摘要:

Ovariectomised rats were treated with either oestradiol benzoate (OB) alone or OB followed by progesterone (P). The effects of the steroid treatments were noted on plasma LH concentration, lordosis quotient and concentration of 5-hydroxytryptamine (5HT) and 5-hydroxyindole acetic acid (5HIAA) in microdissected hypothalamic areas, i.e. the preoptic area (POA), arcuate nucleus (ARC), median eminence (ME), ventromedial nucleus (VMN), suprachiasmatic nucleus (SCN) and zona incerta (ZI). The ratio of 5HIAA:5HT or parallel changes in the concentrations of 5HT and 5HIAA were taken as indices of 5HT neuronal activity. 5 µg OB alone reduced LH release and had no effect on receptivity. This treatment reduced 5HT activity in the SCN and raised it in the ZI. After 5 µg OB plus 0.5 mg P, all the rats exhibited an LH surge and full sexual receptivity. 5HT activity was significantly raised in the ME and reduced in the ARC, VMN and ZI. By using submaximal steroid regimes (2 µg OB plus 0.05 mg P, or 50 µg OB alone) correlations could be made between sexual behaviour, LH release and 5HT activity. There was no correlation between LH release and receptivity indicating that the two functions are controlled by different systems. Correlating 5HT activity in the various sites with the two physiological parameters indicated whether the changes seen after the maximal steroid treatment were concerned with behaviour, LH release or both. The results indicate that the changes seen in the VMN, ARC and ME are correlated with sex behaviour and those in the VMN and ZI with increased LH release. Oestrogen appears to stimulate behaviour by reducing 5HT activity in the ARC and P by reducing 5HT activity in the VMN and increasing it in the ME. Oestrogen seems to exert its feedback effects on LH by altering a stimulatory 5HT system in the SCN and an inhibitory one in the ZI. P stimulates LH release by reducing 5HT in the VMN and the

ISSN:0028-3835    

DOI:10.1159/000125169

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Radioreceptor assays with (-) [125I]-iodopindolol (IPIN) were used to describe circadian variations of β-adrenoceptors in the pineal gland of male Syrian hamsters (Mesocricetus auratus). Single-point experiments (200 pM IPIN, 8–9 pineals pooled per time point) showed a significant circadian variation (p < 0.01) with maximal values (28.9 ± 1.8 fmol/mg protein, x ± SEM, n = 7) between 07:00 and 02:30 h, and minimal values at 04:00 (7.2 ± 2.9 fmol/mg protein, n = 3), 8 h after darkness onset. Either exposure of animals to light at night or treating dark exposed hamsters with a β-adrenergic receptor blocker, propranolol, prevented the nocturnal drop in the number of β-adrenoceptors. Scatchard analysis of saturation isotherms at 02:30, 04:00 and 08:00 h (30–600 pM IPIN, one saturation experiment with 25 pineals pooled per time point) confirmed the circadian

ISSN:0028-3835    

DOI:10.1159/000125170

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Recent findings suggest that vasoactive intestinal peptide (VIP) may be a physiological regulator of prolactin secretion and may also be involved in the control of LH secretion. In the present work we have studied the effect of the blockade of endogenous VIP by means of the injection of a specific rabbit anti-VIP serum, in male and female rats with hyperprolactinemia. The administration of 0.5 ml of the VIP antiserum in ovariectomized rats given an acute or chronic treatment with 17β-estradiol induced a significant decrease in serum prolactin and LH levels as compared with estrogenized-control rats injected with normal rabbit serum. Anti-VIP serum also reduced serum LH levels in ovariectomized rats not treated with estrogens. The administration of the same antiserum decreased serum prolactin levels in male rats implanted with 2 anterior pituitary glands under the kidney capsule. On the other hand, the injection of the anti-VIP serum in the morning in proestrus rats brought about an increase in serum prolactin and LH levels in the afternoon of the same day. These results confirm previous data showing that VIP is a stimulator of prolactin release, and may also participate in the control of LH secretion in ovariectomized rats acting as a facilitatory factor. During proestrus however, VIP may act in an opposite way, inhibiting, rather than stimulating, prolactin and LH release

ISSN:0028-3835    

DOI:10.1159/000125171

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The effect of chronic hyperprolactinemia was studied on (a) GABA concentration in the pituitary anterior lobe; (b) GABA biosynthesis enzyme, glutamate decarboxylase (GAD) activity in the hypothalamic median eminence, and (c) GABA degradation enzyme GABA-transaminase (GABA-T) activity at both levels. In male rats bearing the prolactin-secreting tumor MtTF4 for 1 month or treated for 5 days with estradiol benzoate, the plasma prolactin concentration was markedly increased (between 4- and 10-fold basal values). In both cases, GABA concentration was significantly increased (40–60%) in the anterior pituitary lobe. A slight reduction (20–30%) in GABA-T activity was observed in the anterior lobe while no change in GAD or GABA-T activity was measured in the median eminence. These results are discussed in relationship to a possible feedback input of prolactin on the tuberoinfundibular GABAergic sys

ISSN:0028-3835    

DOI:10.1159/000125172

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Digitalis-like factor (DLF) appears to be widely distributed throughout the body, and has been specifically localized to the mammalian hypothalamus. In this study we monitored the DLF response to insulin-induced hypoglycemia in 11 normal males. Hypoglycemia was associated with a significant increase in serum DLF activity over basal values (40 ± 5 pg digoxin Eq/ml, mean ± SEM) at 60 min (83 ± 8 pg digoxin Eq/ml) and 90 min (86 ± 10 pg digoxin Eq/ml) following insulin administration (p < 0.01). We measured the DLF response to insulin-induced hypoglycemia in other men after infusion of hypertonic saline (n = 8) or after oral water-loading (n = 8). Saline infusion (0.06 ml 5% saline/kg BW/min for 120 min prior to insulin infusion) or water loading (20 ml/kg BW over 60 min completed 30 min before insulin infusion) alone significantly increased serum DLF (saline: 21 ± 5 to 60 ± 18 pg digoxin Eq/ml, p < 0.05; water: 18 ± 11 to 49 ± 15 digoxin Eq/ml, p < 0.05). DLF activity was further significantly increased within each group 60 and 90 min after administration of insulin. In the group infused with hypertonic saline, insulin caused increases of serum DLF from 60 ± 18 at time 0 to 170 ± 17 pg digoxin Eq/ml at peak (p < 0.01). Similarly, in the oral water-loaded group serum DLF increased from 49 ± 15 at time 0 to 127 ± 24 pg digoxin Eq/ml at peak (p < 0.01) after they received insulin. These results suggest that DLF may be involved in the acute stress response to insulin-induced hypoglycemia, and this response may be augmented by salt or fl

ISSN:0028-3835    

DOI:10.1159/000125173

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Effect of estradiol on the spontaneous and thyrotropin-releasing hormone (TRH)-stimulated release of prolactin (PRL) and thyrotropin (TSH) in young and aged ovariectomized (Ovx) rats was investigated. Old (22–26 months) and young (3 months) female rats were Ovx 3 weeks before use. They were injected subcutaneously with estradiol benzoate (EB, 25 µg/kg) or sesame oil for 3 days and were catheterized via the right jugular vein. Twenty hours after the last administration of EB, rats were injected with TRH (10 µg/kg) through the catheter. Blood samples were collected before and 5, 10, 20, 40 and 60 min after TRH injection. On the day following blood sampling, all rats were decapitated. The anterior pituitary glands (APs) were excised, and incubated with or without TRH (10 ng/ml) at 37 ° C for 30 min. The basal level of PRL concentration in plasma samples was 5-fold higher in old Ovx rats than in young Ovx rats. Five min after TRH injection, the increase in plasma PRL was greater in old animals than in young animals. Plasma PRL remained higher in old animals than in young animals at 10, 20, 40 and 60 min following TRH challenge. Administration of EB to old and to young Ovx rats produced increases in both basal and TRH-stimulated secretions of PRL, but did not affect the difference in plasma PRL patterns between old and young animals. The release of PRL from APs was increased significantly in all rats after a 30-min incubation with TRH. In Ovx rats injected with oil, the basal release of PRL in vitro was increased with age. The TRH-stimulated release of PRL from APs of oil- and EB-primed rats was also higher in aged rats than in the corresponding young rats. The concentration of plasma TSH in response to TRH was less in old rats than in young rats. Estradiol seemed to have no effect on the secretion of TSH in vivo. Neither aging nor EB injection appeared to alter the spontaneous release of TSH in vitro. However, the release of TSH from APs in vitro in response to TRH was significantly reduced by age. These results suggest that the increased capability of the basal and TRH-stimulated secretion of PRL as well as the decreased capability of the secretion of TSH in response to TRH in old rats was due at least in part to intrinsic changes in anterior pituitary function, including the discordant patterns of lactotrophs and thyrotrophs responding to TRH during the aging pro

ISSN:0028-3835    

DOI:10.1159/000125174

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Vasoactive intestinal peptide (VIP) is a neuropeptide that is present in the hypothalamus and is probably a neuroen-docrine regulator. The effect of VIP on pulsatile LH secretion in the long-term ovariectomized rat was re-examined in the light of earlier conflicting reports. VIP or saline was infused into the third ventricle at the rat of 15 µl/h and blood was sampled frequently before and during the infusion. VIP at 3.5 nmol/h significantly depressed mean LH levels (p < 0.05) and lowered pulse frequency (p 0.05). We conclude that dopamine is not a likely mediator of the action of

ISSN:0028-3835    

DOI:10.1159/000125175

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The activity of tuberoinfundibular dopamine neurons, as estimated from the amount of dihydroxyphenylalanine (DOPA) formed in the median eminence after the inhibition of DOPA decarboxylase and the concentration of dihydroxyphenyl-acetic acid (DOPAC) in this brain region, was significantly increased 1–8 h following the intracerebroventricular (i.c.v.) administration of neurotensin (20 µg). Neurotensin (5 and 20 µg i.c.v.) also significantly increased DOPAC concentrations in the n. accumbens but had no effect in the striatum. Serum concentrations of corticosterone in rats treated with neurotensin (1–20 µg i.c.v.) were 5–7 times those in vehicle-treated animals. [D-Trp11]-neurotensin (0.5 µg i.v.c.) also significantly increased DOPAC concentrations in the median eminence and serum corticosterone concentrations. It is concluded that neurotensin acutely increases the activity of tuberoinfundibular and mesolimbic dopamine neurons and the secretio

ISSN:0028-3835    

DOI:10.1159/000125176

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Rats bearing kidney grafts of the pituitary pars intermedia were divided into three groups: unstressed, acutely stressed, and chronically stressed. Corresponding sham-operated rats were used for comparisons. Twenty days after grafting, the rats were sacrificed and α-melanocyte-stimulating hormone (α-MSH), adrenocorticotropin (ACTH), and corticosterone were estimated in plasma. The adrenal/body weight ratio and DNA content of the glands were also investigated. The following results were obtained: MSH was found not to be increased in unstressed rats, but it was in grafted animals subjected to acute and chronic swimming stress. ACTH and corticosterone rose in all three groups. Adrenal/body weight ratio and DNA content increased only in grafted chronically stressed rats. Moreover, plasma corticosterone was found higher in grafted hypophysectomized rats than in non-grafted hypophysectomized animals. Administration of ergocryptine to nonstressed grafted rats induced a decrease in the blood content of ACTH and MSH, indicating that the grafts were the source of a part of the circulating ACTH. On the other hand, the fall in MSH levels could show the effect of the drug upon the pars intermedia. Comparison of the ratios of both hormones released in incubations showed that grafts secreted more ACTH than MSH; on the other hand, when intact neurointermediate lobes were incubated, MSH predominated over ACTH. For the first time it is demonstrated that the pars intermedia can secrete ACTH in vivo. Nevertheless, the ability to secrete this hormone is not a property of normal intact pars intermedia, but it manifests in the transplantations probably due to the overactivity of light cells induced by chronic stoppage of dopaminergic inhibitio

ISSN:0028-3835    

DOI:10.1159/000125177

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

We studied the actions of arachidonic acid (AA) on luteinizing hormone (LH) release versus synthesis (translation or glycosylation) by cultured rat anterior pituitary cells. Monolayer cells were incubated for 3–4 h with secretagogues (AA, melittin, gonadotropin-releasing hormone; GnRH) which either increase endogenous AA levels or release AA. LH translation and glycosylation were monitored by measuring the incorporation of [14C]alanine and [3H]glucosamine, respectively, into total (cell plus medium) immunoprecipitable LH. Immunoreactive (IR) LH was measured by radioimmunoassay. Nonlytic doses of AA increased (p < 0.01) IR-LH release without increasing total [3H]glucosamine-LH, [14C]alanine-LH, or [3H]gIucosamine-protein. AA either had no effect or slightly increased (p < 0.05) [3H]glucosamine uptake, but decreased (p < 0.01) [14C]alanine uptake and incorporation into total [l4C]alanine protein. AA at 250 µM lysed cells, thus increasing medium IR-LH and decreasing (p < 0.01 [3H]glucosamine and [l4C]alanine uptake and incorporation into total LH and protein. Melittin, which releases AA by activating phospholipase A2 (245 and 490 nM), increased medium IR-LH (p . < 0.0l) without affecting any other parameter measured. GnRH at 1 nM enhanced (p < 0.01) both LH (IR-LH, [3H]glucosamine-LH and [14C]alanine-LH) release and total [3H]glucosamine-LH, but had no effect on total [14C]alanine-LH. In summary, AA and melittin at doses which stimulated LH release did not stimulate either LH glycosylation or translation. This suggests that increased LH release by nonspecific secretagogues is not necessarily accompanied by increased LH glycosylation or translati

ISSN:0028-3835    

DOI:10.1159/000125178

出版商:S. Karger AG    

年代:1989

数据来源: Karger