Dopamine has its place in horniness as well, and evidenced by many people who take dopamine agonists and experience libido boosts. Even Wellbutrin, the actions of which are complex but include some dopamine receptor activity, can boost libido and is often used in conjunction with SSRI antidepressants to counter their anorgasmic sides. I’ve also read that testosterone itself and other androgens have some effect on the dopamine system, though I forget if they are direct or indirect…so I wonder if the sex hormones directly effect our libido, or if the action is indirect, that is, testosterone causes systemic changes in brain chemistry that increase libido. Given its relationship with dopamine and dopamine’s libido-boosting abilities, the indirect action may be a strong possibility.
Truth is, NOTHING about body chemistry is as simple as some would have you believe, and the addition of any chemical, whether endogenous or otherwise, causes a series of reactions in the body which we are only starting to really understand…humans are organisms complex beyond present medical knowledge and theory, though we are making rapid strides towards a deeper understanding of its mechanisms.