Prospective vasectomy candidates should be told of the extensive research showing testicular fibrosis in all vasectomized mammalian species studied to date, including humans. Fibrosis is essentially scar tissue and must have an effect on the function of the testes. The testes have two main functions: Production of sperm and production of sexual hormones (primarily testosterone). The human studies do show a decrease in spermatogenesis reflecting testicular damage. Sertoli cell support of spermatogenesis has been implicated in this pathology as has pressure induced changes from obstruction by closing off the vas deferens via vasectomy. This should not be surprising as men with obstructive azoospermia show similar testicular pathology associated with obstruction:
CONCLUSIONS: Sperm yields/g testis were significantly decreased in men post-vasectomy and in men with OA, relative to fertile men. Significant reductions were also observed in early (40%) and mature (29%) spermatid numbers and an increase of 31% was seen in the seminiferous tubule wall (basal membrane and collagen thickness) of vasectomized men compared with fertile men. Hum Reprod. 2005 Oct;20(10):2795-800. Epub 2005 Jun 15
The testes produce testosterone, and a relative decline in testosterone levels can cause decrease in erectile potency, decreased libido, fatigue, reduction in muscle mass and strength, change in fat deposition patterns (to that of women), poor concentration, irritability, and reduced bone mass.
The studies of testosterone levels after vasectomy have led to conflicting data. This is partly due to reliance on "normal ranges" that are very wide (300 to 1200 ng/dl), lack of pre-vasectomy levels for comparison purposes, as well as lack of testing for free (bioavailable) testosterone levels. In addition, the studies that show transient increases in testosterone levels reflect damage as opposed to health, and declines in levels surely follow. How could a transient increase in testosterone levels after vasectomy reflect normal function? It is more likely a reflection of damage due to inflammation.
I believe vasectomy causes testicular fibrosis and damages Sertoli cells affecting spermatogenesis. The damage to the testes from obstruction or via immunologic effects may cause earlier "andropause" via relative declines in testosterone causing symptoms of hypogonadism in some men. The total serum testosterone may still be in the "normal" range of 300 to 1200 ng/dl, but a significant decline within the range can still cause symptoms.
The studies cited below from the medical literature show biopsy proven interstitial fibrosis. The possibility that fibrosis (scarring) has no effect on testicular function is implausible. The hypothesis that similar changes seen in all mammalian studies to date are not in any way applicable to humans also seems unsustainable.
OBJECTIVE: To quantify germ cell loss and the extent of testicular fibrosis in vasectomized patients of varying obstructive intervals. CONCLUSION(S): Vasal obstruction results in significant reductions in germ cells in the later stages of spermatogenesis and increases in testicular fibrosis, both worsening with an increasing obstructive interval. Testicular damage after vasectomy might impact upon the prospects for reversal.
To determine whether there are any deleterious changes in the human testis after vasectomy, we obtained testicular biopsy specimens from 31 healthy men undergoing vasectomy reversal and from 21 healthy, fertile volunteers. Morphometric analyses of these specimens revealed a 100 per cent increase in the thickness of the seminiferous tubular walls (P less than 0.001), a 50 per cent increase in the mean cross-sectional tubular area (P less than 0.001), and a significant reduction in the mean number of Sertoli cells (P less than 0.01) and spermatids (P less than 0.01) per tubular cross section in the post-vasectomy group, as compared with the control group. Focal interstitial fibrosis was observed in 23 per cent of the specimens from the post-vasectomy group and in none from the control group. N Engl J Med. 1985 Nov 14;313(20):1252-6
MATERIALS AND METHODS: Forty testicular biopsy specimens from twenty consecutive men were obtained at vasovasostomy. A significant increase in interstitial fibrosis was observed along with the obstructive interval (p < 0.001). CONCLUSION: Interstitial fibrosis, but not the intraseminiferous status, reflects the irreversible damage of vasectomized testes.
Testicular biopsy specimens from 21 consecutive men were obtained at vasovasostomy. Percent of interstitial fibrosis was determined quantitatively by NIH-image after Masson Trichrome staining... increase in interstitial fibrosis were observed along with the obstructive interval (p <0.0001, p = 0.0005, respectively). Interstitial fibrosis contributes to the irreversible damage of vasectomized testes. Contraception. 2002 Mar;65(3):245-9
Vasectomy performed with the traditional technique changes testicular structure. At first, the injuries are slight and restricted, but gradually, and in a time-dependent manner, become more severe and extensive. Ultrastructure studies indicate that the spermatogonia and Sertoli's cells are the most resistant to vasectomy, and are even observed in some regenerating testes lacking a complete germinal epithelium. Morphometric studies revealed a decrease in epithelial depth, an increase in the thickness of the basement membrane and in surface of the interstitial space, all significant (P < 0.01) with respect to the control. However, the percentage of the interstitial tissue occupied by cells, did not show any significant difference. We propose that the increase of intraluminal pressure is the essential factor that provokes testicular atrophy.
Int Surg. 2000 Apr-Jun;85(2):167-74.