摘要:

Circadian rhythm of blood corticosterone in adrenalectomized rats with (AT rat) or without adrenal auto-transplants was investigated. Blood samples were obtained individually at 4-hour intervals for a 24-hour period per week for 5–7 consecutive weeks by the tail tip incision method. Corticosterone responses of the autotransplanted adrenal gland to ACTH gradually increased with time after the implantation, and by 5 weeks had attained a level comparable to that of intact rats. Concurrently with this change, circadian adrenocortical rhythms in AT rats became evident and they were able to respond to a reversed photoperiodic environment. The effects of constant illumination or food restriction on the corticosterone rhythm in AT rats were indistinguishable from those in intact rats in every respect. A sharp drop and disappearance of circadian periodicity were observed in the blood corticosterone levels by removal of autotransplanted adrenals. In some of the adrenalectomized rats, the daily rhythm of the blood corticosterone levels reappeared 5–7 weeks after surgery owing to the hypertrophy of accessory adrenal glands or regeneration from capsular fragment left in situ. These results suggest that neural input to the adrenal is not essential for the occurrence of circadian adrenocortical rhyt

ISSN:0028-3835    

DOI:10.1159/000123294

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

35 male Sprague-Dawley rats, 18 months old, were injected subcutaneously with the catecholamine precursor, L-dihydroxyphenylalanine (L-dopa) (100 mg/kg, twice daily), or vehicle alone, for 8 days in an attempt to increase the amplitude of growth hormone (GH) pulses in old male rats. 40% of young rats had at least one GH pulse greater than 600 ng/ml, over a 6.5 h sampling period, whereas only 22% of old vehicle-treated rats had pulses of similar amplitude. Treatment of old rats with L-dopa increased the number of animals showing elevated GH pulses to 53%. Young animals had mean GH concentrations of 136.5 ± 14.0 ng/ml over the 6.5 h sampling period, whereas vehicle-treated old animals had mean GH levels of 95.2 ± 7.7 ng/ml (p < 0.05). Treatment of old animals with L-dopa increased mean plasma GH concentrations to 132.9 ± 11.2 ng/ml (p < 0.05) which was not significantly different from GH values in young rats. Pituitary GH concentration was less in old than in young rats (301 ± 27.4 vs. 370 ± 17.4 µg/mg protein, p < 0.05). L-Dopa increased pituitary GH concentrations in old rats to 318 ± 32.2 µg/mg protein, which was not significantly different from that in either young or old vehicle-treated animals. Hypothalamic somatostatin content in both rostral and caudal areas was lower in old than in young rats (p < 0.01), and L-dopa had no significant effect on somatostatin content. These data indicate that L-dopa can increase the amplitude of GH pulses and elevate mean plasma GH in old male rats to levels present in young male rats, probably by increasing hypothalamic catecho

ISSN:0028-3835    

DOI:10.1159/000123295

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

Previous studies have shown that neonatal administration of monosodium glutamate (MSG) results in a clearly defined lesion of the arcuate nucleus which disrupts mechanisms regulating normal FSH but not LH secretion in the adult female hamster. The present study was designed to investigate the effects of neonatally administered MSG or hypertonic saline (control) on the in vivo and in vitro responses to LHRH in adult animals. In order to evaluate these responses under a comparable hormonal background, all animals were ovariectomized at 2–3 months of age and given 50 µg of estradiol benzoate 3 weeks later. 24 h later, animals were anesthetized with sodium pentobarbital and a blood sample taken for baseline levels of gonadotropins; they were immediately given 5 or 25 ng LHRH intravenously, and LH and FSH responses to LHRH were determined by sampling at 15-min intervals over a 1-hour period. Pituitary content of LH and FSH was determined in a similar group of control and MSG-treated animals which did not receive the hypothalamic hormone. Basal LH secretion, the dose-response of LH to LHRH, and the pituitary concentration or content were similar in control and MSG-treated hamsters. In contrast to LH, basal FSH levels were significantly lower, the FSH responses to LHRHwere greatly attenuated, and a dose response to LHRH was absent in MSG-treated animals when compared to control values. Pituitary FSH concentration and content did not differ between control and MSG-treated animals. However, when pituitaries were removed, hemidissected, preincubated for 1 h, and incubated in the presence or absence of 8.5 × 10-9 or 8.5 × 10-10 M LHRHfor 3 consecutive 1-hour periods, no differences were noted between control and experimental animals regarding basal (no LHRH) or LHRH-stimulated release of LH and FSH. These results suggest that the decreased basal FSH levels and the attenuated FSH response to LHRH observed in vivo in MSG-treated animals may be due to an alteration in a neural or extraneural component which is involved in regulating the release of FSH by LHRH and which is evident in the absence of a functional arcuate nucleus and/or develops directly as the result of the neonatal administration of

ISSN:0028-3835    

DOI:10.1159/000123296

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

This paper shows for the first time that the dopamine present in the neural and intermediate lobe () of the pituitary gland can be released in vitro by depolarization of the tissue with increased [K+]. The release is Ca++ dependent. This observation is in accordance with the concept that dopamine has a function as a neural transmitter substance in the . At a [Ca++] of 2.5 mM it was also possible to measure the norepinephrine release from the . The dopamine release from the was unaffected by GABA. In contrast, the release of dopamine (but not of norepinephrine) from the medial-basal hypothalamus was enhanced by GABA.

ISSN:0028-3835    

DOI:10.1159/000123297

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

The lysosomotropic agent, chloroquine, has been used to investigate the implication of lysosomal activity and membrane traffic in TRH binding, TRH internalization and TRH-induced stimulation of prolactin secretion in a rat prolactin cell line (GH3/B6). Chloroquine by itself does not affect cell number, cell protein and basal prolactin secretion. It does not alter TRH binding and internalization as well as both effects of TRH on the stimulation of prolactin secretion, i.e., prolactin release and prolactin production. In contrast, chloroquine partially inhibits the spontaneous dissociation of (3H)TRH from cells previously loaded with (3H)TRH and reduces prolactin release following TRH withdrawal. In addition the kinetic pattern of the TRH dissociation is modified in a manner which suggests that TRH is bound to different intracellular compartments. Chloroquine, nevertheless, does not alter the TRH-induced down regulation of (3H)TRH binding sites. Electron microscopic observations and acid phosphatases localization reveal that chloroquine elicits a disorganization of the Golgi zone and accumulation of membrane whorls within large vacuoles. This suggests that the effects of chloroquine on TRH interaction with GH3 cells may be mediated by an inhibition of membrane recycling.

ISSN:0028-3835    

DOI:10.1159/000123298

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

Circadian rhythms occur in hypothalamic serotonin content in the turkey. Inhibition of serotonin (5-HT) synthesis by parachlorophenylalanine (PCPA) blocks circadian variation in hypothalamic serotonin levels suggesting that the major cause of diurnal fluctuations is differing rates of synthesis of the amine. PCPA treatment also abolishes the diurnal rhythm in plasma corticosterone and elevates the basal levels of this steroid suggesting that 5-HT terminals in the hypothalamus may inhibit the release of ACTH at certain times of the day and in this fashion generate diurnal fluctuations in plasma corticosterone. Hypothalamic levels of dopamine (DA) and norepinephrine (NE) also vary diurnally, and synthesis inhibition with alpha-methyl-para-tyrosine abolishes the diurnal rhythm in NE but not DA or in plasma corticosterone. Temporal changes in release and/or degradation of DA are significant factors contributing to the diurnal rhythms of this amine in the hypothalamus. Diurnal fluctuations in plasma corticosterone do not depend on recent synthesis of catecholamines.

ISSN:0028-3835    

DOI:10.1159/000123299

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

Endogenous gonadoliberin was localized by using immunocytological methods in the hypothalamic neurons which synthetize the peptide and in the hypophysial target cells. The rat tissues were fixed and frozen. Ultrathin sections were obtained by cryoultramicrotomy. In the pituitary gland, GnRH was observed in both gonadotropic and prolactin cells. In these cells, endogenous GnRH was observed in the secretory granules, in the cytoplasm and in the nucleus. After castration an increase of immunoreactive GnRH was observed; after injection of a potent agonist (D-Trp6-Pro9-Net-LRF) or an antagonist (D-pGlu1, D-Phe2, Trp3,6 LRF) endogenous GnRH staining was decreased. These data suggest that endogenous GnRH could be bound to a site having a high affinity for GnRH.

ISSN:0028-3835    

DOI:10.1159/000123300

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

This study examined the alterations in episodic luteinizing hormone (LH) release in response to third ventricle infusions of various α- and β-adrenoceptor agonists in ovariectomized (OVX) rats as well as the effects of steroid priming with 50 µg estradiol benzoate (EB) and 25 mg progesterone (P) on the LH responses to these agonists. Unanesthetized rats with indwelling atrial cannulae were bled at 10-min intervals for 0.5–1.5 h prior to infusion and up to 1.5 h following infusion of equimolar amounts (0.06 or 0.3 µmol in 2 µl saline adjusted to pH 5.5 and infused slowly over a 2-min period) of norepinephrine (NE), phenylephrine (Phen, α1-agonist), isoproterenol (Iso, β-agonist) or clonidine (Clon, α2 Iso. However, in OVX-EBP-primed rats, while 0.06 µmol NE significantly stimulated LH release, none of the other adrenoceptor agonists administered at this dosage was effective in altering the low nonpulsatile levels of blood LH characteristic of the steroid-primed animal. Nevertheless, at a concentration 5 times higher (0.3 µmol) Clon and Phen did induce LH surges while Iso, even at this higher dose, was not stimulatory to LH release. These results suggest that the inhibitory action of NE on LH secretion in OVX rats may be exerted via activation of both α- and β-adrenoceptors, whereas primarily α-adrenoceptors are responsible for mediating the NE-induced stimulation of LH release in OVX

ISSN:0028-3835    

DOI:10.1159/000123301

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

In the anesthetized dog, intravenous infusion of 2.5 M saline (40 µl/kg·min) increased plasma and cerebrospinal fluid (CSF) osmolality and the plasma vasopressin (ADH) concentration, but did not increase the CSF ADH concentration. The increase in the plasma ADH concentration coincided with the increase in plasma osmolality, but preceded the increase in CSF osmolality. Intracerebroventricular infusion of hypertonic artificial CSF (2,000 mosm/kg·H2O, 10 µl/min) increased CSF osmolality and plasma and CSF ADH concentrations; plasma osmolality did not increase. Thus, receptors which sense changes in plasma osmolality appear to be outside the blood-brain barrier; different receptors may sense changes in CSF osmolal

ISSN:0028-3835    

DOI:10.1159/000123302

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

This study was conducted to examine the role of the hypothalamus in development of gonadotrophs, thyrotrophs, and mammotrophs up to the time of birth in the rat. The development of the in situ newborn pituitary (22 days post-coitus; dpc) was compared with the development of 12 and 15 dpc pituitary anlagen grown under the kidney capsule of an adult host or in organ culture for a time period equivalent to 22 days of gestation. Morphological development was evaluated by light microscopic histology and gonadotrophin immunocytochemistry. Functional development was analyzed by radioimmunoassay determination of luteinizing hormone, thyrotrophin, and prolactin content of the in situ, kidney capsule grafted, and organ-cultured pituitary. The results provide evidence that factors, perhaps blood-borne, play a significant role in pituitary development but that direct hypothalamic influences are of minimal importance in the development of gonadotrophs and mammotrophs. The fetal hypothalamus may play a significant role in stimulating high storage levels of thyrotrophin in the prenatal pituitary.

ISSN:0028-3835    

DOI:10.1159/000123303

出版商:S. Karger AG    

年代:1982

数据来源: Karger