Researchers have stumbled onto a new drug that blocks the action of sperm in clams, a finding that they said could lead to a male birth control pill. The drug may be superior to other substances now under investigation as possible contraceptives for men, said Sheldon Segal of the Rockefeller Foundation.
In laboratory experiments this summer at the Marine Biological Laboratory in Woods Hole, Mass., Segal and colleagues found that the drug blocked the fertilization of clam eggs by immobilizing sperm.
Clams are useful for the study of fertilization because they produce large quantities of sperm and eggs, and their sperm resemble human sperm.
The new drug, designated Ph CL68A, was discovered accidentally when doctors noticed that a related drug commonly used to treat colitis, an inflammation of the large intestine, produced rare occurrences of infertility in men.
Segal tested the colitis drug, sulfasalazine, and several chemically similar drugs, including Ph CL68A. Only Ph CL68A was effective at preventing fertilization.
Among the other potential candidates as a male contraceptive are gossypol, a cottonseed extract, and a drug called “leutinizing hormone releasing hormone,” or LHRH. But a chief gossypol drawback is that it can lower potassium levels in the blood. The problem with LHRH seems to be that it attacks both sperm and male hormones, and therefore interferes with the sex drive.
A potential problem with Ph CL68A, Segal said, is that it is counteracted by proteins in blood, and thus might have to be given in large doses.