The Pfizer scientists shaped the new compound specifically for the beta-3 receptor, reducing its ability to bind to the other two beta receptors.
Unlike weight loss drugs that work by decreasing appetite, a drug that stimulates the beta-3 receptor would get around a problem that afflicts many dieters: The body's metabolism adapts to the lower intake of calories, making it more difficult to lose weight.
But if Lessey and his research team prove correct about the role of a protein known informally as beta-3 -- the beta-3 subunit of the vitronectin receptor integrin -- they may have taken one step closer to understanding the puzzling nature of endometriosis and its association with infertility.
They find that beta-3 analysis has a "positive predictive value as a nonsurgical diagnostic test for minimal and mild endometriosis." Currently, the only accurate diagnosis of the disease requires a laparoscopy, a procedure involving a "belly-button cut" and insertion of a lighted instrument into the navel.
In normal, healthy women, Lessey says, beta-3 appears on the endometrial epithelium "like clockwork" on the 19th to the 20th day of the menstrual cycle, corresponding to the body's preparation for implantation and pregnancy.
Of these, 22 displayed an absence of beta-3 on day 19 and day 20.
However, the team notes, "Not all patients subsequently found to have endometriosis were missing the beta-3 subunit."
Scientists have no clear understanding of how the egg implants in the uterine wall or beta-3's function in that process, though Lessey believes the protein is indeed involved in implantation.
Even so, Lessey and his colleagues hope that using beta-3 deficiency as a marker will soon lead to the development of "a cheap and easy test" to diagnose endometriosis.