The concentration of testosterone is many times greater in the testes than in serum. Unlike in other androgen-dependent organs, such as the prostate and seminal glands, a multiple of the serum concentration in the testes is also necessary for normal functioning (spermatogenesis). Grateful use is made of this phenomenon in research into a male contraceptive. If testosterone is administered to a man the secretion of, for example, luteinizing hormone (lh) by the hypophysis will be greatly inhibited. Testosterone secretion by the Leydig cells is brought virtually to a halt. A dose of 200 mg of testosterone per week, injected into the lumbar muscle, results in a doubling of testosterone levels. Partly through the inhibition in the Leydig cells and the accompanying fall of the testosterone level in the testes, sperm cell production virtually ceases.
As a young man the Groningen-based researcher Pek van Andel devised a method of measuring sperm production in rats: he severed the seminal ducts as far downstream as possible and implanted them directly into the bladder. In this way it was possible to monitor exactly how many sperm cells a rat produced daily, a process that Pek described in his first publication. He was later to win the alternative Nobel Prize for his idea of using an mri scanner in which couples could have intercourse as a research tool.
In the spring of 2006 The Lancet, one of the world’s most authoritative medical journals, surveyed the state of research. It had been shown that the male version of hormonal contraception was safe and reversible. The study concerned had involved over 1,500 men. The researchers found that the average time required for sperm to recover to a level of 20 million spermatozoa per millilitre (the level at which one speaks of a ‘normal’ sperm count), was between three and four months. Older men, men of Asian origin, men with a high sperm level at the start of the study and men who had used hormonal contraception for only a short time, recovered quickest. The figures: 67 per cent recovered within six months, 90 per cent within twelve months, 96 per cent within sixteen months and 100 per cent were back to their original level after two years. According to the authors of the article in this leading publication their study had proved that the previously demonstrated efficacy of hormonal contraception was accompanied by a high degree of sperm recovery. New research is underway in which an androgen like testosterone is combined with a progestagen.