Effects of cyclosporine at the hypothalamic-pituitary axis in pituitary-grafted young female rats

Neural substrates for behaviorally conditioned immunosuppression in the rat

We have previously demonstrated behaviorally conditioned immunosuppression using cyclosporin A as an unconditioned stimulus and saccharin as a conditioned stimulus. In the current study, we examined the central processing of this phenomenon generating excitotoxic lesions before and after acquisition to discriminate between learning and memory processes. Three different brain areas were analyzed: insular cortex (IC), amygdala (Am), and ventromedial nucleus of the hypothalamus (VMH). The results demonstrate that IC lesions performed before and after acquisition disrupted the behavioral component of the conditioned response (taste aversion). In contrast, Am and VMH lesions did not affect conditioned taste aversion. The behaviorally conditioned suppression of splenocyte proliferation and cytokine production (interleukin-2 and interferon-gamma) was differentially affected by the excitotoxic lesions, showing that the IC is essential to acquire and evoke this conditioned response of the immune system. In contrast, the Am seems to mediate the input of visceral information necessary at the acquisition time, whereas the VMH appears to participate within the output pathway to the immune system necessary to evoke the behavioral conditioned immune response. The present data reveal relevant neural mechanisms underlying the learning and memory processes of behaviorally conditioned immunosuppression.

Toxic effects of methoxychlor on the episodic prolactin secretory pattern: possible mediated effects of nitric oxide production

BACKGROUND

This work addresses the issue of whether methoxychlor (MTX) exposure may modify the ultradian secretion of prolactin through changes in the synthesis of nitric oxide (NO) induced by Nomega-nitro-L-arginine methyl ester (L-NAME) in the hypothalamic-pituitary axis. Associated changes in dopamine (DA) content in the anterior (AH), mediobasal (MBH) and posterior hypothalamus (PH) and median eminence (ME) were evaluated.

METHODS

Two groups of animals (MTX and MTX+L-NAME treated) received subcutaneous (sc) injections of MTX at a dose of 25 mg/kg/day for one month. The other two groups of animals (control and L-NAME treated) received sc vehicle injections (0.5 mL/day of sesame oil), during the same period of time to be used as controls. Forty hours before the day of the experiment, animals were anaesthetized with intrapritoneal injections of 2.5% tribromoethanol in saline and atrial cannulas were implanted through the external jugular vein. Plasma was continuously extracted in Hamilton syringes coupled to a peristaltic bomb in tubes containing phosphate-gelatine buffer (to increase viscosity). The plasma was obtained by decantation and kept every 7 minutes for the measurement of plasma prolactin levels through a specific radioimmnunoassay and DA concentration by high-pressure liquid chromatography (HPLC).

RESULTS

Prolactin release in animals from all experimental groups analyzed was episodic. Mean plasma prolactin levels during the bleeding period, and the absolute pulse amplitude were increased after MTX or Nomega-nitro-L-arginine methyl ester (L-NAME) administration. However MTX and L-NAME did not modify any other parameter studied with the exception of relative pulse amplitude in MTX treated rats. L-NAME administration to rats treated with the pesticide reduced mean plasma prolactin levels and the absolute amplitude of prolactin peaks. Peak duration, frequency and relative amplitude of prolactin peaks were not changed in the group of rats treated with MTX plus L-NAME as compared to either control or MTX treated rats. Whereas MTX decreased DA content in the ME and increased it in the AH, its content did not change in the MBH or PH, as compared to the values found in controls. Also, L-NAME administration decreased DA content in the ME as compared to controls. However, L- NAME administration to MTX exposed rats, markedly increased DA content in the ME as compared to either MTX treated or control rats. L-NAME administration increased DA content in the AH as compared to the values found in non-treated rats. However L-NAME administration to MTX exposed rats did not modify DA content as compared to either MTX treated or control rats. L-NAME administration did not modify DA content at the MBH nor in saline treated nor in MTX treated rats. However, the values of DA in the MBH in MTX plus L-NAME treated animals were statistically decreased as compared to L-NAME treated rats. In the PH, L-NAME administration increased DA content as compared to the values found in non-treated animals. L-NAME administration to MTX exposed rats also increased DA content as compared to either MTX treated or control rats.

CONCLUSION

The results suggest the existence of an interaction between MTX and L-NAME in the modulation of the ultradian prolactin secretion at the pituitary levels. The possibility of an indirect effect mediated by changes in DA content at the ME requires further examination.

Effect of nitric oxide on prolactin secretion and hypothalamic biogenic amine contents

Involvement of nitric oxide (NO) in the episodic secretion of prolactin was studied in conscious freely moving adult rats. Prolactin secretion was pulsatile in all animals of either group during the bleeding period (from 10:30 h to 13:30 h). Administration of N(omega)-nitro-L-arginine methyl ester (L-NAME), a NO synthase inhibitor, increased mean plasma levels of prolactin, and the absolute amplitude of prolactin peaks during the whole bleeding period as compared to values found in the control group. L-NAME increased norepinephrine (170%), dopamine (58.27%) and serotonin contents (30%) in the anterior hypothalamus. In the median eminence, dopamine and serotonin contents decreased (19.79% and 33.9% respectively) after L-NAME as compared to the values found in controls. In addition, norepinephrine content increased in mediobasal hypothalamus (79.6%) of rats treated with L-NAME. The results indicate that changes in NO production may modify the episodic secretion of prolactin. These effects were associated with changes in hypothalamic and median eminence biogenic amines.

Effect of cadmium on 24-h variations in hypothalamic dopamine and serotonin metabolism in adult male rats

This study was designed to analyze the possible cadmium effects on time-of-day variations of anterior, mediobasal, and posterior hypothalamic contents of dopamine (DA), serotonin (5-HT), and norepinephrine (NE) content in adult male rats. Also DA and 5-HT metabolism, as expressed by the ratio 3,4-dihydroxyphenyl acetic acid (DOPAC) to DA and 5-hydroxyindoleacetic acid (5-HIAA) to 5-HT, respectively, were studied. Adult male rats were given cadmium at a dose of 25 ppm of cadmium chloride in drinking water for 1 month. Age-matched rats having access to cadmium-free water were used as controls. Weight gain for the whole period was not changed by cadmium exposure. The metal accumulated in the hypothalamus of rats. In the three hypothalamic regions, significant 24-h variations of NE and 5-HT concentration were found in controls, while DA content changed rhythmically in mediobasal hypothalamus only. Mean content of NE, 5-HT, and DA of anterior, mediobasal, and posterior hypothalamus decreased after cadmium exposure. After cadmium the 24-h pattern of NE changed only in mediobasal hypothalamus, whereas the metal changed significantly the pattern of 5-HT in all regions. DOPAC to DA and 5-HIAA to 5-HT ratios decreased and were differentially changed in all hypothalamic regions analyzed in cadmium-treated rats. There was a statistically significant relationship between time of administration of metal and time that the change took place in biogenic amines in the hypothalamus. These results indicate that cadmium may depress hypothalamic biogenic amine release.

Oral cadmium exposure throughout puberty does not inhibit secretion of prolactin, GH and ACTH through dopamine metabolism changes in male rat

This work analyzed possible dopamine-mediated cadmium effects on plasma prolactin, GH and ACTH levels and if these changes were related to metal accumulation. Male rats were treated from day 30 to 60 of life with 50 mg/L of CdCl2 in the drinking water. Cadmium exposure decreased the dopamine (DA) metabolism (DOPAC/DA ratio) in all brain areas studied, and plasma levels of prolactin, GH and ACTH were diminished. The cadmium concentration did not increase nor in hypothalamus nor in the pituitary after the metal exposure. These results suggest that cadmium inhibits the secretion of these pituitary hormones and this inhibitory effect is not mediated by dopamine or the degree of metal accumulation.

Alternate cadmium exposure differentially affects amino acid metabolism within the hypothalamus, median eminence, striatum and prefrontal cortex of male rats

This work was designed to analyze the possible changes in glutamate, aspartate and glutamine content induced by cadmium exposure in the hypothalamus, striatum and prefrontal cortex of rats, using an alternate schedule of metal administration. Pubertal-adult differences were also evaluated. In adult control rats, glutamate and aspartate contents in the anterior hypothalamus decreased as compared to pubertal controls. After cadmium administration from day 30 to 60 of life, the content of anterior hypothalamic glutamate and aspartate diminished. In adult control animals, the glutamine content increased in mediobasal hypothalamus as compared to pubertal controls. After cadmium exposure from day 30 to 60 of life, the mediobasal glutamine content increased, and after cadmium treatment from day 60 to 90 of life, the mediobasal aspartate content decreased. In adult control rats the content of glutamine, glutamate and aspartate of the posterior hypothalamus decreased significantly. After cadmium administration in pubertal animals, posterior hypothalamic contents of glutamine, glutamate and aspartate diminished. Cadmium treatment of adult animals caused a decrease in glutamine content, as compared to controls. In adult control rats, only glutamate and aspartate content increased in the prefrontal cortex as compared to the values found in pubertal controls. When cadmium was administered to adult animals, only the aspartate content decreased. In the striatum, cadmium decreased the glutamine and aspartate contents when administered from day 60 to 90 of life. These data suggest that cadmium differentially affects amino acid metabolism in the hypothalamus, striatum and prefrontal cortex. Age-dependent effects of cadmium on these brain areas appeared to have occurred.

Cadmium effects on hypothalamic-pituitary-testicular axis in male rats

This study analyzes cadmium effects at the hypothalamic-pituitary-testicular axis. Male rats were given cadmium during puberty or adulthood. Cadmium exposure through puberty increased norepinephrine content in all hypothalamic areas studied, but not in the median eminence. Metal exposure increased serotonin turnover in median eminence and the anterior hypothalamus, while decreased it in mediobasal hypothalamus. Also, decreased plasma levels of testosterone were found. Cadmium exposure during adulthood increased norepinephrine content in posterior hypothalamus and decreased the neuro-transmitter content in anterior and mediobasal hypothalamus. Decreased circulating levels of luteinizing hormone (LH) and testosterone and increased plasma follicle stimulating hormone (FSH) levels were also observed. Cadmium accumulated in all analyzed tissues. Various parameters showed age-dependent changes. These data suggest that cadmium globally effects hypothalamic-pituitary-testicular axis function by acting at the three levels analyzed and that an interaction between cadmium exposure and age emerge.

Changes in substance P content at the hypothalamic-pituitary axis during the Wallerian degeneration of peripheral sympathetic neurons after superior cervical ganglionectomy in male rats: effect of hyperprolactinemia

The effects of Wallerian degeneration of the peripheral sympathetic neurons projecting to the hypothalamus on the mechanism of interaction between prolactin and substance P (SP) were examined. The effects of superior cervical ganglionectomy (SCGx) on SP content in various hypothalamic regions and in the hypophysis were evaluated in control and hyperprolactinemic rats. Male rats that received pituitary transplants at the age of 5 days and age-matched sham-operated controls were used. Pituitary grafting significantly increased circulating values of prolactin, as did SCGx. In hyperprolactinemic rats, SCGx partially decreased plasma prolactin levels. Neonatal hyperprolactinemia decreased SP content in the anterior (AH) and posterior (PH) hypothalamus and in the median eminence (ME), but increased it in the mediobasal hypothalamus (MBH). Acute SCGx significantly increased SP in the MBH, PH, and ME. SCGx in hyperprolactinemic animals further increased SP content in MBH. In the ME and Ah, SCGx in pituitary grafted rats decreased SP content as compared with the controls. In the pituitary gland (PG), SCGx only decreased SP content in hyperprolactinemic, but not in control rats. An interaction between peripheral nor-adrenergic neurons and prolactin to regulate SP within the hypothalamus was positive in the MBH, AH, ME, and PG, but not in the PH. These data indicate the existence of interactive mechanisms between prolactin and the peripheral sympathetic neurons to regulate SP content at the hypothalamic-pituitary axis. Interrelationships between prolactin and SP were also observed.

Pubertal and postpubertal cadmium exposure differentially affects the hypothalamic-pituitary-testicular axis function in the rat

The effects of administration of cadmium on levels of hormones along the hypothalamic-pituitary-testicular axis were studied in rats. Male rats were treated subcutaneously from days 30 to 60 (pubertal rats) or from days 60 to 90 of life (postpubertal rats), with cadmium chloride (CdCl2) at a dose of 0.5 or 1 mg/kg, every 4 days in an alternate schedule, starting from the lower dose. Age-matched control rats received 0.3 m of saline subcutaneously every 4 days. The levels of norepinephrine (NE) increased on cadmium exposure in pubertal rats in all hypothalamic areas studied, but decreased in the median eminence. In contrast, in postpubertal rats the levels of NE only did not decrease in the posterior hypothalamus. Serotonin (5-HT) concentration in pubertal and postpubertal rats decreased in all hypothalamic regions, while serotonin turnover (measured by the ratio 5-hydroxyindolacetic acid/serotonin [5-HIAA/5-HT]) increased in the anterior hypothalamus. The serotonin metabolism was also increased in the median eminence in the pubertal and in the posterior hypothalamus in the postpubertal rats. Plasma levels of luteinizing hormone (LH) were not modified by cadmium in both age groups, but follicle stimulating hormone (FSH) levels decreased in postpubertal rats, but was not altered in pubertal rats. Plasma levels of testosterone increased in pubertal rats but decreased in postpubertal rats. Cadmium accumulation increased in the hypothalamus and testes in all the cadmium-treated animals, whereas in the pituitary accumulation of cadmium was found only in postpubertal rats. These data suggest that cadmium exerts age-dependent effects on the hypothalamic-pituitary-testicular axis function, and a disruption of the regulatory mechanisms of the hypothalamic-pituitary-gonadal axis emerges.

Effect of chronic hyperprolactinemia on daily changes of glutamate and aspartate concentrations in the median eminence and different hypothalamic areas of male rats

The 24h changes of glutamate (GLU) and aspartate (ASP) were studied in the median eminence (ME) and hypothalamic areas. It was analyzed whether prolactin may change their daily patterns. The hypothalamic concentration of these amino acids was measured by high-performance liquid chromatography (HPLC) with fluorometric detection. Plasma prolactin levels increased over the 24h light-dark cycle after pituitary grafting compared to controls, and its circadian rhythm was disrupted. In controls, aspartate and glutamate in the hypothalamic areas studied followed a specific daily variation or showed no rhythmicity. In the median eminence, hyperprolactinemia seem to phase advance the aspartate or glutamate peaks from 16:00 to 12:00. In the mediobasal hypothalamus, hyperprolactinemia altered daily changes of aspartate and significantly decreased its concentration. Also, it seems to delay the nocturnal glutamate peak compared to controls. In the posterior hypothalamus, hyperprolactinemia did not change aspartate and glutamate concentrations and their daily changes, although it increased the glutamine concentration. These data show the existence of 24h changes of amino acid concentration in three of the hypothalamic regions studied. Increased plasma prolactin levels differentially affected these patterns depending on the hypothalamic area analyzed.

Prolactin and cyclosporine modulate adenosine transporters and adenosine A1 receptors in the rat brain

The existence of adenosine A1 receptors and adenosine transporters in the central nervous system has been well demonstrated, although their possible modulation by hormones and/or exogenous drugs is poorly understood. To further analyze these modulatory mechanisms, the effects of prolactin and cyclosporine (CyA) on adenosine A1 receptors and transporters were analyzed in the central nervous system. For this purpose the number and affinity of adenosine A1 receptors were measured using the specific antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) and the transporters with the high affinity ligand nitrobenzylthioinosine (NBTI). This procedure was carried out in hyperprolactinemic and control male rats treated with CyA or its vehicle for 8 days. As expected, pituitary grafting increased plasma prolactin levels (p<0.01). CyA treatment reduced but did not normalize (p<0.05) this parameter in hyperprolactinemic rats and did not modify circulating prolactin in control animals. Both hyperprolactinemia and CyA treatment reduced the number of adenosine transporters by 70% and by 40% the number of A1 receptors. The Kd for transporters was also reduced in all experimental groups. Hyperprolactinemia increased the affinity of A1 receptors (p<0.01) and CyA treatment did not further modify this parameter. These data demonstrated that prolactin and CyA influence adenosine transporters and A1 receptors at the central nervous system and suggest the existence of an interaction between prolactin and CyA may be operating to modulate these processes.

Cadmium affects the episodic luteinizing hormone secretion in male rats: possible age-dependent effects

Cadmium affects luteinizing hormone (LH) secretion through unknown mechanisms. The present study was undertaken to assess whether chronic exposure to low concentrations of cadmium may affect the episodic secretion of LH and if these effects are age-dependent. Male rats were given cadmium at a dose of 50 ppm in the drinking water, from day 30 to 60 or from day 60 to 90 of life. Age-matched rats with access to cadmium-free water were used as controls. At the end of the treatment, blood samples were collected every 7 min for 3 h, from 10:30 to 13.30 in conscious, freely moving rats. In control animals, mean serum LH levels and pulse duration increased with age (P < or = 0.001), and pulse frequency and the relative amplitude of LH pulses decreased (P < or = 0.001). Cadmium administration, from day 30 to 60 of life, decreased the pulse frequency and mean half-life of the hormone (P < or = 0.05, P < or = 0.01, respectively). However, no changes in any other parameters studied were observed as compared to the control group. When cadmium was administered from day 60 to 90, mean serum LH levels and the duration of LH pulses decreased (P < or = 0.05), whereas the pulse frequency increased (P < or = 0.05). The absolute and relative amplitude of the LH peaks and the mean half-life of the hormone were not changed after cadmium administration from day 60 to 90. These results indicate that low doses of cadmium change the pulsatile secretion of LH in male rats and that the effect of cadmium on episodic LH release was age-dependent.

Daily variations of amino acid concentration in mediobasal hypothalamus, in rats injected with Freund's adjuvant. Effect of cyclosporine

Although the existence of central responses to inflammatory injuries was already reported, the existence of hypothalamic amino acid responses has been less explored. The present study was designed to characterize the 24-h changes in mediobasal hypothalamic excitatory and inhibitory amino acid neurotransmitter contents and to analyze the effect of Freund's complete adjuvant administration on these patterns. Also the effects of the immunosuppressant drug Cyclosporine was studied. The content of aspartate, glutamate, glutamine, GABA and taurine was measured by HPLC with fluorimetric detection. The results show the existence of specific daily rhythms of aspartate, glutamate, glutamine, GABA and taurine contents in the mediobasal hypothalamus of control rats. Maxima for these amino acids was found at midnight, although another peak of lesser magnitude, occurred during the light phase of the photoperiod, except for TAU in which both peaks were of similar magnitude. Freund's complete adjuvant administration did not modify the 24-h pattern of any amino acid studied. It reduced the midnight peak of glutamate, glutamine and GABA and increased that of taurine. Moreover, it increased and extended the midday peak of glutamate. Besides, Freund's adjuvant did not modify aspartate content at any time point studied. Cyclosporine pretreatment did not prevent the inhibitory effects of Freund's complete adjuvant on glutamate, glutamine and GABA midnight peaks. However, the drug blocked the increase in the content of taurine at midnight and increased its midday peak. Moreover, cyclosporine administration abolished the variations of ASP during the scotophase, as compared to control animals and shift delayed both peaks of glutamate. The results indicate the existence of a significant effect of immune-mediated inflammatory response of the mediobasal hypothalamic amino acids studied, at an early phase after Freund's adjuvant administration, and that these changes were partially sensitive to the immunosuppression induced by cyclosporine.

Intrahypothalamic growth hormone feedback: from dwarfism to acromegaly in the rat

Two different dwarf rat models with primary (dw/dw, DW) or secondary (transgenic growth retarded, WF/Tgr) GH deficiency and contrasting hypothalamic GH-releasing hormone (GHRH) and somatostatin (SRIH) expression were implanted sc with GC cells. These form encapsulated rat GH-secreting tumors that maintain high plasma rat GH levels for several weeks. In both strains, GC cell tumors stimulated growth and raised GHBP levels, without affecting pituitary GH content. In DW rats, GC cell implants increased SRIH expression in the periventricular nucleus (PeV), but not in the arcuate nucleus (ARC), whereas their high GHRH expression in ARC was decreased by GC cells. In contrast, GC cell implants in WF/Tgr rats had little effect on the already high SRIH expression in PeV or low GHRH expression in ARC, although they reduced SRIH expression in ARC. GC cell implants also reduced GH receptor expression in both ARC and PeV in the WF/Tgr dwarves. Thus, chronic GH overexposure stimulates rapid growth in both dwarf strains, but has differential hypothalamic effects in these models. This experimental approach now makes it possible to study the effects of pathophysiological concentrations of GH ranging from dwarfism to acromegaly in the same animal model.

Twenty-four-hour rhythms of serum ACTH, prolactin, growth hormone, and thyroid-stimulating hormone, and of median-eminence norepinephrine, dopamine, and serotonin, in rats injected with Freund's adjuvant

The effect of Freund's adjuvant injection on 24-h variation of circulating ACTH, prolactin, growth hormone (GH), and thyroid-stimulating hormone (TSH) levels, and of norepinephrine (NE) content, and dopamine (DA) and serotonin (5HT) turnover in median eminence, was examined in adult rats kept under light between 0800 and 2000 h daily. Groups of 6-10 animals received Freund's complete adjuvant or its vehicle at 1100 h 3 days before sacrifice and were killed by decapitation at six different time intervals throughout a 24-h cycle. In rats injected with adjuvant's vehicle, serum ACTH and prolactin exhibited peak values around the light-dark transition (p < 0.0001 and < 0.04, respectively), while the maximum in TSH was found in the late afternoon (p < 0.0001, one-way ANOVA). GH levels did not vary on a 24-h basis. In Freund's adjuvant-injected rats, 24-h variations of TSH levels became blunted, while 24-h variations of prolactin and ACTH persisted. Freund's adjuvant augmented serum ACTH and prolactin levels, and decreased GH and TSH levels (p < 0.0007, factorial ANOVA). Median-eminence NE content, and turnover of DA, assessed by measuring dihydroxyphenylacetic acid, DOPAC/DA ratio, and of 5HT, assessed by measuring 5-hydroxyindoleacetic acid, HIAA/5HT ratio, varied on a 24-h basis in rats receiving adjuvant's vehicle (p < 0.02). Median-eminence NE content attained its maximum at 1600-2000 h, while maxima in DOPA/DA and HIAA/5HT ratios occurred at 0400 h. Injection with Freund's adjuvant reduced the amplitude of the daily variation of NE content, shifted the maximum of DOPAC/DA ratio toward the light-dark transition, and blunted the daily variation in HIAA/5HT ratio in median eminence. The administration at 1200 of the immunosuppressant drug cyclosporine (5 mg/kg, 5 days) restored the augmented ACTH and prolactin levels (p < 0.0001, factorial ANOVA) and depressed GH and TSH levels (p < 0.02) found in Freund's adjuvant-injected rats. Cyclosporine was also effective in restoring 24-h rhythmicity of serum ACTH and TSH, but not of prolactin, levels. Cyclosporine did not modify the effect of Freund's adjuvant on time-of-day changes of median-eminence NE content, but it was effective in counteracting the changes of DA and 5HT turnover found after immunization. The results are compatible with a significant effect of immune-mediated inflammatory response at an early phase after Freund's adjuvant injection on ACTH, GH, prolactin, and TSH release, which is partially sensitive to immunosuppression by cyclosporine.

Hyperprolactinaemia and cyclosporine treatment on secretion of adenohypophyseal hormones

The possibility of interactions between the effects of cyclosporine (CyA) and prolactin to regulate various physiological functions has been suggested. To further analyze these interactions, the effect of chronic CyA administration on the secretion of adenohypophyseal hormones in hyperprolactinemic male rats, was studied. Male rats were grafted one pituitary gland under the kidney capsule or were sham-operated at 30 days of age. Both pituitary-grafted and sham-operated rats were given s.c. injections of vehicle or CyA (5 mg/kg/day) for 30 days beginning on the day of surgery. Pituitary-grafting increased the plasma levels of prolactin and decreased the plasma levels of luteinizing hormone (LH), whereas growth hormone (GH), thyroid stimulating hormone (TSH) and follicle stimulating hormone (FSH) did not change. CyA treatment to sham-operated rats did not modify plasma prolactin levels and decreased plasma levels of GH and LH. Administration of the immunosuppressor to pituitary-grafted rats decreased plasma prolactin levels and augmented plasma levels of LH and FSH. Plasma TSH levels did not change after CyA treatment either in sham-operated or in pituitary-grafted rats. These data suggest that CyA may modify the effects induced by prolactin on pituitary hormone secretion, although direct effects of the drug on the hypothalamic-pituitary axis cannot be excluded, according to the data obtained in sham-operated rats.

Effects of cyclosporin treatment on prolactin pulsatility in chronic hyperprolactinemic male rats

Neuroendocrine effects of cyclosporin (CsA) have been demonstrated, but the mechanisms involved are poorly understood. This work was designed to analyse (i) if chronic CsA administration could influence the episodic secretion of prolactin in adult male rats; and (ii) the effects of the chronic administration of the drug, in adult animals with elevated plasma prolactin levels. Male rats were implanted with one anterior pituitary gland under the kidney capsule or were sham-operated, at 30 days of age. Both pituitary-grafted and sham-operated rats were injected subcutaneously with vehicle or CsA (5 micrograms/kg/day) for 9 days beginning at the 60th day of age. In pituitary-grafted male rats, mean prolactin levels, absolute prolactin pulse amplitude and mean half-life of the hormone increased, while the pulse frequency and relative amplitude of the peaks decreased, as compared with sham-operated rats. CsA administration to sham-operated rats decreased the relative pulse amplitude of prolactin but increased the mean half-life of the hormone, the pulse duration and the mean hormone levels, as compared with rats of the same group treated with vehicle. However, CsA treatment to pituitary-grafted rats decreased mean prolactin levels and the absolute amplitude of its peaks and increased the relative amplitude of its pulses, whereas all the other parameters showed no change. When considering circulating values of prolactin in plasma from the trunk blood, CsA administration was followed by changes similar to those described when mean values of the serial samples were considered. These data suggest the existence of an interrelationship between elevated circulating prolactin levels and CsA, which probably takes place at the hypothalamic level, to regulate the pulsatile pattern of prolactin secretion in male rats, although a direct effect of the drug on the ectopic gland in pituitary-grafted male rats cannot be excluded.

Changes in mediobasal hypothalamic dopamine and indoleamine metabolism after superior cervical ganglionectomy of rats

Eight days after bilateral superior cervical ganglionectomy (Gx) of rats, norepinephrine content of medial basal hypothalamus (MBH) decreased significantly by 44-50%. To obtain information on other possible neurochemical sequela of Gx in MBH, we examined the metabolism of dopamine and serotonin in MBH of Gx rats by employing a high pressure liquid chromatography procedure. Eight days after Gx, MBH dopamine levels augmented significantly. Assessment of dopamine metabolism by measuring dihydroxyphenylacetic acid (DOPAC)/dopamine and homovanillic acid (HVA)/dopamine indexes indicated a significant decrease of MBH DOPAC/dopamine ratio after Gx. MBH serotonin levels increased, and 5-hydroxyindoleacetic acid (5-HIAA)/serotonin index decreased significantly in Gx rats. To examine the interaction Gx-induced changes on MBH dopamine and serotonin with the modified hormonal milieu produced by an ectopic pituitary transplant, adult male rats bearing an ectopic pituitary within the pectoral muscles from day 5 of life were submitted to Gx on day 60 of life and were studied 8 days later. MBH dopamine content increased significantly after pituitary grafting, an effect counteracted by a subsequent Gx, while Gx alone augmented MBH dopamine levels. DOPAC and HVA contents augmented in pituitary-grafted animals, an effect counteracted by Gx. Gx increased MBH serotonin content in control but not in pituitary-grafted rats. After pituitary grafting a decrease in MBH 5-HIAA levels was found, an effect reversed by Gx. Pituitary transplants brought about a significant increase of MBH DOPAC/dopamine index, and a significant decrease in 5-HIAA/serotonin index, both effects being counteracted by Gx. Gx of control rats resulted in a significant decrease of MBH 5-HIAA/serotonin index. Analyzed as a main effect in a factorial analysis of variance, Gx decreased MBH DOPAC/dopamine and HVA/dopamine indexes significantly. Plasma prolactin increased in pituitary-grafted rats, an effect further increased by a subsequent Gx. In pituitary-grafted, Gx rats plasma GH levels augmented significantly. The data suggest that superior cervical ganglion removal affects differentially dopamine and indoleamine metabolism in MBH of control and pituitary-grafted rats.

Effect of stress and cyclosporine on ornithine decarboxylase activity in rat submaxillary lymph nodes

This study was performed: (1) to assess whether the stress produced in rats by daily turpentine oil injections for 5 days, or by restraining the animals for 30 min during 5 days, affected basal and Freund's adjuvant-stimulated submaxillary lymph node ornithine decarboxylase activity, an indicator of cell proliferation; (2) to analyze whether the activity of the immunosuppressive drug cyclosporine on submaxillary lymph node ornithine decarboxylase activation after Freund's adjuvant injection was modified in stressed rats; (3) to examine the mediation of stress effects on submaxillary lymph node ornithine decarboxylase activation by regional sympathetic or parasympathetic nerves. Animals subjected to a unilateral superior cervical ganglionectomy, or to a unilateral chorda tympani section, together with a contralateral sham-operation were employed. After turpentine oil or restraint stress, a significant decrease in submaxillary lymph node ornithine decarboxylase was found. A unilateral sympathetic denervation of submaxillary lymph nodes counteracted in part the inhibitory effect of stress on ornithine decarboxylase activation, as well as augmented the enzyme response in innervated submaxillary lymph nodes. Ornithine decarboxylase activation attained similar values in parasympathetic decentralized or intact submaxillary lymph nodes and the unilateral parasympathetic decentralization did not interfere with the inhibition of enzyme activity found in turpentine oil-stressed rats. Cyclosporine administration (5 or 20 mg/kg) significantly decreased Freund's adjuvant-induced ornithine decarboxylase activity in the submaxillary lymph nodes of control rats, but failed to modify it in turpentine oil-stressed animals. In this latter group, a higher (40 mg/kg) dose of cyclosporine decreased ornithine decarboxylase activity on the innervated side only. A diminished inhibitory response to cyclosporine was found in the parasympathetic decentralized submaxillary lymph nodes of unstressed rats. The results support the view that the immunosuppressive effects of cyclosporine may diminish during stress, in part due to changes in the traffic of neural signals in local sympathetic nerves.

Cyclosporine effects on in vitro responsiveness of anterior pituitary hormone release to dopamine and thyrotropin-releasing hormone in young female rats

Endocrine side effects of the immunosuppressive drug cyclosporine (CyA) include changes in anterior pituitary hormone secretion. The aim of the present study was to examine the effects of CyA on the responsiveness of in situ and ectopic anterior pituitary prolactin (PRL), growth hormone (GH) and luteinizing hormone (LH) release response to dopamine (DA) and thyrotropin-releasing hormone (TRH) treatment in young female rats, and to evaluate the possible PRL participation in these effects. Thirty day old rats were rendered hyperprolactinemic by transplanting an anterior pituitary gland of a littermate donor, under the kidney capsule, and were then injected with CyA or vehicle for 2 or 8 days. Sham-operated rats were used as controls and treated in the same way. CyA treatment prevented the increase in plasma PRL levels which occurred in controls after pituitary grafting. In vitro basal PRL release of in situ pituitaries from either sham-operated and/or pituitary-grafted animals was decreased by CyA treatment at any point studied. Basal in vitro secretion of GH was only decreased in the in situ pituitaries from grafted animals after 2 days of CyA therapy. The presence of an ectopic pituitary lead to an increase in the in vitro basal LH secretion from in situ pituitaries as compared to those from sham-operated rats. Basal LH release rates were not changed by CyA treatment, although the LH release in vitro did increase in the in situ pituitaries from sham-operated animals treated with the drug for 2 days. DA addition to the incubation media decreased the in vitro release of PRL, GH and LH from the in situ pituitaries of sham-operated and pituitary-grafted animals treated with vehicle. In CyA treated animals, DA decreased in vitro PRL release from the in situ pituitaries of animals, independently of the presence or absence of an ectopic pituitary. Reductions of the in vitro GH and LH release release after DA treatment were higher in the in situ pituitaries from grafted animals on day 8 of CyA or vehicle treatment. TRH increased the in vitro release of the three hormones with differential effects related to the length of the treatment with CyA and/or the presence of an ectopic pituitary. In vitro release of PRL and GH by ectopic pituitaries was inhibited by previous treatment with CyA and this effect was decreased proportional to the duration of the treatment with the drug, while LH secretion was not modified. Addition of DA to the incubation media resulted in a marked reduction of in vitro PRL and GH release, but only at day 8 of vehicle treatment on GH release did DA addition to media further decrease the release of both hormones from ectopic pituitaries from animals treated for 2 or 8 days with the drug, whereas LH secretion was not modified. TRH addition to the incubation media of ectopic pituitaries surprisingly reduced PRL and GH secretion on day 8 of CyA treatment or after surgery. The results of these studies suggest that CyA can act directly at the hypophyseal level modifying pituitary responsiveness to external stimuli. CyA seems to exert its main effects on lactotroph activity while its effects on somatotrophs and gonadotrophs are less.