Alpha-adrenergic agonists inhibit the dipsogenic effect of angiotensin II by their stimulation of atrial natriuretic peptide release

Angiotensin II (ANG-II) and atrial natriuretic peptide (ANP) have opposing actions on water and salt intake and excretion. Within the brain ANP inhibits drinking induced by ANG-II and blocks dehydration-induced drinking known to be caused by release of ANG-II. Alpha-adrenergic agonists are known to release ANP and antagonize ANG II-induced drinking. We examined the hypothesis that alpha agonists block ANG-II-induced drinking by stimulating the release of ANP from ANP-secreting neurons (ANPergic neurons) within the brain that inhibit the effector neurons stimulated by ANG-II to induce drinking. Injection of ANG-II (12.5 ng) into the anteroventral region of the third ventricle (AV3V) at the effective dose to increase water intake increased plasma ANP concentrations (P<0.01) within 5 min. As described before, previous injection of phenylephrine (an alpha(1)-adrenergic agonist) or clonidine (an alpha(2)-adrenergic agonist) into the AV3V region significantly reduced ANG-II-induced water intake. Their injection also induced a significant increase in plasma ANP concentration and in ANP content in the olfactory bulb (OB), AV3V, medial basal hypothalamus (MBH) and median eminence (ME). These results suggest that the inhibitory effect of both alpha-adrenergic agonists on ANG-II-induced water intake can be explained, at least in part, by the increase in ANP content and presumed release from these neural structures. The increased release of ANP from the axons of neurons terminating on the effector neurons of the drinking response by stimulation of ANP receptors would inhibit the stimulatory response evoked by the action of ANG-II on its receptors on these same effector neurons.

Possible involvement of A1 receptors in the inhibition of gonadotropin secretion induced by adenosine in rat hemipituitaries in vitro

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 microM and 10 microM). 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 microM. The addition of an A2 receptor-specific agonist, 5-N-methylcarboxamidoadenosine (MECA), at the doses of 1 nM to 1 microM 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 microM 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 microM) 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.

Atrial natriuretic peptide and oxytocin induce natriuresis by release of cGMP

Our hypothesis is that oxytocin (OT) causes natriuresis by activation of renal NO synthase that releases NO followed by cGMP that mediates the natriuresis. To test this hypothesis, an inhibitor of NO synthase, L-nitroarginine methyl ester (NAME), was injected into male rats. Blockade of NO release by NAME had no effect on natriuresis induced by atrial natriuretic peptide (ANP). This natriuresis presumably is caused by cGMP because ANP also activates guanylyl cyclase, which synthesizes cGMP from GTP. The 18-fold increase in sodium (Na+) excretion induced by OT (1 microgram) was accompanied by an increase in urinary cGMP and preceded by 20 min a 20-fold increase in NO3- excretion. NAME almost completely inhibited OT-induced natriuresis and increased NO3- excretion; however, when the dose of OT was increased 10-fold, a dose that markedly increases plasma ANP concentrations, NAME only partly inhibited the natriuresis. We conclude that the natriuretic action of OT is caused by a dual action: generation of NO leading to increased cGMP and at higher doses release of ANP that also releases cGMP. OT-induced natriuresis is caused mainly by decreased tubular Na+ reabsorption mediated by cGMP. In contrast to ANP that releases cGMP in the renal vessels and the tubules, OT acts on its receptors on NOergic cells demonstrated in the macula densa and proximal tubules to release cGMP that closes Na+ channels. Both ANP- and OT-induced kaliuresis also appear to be mediated by cGMP. We conclude that cGMP mediates natriuresis and kaliuresis induced by both ANP and OT.

Salt overload does not modify plasma atrial natriuretic peptide or vasopressin during pregnancy in rats

The present study was carried out to determine whether the increased salt intake induce by increased specific sodium appetite in pregnant rats modifies water-salt homeostasis throughout pregnancy. Two groups of pregnant rats were used, one fed ad libitum with a normal sodium (NS) diet consisting of standard rat chow and distilled water, and the other fed with a high-sodium (HS) diet with free access to chow, distilled water plus saline solution (1.5% NaCl). Virgin rats in dioestrus were also studied as non-pregnant controls. Pregnant animals were studied on days 4, 9, 14, 20 and 21 of gestation at which time body weight, water and saline intake, sodium excretion, plasma atrial natriuretic peptide (ANP) and arginine vasopressin (AVP) concentrations, as well as plasma osmolality were determined. Data showed that water intake was higher in the NS group, but total fluid intake (water plus saline) was higher in the HS group throughout pregnancy. Dietary sodium intake was the same for both groups but total sodium intake (chow plus saline) was 60-98% higher in the HS rats. Pregnant HS rats excreted more fluid (35-50%) and sodium (up to 100%) compared with NS rats, indicating that the animals could change their renal excretion in response to a 2.5-fold higher dietary sodium intake compared with the control level. Salt satiety during pregnancy did not modify plasma ANP concentration. In both groups of pregnant rats ANP levels increased 3-fold on day 14 without significant alteration in sodium excretion, suggesting that the natriuretic action of ANP is attenuated at least after the second week of pregnancy. High sodium intake did not change plasma AVP concentration or osmolality and both groups showed the same gradual decrease in plasma osmolality (approximately 8 mosmol kg-1) at the end of pregnancy that was not accompanied by decreased plasma AVP concentration. The present data show that rats maintain the special homeostatic equilibrium that occurs in normal pregnancy even when they are allowed to increase sodium intake to satisfy their salt appetite during this period of the reproductive cycle.

The neuroendocrine control of atrial natriuretic peptide release

In the initial experiments reviewed here, we show that atrial natriuretic peptide (ANP) plays an important inhibitory role in the control of sodium chloride and water intake since injections of ANP into the third ventricle (3V) caused a reduction in dehydration-induced drinking and also the drinking of salt in salt-depleted rats. Attention was then turned to the possible role of the brain ANP neurons in producing natriuresis which had earlier been shown to be caused by stimulations within the anterior ventral third ventricular region (AV3V). Stimulation in this region by carbachol produced natriuresis accompanied by a dramatic increase in plasma ANP concentrations and increased content of the peptide in medial basal hypothalamus (MBH), neurohypophysis (NH) and anterior pituitary gland (AP), without alterations in the content of ANP in lungs or atria. This suggested that the natriuresis resulting from the stimulation is brought about, at least in part, by the release of ANP from the brain. Conversely, there was a dramatic decline in plasma ANP at both 24 and 128 h after AV3V lesions had been placed. In view of the much larger quantities of the peptide stored in the atria, it is probable that the changes in the atrial release of the peptide were the main factors altering plasma ANP, but that there was concomitant alteration in the release of brain ANP as well. Blood volume expansion (BVE) by intraatrial injection of isotonic saline in the rat is a profound stimulus for ANP release. Lesions in the AV3V region, median eminence, or neurohypophysectomy blocked BVE-induced release of ANP indicating the crucial participation of the CNS in the response of ANP and natriuresis. Baroreceptor impulses from the carotid-aortic sinus regions and the kidney are important in the neuroendocrine control of ANP release since deafferentation of these regions lowered basal plasma ANP concentrations and prevented the increase after BVE. The evidence indicates that the ANP release, in response to BVE, is mediated by afferent baroreceptor impulses to the AV3V, which mediates the increased ANP release via activation of the hypothalamic ANP neuronal system. Our recent data support the hypothesis that BVE causes the release of ANP from ANPergic neurons in the hypothalamus that in turn stimulates release of oxytocin from the neurohypophysis. This oxytocin acts to release ANP from the right atrium that has negative chrono- and inotropic effects in the right atrium to reduce cardiac output, thereby reducing effective circulating blood volume. Then, the released ANP circulates to the kidneys and evokes natriuresis to return circulating blood volume to normal. This is further accomplished by reduction in intake of water and salt mediated also by brain ANP.

Neuroendocrine regulation of salt and water metabolism

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 hypothalamus 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 to 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.

Does plasma ANP participate in natriuresis induced by alpha-MSH?

alpha-Melanocyte-stimulating hormone (alpha-MSH; 0.6 and 3 nmol) micro-injected 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 in 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.

Correlations between ANP concentrations in atria, plasma and cerebral structures and sodium chloride preference in Wistar rats

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 glad correlated with differences in sodium preference among 40 Wistar male rats (180-220 g). Sodium preference was measured as mean spontaneous ingestion of 1.5% 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 content 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 a 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 individual 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 suggests that the OB ANP level may play a role mainly in day-to-day variations of sodium ingestion in the individual rat.

Ultrasound stimulation of rat testes damaged by busulfan

The purpose of the present study was to investigate whether or not low-intensity ultrasound exposure (20 mW/cm2 average intensity) accelerates the repair of rat germinal epithelium damaged by an antispermatogenic agent. The results from analysis of testicular weight and DNA content, sperm production and epididymal sperm concentration showed that the time needed for the reestablishment of the spermatogenic process following busulfan treatment was not reduced by ultrasound energy suggesting that, in contrast to many other mammalian tissues, the seminiferous epithelium is refractory to ultrasound stimulation.

Oxytocin releases atrial natriuretic peptide from rat atria in vitro that exerts negative inotropic and chronotropic action

Our previous experiments suggested that natriuresis induced by blood volume expansion, was brought about by oxytocin (OT)-stimulated atrial natriuretic peptide (ANP) release from the right atrium. We hypothesized that the ANP released might exert effects on the atrium itself and therefore carried out in vitro experiments to test this hypothesis. Heart rate and isometric tension were recorded from isolated rat atria mounted in an organ bath. Oxytocin exerted a dose-related, negative chrono- and inotropic effect with a minimal effective concentration (MEC) of 3 microM, 10-fold higher than required for ANP to exert comparable effects. The effects of OT were not blocked by atropine suggesting that they were not mediated via release of acetylcholine. Eight-bromoguanosine 3'-5'-cyclic monophosphate (cGMP) had similar effects to those of OT and ANP, suggesting that the effects of ANP were mediated by cGMP. When isolated ventricles, left or right atria, were incubated in vitro, OT had a dose-related effect to stimulate the release of ANP into the medium only from right atria with a MEC of 0.1 microM. A specific OT antagonist, F792 (1 microM), inhibited basal release of ANP and blocked the stimulatory action of OT on ANP release. The results support the hypothesis that OT, acting on its putative receptors in the right atrium, stimulates the release of ANP which then exerts a negative chrono- and inotropic effect via activation of guanylyl cyclase and release of cGMP. The ability of the oxytocin antagonist to reduce basal release of ANP from atria incubated in vitro supports the hypothesis that these effects could be physiologically significant. We hypothesize that blood volume expansion via baroreceptor input to the brain causes the release of OT which circulates to the heart and stimulates the release of ANP from the right atrium. This ANP then has a negative ino- and chronotropic effect in the atrium and possibly a negative inotropic effect in the right ventricle, left atrium and left ventricle, to produce an acute reduction in cardiac output that, coupled with its peripheral vasodilating actions, causes a rapid reduction in effective circulating blood volume. The ANP released would also act on the kidneys to cause natriuresis and ANP acts within the brain to inhibit water and salt intake leading to a gradual recovery of circulating blood volume to normal.

ANP as a neuroendocrine modulator of body fluid homeostasis

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 findings 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. Oxytocin 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.

On the purinergic regulation of hormonal secretion from the anterior pituitary gland

Purinergic regulation of hormonal secretion from the anterior pituitary may be characterized by effects with biphasic secretory response. This response may be started by activation of different subtypes of membrane prurinergic receptors (A1 and/or A2). A putative autocrine mechanism has been proposed to explain the action of adenosine on pituitary hormonal secretion. This mechanism may be dependent on adenosine degradation by the enzyme adenosine deaminase into the extracellular space. The regulation of AMPc and calcium levels in cytoplasm may be part of putative intracellular mechanisms involved in purinergic action. Additionally, hypophysiotrophic effects induced by hypothalamic substances may be modulated by adenosine. The mechanisms involved in this modulatory effects, however, remain elusive.

Sodium balance of hyper- and hypo-natriophilic rats under basal conditions and during sodium deprivation

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 stain were selected for an average ingestion of 1.5% NaCl solution of more than (HR) or less than (HO) 4 ml 100 g body weight (-1) day (-1), during a 10-day period. HR rats (N = 17) presented markedly higher sodium intake under basal conditions (2.983 +/- 0.316 mEq 100 g body weight (-1) day (-1)) than HO rats (N = 12; 0.406 +/- 0.076 mEq 100 g body weight (-1) day (-1); Mann-Whitney test, P < 0.01). Water (HR: 8.6 +/- 0.57; HO: 7.7 +/- 0.32 ml 100 g body weight (-1) day (-1)) and sodium balances (HR: 0.936 +/- 0.153; HO: 0.873 +/- 0.078 mEq 100 g body weight (-1) day (-1)) were similar in both strains, despite a higher sodium and total fluid (HR: 16.3 +/- 1.06; HO: 10.8 +/- 0.49 ml 100 g body weight (-1) day (-1); 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 +/- 0.011; HO: -0.129 +/- 0.019 mEq 100 g body weight (-1) day (-1)), and, in addition, an adequate suppression of natriuresis (HR: 0.049 +/- 0.011; HO: 0.026 +/- 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.

Oxytocin mediates atrial natriuretic peptide release and natriuresis after volume expansion in the rat

Our previous studies have shown that stimulation of the anterior ventral third ventricular region increases atrial natriuretic peptide (ANP) release, whereas lesions of this structure, the median eminence, or removal of the neural lobe of the pituitary block ANP release induced by blood volume expansion (BVE). These results indicate that participation of the central nervous system is crucial in these responses, possibly through mediation by neurohypophysial hormones. In the present research we investigated the possible role of oxytocin, one of the two principal neurohypophysial hormones, in the mediation of ANP release. Oxytocin (1-10 nmol) injected i.p. caused significant, dose-dependent increases in urinary osmolality, natriuresis, and kaliuresis. A delayed antidiuretic effect was also observed. Plasma ANP concentrations increased nearly 4-fold (P < 0.01) 20 min after i.p. oxytocin (10 nmol), but there was no change in plasma ANP values in control rats. When oxytocin (1 or 10 nmol) was injected i.v., it also induced a dose-related increase in plasma ANP at 5 min (P < 0.001). BVE by intra-atrial injection of isotonic saline induced a rapid (5 min postinjection) increase in plasma oxytocin and ANP concentrations and a concomitant decrease in plasma arginine vasopressin concentration. Results were similar with hypertonic volume expansion, except that this induced a transient (5 min) increase in plasma arginine vasopressin. The findings are consistent with the hypothesis that baroreceptor activation of the central nervous system by BVE stimulates the release of oxytocin from the neurohypophysis. This oxytocin then circulates to the right atrium to induce release of ANP, which circulates to the kidney and induces natriuresis and diuresis, which restore body fluid volume to normal levels.

Hypothyroidism affects pulsatile LH secretion in pubertal orchiectomized rats

The present study evaluated the effect of hypothyroidism on the pituitary-testicular axis in rats rendered hypothyroid on the beginning of puberty. Rats were treated with propylthiouracil for 8 weeks and killed for determination of hormonal status and body parameters. For determination of pulsatile LH secretion other animals were orchiectomized two weeks before sampling. Analysis of the results led us to conclude that although the absolute weight of sex organs tended to decrease in hypothyroid animals, the relative weights were equal or higher than control, suggesting that the development of these organs were not affected by hypothyroidism; the androgenic activity of hypothyroid rat testes were preserved; basal plasma levels of pituitary hormones were similar in control and hypothyroid groups; the pulsatile LH secretion showed a decrease in the number of pulses, nadir mean and total LH secretion in hypothyroid animals. Our results demonstrate that although hypothalamic-pituitary axis of hypothyroid pubertal rats displays an abnormal pulsation LH release, no evidences of abnormalities in the reproductive system functions were found.

Is ovarian adrenergic innervation essential to gonadal function in adult rats?

We studied the relative importance of ovarian innervation during different phases of female rat sexual development, 30, 40, 45 and 60-day-old. Chemical sympathectomy was promoted by long term postnatal treatment with guanethidine (GD), an adrenergic neuron blocking agent. The sympathectomized rats exhibited delayed puberty and alterations in estrous cycle. Reduced circulating E2, LH and Prl levels at 30 days of age were observed, besides decreased steroidal secretory responsiveness to gonadotropins in vitro. On the other hand, normal pituitary secretory responsiveness to LHRH in vivo and plasma gonadotropin concentrations were observed in 60-day-old rats. These data reinforce the view that ovarian sympathetic innervation contributes to the regulation of the prepubertal development of the ovarian functions.

The hypophyseal-testicular axis and sex accessory glands following chemical sympathectomy with guanethidine of pre-pubertal to mature rats

Selective chemical sympathectomy of the internal sex organs of prepubertal to mature male Wistar rats was performed by chronic treatment with low doses of guanethidine. Plasma testosterone and luteinizing hormone and the intratesticular level of testosterone were determined. The weight and fructose content of seminal vesicle and ventral prostate were also investigated. The results showed that sympathetic innervation is related to the control of the hypophyseal-testicular axis as well as to the growth and potential secretory activity of the male sex accessory glands.

Participation of the ascending serotonergic system in the stimulation of atrial natriuretic peptide release

Results obtained in our laboratories have provided evidence for the participation of the hypothalamic atrial natriuretic peptide (ANP) neuronal system in the regulation of water and electrolyte homeostasis. The anterior ventral third ventricular (AV3V) region, a site of the perikarya of the ANP neurons, receives important afferent input from ascending serotoninergic axons. We hypothesized that the ascending serotoninergic tract might be involved in control of the liberation of ANP. Therefore, electrolytic lesions were produced in the mesencephalic dorsal raphé nucleus (DRN), the site of perikarya of serotonin (5-HT) neurons whose axons project to the AV3V region. Rats with sham lesions constituted the control group. In a second group of animals, the serotoninergic system was depleted of 5-HT by lateral ventricular administration of p-chlorophenylalanine (PCPA), an amino acid that causes depletion of 5-HT from the serotoninergic neurons. Control animals were injected with an equal amount of isotonic saline. The DRN lesions induced an increase of water intake and urine output beginning on the first day that lasted for 1 week after lesions were produced. There was a concomitant sodium retention that lasted for the same period of time. When water-loaded, DRN-lesioned and PCPA-injected animals showed diminished excretion of sodium, accompanied by a decrease in basal plasma ANP concentrations, and blockade of the increase in plasma ANP, which followed blood volume expansion by intraatrial injection of hypertonic saline. The results are interpreted to mean that ascending stimulatory serotoninergic input into the ANP neuronal system in the AV3V region produces a tonic stimulation of ANP release, which augments sodium excretion and inhibits water intake. Therefore, in the absence of this serotoninergic input following destruction of the serotoninergic neurons by DRN lesions or intraventricular injection of PCPA, an antinatriuretic effect is obtained that is associated with increased drinking, either because of sodium retention per se or removal of ANP-induced inhibition of release of the dipsogenic peptide, angiotensin II. The serotoninergic afferents also play an essential, stimulatory role in volume expansion-induced release of ANP and the ensuing natriuresis.

Time-dependent effects of lead on rat reproductive functions

The effects of exposure to lead on endocrine function and the reproductive parameters were studied in pubertal rats treated with 1.0 g l-1 lead acetate in drinking water for 20 days (subacute group) or 9 months (chronic group) in addition to i.v. injections of lead acetate (0.1 mg 100 g-1 body wt.) every 10 (subacute group) or 15 days (chronic group). Although basal levels of testosterone were higher both in plasma and in testes of acutely intoxicated animals, the circulating levels of luteinizing hormone (LH) were not affected in either group, nor was the LH-releasing hormone content of the median eminence. The density of [125I]LH/human chorionic gonadotrophin (hCG) binding sites in testicular homogenates was reduced by saturnism in both groups, concomitant with a significantly increased apparent affinity constant of the hormone-receptor complex. 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).

The male reproductive organs in experimental Chagas' disease. III. Plasma testosterone and accessory sex glands in the acute phase of the disease

Male Wistar rats were injected i.p. with 2 x 10(5) trypomastigotes of the Bolivia strain. Fifteen days later, few parasite nests were observed in the fibromuscular layer surrounding the seminal vesicle acini of chagasic animals and no parasites were detected in the testis and ventral prostate. A significant decrease was observed in the absolute weight and fructose content of the seminal vesicle and ventral prostate of chagasic rats, which also presented a sharp decrease in plasma testosterone levels.

Hypothalamic control of water and salt intake and excretion

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.

Brain atrial natriuretic peptide neurons play an essential role in volume expansion-induced release of atrial natriuretic peptide and natriuresis

The brain atrial natriuretic peptide (ANP) neuronal system appears to be involved in the increase in plasma ANP which follows blood volume expansion in the rat. To determine if this neuronal system is essential to the natriuresis and increase in plasma ANP which follow volume expansion, highly specific antiserum against ANP (ANP-AB) and/or normal rabbit serum as a control was microinjected into the third cerebral ventricle (3V) of conscious rats, and the effect on the natriuresis and increase in plasma ANP induced by intravenous injection of 2 ml/100 g body weight of 0.3 M NaCl was examined. Although there was no effect of ANP-AB on initial levels of plasma ANP or natriuresis 3 h after 3V injection, the natriuresis in response to blood volume expansion was significantly inhibited. The increase in plasma ANP which followed volume expansion was also significantly reduced at 5 min but recovered at 15 min. The results indicate that the brain ANP neuronal system plays an essential role in the mediation of volume expansion-induced increase in plasma ANP and natriuresis. The failure to block these responses completely may be due to the use of an inadequate dose of antiserum or other brain mechanisms may be able to mediate these responses.

Possible role of endothelin acting within the hypothalamus to induce the release of atrial natriuretic peptide and natriuresis

Since endothelin has been localized in neurons in areas involved in water and electrolyte metabolism, areas which also contain atrial natriuretic peptide (ANP) neurons, we determined whether endothelin would release ANP and induce natriuresis. Endothelin-3 (ET-3) in doses ranging from 38 to 760 pmol was microinjected into the third ventricle (3V) of conscious, water-loaded male rats, and the effect on natriuresis and plasma ANP was determined. ET-3 evoked a dose-related natriuresis beginning within 20 min of injection. Even the lowest dose tested (38 pmol) was effective. At a dose of 95 pmol, it produced a rapid increase of plasma ANP within 5 min peaking at 20 min. A slight kaliuresis and antidiuresis was observed at the 2 highest doses of 380 and 760 pmol. The urinary changes following 3V injection of ET-3 were similar to those evoked by ANP, except for the antidiuresis with increased sodium concentration which followed injection of the 2 higher doses. These results suggest that these 2 higher doses also released vasopressin. Alternatively, activation of the sympathetic nervous system by these higher doses may have decreased glomerular filtration rate and been in part responsible for the antidiuresis. The results with 3V injection of ET-3 contrasted sharply with those obtained following intravenous injection of the 95-pmol dose injected intraventricularly. This intravenous dose of ANP induced a transient decrease in sodium and potassium excretion and urine volume, maximal at 20 min, and had no effect on plasma ANP concentrations at 5 or 20 min after injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Essential role of hypothalamic muscarinic and alpha-adrenergic receptors in atrial natriuretic peptide release induced by blood volume expansion

Expansion of the blood volume induces natriuresis, which tends to return the blood volume to normal. This response is mediated at least in part by the release of atrial natriuretic peptide (ANP) into the circulation. Previous experiments have shown the participation of the anterior ventral third ventricular (AV3V) region of the hypothalamus in the ANP release that follows volume expansion. When injected into the AV3V region, the cholinergic drug carbachol induces natriuresis and the release of ANP. In the present experiments, microinjection of norepinephrine into the AV3V region induced natriuresis and an increase in plasma ANP. To determine whether cholinergic and alpha-adrenergic pathways are crucial to the volume expansion-induced release of ANP, certain receptor-blocking drugs were injected into the AV3V region of conscious rats. Thirty minutes later blood volume was expanded by intravenous injection of 2.0 ml/100 g of body weight of hypertonic saline (0.3 M NaCl). Microinjection of isotonic saline (2 microliters) into AV3V region of control animals 30 min prior to volume expansion had no effect on the 3-fold increase in plasma ANP concentrations measured 5 min after volume expansion. In contrast, although the receptor-blocking drugs did not alter the initial concentrations of plasma ANP 30 min later, just prior to volume expansion, blockade of muscarinic cholinergic receptors by intraventricular injection of 5 nmol (2 microliters) of atropine sulfate or methylatropine markedly reduced the response to volume expansion but did not obliterate it. Microinjection of the alpha receptor blocker phentolamine (5 nmol) into the AV3V 30 min prior to volume expansion also markedly suppressed the ANP response. Intraperitoneal (i.p.) injection of methylatropine (0.01 mmol/100 g of body weight), which does not cross the blood-brain barrier, also did not affect the basal levels of ANP 30 min after i.p. injection. But, in striking contrast with the blockade of the response to volume expansion induced by intraventricular injection of methylatropine, the response to volume expansion was markedly enhanced by i.p. injection of methylatropine. The results therefore indicate that hypothalamic muscarinic and alpha-adrenergic synapses are essential to release of ANP in response to volume expansion. These results are consistent with a hypothetical pathway for physiological control of ANP release which involves distension of baroreceptors within the right atria, carotid and aortic sinuses, and kidney which alters afferent input to brain stem noradrenergic neurons with axons projecting to the AV3V region. There they activate cholinergic interneurons by an alpha 1-adrenergic synapse. The cholinergic neurons in turn stimulate ANP neurons in this brain region via muscarinic receptors. The stimulation of these neurons activates efferent pathways which induce the release of ANP.

Inhibitory role of cholinergic agonists on testosterone secretion by purified rat Leydig cells

The effects of cholinometics on basal or hCG-induced testosterone (T) release by Percoll-purified Leydig cells of the rat were studied. Acetylcholine and carbachol as well as nicotine decreased basal and hCG-induced T secretion. The ganglionic nicotine antagonist hexamethonium promoted a partial reversal of the inhibitory effect of nicotine on basal or hCG-stimulated T secretion. Atropine also reduced the inhibitory effect of carbachol on basal or stimulated androgen release. These data indicate that, in short-term incubations, testosterone released by purified Leydig cells is inhibited by nicotinic and muscarinic cholinergic agonists, thus supporting the hypothesis that parasympathetic autonomic system may be involved in the negative regulation of testicular androgen secretion.

[Traffic accidents in a metropolitan area of southern Brazil--victim and lesion characterization]

Casualties treated in a Emergency Hospital of Porto Alegre, Brazil, during the year 1988, for injuries received as a result of traffic accidents, are described by means of a retrospective study of the data provided by the Documentation and Statistics Sector of the hospital (n = 6.099). The results, similar to those described in the literature, draw special attention to the predominance of the male sex (69.2%), to the concentration of accidents involving individuals of between 20 and 39 years of age, inclusive, (52%) and to the frequency which the head is injured (49.6%) of the patients. Severe injuries such as bruises and fractures were found, respectively, in 61.5% and 24.2% of the patients. The data reveal, further, the large number and the seriousness of the injuries caused by accidents involving pedestrians which accounted for 32.7% of the total number of attendances related to traffic accidents, 57.2% of hospital internments; 54.6% of the victims of this kind of accident were under 9 years of age and 42.8% were over 60.

Morphometric evaluation of the rat testis, epididymis and vas deferens following chemical sympathectomy with guanethidine

Selective chemical sympathectomy of the internal sex organs of adult male rats was undertaken by long term administration of low doses of guanethidine. The spermatogenic activity of the testis was unaffected by treatment. Examination of the vas deferens using morphometric methods revealed a marked increase in luminal area in contrast to a decrease in muscle layer area and in epithelial height. This is morphological evidence of sperm accumulation caused by a disorder in ductal contractile activity. No structural changes were observed in the epididymis. However, the concentration of spermatozoa in the sperm suspension stored in the cauda epididymidis was significantly increased in denervated rats. This result is discussed in terms of a sympathetic control of resorption mechanisms in the epididymis.

Prepubertal development of rat prostate and seminal vesicle following chemical sympathectomy with guanethidine

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.

Carotid-aortic and renal baroreceptors mediate the atrial natriuretic peptide release induced by blood volume expansion

Our previous studies have shown that stimulation of the anteroventral third ventricle (AV3V) region of the brain increases atrial natriuretic peptide (ANP) release, whereas lesions of the AV3V region or median eminence of the tuber cinereum block the release of ANP caused by blood volume expansion. These results suggest that participation of the central nervous system is critical to this response. The role of baroreceptors in the response was evaluated in the current research by studying the response of plasma ANP to blood volume expansion induced by intravenous injection of hypertonic saline solution (0.3 M NaCl, 2 ml/100 g of body weight, over 1 min) in conscious, freely moving male rats. Plasma samples were assayed for ANP by radioimmunoassay. In sham-operated rats, blood volume expansion induced a rapid increase in plasma ANP: the concentration peaked at 5 min and remained elevated at 15 min after saline injection. One week after deafferentation of the carotid-aortic baroreceptors, basal plasma ANP concentrations were highly significantly decreased on comparison with values of sham-operated rats; plasma ANP levels 5 min after blood volume expansion in the deafferented rats were greatly reduced. Unilateral right vagotomy reduced resting levels of plasma ANP but not the response to blood volume expansion; resting concentrations of plasma ANP and responses to expansion were normal in bilaterally vagotomized rats. In rats that had undergone renal deafferentation, resting levels of ANP were normal but the response to blood volume expansion was significantly suppressed. The evidence indicates that afferent impulses via the right vagus nerve may be important under basal conditions, but they are not required for the ANP release induced by blood volume expansion. In contrast, baroreceptor impulses from the carotid-aortic sinus regions and the kidney are important pathways involved in the neuroendocrine control of ANP release. The evidence from these experiments and our previous stimulation and lesion studies indicates that the ANP release in response to volume expansion is mediated by afferent baroreceptor input to the AV3V region, which mediates the increased ANP release via activation of the hypothalamic ANP neuronal system.

Morphometric and biochemical evaluation of rat prostate and seminal vesicle following chemical sympathectomy with guanethidine

Selective chemical sympathectomy of the internal genital organs of adult male rats was undertaken by chronic treatment with low doses of guanethidine. Biochemical and morphometric methods revealed that removal of sympathetic innervation prevents fructose secretion in the prostate and seminal vesicle, in addition to promoting reduced efficiency of delivery by the latter.

Role of the hypothalamus in the control of atrial natriuretic peptide release

Stimulation of the region antero-ventral to the third cerebral ventricle (AV3V) by a cholinergic drug, carbachol, and lesions of the AV3V have been demonstrated in previous studies to either augment or decrease sodium excretion, respectively. Atrial natriuretic peptide (ANP) dramatically increases renal sodium excretion and has been localized to brain areas previously shown to be involved in control of sodium excretion. Consequently, to evaluate a possible role of brain ANP in evoking the changes in renal sodium excretion that follow stimulations or lesions of the AV3V, we determined the effect of injection of carbachol into the AV3V of rats on the concentration of plasma ANP and its content in several neural tissues, the pituitary gland, lungs, and atria. Conversely, the effect of lesions in the AV3V on plasma ANP and the content of the polypeptide in the various organs was determined. Injection of carbachol into the AV3V produced the expected natriuresis, which was accompanied within 20 min by a dramatic rise in the plasma ANP concentration and a rise in ANP content in the medial basal hypothalamus, the neurohypophysis, and particularly the anterior hypophysis but without alterations in the content of ANP in the lungs or the right or left atrium. Conversely, there was a dramatic decline in plasma ANP at both 24 and 120 hr after the AV3V lesions had been placed. This was accompanied by a slight decline in the content of the peptide in the lungs. There was no change in its content in the right atrium at 24 hr after lesions, but there was a significant increase at 120 hr. There was a small decline in the content in the left atrium at 24 hr, followed by a rebound to slightly elevated levels at 120 hr. These small changes contrasted sharply with the dramatic decline in content of the peptide in the medial basal hypothalamus, median eminence, neurohypophysis, choroid plexus, anterior hypophysis, and olfactory bulb. These declines persisted or became greater at 120 hr; except in the olfactory bulb in which the decline was no longer significant. The dramatic increase in plasma ANP after carbachol stimulation of the AV3V that was accompanied by marked elevations in content of the peptide in basal hypothalamus and neuro- and adenohypophysis suggests that the natriuresis resulting from this stimulation is brought about at least in part by release of ANP from the brain. Conversely, the dramatic decline in plasma ANP after AV3V lesions was accompanied by very dramatic declines in content of ANP in these same structures, which suggests that the previously shown decrease in sodium excretion obtained after these lesions may be at least in part due to a decrease in release of ANP from the brain. In view of the much larger quantities of the peptide stored in the atria, it is still possible that changes in atrial release may contribute to the alterations in plasma ANP observed after stimulation or ablation of the AV3V region; however, these results suggest that the dramatic changes in plasma ANP that followed these manipulations may be due to altered release of the peptide from brain structures as well as the atria and lungs.

[Characterization of a chondrocyte primary culture from rib cartilage of the rat]

In order to standardize and to characterize a chondrocyte primary culture, cells from rat rib resting cartilage were used. High yield (0.99 +/- 0.18 x 10(6) cells/rat) and viability (91.76%) of costal cartilage cells was reached by enzymatic digestion with collagenase. The cells were cultivated in Dulbecco's medium (DME) supplemented with 10%. Heat inactivated newborn calf serum, at 37 degrees under humidified atmosphere of 5% CO2 in air. Two or three days after plating, the cells were attached to the surface of tissue culture weel, and began dividing. Adhesion was independent of plating density. The doubling time of cell population was found to be 23.19 hours. The cells became a monolayer and required easy maintenance. The results support the contention that rat costal cartilage is a good source of chondrocytes for primary culture cells experiments.

Influence of age on the production of rat spermatozoa, on their concentration in the cauda epididymidis, and on FSH, LH and testosterone plasma levels

Testis samples were taken from young (3 months), middle-aged (12 months) and aged (24 months) male rats, processed, stained and examined via a light microscope. There were no prominent abnormal germinal epithelium and interstitial tissue. However, the aging process promoted a significant decrease in the mean amount of spermatids 19 per cross tubular section, and in the amount of Sertoli cells per cross tubular section in 24-month-old rats. The concentration of spermatozoa in the cauda epididymidis showed a gradual decrease from 3 to 12 and 24 months. After hCG injection all groups of animals exhibited an increase in plasma testosterone level, although the response was smaller in 12- and 24-month animals compared to the young mature (3 months) ones.