Paul indicts both men and women in his brief. Although this is commonly understood as a reference to lesbianism, it may not be at all. Given the general Roman silence, in fact, indifference, about Lesbian relations, this makes more sense than the proposal that the reference is to lesbian relations. It also signals Paul's concerns, that his concern is sexual abuse in both its heterosexual and homosexual forms. Here, the reference is clear.
Heterosexual males abandon their natural sexuality to cross over and commit same-gender sexual acts.
This activity is found in the context of the Roman orgy, perhaps in temple prostitution as well, but more importantly, it was the standard feature of pederasty, in which heterosexual married men enlisted the services of prepubescent boys, abandoning their natural sexual orientation to indulge their lust. To illustrate his theological point, namely that idolatry leads to cultural decay, Paul has selected what was to his mind, most typical to Roman culture. One of its signatures, to condemn the whole, in light of the gospel. In order to be rhetorically convincing, his illustration has to be obvious and conceded by all. He is saying in effect, that gentiles exchange their knowledge of God to worship idols, with the result that they revel in sexual abuse and exploitation, a sure and certain sign of God's wrath being worked out in gentile cultural patterns.