The dose/response for prolactin increases by nandrolone is unknown, the cited study by Maeda and colleagues used low dose nandrolone in male haemodialysis patients and showed no significant effect.
If it were as simple as dopamine high, prolactin low; dopamine low, prolactin high, then heroin would potently stimulate libido & decrease prolactin. Instead, it acts as a "chemical orgasm" and potently suppresses libido (by acting on the inhibitory system), and increases prolactin.
Though dopamine serves a predominant role in regulating prolactin secretion, the effect of nandrolone on prolactin is not as simple as nandrolone high, dopamine low, therefore prolactin high. Rather, because nandrolone increases dopamine metabolism (i.e., net breakdown) as reflected by serum homovanillic acid, whether this reflects changes to dopamine from intra- and/or extra- ceberbral sources is unknown. We think that it's likely related to decreased dopamine receptor number.