Long Term Superfusion of Rat Anterior Pituitary Cells: Effects of Repeated Pulses of Gonadotropin-Releasing Hormone at Different Doses, Durations, and Frequencies*

Liu, Tsuei-Chu; Jackson, Gary L.

doi:10.1210/endo-115-2-605

Cited by 36 publications

(13 citation statements)

References 33 publications

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“…The present results clearly demonstrated that these changes in LH secretion were due to an increase in the fre quency of LHRH pulses released into the pituitary portal circu lation. Consistently, it has been reported in both in vivo and in vitro studies that an increase in the frequency of the pulsatile administration of LHRH resulted in an increase in the mean LH concentration and a decrease in the amount of LH secreted in response to each LHRH pulse [21][22][23].…”

Section: Discussionsupporting

confidence: 82%

Naloxone Increases the Frequency of the Electrical Activity of Luteinizing Hormone-Releasing Hormone Pulse Generator in Long-Term Ovariectomized Rats

et al. 1991

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Characteristic increases in neuronal activity accompanied by the initiation of each luteinizing hormone (LH) pulse have been successfully recorded in freely moving ovariectomized rats by means of multiunit activity (MUA) recording techniques. In the present study, the effect of the opioid receptor antagonist naloxone on this neuronal activity was examined in rats ovariectomized for 6–10 weeks. Electrodes were chronically implanted into the medial basal hypothalamus (n = 78) or the medial preoptic area (n = 29). During the MUA recording, blood samples were taken through an indwelling atrial cannula at 3- or 6-min intervals to determine the serum LH concentration. Naloxone was administered intravenously for 1 h by either intermittent injection every 6 min (0.05 mg/kg, 10 times) or continuous infusion (0.1, 0.2 and 0.5 mg/kg/h). Explosive rises in the MUA (volleys) associated with the initiation of LH pulse were recorded in 7 animals in which the tips of electrodes were located in the arcuate nucleus-median eminence region. In 5 animals studied, the mean ( ± SE) duration and interval of the MUA volleys were 2.1 ± 0.1 and 22.1 ± 0.9 min, respectively. Naloxone given every 6 min significantly increased the duration to 2.6 ± 0.1 min, and decreased the interval to 9.5 ± 0.9 min. This naloxone treatment disturbed the clear pulsatility of LH secretion observed in the pretreatment control period. Analysis of the effects of naloxone infused at 3 different doses revealed that the facilitatory effects of naloxone on the duration and frequency of the MUA volleys were dose-dependent. These results suggest that endogenous opioid peptides have tonic inhibitory effects on the LH-releasing hormone pulse generator activity and are profoundly involved in the control of the frequency of pulsatile LH secretion in the ovariectomized rat.

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Section: Discussionsupporting

confidence: 82%

Naloxone Increases the Frequency of the Electrical Activity of Luteinizing Hormone-Releasing Hormone Pulse Generator in Long-Term Ovariectomized Rats

et al. 1991

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“…The LH release in response to 0.5 and 2.5 ng GnRH was not influenced by thyroid ectomy and reflected a desensitization of a releasable pool of LH in Tx rat AP to higher doses of GnRH ranging between 0.5 and 2.5 ng, as described by Liu and Jackson [ 17] in the study of LH release by rat AP cells superfused with repeated pulses of GnRH at different doses. They found that rat AP cells subjected to pulsatile administration of low doses of GnRH (e.g.…”

Section: Discussionsupporting

confidence: 56%

Effects of Thyroidectomy and Thyroxine Replacement on the Release of Luteinizing Hormone and Gonadotropin-Releasing Hormone in vitro

Wang¹,

Pu²,

Chiang³

et al. 1987

Horm Res

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The effects of thyroidectomy and thyroxine (T4) replacement on the release of luteinizing hormone (LH) and gonadotropin-releasing hormone (GnRH) in ovariectomized (Ovx) rats were studied. Immediately after ovariectomy, rats were thyroidectomized (Tx) or sham-Tx. The Ovx-Tx rats were injected subcutaneously with either saline or T4 (2 µg/100 g body weight) daily for 30 days before sacrifice. Sham-Tx rats were treated with saline only. Twenty hours after the last injection, the blood sample was obtained by decapitation. The excised anterior pituitary gland (AP) was bisected and incubated in vitro with or without 0.1 0.5, 2.5, and 50 ng GnRH at 37 °C for 4 h. The mediobasal hypothalamus (MBH) was bisected and incubated with or without the AP of Ovx donor rat in vitro. Concentrations of LH and GnRH in the medium and that of LH in the serum were measured by radioimmunoassay. LH in the serum of Tx rats was higher than that in the serum of sham-Tx and Tx-T4 rats. Thyroidectomy resulted in an increase of LH release by Ovx rat AP, stimulated with or without 0.1 and 50 ng GnRH, as well as in an increase of immunoreactive GnRH release from MBH of Ovx rats in vitro. After a 4-hour incubation with donor APs, the LH in the medium containing MBH obtained from Tx rats was significantly higher than that obtained from sham-Tx and Tx-T4 rats. LH concentrations, in both sera and media, as well as GnRH concentration in the media of euthyroid and T4-replaced Tx groups were nonsignificantly different. These results suggest that T4 is inhibitory to the basal and GnRH-stimulated LH release as well as to the release of GnRH in the absence of ovarian hormones.

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“…(i) There is a linear relation between the quantity of LH released by gonadotropes, either in vitro (10,11) or in vivo (12,13), and the quantity of GnRH administered acutely. The concentrations of GnRH achieved in these studies fell within the range measured in pituitary portal blood of ovariectomized monkeys (14)(15)(16), humans (16), ovariectomized ewes (17), and rats (18) or in the extracellular fluid of the medial basal hypothalamus of rats (19) and sheep (20) sampled by "push-pull" perfusion.…”

Section: Discussionmentioning

confidence: 99%

Duration of phasic electrical activity of the hypothalamic gonadotropin-releasing hormone pulse generator and dynamics of luteinizing hormone pulses in the rhesus monkey.

Williams

Thalabard

O’Byrne

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

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The secretion of luteinizing hormone (LH) by the pituitary gland is a pulsatile phenomenon. In the rhesus monkey, each pulse of LH in the peripheral circulation is associated with a characteristic increase in multiunit electrical activity (MUA) recorded from the medial basal hypothalamus. These "volleys" of electrical activity initiate the release of gonadotropin-releasing hormone (GnRH) into the pituitary portal circulation from the terminals of neurosecretory cells. Their duration varies from 1-3 min in normal, adult intact females to 10-25 min in long-term ovariectomized monkeys. A variety of pharmacological interventions also modify volley duration. The purpose of this investigation was to determine the physiological significance of alterations in volley duration. The dynamics of LH pulses in ovariectomized animals were observed in a number of experimental circumstances in which MUA volley duration was reduced from a maximum of 23 min to a minimum of 4 min without significantly altering their frequency. The magnitude of each LH pulse was assessed by calculating the area under the curve delineated by the time course of LH above baseline. In eight experiments, a linear regression of these values on volley duration failed to reveal a significant correlation between MUA volley duration and the magnitude of LH pulses. These results suggest that all of the GnRH secreted per pulse is released at the onset of each MUA volley, the remainder of the increase in electrical activity having no further action on GnRH secretion, although effects on other systems cannot be excluded.

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Long Term Superfusion of Rat Anterior Pituitary Cells: Effects of Repeated Pulses of Gonadotropin-Releasing Hormone at Different Doses, Durations, and Frequencies*

Cited by 36 publications

References 33 publications

Naloxone Increases the Frequency of the Electrical Activity of Luteinizing Hormone-Releasing Hormone Pulse Generator in Long-Term Ovariectomized Rats

Naloxone Increases the Frequency of the Electrical Activity of Luteinizing Hormone-Releasing Hormone Pulse Generator in Long-Term Ovariectomized Rats

Effects of Thyroidectomy and Thyroxine Replacement on the Release of Luteinizing Hormone and Gonadotropin-Releasing Hormone in vitro

Duration of phasic electrical activity of the hypothalamic gonadotropin-releasing hormone pulse generator and dynamics of luteinizing hormone pulses in the rhesus monkey.

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