A G1-specific spermatogonial chalone.

What is known about spermatogonial chalones in rats and mice and by implication whether they may have a future as male contraceptives is discussed. Chalones are putative factors that inhibit or control cell division. By definition they are naturally occurring produced in and active in specific tissue or cell lines and are not species specific. There are 2 chalones in spermatogonia acting in cell phases G1 and G2 based on research in rats and mice. The G1 chalone is heat labile precipitable with ethanol tissue specific not species specific and less than 5000 molecular weight. Rats less than 40 days old have demonstrable receptors for the G1 spermatogonial chalone. Using testicular extracts as a source of the chalone the authors presented evidence that intracellular cyclic AMP may mediate its effects on inhibition of mitosis. Their work supports the idea that chalones maintain cAMP levels thus inhibiting nucleoside kinase activity needed for DNA synthesis. Initial studies with antisera raised against testicular extract suggested that chalone activity could be neutralized but the active site was not affected. Experiments on mice involving longterm injections of testicular extracts have not resulted in any effect on spermatogonial proliferation. Thus there is not yet any indication that these factors will provide a lead for a new type of male contraception.