Neuroendocrine measures of dopaminergic function in chronic cocaine users

Plasma prolactin (PRL) and growth hormone (GH) levels are determined, in part, by the effects of dopamine (DA) at pituitary and hypothalamic DA receptors, respectively. To determine if chronic cocaine abuse alters dopaminergic activity, basal PRL and GH concentrations were measured in 16 male patients meeting DSM-III-R criteria for cocaine dependence (8 cocaine users and 8 cocaine + alcohol users) and 8 normal controls. In addition, the functional responsivity of DA receptors was assessed in the same group of patients by measuring the change in plasma PRL and GH concentration following the administration of the direct-acting DA agonist, apomorphine (0.01 mg/kg, s.c.) or saline. No difference in basal plasma PRL and GH levels or plasma PRL and GH responses to apomorphine administration was found between the entire group of cocaine patients and normal controls. However, three of the cocaine patients had basal plasma PRL levels that were more than 2.5 SD greater than that of the normal controls, suggesting that some interference of dopaminergic inhibition of PRL secretion might be present in at least some cocaine users. Although baseline plasma PRL levels were elevated in a subgroup of cocaine users, these data do not support the hypothesis that chronic cocaine abuse produces consistent abnormalities in dopaminergic function at the pituitary or hypothalamus.