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ABSTRACT
Previous studies using the isolated rat hypothalamus in vitro have shown that both acetylcholine and 5-hydroxytryptamine (5-HT) stimulate the secretion of bioactive corticotrophin-releasing factor (CRF). However, the CRF complex consists of a number of bioactive substances, and in this study we examined the effect of acetylcholine and 5-HT on the release of immunoreactive (ir)-CRF-41 and ir-arginine vasopressin (AVP) in vitro. Acetylcholine caused a dose-dependent (10 pmol–10 nmol/l) release of both neuropeptides, and the effect was partially antagonized by both atropine and hexamethonium. Nicotine (0·1–10 μmol/l) also stimulated the release of both peptides, whereas bethanacol had no effect on AVP release, but had a variable action on CRF-41 release. 5-HT caused a dose-dependent (10 pmol–1 nmol/l) stimulation of CRF-41 release without any effect on AVP release, and this effect was antagonized by cyproheptadine, suggesting the participation of specific 5-HT receptors.
Journal of Endocrinology (1989) 122, 713–718
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Oestrogen receptors were measured by an exchange assay in cell nuclei of the hypothalamus–preoptic area-amygdala (HPA) of ovariectomized-adrenalectomized (OVX-ADX) rats following an intravenous injection of oestradiol or an antioestrogen, CI-628. Receptors were translocated to the nucleus by both compounds. Receptors translocated by the antioestrogen were specific for oestrogens; testosterone, corticosterone and progesterone were not bound by these receptors. Several properties of antioestrogen– and oestradiol–receptor complexes were compared.
The time-course in cell nuclei in vivo showed that receptors were still present in HPA nuclei 24 h after administration of CI-628 but not 24 h after oestradiol. This prolonged increase of nuclear receptors after the antioestrogen treatment was attributed to the continued presence of CI-628 and its metabolites in plasma.
The maximum level of receptors produced in the HPA cell nuclei following CI-628 treatment was lower than the peak level of nuclear receptors following oestradiol. The dissociation rate in vitro of nuclear antioestrogen–receptor complexes formed in vivo was more rapid at 0 °C than that of nuclear oestradiol–receptor complexes. This property may be related to the lower peak level of binding after CI-628 treatment and to the inhibitory actions of antioestrogens.
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The role of nerve cells of the arcuate nucleus and endogenous opioid peptides in the regulation of GH and prolactin secretion has been investigated. Electrical stimulation of the medial-basal hypothalamus (MBH) for 10 min raised plasma levels of both hormones in male rats anaesthetized with pentobarbitone sodium. Plasma hormone levels increased within 5 min after the termination of the stimulus, while no marked changes were found during stimulation. The GH response to the electrical stimulus was substantially reduced in rats with arcuate lesions induced by neonatal treatment with monosodium-l-glutamate (MSG). By contrast, the size of the prolactin response was not altered by MSG treatment. The opiate receptor antagonist naloxone (10 mg/kg, i.v.) failed to influence GH secretion induced by electrical stimulation in either control or MSG-treated animals. The post-stimulus rise of plasma prolactin levels was attenuated by naloxone in control rats, while the same dose of the drug was ineffective in rats which had been exposed to MSG. We conclude that endogenous opioids participate in the increase of prolactin release upon electrical stimulation of the MBH but are not involved in the GH secretory response. Arcuate neurones are important in the maintenance of the GH response to electrical stimulation. By contrast, lesioning of the arcuate nucleus failed to affect the prolactin secretory response elicited by MBH stimulation. However, prolactin release in MSG-treated rats appeared less susceptible to the inhibitory action of naloxone, suggesting a possible supersensitivity towards endogenous opioids.
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Department of Physiology, University of Texas Health Science Center at Dallas, Southwestern Medical School, Dallas, Texas 75235, U.S.A.
(Received 5 January 1978)
The concentrations of gonadotrophins in the plasma of the female rat are raised during the first 2 weeks of life, but thereafter decline to low values before puberty (Ojeda, 1976). The decrease is related, in part, to a diminished pituitary reponsiveness to luteinizing hormone releasing hormone (LH-RH; Ojeda, 1976). In contrast, the capability of the hypothalamic-pituitary unit to release luteinizing hormone (LH) in response to oestrogen injected s.c. increases during the same period (Caligaris, Astrada & Taleisnik, 1972). These findings and the observation that the gonadotrophic response of the hypothalamus to electrical stimulation also becomes more pronounced with age (Meijs-Roelofs, 1972) suggest that the capability of the prepubertal hypothalamus to release LH-RH increases concomitantly with a decline in pituitary responsiveness to the neurohormone. To test this hypothesis, the
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ABSTRACT
Some physicochemical properties of partially purified hypothalamic material from the spontaneously hypertensive rat, and of plasma from man and the rat, have been characterized using a validated cytochemical bioassay which measures the ability of biological fluids to stimulate fresh guinea-pig kidney glucose-6-phosphate dehydrogenase (G6PD) after 2 min of exposure to the test substance, as an indication of their ability to inhibit Na+/K+ adenosine triphosphatase (Na+/K+-ATPase) after 4–6 min of exposure.
The G6PD-stimulating activity of both hypothalamic extract and plasma is soluble in water and insoluble in chloroform. During electrophoresis the activity from both sites appears in the same fractions and travels considerably further than lysine. After high-pressure liquid chromatography the activity of hypothalamic extract appears in a discreet fraction which does not absorb u.v. light. The activity of both the hypothalamic extract and plasma survives boiling and acid hydrolysis, but is substantially inhibited by prior incubation with digoxin antibody. From ultrafiltration studies, the substance responsible for the ability to stimulate G6PD appears to have a molecular weight of less than 500. The G6PD-stimulating activity of hypothalamic extracts was destroyed by ashing and by base hydrolysis. The ability of plasma of high activity to stimulate G6PD is considerably increased by incubating at 37 °C for 15 min and destroyed by incubation for 45 min.
It is concluded that these and several other previously noted similarities suggest that the cytochemically assayable Na+/K+-ATPase-inhibiting/G6PD-stimulating activity in the plasma and hypothalamus may be due to the same ouabain-like substance.
J. Endocr. (1987) 112, 299–303
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ABSTRACT
Variations in the concentrations of plasma and pituitary GH were determined in ducks for 66 and 87 days after hatch, and compared with somatostatin-like immunoreactivity (SLI) in the plasma, hypothalamus and neural lobe. Plasma GH levels gradually decreased during growth, while pituitary GH content increased. The concentration of pituitary GH increased during the first 3 weeks of age and remained relatively constant thereafter. The decline in plasma GH concentration was paralleled by a similar fall in the level of plasma SLI. While the content of hypothalamic SLI increased during development, the SLI concentration was maximal at 14 days of age and lowest in adults. The content and concentration of SLI in the neural lobe, in contrast, increased progressively during development. Gel filtration of hypothalamic and neural lobe extracts demonstrated that both young and older birds had two main peaks of SLI, corresponding to somatostatin-14 and somatostatin-28, and a third, larger form. The elution pattern of plasma SLI was similar in young and older birds and was principally composed of a large molecular species ('big' somatostatin), although an additional small peak eluting between somatostatin-28 and somatostatin-14 was eluted from a large pool of plasma from 90-day-old ducks. These results suggest that increased plasma GH levels in young birds do not result from a hypothalamic somatostatin deficiency nor from variations in molecular forms of SLI, and that the age-related decline in plasma GH concentration is not due to a deficiency in pituitary GH content. The decline in the circulating GH level during growth is probably due to an increase in hypothalamic somatostatin release.
J. Endocr. (1987) 113, 57–63
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ABSTRACT
The presence of adrenaline within the central nervous system appears to be essential for the occurrence of an oestrogen-stimulated surge of LH in both pro-oestrous and ovariectomized rats. Previous measurements of adrenergic activity based on the rate of decline of adrenaline (RDA) 2 h after injection of a synthesis inhibitor (SKF 64139) suggested that adrenergic activity increases in both the medial preoptic area (MPOA) and the mediobasal hypothalamus (MBH) at the start of the LH surge (15.00–17.00 h). The purpose of the present studies was to see whether oestrogen and progesterone affected this increase in adrenergic activity at the sites of the cell bodies (MPOA) and axon terminals (MBH) of the gonadotrophin-releasing hormone-synthesizing neurone. Rats ovariectomized at dioestrus showed a reduction in both plasma LH concentrations and RDA (P < 0·01) in the MBH between 15.00 and 17.00 h on the day of expected pro-oestrus. Oestrogen replacement at operation restored LH levels and the RDA to values found in intact rats. Injection of an antioestrogen (Cl-628), with or without oestrogen, also reduced plasma LH levels and the RDA (P < 0·01) in the MBH. Removal or replacement of oestrogen apparently had little effect on the RDA in the MPOA. In ovariectomized oestrogen-primed rats an injection of progesterone on the morning of expected pro-oestrus advanced and enhanced not only the LH surge but also the RDA in the MBH (P< 0·001). Moreover, concentrations of adrenaline in the MBH (but not the MPOA) decreased (P < 0·001) consistently over a 2-h period following injection of progesterone. These results support the suggestion that steroid-stimulated adrenergic activity in the MBH may be concerned with the preovulatory release of gonadotrophins.
J. Endocr. (1985) 104, 129–135
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ABSTRACT
In the mediobasal hypothalamus (MBH) of prooestrous rats or acutely ovariectomized oestrogentreated adults a marked but short-lived increase in adrenergic activity occurs at 16.00 h, 2 h before the oestrogen-dependent surge of gonadotrophins at 18.00 h. In this study oestrogen-stimulated (noon on day 1) 22-day-old female rats were used which are known to produce surge levels of prolactin at 18.00 h on day 2 and surges of both prolactin and LH at 18.00 h on day 3; although similar treatment of 18-day-old animals or oil-treated 22-day-old rats failed to produce these effects. Radioenzymatic assays of adrenaline concentrations and of the activity of its synthesizing enzyme (phenylethanolamine-N-methyl transferase; PNMT, EC 2.1.1.28) in the MBH of oestrogen-treated 22-day-old rats showed significant (P< 0·05–0·01) increases in both parameters at 16.00 h (i.e. 2 h before surge levels of gonadotrophins) on days 2 and 3 when compared with other times of day. Such effects were not seen in oil-treated 22-day-old animals or in oestrogen-treated 16-day-old rats. Noradrenaline and dopamine concentrations in the MBH of oestrogen-treated 22-day-old rats remained at baseline levels on days 2 and 3 with the exception of noradrenaline at 17.00 h on day 3 when levels appeared higher (P<0·05) than at either 15.00 or 16.00 h. Subsequent measurements of PNMT activity in oestrogen-treated 22-day-old rats at 4-hourly intervals throughout days 2 and 3 showed the presence of a clear circadian rhythm with peak levels occurring at 16.00 h. In conclusion, a temporal relationship (not necessarily specific) exists between increased adrenergic activity in the MBH of oestrogen-treated 22-day-old rats and a surge of gonadotrophins (LH and/or prolactin) 2 h later. This relationship apparently depends on an oestrogen-stimulated circadian rhythm of PNMT activity.
J. Endocr. (1986) 109, 45–51
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GalR3; Wang et al . 1997 , 1998 , Smith et al . 1998 , Waters & Krause 2000 ) within the hypothalamus and pituitary gland, roles both as a neurotransmitter and as a neuromodulator have been proposed ( Lopez & Negrovilar 1990 , Merchenthaler et
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Pinealectomy in immature (25-day-old) male Wistar rats significantly decreased the content of 5-hydroxytryptamine (5-HT) in the hypothalamus and increased concentrations of plasma LH and FSH 3 days after surgery. Extremely small amounts (10−4 pg) of arginine-vasotocin (AVT) injected into the third ventricle (pineal recess) 5 min after pinealectomy completely prevented the decrease in the hypothalamic content of 5-HT and the increase in the concentration of LH and FSH in the plasma. It is suggested that AVT prevented the increase of plasma levels of LH and FSH after pinealectomy by increasing levels of 5-HT at postsynaptic receptor sites.
