The Mammalian Pars Intermedia: A Review of Its Structure and Function

Howe, Alan K.

doi:10.1677/joe.0.0590385

Cited by 94 publications

(44 citation statements)

References 99 publications

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“…As well as containing «MSH [Howe, 1973], the cells of the PI also contain a significant quantity of ACTH, as defined both biologically [Kraicer et al, 1973] and with immunological techniques [Phifer and Spicer, 1970;Moriarty and H almi, 1972;Baker and D rummond, 1972;Kraicer et al, 1973] , with the immunohistochemical evidence demonstrating the presence of ACTH in all of the parenchymal cells of the PI. Thus the same cell appears to contain a number of peptides including *MSH, ACTH activity, and a corticotrophin-like intermediate lobe peptide (CLIP) [Scott et al, 1974] and perhaps also lipotrophins [Dessy and Herlant.…”

Section: Discussionmentioning

confidence: 99%

<i>In vitro </i>Release of ACTH from Dispersed Rat Pars Intermedia Cells. I. Effect of Secretagogues

Kraicer¹,

Morris²

1976

Neuroendocrinology

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Studies were made to test the responsiveness of dispersed pars intermedia (PI) cells to a number of secretagogues that are known to alter ACTH release from the pars distalis (PD) in vitro. In summary, (a) incubation in high [K+], which will increase ACTH release from the PD, did not alter ACTH release from the PI; (b) a crude extract of rat hypothalamus (HE) increased ACTH release from PD and PI; (c) the effect of HE was not due to its vasopressin content, since pretreatment of the extract with thioglycolic acid did not modify its ACTH-releasing activity and neither lysine nor arginine vasopressin stimulated ACTH release from the PI; and (d) a partially purified CRF preparation, which will stimulate ACTH release from the PD, did not alter ACTH release from the PI. We conclude that the hypothalamus contains a substance(s) that will stimulate ACTH release from the PI and that the ‘secretagogue’ is neither vasopressin nor the same CRF that will stimulate ACTH release from the PD.

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Section: Discussionmentioning

confidence: 99%

<i>In vitro </i>Release of ACTH from Dispersed Rat Pars Intermedia Cells. I. Effect of Secretagogues

Kraicer¹,

Morris²

1976

Neuroendocrinology

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“…However, the physiological role of this and other PI hormones in mammals is not clear (Howe, 1973). Nonetheless these cells provide a useful model for examining many aspects of the control of pituitary function by the central nervous system (CNS).…”

Section: Introductionmentioning

confidence: 99%

A patch clamp study of γ‐aminobutryic acid (GABA)‐induced macroscopic currents in rat melanotrophs in cell culture

Kehl

Hughes

McBurney

1987

British J Pharmacology

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1The macroscopic currents induced in cultured rat melanotrophs by exogenous y-aminobutyric acid (GABA) were analysed using the patch clamp recording technique. 2 Using various concentrations of intra-and extracellular chloride it was demonstrated that the conductance activated by GABA was chloride selective. Since these currents were blocked with bicuculline and enhanced with chlordiazepoxide the involvement of GABAA receptors similar to those in the CNS is indicated. 3 When chloride was symmetrically distributed across the membrane the voltage/current relationship was linear; pronounced rectification of GABA mediated currents was evident when there was an asymmetrical distribution of chloride. 4 With concentrations of GABA greater than 1O 1M a fading of the current was seen during prolonged (5-10 s) applications. This effect appeared to be due to a decline of conductance rather than a shift of the chloride equilibrium potential. 5 Values for the Hill coefficient derived from dose-response curves suggested that the binding of 2 molecules of GABA to the receptor is required for the activation of the chloride channel. 6 There was no indication of a direct, GABAB receptor-mediated change of conductance.

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“…Our experiments show that Ba is a potent, long-lasting and direct stimulus to MSH secretion. This property we have used to analyse the comparatively feeble and evanescent response to excess K. In addition, as the effect of Ba is so pronounced, it should prove useful for other purposes since no physiological stimulus to melanotrophs has been found (Howe, 1973;Thody, 1977).…”

Section: Introductionmentioning

confidence: 99%

Secretagogue effect of barium on output of melanocyte‐stimulating hormone from pars intermedia of the mouse pituitary.

Douglas¹,

Taraskevich²,

Tomiko³

1983

The Journal of Physiology

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Ba ions caused an intense and prolonged discharge of melanocyte‐stimulating hormone (MSH) from perifused neurointermediate lobes of mouse pituitaries and dispersed pars intermedia cells. The effect persisted in chronically cultured lobes or cells. It did not require Ca, but, like the Ca‐dependent response to excess K, was blocked by cyanide combined with glucose lack. The secretagogue effect of Ba was blocked or prevented by Co or by excess Ca, both of which can reduce inward Ba currents through Ca channels. Prior exposure to excess K partially reduced the secretagogue effect of Ba, suggesting that depolarization caused some inactivation of Ba current. In contrast to Ba, excess K elicited secretion that was transient, and prior exposure of preparations to excess K (in the absence of Ca) profoundly suppressed the secretagogue effect of Ca. The evidence is consistent with the view that inward Ca current rapidly inactivates in these cells. It is concluded that Ba ions have a potent and persistent direct secretagogue effect on the melanotrophs that may reflect, in part, their ability to penetrate Ca channels more easily than Ca ions. The strong secretagogue effects of Ba on melanotrophs may be of considerable utility in studies on MSH secretion since a physiological secretagogue has yet to be discovered. Moreover, since the responses of melanotrophs (and other endocrine cells) to Ba can be distinguished from those of various other secretory cells and neurones, it is suggested that Ba may provide a tool for characterizing the distinctive membrane properties of the Ba‐responsive endocrine cells.

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The Mammalian Pars Intermedia: A Review of Its Structure and Function

Cited by 94 publications

References 99 publications

<i>In vitro </i>Release of ACTH from Dispersed Rat Pars Intermedia Cells. I. Effect of Secretagogues

<i>In vitro </i>Release of ACTH from Dispersed Rat Pars Intermedia Cells. I. Effect of Secretagogues

A patch clamp study of γ‐aminobutryic acid (GABA)‐induced macroscopic currents in rat melanotrophs in cell culture

Secretagogue effect of barium on output of melanocyte‐stimulating hormone from pars intermedia of the mouse pituitary.

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