Changes in the Luteinizing Hormone Content of the Rat Pars tuheralis during the Estrus Cycle and after Lesions in the Preoptic Area

Aguado, Luis I.; Hancke, Juan L.; Rodrı́guez, Sara; Rodríguez, Estéban M.

doi:10.1159/000123378

Cited by 14 publications

(3 citation statements)

References 25 publications

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“…This is in con trast to the general observation that in other species ex amined the PT contains both glycoprotein hormone con taining cell types, i.e., thyrotrophs as well as gonadotrophs [18]. PT gonadotrophs are similar to those of the pars distalis in terms of the immunological nature of stored homones [ 1,18], response to alteration in the levels of gonadal steroid hormones [18], and secretion of luteinizing hormone (LH) in response to exogenous GnRH in vitro [19]. The ovine PT is proportionately larger than in the other species examined [20] and is easily separated from pars distalis; therefore, it represents a naturally occurring and readily available source of gonadotrophs in which the possibility of con tamination from other hormone-containing cell types is negligible.…”

supporting

confidence: 78%

Electrophysiological Recordings from Gonadotrophs

Mason

Waring²

1985

Neuroendocrinology

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The electrophysiological properties of gonadotrophs have been studied in vitro, using the ovine adenohypophyseal pars tuberalis as a naturally enriched source of this cell type. Trypsin-dispersed pars tuberalis cells maintained in primary tissue culture had a membrane potential of -72 ± 4 mV (mean ± SEM) and an input resistance of 314 ± 38 MΩ. Spontaneous action potentials were not observed; however, a single spike could be induced by depolarizing current injection. The hypophysiotrophic peptide gonadotrophin-releasing hormone (GnRH) increased membrane voltage fluctuations, but these fluctuations (± 5–10 mV) did not induce action potentials or changes in membrane potential or resistance. Power spectra obtained from analysis of this noise indicated that the fundamental event underlying GnRH action has a mean life-time of 38.4 ± 4.5 ms. The obervations that cells incubated in recording medium secreted luteinizing hormone in response to GnRH and that the GnRH-induced increase in voltage noise was inhibited by Ca²⁺ channel antagonists support the hypotheses (1) that gonadotrophin secretion is initiated by GnRH-induced Ca²⁺ channel activation and (2) that action potentials are not a prerequisite for gonadotrophin release.

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supporting

confidence: 78%

Electrophysiological Recordings from Gonadotrophs

Mason

Waring²

1985

Neuroendocrinology

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“…In our study, the hormonal content of the pars tuberalis was much lower than that of the pars distalis, as pointed out in rats (Chafuen and Cannata, 1979). These hormones in the pars tuberalis were immunologically identical to those in the pars distalis and show the same biological activity (Aguado et al, 1982). However, even if these hormones are released from the pars tubelalis, the amounts are too small to have much influence on target organs.…”

Section: ) Pars Tuberalissupporting

confidence: 64%

Endocrine Control of the Reproductive Activity in Hibernating Bats

Kawamoto

2003

Zoological Science

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Bats, Chiroptera, constitute the second largest order of the class Mammalia and vary greatly in habitats, available foods and mating systems. The timing, duration and patterns of reproduction in bats vary considerably among species and different localities. Though much is known about the reproductive phenomena and associated endocrine characteristics of various species, the central mechanism regulating the peculiar delay and asynchrony in reproductive activity remains to be elucidated. The current understanding on the endocrine characteristics and possible mechanism of regulation of the hypothalamo-adenohypophysial-gonadal axis of bats will be reviewed, based mainly on our own studies in hibernating rhinolophid bats.

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“…However, the discovery that the ovine pars tuberalis contains gonadotrophs as the only hormone-secreting cell type (Gross, Turgeon & Waring, 1984) has made possible the isolation and long-term culture of a pure population of gonadotrophs (Mason & Waring, 1985. These cells are similar to those of the pars distalis in immunocytochemical staining for LH, and have functionally identical responses to GNRH and steroids (Gross, 1978; Agnado, Hancke, Rodriguez & Rodriguez, 1982;Gross et al 1984).…”

Section: Introductionmentioning

confidence: 68%

Characterization of voltage‐gated sodium channels in ovine gonadotrophs: relationship to hormone secretion.

Mason

Sikdar

1988

The Journal of Physiology

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1. The properties of whole-cell Na+ currents (INa) were studied in immunocytochemically identified ovine gonadotrophs using the patch clamp technique. 2. Voltage recording under current clamp revealed that gonadotrophs did not fire spontaneously, and fired only a single action potential in response to a depolarizing current clamp step. 3. Under voltage clamp, INa was found to be sensitive to tetrodotoxin (TTX) and had an activation threshold of about -75 mV, with peak current occurring at -20 to -30 mV. 4. Using a two-pulse protocol a delay in the onset of inactivation was observed, suggesting that inactivation is dependent on and preceded by the activation phenomenon. 5. Kinetics of recovery from inactivation of the Na+ channels were studied with test pulses applied at various times after a depolarizing pre-pulse. Recovery from inactivation showed an initial delay, in contrast to the predictions of the Hodgkin-Huxley equations. 6. Recovery from inactivation was examined by using a repetitive pulse protocol, showing approximately 1 s is required for the channels to achieve a 95% recovery. 7. The steady-state inactivation (h infinity -V) curve was sigmoidal and fitted by a logistic growth curve model. The half-inactivation value of the Na+ current occurred at a membrane potential of -70 +/- 8 mV. 8. Noise power spectra derived from fluctuations of INa could be fitted with a single Lorentzian function, and the time constant value was slower at more depolarizing potentials. 9. The single-Na+-channel conductance was estimated from fluctuation analysis under conditions of reduced Na+ current amplitude by depolarizing pre-pulses. The single-channel conductance derived by the above method (approximately equal to 11 pS) corresponded to the single-channel conductance derived from single-channel current measurements using the outside-out version of the patch clamp technique (approximately equal to 13 pS). 10. Inactivation of INa was slowed by including 15 mM-iodate in the pipette. Ensemble fluctuation analysis of INa under these conditions was carried out using the steady state portion of the inactivation phase of the modified INa records, revealing a process best fitted by a double Lorentzian power spectrum, consistent with inactivation kinetics involving both a fast and a slow process. The time constant values correlated well with those obtained from a double-exponential fit to the decaying inactivation phase of the iodate-modified INa.(ABSTRACT TRUNCATED AT 400 WORDS)

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Changes in the Luteinizing Hormone Content of the Rat Pars tuheralis during the Estrus Cycle and after Lesions in the Preoptic Area

Cited by 14 publications

References 25 publications

Electrophysiological Recordings from Gonadotrophs

Electrophysiological Recordings from Gonadotrophs

Endocrine Control of the Reproductive Activity in Hibernating Bats

Characterization of voltage‐gated sodium channels in ovine gonadotrophs: relationship to hormone secretion.

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