ABSTRACT
We investigated the effects of adenosine on prolactin (PRL) secretion from rat anterior pituitaries incubated in vitro. The administration of 5-N-methylcarboxamidoadenosine (MECA), an analog agonist that preferentially activates A2 receptors, induced a dose-dependent (1 nM to 1 æM) increase in the levels of PRL released, an effect abolished by 1,3-dipropyl-7-methylxanthine, an antagonist of A2 adenosine receptors. In addition, the basal levels of PRL secretion were decreased by the blockade of cyclooxygenase or lipoxygenase pathways, with indomethacin and nordihydroguaiaretic acid (NDGA), respectively. The stimulatory effects of MECA on PRL secretion persisted even after the addition of indomethacin, but not of NDGA, to the medium. MECA was unable to stimulate PRL secretion in the presence of dopamine, the strongest inhibitor of PRL release that works by inducing a decrease in adenylyl cyclase activity. Furthermore, the addition of adenosine (10 nM) mimicked the effects of MECA on PRL secretion, an effect that persisted regardless of the presence of LiCl (5 mM). The basal secretion of PRL was significatively reduced by LiCl, and restored by the concomitant addition of both LiCl and myo-inositol. These results indicate that PRL secretion is under a multifactorial regulatory mechanism, with the participation of different enzymes, including adenylyl cyclase, inositol-1-phosphatase, cyclooxygenase, and lipoxygenase. However, the increase in PRL secretion observed in the lactotroph in response to A2 adenosine receptor activation probably was mediated by mechanisms involving regulation of adenylyl cyclase, independent of membrane phosphoinositide synthesis or cyclooxygenase activity and partially dependent on lipoxygenase arachidonic acid-derived substances
Subject(s)
Animals , Male , Rats , Adenosine , Pituitary Gland, Anterior , Prolactin , Adenylyl Cyclases , Lipoxygenase , Pituitary Gland, Anterior , Prostaglandin-Endoperoxide Synthases , Rats, WistarABSTRACT
We investigated the participation of A1 or A2 receptors in the gonadotrope and their role in the regulation of LH and FSH secretion in adult rat hemipituitary preparations, using adenosine analogues. A dose-dependent inhibition of LH and FSH secretion was observed after the administration of graded doses of the R-isomer of phenylisopropyladenosine (R-PIA; 1 nM, 10 nM, 100 nM, 1 µM and 10 µM). The effect of R-PIA (10 nM) was blocked by the addition of 8-cyclopentyltheophylline (CPT), a selective A1 adenosine receptor antagonist, at the dose of 1 µM. The addition of an A2 receptor-specific agonist, 5-N-methylcarboxamidoadenosine (MECA), at the doses of 1 nM to 1 µM had no significant effect on LH or FSH secretion, suggesting the absence of this receptor subtype in the gonadotrope. However, a sharp inhibition of the basal secretion of these gonadotropins was observed after the administration of 10 µM MECA. This effect mimicked the inhibition induced by R-PIA, supporting the hypothesis of the presence of A1 receptors in the gonadotrope. R-PIA (1 nM to 1 µM) also inhibited the secretion of LH and FSH induced by phospholipase C (0.5 IU/ml) in a dose-dependent manner. These results suggest the presence of A1 receptors and the absence of A2 receptors in the gonadotrope. It is possible that the inhibition of LH and FSH secretion resulting from the activation of A1 receptors may have occurred independently of the increase in membrane phosphoinositide synthesis
Subject(s)
Rats , Male , Animals , Adenosine/pharmacology , Follicle Stimulating Hormone/metabolism , Gonadotropins/metabolism , In Vitro Techniques , Luteinizing Hormone/metabolism , Pituitary Gland, Anterior/drug effects , Receptors, Purinergic P1/physiology , Adenosine/analogs & derivatives , Gonadotropins/metabolism , Phosphatidylinositols/chemical synthesisABSTRACT
Neurons which release atrial natriuretic peptide (ANPergic neurons) have their cell bodies in the paraventricular nucleus and in a region extending rostrally and ventrally to the anteroventral third ventricular (AV3V) region with axons which project to the median eminence and neural lobe of the pituitary gland. These neurons act to inhibit water and salt intake by blocking the action of angiotensin II. They also act, after their release into hypophyseal portal vessels, to inhibit stress-induced ACTH release, to augment prolactin release, and to inhibit the release of LHRH and growth hormone-releasing hormone. Stimulation of neurons in the AV3V region causes natriuresis and an increase in circulating ANP, whereas lesions in the AV3V region and caudally in the median eminence or neural lobe decrease resting ANP release and the response to blood volume expansion. The ANP neurons play a crucial role in blood volume expansion-induced release of ANP and natriuresis since this response can be blocked by intraventricular (3V) injection of antisera directed against the peptide. Blood volume expansion activates baroreceptor input via the carotid, aortic and renal baroreceptors, which provides stimulation of noradrenergic neurons in the locus coeruleus and possibly also serotonergic neurons in the raphe nuclei. These project to the hypotlalamus to activate cholinergic neurons which then stimulate the ANPergic neurons. The ANP neurons stimulate the oxytocinergic neurons in the paraventricular and supraoptic nuclei to release oxytocin from the neural lobe which circulates to the atria to stimulate the release of ANP. ANP causes a rapid reduction in effective circulating blood volume by releasing cyclic GMP which dilates peripheral vessels and also acts within the heart slow its rate and atrial force of contraction. The released ANP circulates to the kidney where it acts through cyclic GMP to produce natriuresis and a return to normal blood volume.
Subject(s)
Animals , Adrenocorticotropic Hormone/metabolism , Atrial Natriuretic Factor/metabolism , Cerebral Ventricles/physiology , Homeostasis/physiology , Hypothalamus/metabolism , Natriuretic Agents/metabolism , Salts/metabolism , Water/metabolism , Atrial Natriuretic Factor/biosynthesis , Neuroendocrinology , Receptors, Atrial Natriuretic Factor/physiologyABSTRACT
Alpha-Melanocyte-stimulating hormone (alpha-MSH;0.6 and 3 nmol) microinjected into the anteroventral region of the third ventricle (AV3V) induced a significant increase in diuresis without modifying natriuresis or kaliuresis. Intraperitoneal (ip) injection of alpha-MSH (3 and 9.6 nmol) induced a significant increase urinary sodium, potassium and water excretion. Intraperitoneal (3 and 4.8 nmol) or iv (3 and 9.6 nmol) administration of alpha-MSH did not induce any significant changes in plasma atrial natriuretic peptide (ANP), suggesting that the natriuresis, kaliuresis and diuresis induced by the systemic action of alpha-MSH can be dissociated from the increase in plasma ANP. These preliminary results suggest that alpha-MSH may be involved in a gamma-MSH-independent mechanism of regulation of hydromineral metabolism.
Subject(s)
Rats , Male , Animals , alpha-MSH/physiology , Atrial Natriuretic Factor/physiology , Cerebral Ventricles/physiology , Diuresis/physiology , Natriuresis/physiology , Atrial Natriuretic Factor/blood , Injections, Intraperitoneal , Injections, Intravenous , Rats, WistarABSTRACT
We determined whether ANP (atrial natriuretic peptide) concentrations, measured by radioimmunoassay, in the ANPergic cerebral regions involved in regulation of sodium intake and excretion and pituitary gland correlated with differences in sodium preference among 40 Wistar male rats (l80-220 g). Sodium preference was measured as mean spontaneous ingestion of 1.5 per cent NaCl solution during a test period of 12 days. The relevant tissues included the olfactory bulb (OB), the posterior and anterior lobes of the pituitary gland (PP and AP, respectively), the median eminence (ME), the medial basal hypothalamus (MBH), and the region anteroventral to the third ventricle (AV3V). We also measured ANP contens in the right (RA) and left atrium (LA) and plasma. The concentrations of ANP in the OB and the AP were correlated with sodium ingestion during the preceding 24 h, since an increase of ANP in these structures was associated with a reduced ingestion and vice-versa (OB: r = -0.3649, P<0.05; AP: r = -0.3291, P<0.05). Moreover, the AP exhibited correlation between ANP concentration and mean NaCl intake (r = -0.4165, P<0.05), but this was not the case for the OB (r = 0.2422. This suggests that differences in sodium preference among individu male rats can be related to variations of AP ANP level. Earlier studies indicated that the OB is involved in the control of NaCl ingestion. Our data suggest that the OB ANP level may play a role mainly in day-today variations of sodium ingestion in the individual rat.
Subject(s)
Rats , Animals , Male , Atrial Natriuretic Factor/analysis , Cerebral Ventricles/chemistry , Heart Atria/chemistry , Hypothalamus, Middle/chemistry , Median Eminence/chemistry , Olfactory Bulb/chemistry , Pituitary Gland/chemistry , Plasma/chemistry , Sodium Chloride, Dietary/metabolism , Rats, WistarABSTRACT
Sodium and water balance was determined in two strains of Wistar rats selectively bred for high (hypernatriophilic, HR) or low salt preference (hyponatriophilic, HO) under basal conditions and during sodium deprivation. Male rats from each strain were selected for an average ingestion of 1.5 per cent NaCl solution of more than (HR) or less than (HO) 4 ml 100 g body weight-1 day-l, during a 10-day period. HR rats (N = 17) presented markedly higher sodium intake under basal conditions (2.983 ñ 0.316 mEq 100 g body weight-1 day-l) than HO rats (N = 12; 0.406 ñ 0,076 mEq 100 g body weight-1 day-l; Mann-Whitney test, P<0.01). Water (HR: 8.6 ñ 0.57; HO: 7.7 ñ 0.32 ml 100 g body weight-1 day-1) and sodium balances (HR: 0.936 ñ 0.153; HO: 0.873 ñ 0.078 mEq 100 g body weight-1 day-l) were similar in both strains, despite a higher sodium and total fluid (HR: 16.3 ñ 1.06; HO: 10.8 + 0.49 ml 100 g body weight-1 day-l; P<0.01) ingestion in HR rats. During sodium deprivation HR rats (N = 13) exhibited a sodium balance similar to that of HO rats (N = 13) (HR: -0.159 ñ 0.011; HO: -0.129 ñ 0.019 mEq 100 g body weight-1 day-1), and, in addition, an adequate suppression of natriuresis (HR: O.049 ñ 0.011; HO: 0.026 ñ 0.004 mEq 100 g body weight-1 day-1). These data show that HR rats present hypernatriophilia as a primary trait, since their sodium-conserving mechanisms are intact. Therefore, these rats provide an adequate model to study factors that determine innate sodium preference.
Subject(s)
Rats , Animals , Male , Female , Disease Models, Animal , Hypernatremia , Hyponatremia , Sodium Chloride, Dietary , Sodium Chloride/analysis , Breeding , Postural Balance/physiology , Rats, WistarABSTRACT
The role played by the central nervous system (CNS) in the control of body fluid homeostasis has been demonstrated by several authors. The AV3V plays a key role in central control of sodium excretion since its cholinergic, adrenergic, angiotensinergic and osmotic stimulation enhances and its destruction blocks sodium excretion in rats and goats. Cholinergic stimulation of the AV3V induced an increase in plasma ANP as well as a marked elevation in content of the peptide in medial basal hypothalamus, neuro and adenohypophysis. On the other hand, a decline in plasma ANP after AV3V lesions was accompanied by dramatic declines in content of ANP in these same structures. Our previous work has also indicated the essential role of the AV3V region and its ANPergic neurons in the control of ANP release in response to volume expansion (BVE) and indicated that alpha-adrenergic and muscarinic receptors are critical in mediating these responses. Lesions of the AV3V region, or of the median eminence or posterior lobe of pituitary gland blocked the increase in plasma ANP concentration in response to BVE. That this effect is related to blockage of the activity of the brain ANPergic neurons is supported by fyndings in sheep and in rats that the injection of the antiserum directed against ANP into the AV3V region at least partially blocked the BVE-induced release of ANP. We and others have also previously shown that denervation of baroreceptors inhibits ANP release induced by BVE. Activation of the ANP neurons also cause release of ANP from the anterior and neural lobe of pituitary gland. ANP neurons may activate oxytocinergic neurons in the supraoptic and paraventricular, which projects to neural lobe. Oxytocin would circulate to the atria and may directly activate release of ANP from the atrial myocytes, since i.v. or i.p. injection of oxytocin increases sodium excretion as well as elevates plasma ANP. Oxytoxin is present in the neural lobe in large quantity, which could reach the atria myocytes in high concentration and release ANP that circulate to the kidneys and evokes natriuresis to return circulating blood volume to normal.
Subject(s)
Atrial Natriuretic Factor/physiology , Body Fluids/physiology , Homeostasis/physiology , Neurosecretory Systems/physiology , Diuresis/physiology , Natriuresis/physiology , Oxytocin/physiology , Vasopressins/physiologyABSTRACT
The sexual development of normonatriophilic (Normo) and hypemrntriophilic (Hyper) male Wistar rats was compared from 30 to 60 days of age (N = 8-10 per group) with emphasis on the onset of puberty. Hyper rats (more than 5 ml of saline a day in a situation of free access to tap water and 1.5 per cent NaCl) had a 20-39 per cent body weight reduction and a 22-29 per cent testicular growth rate decrease compared to Normo rats. Plasma testosterone (ng/ml) of Normoo rats increased from 0.29 ñ 0.02 at 30 days to 1.42 ñ 0.18 at 50 days, decreasing to 0.87 ñ 0.15 at 60 days of age, with no significant difference compared to Hyper animals. Plasma concentration (ng/ml) of luteinizing hormone (LH) was significantly lower in Hyper (0.21 ñ 0.03) than in Normo (0.43 ñ 0.06) rats at 40 days. At 30 days, plasma follicle stimulating hormone (FSH) levels (ng/ml) were significantly higher in Hyper (18.9 ñ 1.3) than in Normo (15.6 ñ 0.5) rats. It is possible that increased levels of FSH compensated for a reduced amount of LH, thus allowing similar testosterone production by Hyper and Normo rats. At 30 days, testis maturation was higher in Hyper rats, as indicated by a 22 per cent increase in tubular cross-sections with young spermatids. At 50 days, spermatogenesis progressed to the production of mature spermatids (onset of puberty) and Hyper rats exhibited an 18.7 per cent lower rate of testis maturation. Testis maturation was similar in Hyper and Normo rats at 60 days.
Subject(s)
Animals , Male , Rats , Spermatogenesis/physiology , Puberty/physiology , Sexual Maturation/physiology , Rats, WistarABSTRACT
This article provides a personal and historical review of research concerning the hypothalamic control of water and salt intake and excretion. The following major points will be considered: 1. Electrical, osmotic, cholinergic, alpha-adrenergic and peptidergic stimulation of the hypothalamus. 2. Determination of the pathways involved in these neuroendocrine responses. 3. The participation of ANP in the control of thirst and salt excretion. 4. The participation of the brain ANPergic neuronal system in ANP release. 5. The role of hypothalamic ANPergic neurons and of sinoaortic and renal baroreceptors in the regulation of volume expansion-induced release of ANP. 6. Effects of the brain ANP system on other hormones.
Subject(s)
Animals , Male , Cats , Dogs , Rats , Atrial Natriuretic Factor/physiology , Hypothalamus/physiology , Drinking/physiology , Natriuresis , Water-Electrolyte Balance , Angiotensin II , Cerebrum , Goats , Melanocyte-Stimulating Hormones , Oxytocin , Saline Solution, Hypertonic/administration & dosage , VasopressinsABSTRACT
1. The internal genital organs of prepubertal, 21-day old male Wistar rats were sympathectomized by ip injection of guanethidine (G), at doses of 5 mg/kg per day (N = 10) or 10 mg/kg per day (N = 10), for 20 days. Controls (N = 10) received saline. 2. Plasma testosterone level (measured by radioimmunoassay) decreased significantly in sympathectomized rats from 4.11 +/- 0.57 to 1.76 +/- 0.37 ng/ml (5 mg/kg G) and to 1.17 +/- 0.26 ng/ml (10 mg/kg G). Plasma levels of luteinizing and follicle-stimulating hormones and of prolactin were unaltered. 3. Chemical denervation caused a significant decrease in ventral prostate wet weight from 74.3 +/- 5.5 to 59.3 +/- 4.7 mg (5 mg/kg G) and to 54.6 +/- 4.1 mg (10 mg/kg G) and in seminal vesicle wet weight from 36.5 +/- 6.8 to 31.7 +/- 5.2 mg (5 mg/kg G) and to 21.3 +/- 1.6 mg (10 mg/kg G). 4. The potential secretory activity of the prostate (measured in terms of fructose content) decreased significantly in guanethidine-treated rats from 0.38 +/- 0.02 to 0.30 +/- 0.02 mg/g (5 mg/kg G) and to 0.20 +/- 0.02 mg/g (10 mg/kg G). The seminal vesicle fructose content (0.33 +/- 0.04 mg/g for controls), however, was not altered by chemical denervation. 5. Our data suggested that sympathetic neurons may be involved in the control of LH receptors, at least in the prepubertal phase of sexual development. They may also be directly related to growth and secretory activity of the male accessory sex glands
Subject(s)
Animals , Male , Rats , Prostate/growth & development , Sympathectomy, Chemical , Seminal Vesicles/growth & development , Guanethidine , Organ Size , Prostate , Radioimmunoassay , Rats, Wistar , Testosterone/bloodABSTRACT
The effect of exposure to lead on endocrine function was studied in pubertal rats treated with 1.0 g/l lead acetate (PbAc) in drinkin water for 20 days (subacute group) or 9 months (chronic group) in addition to iv injections of PbAc (0.1mg/100g body weight) every 10(subacute group) or 15 days (chronic group). Although basal levels of testosterone were higher both in the plasma and in the testes of acuctely intoxicated animals, the ciruclating levels of lutinizing hormone (LH) were not affected in either group, nor was the LHRH content of the median eminence. The density of [125I]LH/hCG biding sites in testicular homogenates was reduced by saturnism in both groups. Howeverm the apparent affinity constant of the hormone-receptor complex significantly increased. These data can be viewed as the result of a mixture of specific lead toxicity (e.g., at the enzyme level) with other more general actions (e.g., at the level of the hypothalamus-pituitary-testicular axis)
Subject(s)
Rats , Animals , Male , Gonadotropin-Releasing Hormone/blood , Lead Poisoning/blood , Luteinizing Hormone/blood , Testis/metabolism , Testosterone/blood , Receptors, Androgen/drug effects , Receptors, Gonadotropin/drug effects , Testis/drug effects , Testosterone/drug effects , Testosterone/metabolismABSTRACT
Intraperitoneal injection of guanethidine (50 mg Kg-1 day-1) in newborn rats produeces complete and permanent sympathectomy. The present study was performed to evaluate the effect of this form of denervation on the onset of puberty in female rats. Treatment began 7 days after birth and was maiantained for 3 weeks. In the 45th day, animals were killed by decaptation and plasma LH and FSH levels wee measured. Based on the day of vaginal opening (puberty index), the results show that guanethidine induces a delay in the onset of puberty. The concentrations of LH and FSH in the plasma were not statistically different from those in control rats
Subject(s)
Rats , Animals , Female , Guanethidine , Sexual Maturation/physiology , Sympathetic Nervous System , Sympathectomy, Chemical , Follicle Stimulating Hormone/blood , Luteinizing Hormone/blood , Rats, Inbred Strains , Vagina/drug effectsABSTRACT
To study effects of clonidine on growth and plasma somatomedin C (SmC) lelvels, 42 male Wistar rats aged 28 days and weighing 75 to 105 g were given clonidine (1,5 microng/ml in drinking water), or filtered water alone and were weighed weekly. After 0,4 and 8 weeks, the animals were sacrificed under ether anesthesia, their length was measured and blood was collected by cardiac puncture for measurement of SmC concentration. Growth and the weigh/lengh ratio were lower, and plasma SmC levels (mean ñ SEM) were greater in the treated groups after 4 (616 ñ 44.7 vs 433.2 ñ 39.38 ng/ml, P < 0.01) and 8(595.2 28.3 vs 412.66 ñ 39.01 ng/ml, P < 0.01) weeks of treatment, suggesting that clonidine treatment increased growth hormone secretion. In other experiments, treated showed increased food intake only during the first week of treatment and decreased epididymal fat weight afther 3 weeks (1.412 ñ 0.0536 vs 1.6 ñ 0.1335 mg/100 g body weight, P < 0.01). The results suggest that clonidine acts at the level of the central nervous system involving transitory modulation of food intake, as well as on the regulation of energy metabolism
Subject(s)
Rats , Animals , Male , Clonidine/pharmacology , Feeding Behavior/drug effects , Growth/drug effects , Insulin-Like Growth Factor I/blood , Energy Metabolism , Rats, Wistar , Weight Gain/drug effectsABSTRACT
The reproductive system of immature rats is held to be more influenced thyroid dysfunction than that of adult animals. The effect of hypothyroidism on the spermatogenic process of the rat has not been reported previously. th objetive of the present study was to investigate the spermatogenic and been reported previously. The objetive of the present study was to investigate the spermatogenic and steroidogenic functions of pubertal hypothyroid rats. Hypothyroidism by ad libitum ingestion of a 0.05% solution of propylthiouracil for 60 days, and confirmed by reduced plasma thyroxine levels in treated rats. Plasma testosterone level, the histological features of the testis and epididymis and the concentration of spermatozoa stored in the cauda epididymis were unchanged by hypothyroidism
Subject(s)
Rats , Animals , Male , Spermatogenesis/drug effects , Hypothyroidism/physiopathology , Propylthiouracil/therapeutic use , Rats , Testis/physiopathology , Rats, Wistar , Thyroxine/bloodABSTRACT
Benznidazole is used extensively throughout Latin America as an antiparasitic chemotherapeutic agent against chagasica infection. We have shown that rats chronically treated with 80 mg benznidazole Kg-1 day-1 for 30, days present severe testicular atrophy and arrest of spermatognesis. In the present experiments, plasma levels of testosterone (T), luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (Prl- were inbestigated in rats receiving 10, 40 and 80 mg benznidazole Kg-1 day-1 for 30 days. No significant change in T, LH or Prl levels was observed in treated rats (P > 0.05). Plasma FSH concentration, however, was markedly invreased (P < 0.05 by benzidazole treatment (40 and 80 mgKg-1 day-1) and remained high for 90 days after drug treatment was discontinued
Subject(s)
Rats , Antiprotozoal Agents/pharmacology , Benzimidazoles/pharmacology , Follicle Stimulating Hormone/blood , Luteinizing Hormone/blood , Prolactin/blood , Testosterone/blood , Rats, Wistar , Testis/drug effectsSubject(s)
Rats , Animals , Male , Spermatogenesis , Nitroimidazoles/therapeutic use , Testis/pathology , Prostate/pathology , Testis/drug effects , Seminal Vesicles/pathologyABSTRACT
Incubation of hemipituitaries from male rats (200-220 g) with 10 nM to 1 micronM adenosine induced a dose-dependent decrease of the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) into the medium, and increased prolactin (PRL) secretion. The effects of 10 nM adenosine were blocked by 100 nM ceffeine, wereas 100 nM ceffeine alone had also inhibited 10 nM luteinizing hormone-releasing hormone (LHRH)-induced LH and FSH release by > 90%. These data indicate a regulatory role for adenosine in pituitary LH, FSH and PRL release, and also a possible modulatory effect of adenosine on the LHRH-LH and FSH system
Subject(s)
Rats , Animals , Male , Adenosine/pharmacology , Caffeine/pharmacology , Follicle Stimulating Hormone/metabolism , Pituitary Gland/metabolism , Luteinizing Hormone/metabolism , Prolactin/metabolismABSTRACT
Freshly dispersed testicular interstitial cells as well as Percoll-purified Leydig cells were studied in vitro in order to evaluate the effect of adrenergic agonists on testosterone (T) secretion. Epinephrine and phenylephrine did not change the rate of T release under basal conditions in freshly dispersed interstitial cells, but enhanced it during human chorionic gonadotropin (hCG) stimulation. Norepinephrine and clonidine had no effect on T secretion. In contrast, in Percoll-purified Leydig cells epinephrine increased T release both under basal and hCG-stimulated conditions. These data demonstrate that neurotransmitters may participate in T secretion from isolated Leydig cells