REPEATED INJECTIONS OF COCAINE INHIBIT THE SEROTONERGIC REGULATION OF PROLACTIN AND RENIN SECRETION IN RATS

Alterations in serotonergic function following repeated cocaine injections were examined using neuroendocrine responses to a serotonin (5-HT) releaser and 5-HT agonists. Forty-two hours following administration of cocaine (1-15 mg/kg i.p.) twice daily for 7 or 30 days, male Sprague-Dawley rats were injected with the 5-HT releaser p-chloroamphetamine (PCA; 8 mg/kg i.p.) and blood samples were collected 1 h later for radioimmunoassays of plasma prolactin, plasma renin activity (PRA) and plasma renin concentration (PRC). PCA significantly increased secretion of prolactin and renin. These responses were attenuated in rats pretreated with cocaine for 30 days. In rats receiving cocaine for 7 days, the attenuation of PCA-induced secretion of prolactin and renin was less consistently observed. To determine whether these alterations were due to pre- or postsynaptic effects, rats were injected with cocaine (15 mg/kg i.p.) twice daily for 7 days, and the neuroendocrine responses to the direct 5-HT agonists RU 24969 and m-CPP were examined, 42 h after the last cocaine injection. Pretreatment with cocaine potentiated RU 24969-induced stimulation of plasma prolactin concentration. However, cocaine did not alter the ability of m-CPP to increase plasma prolactin concentrations. The stimulation of renin secretion in response to both 5-HT agonists was not altered by cocaine pretreatment. The data suggest that repeated cocaine impairs the function of serotonergic nerve terminals that regulate these endocrine responses. Furthermore, the 5-HT receptors that mediate prolactin secretion may exhibit supersensitivity.