ICV injection of the serotonin 5-HT1B agonist CP-93,129 increases the secretion of ACTH, prolactin, and renin and increases blood pressure by nonserotonergic mechanisms.

This study tested whether a new serotonin (5-HT1B) agonist, 3-(1,2,5,6-tetrahydro-4-pyridyl)-5-propoxy-pyrrolo[3,2-b]pyridine (CP-93,129), could be used to study the potential role of 5-HT1B receptors in the secretion of adrenocorticotropic hormone (ACTH), prolactin, and renin. CP-93,129 has a high affinity for 5-HT1B receptors but low affinity for other 5-HT receptor subtypes. In addition, CP-93,129 does not readily cross the blood-brain barrier. The secretion of ACTH, prolactin, and renin is known to be increased after activation of 5-HT receptors. ICV injections of CP-93,129 (100 micrograms/kg) increased the plasma concentrations of ACTH, prolactin, and renin. CP-93,129 also increased blood pressure and reduced heart rate. To determine whether these effects of CP-93,129 are centrally mediated, we compared them with IP injection of the same dose of CP-93,129. IP-injected CP-93,129 did not alter blood pressure or heart rate and did not elevate plasma prolactin and renin concentrations. To determine whether 5-HT1B receptors mediate the central effects of CP-93,129, rats were pretreated with the 5-HT antagonists l-propranolol or metergoline prior to ICV injections of doses of CP-93,129 (0-100 micrograms/kg). The 5-HT1A/1B/2A/2C antagonist metergoline (0.5 mg/kg, IP) failed to inhibit the CP-93,129-induced elevation of ACTH, prolactin, or renin concentrations. In contrast, the 5-HT1A/1B/beta antagonist l-propranolol (20 micrograms/kg, ICV) inhibited the renin but not the ACTH or prolactin responses to ICV CP-93,129.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeated exposure to cocaine produces long-lasting deficits in the serotonergic stimulation of prolactin and renin, but not adrenocorticotropin secretion.

To determine whether cocaine-induced deficits in serotonergic function are long-lasting, the neuroendocrine responses to the serotonin (5-hydroxytryptamine, 5-HT) releaser, p-chloroamphetamine were evaluated 1-8 weeks subsequent to 7 days of cocaine exposure (15 mg/kg b.i.d.). In cocaine-pretreated rats, the p-chloroamphetamine-induced elevations of prolactin and renin secretion were significantly reduced for 8 and 4 weeks, respectively. In contrast, the p-chloroamphetamine-induced elevation of adrenocorticotropic hormone (ACTH) secretion was at control values 1 week after cocaine exposure. The data suggest that some cocaine-induced deficits in serotonergic function are long-lasting.

Neuroendocrine responses to the serotonin2 agonist DOI are differentially modified by three 5-HT1A agonists.

Evidence suggests that activation of 5-HT1A receptors leads to inhibition of 5-HT2-mediated behavior. The purpose of this study was to investigate the interaction between 5-HT1A and 5-HT2 receptor-mediated hormone secretion. Rats were pretreated with the 5-HT1A agonists buspirone (0, 0.5, 2.0 mg/kg, i.p.), 8-OH-DPAT (0, 0.05, 0.2 mg/kg, s.c.) or ipsapirone (0, 1.0, 2.5 mg/kg, i.p.), 45 min before decapitation. The 5-HT2 agonist DOI was administered (0-10 mg/kg, i.p.) 15 min after injection of the 5-HT1A agonists. The three 5-HT1A agonists differentially altered the DOI-induced increase of concentrations of hormone in plasma. None of the three 5-HT1A agonists influenced the basal levels of renin, ACTH and prolactin but 8-OH-DPAT and buspirone increased the basal level of corticosterone in plasma. Also, 8-OH-DPAT increased the effects of DOI on the concentration of ACTH in plasma but ipsapirone and buspirone did not. None of the 5-HT1A agonists significantly affected DOI-induced increase of concentration of corticosterone in plasma. Buspirone and 8-OH-DPAT potentiated the effect of DOI on prolactin in plasma, but ipsapirone did not. Ipsapirone potentiated the effect of DOI on the concentration of renin in plasma but this effect was not observed in 8-OH-DPAT- and buspirone-pretreated rats. The results do not support the hypothesis for a functional interaction between 5-HT1A and 5-HT2 receptors, since the three 5-HT1A agonists did not have the same influence on the hormonal effects of DOI.

Repeated cocaine modifies the neuroendocrine responses to the 5-HT1C/5-HT2 receptor agonist DOI.

Endocrine responses to the serotonin (5-HT) 5-HT1C/5-HT2 agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) were utilised to evaluate cocaine-induced alterations in postsynaptic 5-HT receptor function. Rats received cocaine HCl (0, 5 or 15 mg/kg i.p.) twice daily for 7 days. Effects of DOI (0, 0.5, 2 or 10 mg/kg i.p.) on plasma adrenocorticotropic hormone (ACTH), corticosterone, prolactin, oxytocin and renin concentrations were assessed 42 h after the final cocaine injection. DOI dose dependently increased the plasma concentrations of each hormone. Cocaine potentiated the DOI-induced elevations of plasma ACTH, corticosterone and prolactin concentrations. In contrast, the oxytocin response was reduced, and the renin response was unaltered by cocaine exposure. The data suggest that 5-HT2 receptor-mediated responses for ACTH, corticosterone and prolactin secretion become supersensitive following repeated cocaine. In contrast, the 5-HT2 receptor-mediated response for oxytocin secretion is subsensitive. The cocaine-induced changes in postsynaptic 5-HT receptor function are likely a consequence of deficits in the function of 5-HT nerve terminals, that we have documented previously.

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.

Cocaine-induced suppression of renin secretion is mediated in the brain: investigation of cardiovascular and local anesthetic mechanisms.

Acute cocaine reduces renin secretion. To determine a peripheral versus central site of action, intracerebroventricular (ICV) versus intraperitoneal (IP) injections of cocaine were compared. Cocaine was more potent reducing plasma renin activity (PRA) and concentration (PRC) when injected ICV (0.050 mg/kg) than IP (5 mg/kg), suggesting a central site of action. Furthermore, addition of cocaine (10(-4) M) to kidney slices in vitro did not influence renin release, indicating that cocaine does not suppress renin secretion by acting directly in the kidney. We also investigated whether the hypertensive or local anesthetic properties of cocaine mediate its inhibition of renin secretion. Therefore, we compared the cardiovascular and endocrine effects of cocaine with those of the local anesthetic drug procaine. Both cocaine and procaine (500 micrograms/kg, ICV) produced rapid and short-term increases in blood pressure, but cocaine decreased PRC whereas procaine increased PRC. Intra-arterial (IA) and IP injections of cocaine also reduced PRC whereas procaine had no effect (IA) or elevated PRC (IP). Together, the data suggest that cocaine decreases renin secretion by acting in the brain. It is not likely that the cardiovascular or local anesthetic actions of cocaine are the main cause of its suppressive effect on renin secretion.

Prior chronic exposure to cocaine inhibits the serotonergic stimulation of ACTH and secretion of corticosterone.

The effect of long-term pretreatment with cocaine on serotonergic regulation of ACTH (adrenocorticotropic hormone; corticotropin) and secretion of corticosterone in rats was investigated. The following observations were made: (1) Pretreatment with cocaine had no significant effect on basal levels of ACTH and corticosterone in plasma. However, cocaine caused a reduction in the ability of the 5-HT (5-hydroxytryptamine, serotonin) releaser p-chloroamphetamine (PCA) to increase corticosterone in plasma, 42 hr after the last injection of cocaine. (2) Exposure to cocaine for 7 days was sufficient to produce a maximal inhibition of the PCA-induced increase in ACTH in plasma. (3) The inhibitory effect of cocaine on PCA-induced release of ACTH was more marked than on corticosterone. (4) Conversely, the dose-dependent stimulatory effect of two 5-HT1 agonists, RU 24969 (5-methoxy-3-(1,2,3,4-tetrahydro-4-pyridinyl)-1H-indole) and m-CPP (m-chlorophenylpiperazine), on ACTH and corticosterone was not reduced by 7 days of exposure to cocaine. Taken together, these findings indicate that pretreatment with cocaine reduced the function of serotonergic nerve-terminals but not postsynaptic receptors, that stimulate ACTH and secretion of corticosterone.

Neuroendocrine responses to cocaine do not exhibit sensitization following repeated cocaine exposure.

Cocaine-induced enhancement of motor activity and extracellular dopamine concentrations exhibits sensitization upon repeated exposure. In this study, the neuroendocrine responses to cocaine were examined following cocaine pretreatment regimens which have been shown to produce behavioral sensitization. Adult male rats were injected with cocaine (15 mg/kg, IP) once daily for 14 days, followed by a dose-response challenge with cocaine (1-15 mg/kg, IP) either 18 hours or 7 days after the final pretreatment injection. Blood was collected 15 minutes following injections for radioimmunoassay of ACTH, corticosterone, prolactin, and renin. Cocaine increased plasma ACTH and corticosterone, while it decreased prolactin and renin concentrations. Pretreatment with cocaine for 2 weeks did not alter any of these endocrine responses after either the 18 hour or 7 day interval between pretreatment and challenge injections. In contrast, sensitization to the locomotor stimulant effects of cocaine was observed on the final day of pretreatment injections, and 7 days later. These data suggest that these endocrine effects of cocaine do not exhibit sensitization following repeated cocaine exposure.

Cocaine-induced elevation of plasma adrenocorticotropin hormone and corticosterone is mediated by serotonergic neurons.

We investigated the hypothesis that cocaine-induced elevations of plasma adrenocorticotropin hormone (ACTH) and corticosterone are mediated by brain serotonin (5-HT) neurons. Adult male rats were pretreated with the 5-HT depleting agent p-chlorophenylalanine, the 5-HT neurotoxin 5,7-dihydroxytryptamine, the partial 5-HT1A agonist 8-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-8- azaspirol[4,5]-decane-7,9-dione (BMY 7378) or the 5-HT1C/2 antagonist ritanserin. The effects of cocaine (2-15 mg/kg, i.p.) on plasma ACTH and corticosterone were then examined. Cocaine dose-dependently increased ACTH and corticosterone concentration. This increase was prevented by 5-HT depletion with PCPA and by destruction of 5-HT neurons with i.c.v. injections of 5,7-dihydroxytryptamine. The cocaine-induced elevation of ACTH and corticosterone was not significantly modified by administration of the partial 5-HT1A agonist BMY 7378, suggesting that 5-HT1A receptors probably do not mediate ACTH and corticosterone secretion. However, pretreatment with the 5-HT2/5-HT1C antagonist ritanserin virtually eliminated the cocaine-induced elevation of corticosterone. To determine whether these effects of cocaine are centrally mediated, conscious rats received cocaine injections into the cerebral ventricle through chronically implanted cannulas. Plasma ACTH concentrations were dose-dependently increased, whereas low doses (50 micrograms/kg, i.c.v.) produced a maximal increase in corticosterone concentration. These data indicate that the cocaine-induced stimulation of ACTH and corticosterone secretion is mediated by 5-HT neurons in brain, and furthermore, that 5-HT2 or 5-HT1C receptors are responsible for this effect.

Effect of dietary protein on morphologic development of rat mammary gland.

Isocaloric diets, containing 8% casein [low protein (LP)], 19.5% casein [normal protein (NP)], or 31% casein [high protein (HP)] and 10% corn oil, were fed to adult virgin female Sprague-Dawley rats prior to conception and were continued through mating, gestation, and lactation. Female pups, 8 per litter, were fed on their mother's diet for the duration of the study. The pups' sexual maturation occurred at 33, 35, and 70 days of age for the HP, NP, and LP groups, respectively. At 7 weeks of age, duct development in the mammary gland was markedly delayed in the LP group. No significant differences in the extent of ductal development were noted between the HP and NP groups. Morphologic development into terminal end buds, alveolar buds, lobules, and terminal ducts was determined for each diet group at 7 weeks and at sexual maturity plus 3 weeks (SM+3) of age. At 7 weeks, the terminal end bud was the dominant structure in the LP group and was significantly greater in number than in the HP and NP groups. The latter groups were dominated by the alveolar bud structures. At SM+3, the number of terminal end buds decreased, and the alveolar buds increased in the LP group; however, the numbers were still significantly different than in the HP and NP groups. This study indicates that dietary protein affects mammary duct proliferation and morphologic development.