment Mean* Frequency of contraction (c/hr.) Proximal segment Central segment Distal segment Mean* * Weighted mean of splints, permit the surgeon to produce a perfect anatomical anastomosis of the two parts of the vas. Nevertheless, viable sperm output takes place in only some of the patients, sperm output per ejaculate is evidently less than before vasectomy, and conception rate is very low (5-15% in most series). Why? A working hypothesis may be proposed to explain the failure to produce a functional vasovasostomy even though an anatomical vasovasostomy is routinely produced by the surgeon. This hypothesis is based on experimental observations made in this laboratory and on an understanding of the effects of vasectomy on the nerve supply to the musculature of the vas deferens. As the first experimental observation, Freund and Davis reported that "approximately 60-70% of the sperm in a normal ejaculate from an intact, i.e., unoperated, man comes from the part of the vasa proximal to the point of vasectomy and from the epididymides, since the first specimen after vasectomy contained about 30-40% of the sperm found in the preoperative specimen." It follows from this observation that a powerful series of coordinated contractions of the vas deferens is required to transport large numbers of sperm from the epididymis and the proximal vas along the length of the vas to the urethra during seminal emission and ejaculation. Moreover, in this study it has been found that the human vas deferens has spontaneous motility in vitro and that it responds to the administration of norepinephrine with a series of powerful contractions. This observation fits in well with the knowledge that the muscle layers of the vas are innervated by sympathetic nerve fibers that are norepinephrine releasers. One may then propose that the vas deferens has spontaneous motility in vivo, as well as in vitro, and that this motility is modulated by the regular release of small quantities of norepinephrine from the sympathetic fibers. One may also pro-

9 76 VENTURA ET AL. Vol. 24 pose that the coordinated series of contractions of the vas associated with seminal emission and ejaculation is mediated by the release of larger quantities of norepinephrine, since it is known that ejaculation is controlled by the sympathetic nervous system. If one adds to these experimental data the knowledge that the nerve supply to that part of the vas deferens proximal to the point of vasectomy and to the epididymis in man (and cat and rat) includes the sympathetic fibers which run in the inferior spermatic nerve, 34 one can begin to understand what happens as a result of vasectomy. Vasectomy results in a division of the inferior spermatic nerve which runs parallel to and innervates the vas. The sympathetic fibers are strongly regenerative and, after division, would most probably grow proximally from the distal vas to reinnervate the proximal vas and epididymis but the surgeon (1) has removed a segment of the vas; (2) has (most probably) tied a suture or placed a clip to close the sheath around the stump of the distal vas; and (3) has created an inflammatory response and scar tissue in response to the trauma of the operation. All or any of these iatrogenic factors may serve to prevent regeneration and a restoration of the proximal sympathetic nerve supply. An intact sympathetic nerve supply may be vital to the transport of sperm from the epididymis at the time of ejaculation. The question, will this sympathetic nerve supply regenerate upon vasovasostomy, 5, 10, or even more years after vasectomy, remains unanswered. Without an intact sympathetic nerve supply to the proximal vas and to the epididymis, it is difficult to see how complete recovery in sperm output after vasovasostomy, that is functional vasovasostomy, can be achieved. SUMMARY The results of this investigation demonstrate the existence of spontaneous motility of the human vas deferens in an organ bath with perfusion. There is a rhythmicity gradient in the human vas deferens with an increase in frequency of contraction in each successive 3-cm. segment, progressing distally from the epididymis toward the urethra. The source and technic used to obtain vasa are important when studying the motility patterns and response to drugs. vas segments and vas segments obtained from vasectomies under general anesthesia exhibited similar motility patterns of high force-low frequency series of contractions. These motility patterns differed, however, from the motility patterns of vas segments obtained from vasectomies under spinal anesthesia which were characterized by low force-high frequency series of contractions. None of the 54 vas segments obtained from vasectomies under local anesthesia exhibited spontaneous motility, but 26 responded to norepinephrine. Norepinephrine infusion at a constant concentration of Ys,ug./ml. markedly increased the force and frequency of contraction of the spontaneously active vas segments. We propose that the intrinsic rhythmicity of the human vas deferens is dependent upon the local concentration of norepinephrine, while the powerful and coordinated series of contractions that propel the sperm from the epididymis to the urethra during ejaculation are initiated and controlled by the release of substantial amounts of norepinephrine from the sympathetic nerve endings. REFERENCES 1. FREIBERG, H. B., AND LEPSKY, H. O. Restoration of the continuity of the vas deferens eight years after bilateral vasectomy. J UroI41:934, DORSEY, J. W. Anastomosis of the vas deferens to correct postvasectomy sterility. JUral 70:515, ROLAND, S. L Splinted and non-splinted vasovasostomy. A review of the literature and a report of nine new cases. Fertil Steril 12:191, MACHT, D. L A contribution to the physiology of the ureter and vas deferens JUral 1 :96, 1917.

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