摘要:

Angiotensin II (AII), arginine vasopressin (AVP) and prolactin (PRL) were measured by radioimmunoassay in plasma and cerebrospinal fluid (CSF) in concurrent daily samples from conscious unrestrained steers. Packed cell volume, [Na+] and osmolality were also measured from these samples. Salt appetite was assessed during a 5-min daily session of operant conditioning. Food and water was always available. Unilateral parotid duct fistulation was effected under xylazine analgesia and halothane/Ch anaesthesia. To prevent a sodium deficit developing from loss of [Na+] in the extruded saliva, 0.3 M NaHC03 was available ad libitum so that each animal could ingest sufficiently to balance the salivary loss. A week later epidural cannulae were implanted in the cisternae magna using the same anaesthesia. Three days afterwards when the saliva [Na] was 78 mmol/l, the 0.3-M NaHCO3 supplement was withdrawn for 7 days so that sodium deficiency developed to a degree which evoked salt appetite. When the NaHC03 supplement was restored ad libitum, all aspects of [Na+] deficiency and salt appetite were completely ameliorated within 2–3 days. Packed cell volume increased and body weight decreased (p < 0.05) during depletion, but rapidly returned to normal on day 2 of repletion. Both plasma and CSF osmolality were reduced during depletion as were plasma [Na+] (p < 0.01) and CSF [Na+] (p < 0.001). From a basal value of 64.7 ± 9.35 fmol/ml on day 0, plasma AII increased to 229.2 ± 46.65 fmol/ml (p < 0.001) on day 3, prior to the onset of salt appetite on days 4–7. In marked contrast to plasma AII during sodium depletion, CSF AII was unchanged during salt appetite. There was no correlation between plasma and CSF AII during behavioural salt appetite. The CSF AII suggests slight plasma ‘escape’ via circumventricular organs rather than synthesis in the brain, but is not correlated with salt appetite. The effect of sodium depletion on plasma AVP and plasma PRL was to suppress plasma levels consistent with the homeostatic response arising from sodium deficiency. In cattle the perturbations of endogenous neuropeptides evoked during sodium deficit arise from physiological homeostatic responses and are not directly related to salt

ISSN:0028-3835    

DOI:10.1159/000125014

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

To help elucidate potential sites for the central actions of a new angiotensin-converting enzyme (ACE) inhibitor, perindopril, ACE levels were measured in the brain of Sprague-Dawley rats by quantitative in vitro autoradiography after administration of the drug. Following acute oral administration of 1 mg/kg perindopril, ACE in the two circumventricular organs, the subfornical organ and organum vasculosum of the lamina terminalis, was markedly inhibited and had only partially recovered after 24 h. The ACE inhibition in the circumventricular organs did not correlate with the inhibition of ACE in plasma but with that of pressor response to intravenous angiotensin I. No or little change in ACE was observed in other brain structures which are rich in the enzyme, including the choroid plexus and basal ganglia. However, large doses of perindopril (up to 16 mg/kg) did progressively inhibit ACE in all brain structures measured, including the basal ganglia. These findings fit with the deficient blood-brain barrier known to occur in the circumventricular organs. These regions are rich in ACE and angiotensin II receptors and exhibit physiological responses to angiotensin II with effects on fluid, electrolyte, and blood pressure homeostasis. Combined with current observations, the circumventricular organs are potential targets for the centrally mediated actions of ACE inhibitors.

ISSN:0028-3835    

DOI:10.1159/000125015

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The purpose of this study was to compare the response of Syrian hamster pineal glands in organ culture either to isoproterenol, a β-adrenergic agonist, or to dibutyryl cyclic AMP. When pineal glands were collected at night, hamsters were exposed to light for 30 min to depress pineal N-acetyltransferase (NAT) activity and melatonin values to low levels. Pineal glands were removed and placed in organ culture containing either isoproterenol or dibutyryl cyclic AMP and subsequent changes in NAT activity and melatonin levels were measured. At night, isoproterenol (10–7 or 10–6M) induced an increase in the NAT activity and melatonin levels in both pineals and culture media. However, dibutyryl cyclic AMP was either ineffective or minimally effective in stimulating these parameters at either different incubation times (2,4, and 6 h) or drug concentrations (0.1, 0.5, and 1.0 mM). Conversely, when rat pineal glands were incubated with either isoproterenol (10–7) or dibutyryl cyclic AMP (0.5 mM) dramatic rises in NAT activity and melatonin levels were observed. In another experiment, hamster pineal glands were collected from animals killed either late in the light period (19.00 h) or in the latter half of the dark period. Isoproterenol promoted NAT activity and melatonin production only in glands collected in the latter half of the dark

ISSN:0028-3835    

DOI:10.1159/000125016

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The effect of in vivo corticosterone manipulation on binding sites for the excitatory neurotransmitter glutamate was determined using radioligand binding to rat brain cryostat sections and crude synaptic membranes. 3H-glutamate binding to regions of the dorsal hippocampal formation was significantly decreased in adrenalectomized animals following 5–10 days of corticosterone treatment. Corticosterone did not alter 3H-glutamate binding in several other brain regions. The loss in 3H-glutamate binding appeared to be due to a decrease in the maximal number of binding sites, with little change in binding affinity. Both chloride-dependent and chloride-independent 3H-glutamate binding sites were decreased by corticosterone treatment. Results indicate that corticosterone can selectively alter binding sites for excitatory amino acids in hippocampal tissu

ISSN:0028-3835    

DOI:10.1159/000125017

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Hypophyseal and ovarian receptors for the neurohormone LHRH (LHRH-R) have been measured in young (3–4 months), middle-aged (8–11 months), constant estrous (CE, 10–14 months) and pseudopregnant (PR, 16–18 months) rats in order to study whether changes in hypothalamic and/or peripheral LHRH-like peptide production might precede and/or accompany the onset of reproductive failure observed in aging rats. Furthermore, we have investigated whether the neural efferent system from the brain to the ovary is affected with aging. The pattern of pituitary LHRH-R modifications during the estrous cycle of middle-aged rats shows lower LHRH-R levels on the second day of diestrus, resulting in a shift of the maximal LHRH binding capacity in the morning of proestrus. On the other hand, when comparing pituitary LHRH-R of animals exhibiting constant vaginal cornification (CVC) or repetitive PP with young estrus rats, no significant difference could be observed. Young rats responded to electrical stimulation (ES) of the medial preoptic area with an acute elevation of LHRH-R while ES performed in CVC, or PP animals resulted in a significant increase of hypophyseal LHRH binding capacity similar to the one observed in young estrous controls, indicating an impairment in the neural signals impinging in the pulse generating system, in old rats, and not an intrinsic defect of the LHRH-R per se. Ovarian LHRH-R concentration is higher in middle-aged cycling animals on the day of vaginal proestrus, compared to levels measured in young animals at any phase of the estrous cycle. Similarly, CE rats displaying CVC as well as PP animals show significantly higher numbers of LHRH-R with no change in affinity, than young estrus rats. CVC and PP rats receiving unilaterally an intraovarian injection of the potent LHRH antagonist, Ac-D-Cl-Phe1,2, D-Trp3, D-Phe6, D-Ala10, LHRH, showed an acute drop of LHRH-R measured within the treated ovary with no significant changes taking place in the vehicle-treated contralateral gland, suggesting that changes of endogenous ovarian LHRH-like peptide might participate in the mechanism(s) responsible for LHRH receptor increase observed in aging rats. In order to investigate the participation of a direct neural efferent pathway in ovarian LHRH-R regulation, young and old rats were subjected to spinal cord transection (above T10–T11). Bilateral transection of the spinal cord in young animals in the morning of proestrous markedly increased ovarian LHRH-R concentration in the afternoon (17.00 h) of the same day. When spinalectomy was performed unilaterally, a marked increase of ovarian LHRH-R capacity in the gonad ipsilateral to the intervention was measured, with no effect taking place in the contralateral gland. On the other hand, the same intervention did not modify the already stimulated LHRH-R levels measured in old rats. It is suggested that an increase of ovarian LHRH-R activity might trigger the neuroendocrine mechanisms leading to reproductive dysfunction in aging female rats. Furthermore, present data also suggest that the establishment of a central defect in aging animals might directly interfere with ovarian function, by means of a neural signal, modulating ovarian LHRH-R activity, which further reinforces our view that the brain and the gonads can directly communicate via a neura

ISSN:0028-3835    

DOI:10.1159/000125018

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

In an attempt to identify a physiological prolactin-releasing factor in the sheep, ovariectomized ewes were given intracarotid injections (10–8–10–7 mol/animal) of thyrotropin-releasing hormone (TRH), vasoactive intestinal polypeptide (VIP), peptide histidine-isoleucine amide (PHI), oxytocin (OT), arginine vasopressin (AVP), substance P (SP), bombesin (BB), neurotensin (NT) and neuropeptide Y (NPY). Administration of TRH, AVP, NT and OT resulted in immediate and significant increases in plasma prolactin concentrations, the greatest stimulatory effect being obtained after TRH; other peptides had no effect in ovariectomized hypothalamo-pituitary intact ewes. AVP, NT and OT failed to release prolactin in ovariectomized ewes that had been subjected to hypothalamo-pituitary disconnection (HPD). Injection of TRH (3 × 10–9–3 × 10–7 mol/animal) resulted in a significant dose-dependent increase in plasma prolactin concentrations in ovariectomized HPD ewes. These results suggest that (1) AVP, NT and OT may act via the hypothalamus to regulate prolactin secretion in hypothalamo-pituitary intact ewes; (2) VIP, PHI, SP, BB and NPY appear to have no direct roles at the pituitary level to control prolactin secretion in sheep, and (3) TRH stimulates prolactin secretion in ovariectomized ewes by a direct pit

ISSN:0028-3835    

DOI:10.1159/000125019

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

To investigate whether somatostatin systems plays a significant role in the regulation of the hypothalamic-pituitary-adrenal axis, the effects of cysteamine, a drug which reduces somatostatin levels, on the dexamethasone-induced suppression of plasma corticosterone levels were examined in the rat. Male Long Evans rats were handled daily for 1 week prior to receiving a standard dexamethasone suppression test. On the 1st day, rats received a 9.00 a.m. saline injection and blood samples were taken from the tail at 1.00 p.m. On the 2nd day, rats received dexamethasone or saline at 9.00 a.m. and a second blood sample was taken at 1.00 p.m. Experimental groups were pretreated with systemic injections of cysteamine, 5 min or 14 h, prior to receiving dexamethasone. Additional groups, previously implanted with guide cannulae, were given an infusion of cysteamine or saline into the lateral ventricle 14 h prior to dexamethasone. Circulating corticosterone levels were determined by radioimmunoassay. Rats were sacrificed immediately following each experiment and the hypothalamus dissected and assayed for levels of somatostatin immunoreactivity. The results of the first experiment showed that dexamethasone (10 µg/kg) alone reduced plasma corticosterone levels from control values (174 + 36 ng/ml) to undetectable levels ( < 25 ng/ml). Pretreatment with cysteamine 5 min prior to dexamethasone, while having no significant effect on basal corticosterone levels, completely blocked the dexamethasone-induced suppression of corticosterone levels. Similar observations were obtained with rats pretreated with cysteamine 14 h prior to dexamethasone. In contrast, intracerebroventricular cysteamine pretreatment did not block the dexamethasone-induced suppression of corticosterone levels. These results add further evidence in support of an involvement of somatostatin systems in the regulation of the hypothalamic-pituitary-adrenal axis

ISSN:0028-3835    

DOI:10.1159/000125020

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The 24-hour pattern of melatonin secretion was determined in 5 Suffolk ewes during extended exposure to a long day length to assess whether the eventual loss of response (photorefractoriness) to inhibitory long days resulted from an alteration in the circadian secretion of melatonin. Determinations of the secretory profile of melatonin were made once in short days (8 h light/day) before the switch to long days, and 11 times throughout the 250-day period of exposure to long days (16 h light/day). Samples were obtained hourly for 24 or 48 h. Reproductive state was assessed by response to estradiol-negative feedback, monitored as serum LH in ovariectomized ewes bearing estradiol implants. The characteristic secretory pattern of melatonin (low during the day, high at night), the duration of the melatonin elevation, and its phase relative to the light/dark cycle did not change as ewes became refractory to the inhibitory effects of long days. These results are consonant with the hypothesis that refractoriness of the ewe to inhibitory day length does not result from an alteration of the circadian rhythm of melatonin secretion.

ISSN:0028-3835    

DOI:10.1159/000125021

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The effects of 2 days of water deprivation on local rates of methionine incorporation into protein in 54 brain and 5 circumventricular structures of conscious freely moving rats have been examined by means of a recently developed quantitative autoradiographic method with L-[35S]-methionine. The results show that 2 days of water deprivation does not affect methionine metabolism in the majority of the brain areas analyzed, but reveals selective increases in the hypothalamoneurohypophyseal system, in cerebral structures surrounding the third ventricle, in the locus ceruleus, raphe dorsalis, nucleus ambiguus and hippocampal CA3 layer. In contrast, decreases were observed in the central amygdala, lateral habenula and interpeduncular nucleus. Although the highest increases were located in brain areas involved in body fluid homeostasis, several aspecific responses, perhaps due to chronic stress, were also observed, notably in the locus ceruleus, raphe dorsalis and in a restricted number of limbic system structures.

ISSN:0028-3835    

DOI:10.1159/000125022

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Djungarian hamsters (Phodopus sungorus) kept under a long-day photoperiod (16 h light :8 h dark) were injected with melatonin each day. Hamsters which responded physiologically to this treatment (gonadal regression, molt, body weight loss) phase-advanced onset and extended duration of activity. Hamsters which were physiologically insensitive to melatonin injections did not exhibit such changes in activity pattern and often failed to entrain to the light :dark cycle. Hamsters given saline injections did not alter activity or exhibit gonadal regression, weight loss and molt to the winter pelt. Melatonin-sensitive hamsters compressed duration of activity when they became physiologically refractory to the melatonin treatment (weeks 27–29). At the same time, melatonin-insensitive hamsters became entrained to the light :dark cycle. Thus, daily melatonin injections induce short-day-like adjustments in activity under a long-day photoperiod. These changes in activity are correlated with melatonin-induced gonadal regression, weight loss and mol

ISSN:0028-3835    

DOI:10.1159/000125023

出版商:S. Karger AG    

年代:1988

数据来源: Karger